ALBERT

Description: The Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238–lead-206 (238U–206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U–Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium–osmium (Re–Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U–Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5–10 km Ma−1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50–100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

Description: An Ordovician subvolcanic intrusive complex hosted by Neoproterozoic metasediments crops out at Souter Head about 6km S of Aberdeen, Scotland. The complex is composed mainly of two-mica red granite and breccia with minor dykes of pegmatite, quartz porphyry, felsite and dolerite, and widespread quartz veining, hydrothermal alteration and minor molybdenite mineralisation. Anomalous levels of bismuth (Bi), arsenic (As) and gold (Au) occur in quartz–pyrite veins. The complex has been mapped and the major- and minor-element geochemistry, including rare-earth elements of intrusives and mineralisation, has been determined. These data reveal a complex tectonic, intrusive and hydrothermal history. The intrusives are peraluminous and magnetite-, muscovite- and garnet-bearing. The youngest member, a quartz porphyry, is highly fractionated. There are two stages of hydrothermal activity: the first is linked to the explosive release of volatiles from a granite cupola and breccia formation; and the second, widespread quartz veining. Mo is associated with both stages, and Bi–As–Au anomalies are found in late quartz–pyrite veins. The mineralisation is classified as a granite-related vein-type Mo system. The unique preservation, in the Grampian terrane, of an Ordovician subvolcanic complex may be attributed to pre-Devonian movements on the nearby Dee fault and possibly also the collapse of the magma chamber following the explosive release of volatiles. The combination of large size, poor exposure and abundant multi-stage hydrothermal activity suggests that there is potential for further Mo and possibly Au mineralisation in this complex. Further mineralisation of this style may be present in the NE Grampian terrane.

Description: This study aims to evaluate the tectonic activities of the Vark basin, located in the great basin of Dez River in northwestern Iran, using geomorphologic indices combined with the geographical information system technique. Some geomorphic indices were used to achieve this aim. In this regard, the indices of stream length (SL), drainage asymmetry (Af), hypsometric integral (Hi), valley floor ratio (Vf), basin shape (Bs), and mountain sinuosity (Smf) were estimated to reach an average index of relative tectonics (Iat), indicating the intensity classes of tectonic activity. The mean SL, Hi, Vf, and Bs values were estimated as 2273, 0.55, 0.45, and 1.75, respectively, regarding the active class of tectonic activity. Therefore, considering the Af and Smf indices with values of 27 and 1.14, the basin was categorised as having semi-active conditions. The overall Iat, with a value of 1.33, represented the very high class (1.0 〈 Iat 〈 1.5) of tectonic activity. Hence, by calculating the index of relative active tectonics, the study area is observed as the intensive class concerning tectonic movements. Overall, the mean values of the Iat for all sub-basins were calculated as 1.50, 1.17, and 1.83, revealing the very high and high classes of active tectonics in the basin. The results obtained on tectonic activity were further confirmed during field observations by examining the structurally complex joints, folds, slips, faults, and fractures of the area, which reflect the dynamic nature of the regional tectonics.

Description: Dinosaur body fossil material is rare in Scotland, previously known almost exclusively from the Great Estuarine Group on the Isle of Skye. We report the first unequivocal dinosaur fossil from the Isle of Eigg, belonging to a Bathonian (Middle Jurassic) taxon of uncertain affinity. The limb bone NMS G.2020.10.1 is incomplete, but through a combination of anatomical comparison and osteohistology, we determine it most likely represents a stegosaur fibula. The overall proportions and cross-sectional geometry are similar to the fibulae of thyreophorans. Examination of the bone microstructure reveals a high degree of remodelling and randomly distributed longitudinal canals in the remaining primary cortical bone. This contrasts with the histological signal expected of theropod or sauropod limb bones, but is consistent with previous studies of thyreophorans, specifically stegosaurs. Previous dinosaur material from Skye and broadly contemporaneous sites in England belongs to this group, including Loricatosaurus and Sarcolestes and a number of indeterminate stegosaur specimens. Theropods such as Megalosaurus and sauropods such as Cetiosaurus are also known from these localities. Although we find strong evidence for a stegosaur affinity, diagnostic features are not observed on NMS G.2020.10.1, preventing us from referring it to any known genera. The presence of this large-bodied stegosaur on Eigg adds a significant new datapoint for dinosaur distribution in the Middle Jurassic of Scotland.

Description: To understand the physico-chemical processes associated with migmatisation is an interesting petrological problem. New developments in microfluidics and chaotic mixing experiments have helped us to better perceive these processes from the migmatic rocks of the Proterozoic Chotanagpur Granite Gneiss Complex (CGGC), eastern India. The migmatic rocks of CGGC have preserved folded leucocratic veins in amphibolites representing viscous folding. The viscous folding phenomenon occurred due to the interaction between leucosome and melanosome. Based on textural features and mineral chemical data interpretations, we infer that when granitic and pegmatitic magmas intruded the gneissic rocks and amphibolites of our study area, diffusion of heat and volatiles from the hotter felsic magmas to the colder country rocks initiated partial melting in the amphibolites, forming melanosomes. After their formation, the highly viscous felsic magmas veined into the melanosomes, by progressively melting them and then interacting, leading to chaotic mixing dynamics. The development of chaotic mixing allowed the leucosome to venture into the melanosome as veins by stretching and folding dynamics. As the leucocratic veins or leucosome traversed through the partially molten rock or melanosome due to advection, the veins underwent viscous folding owing to the exertion of compressional stress brought about by the viscosity difference between the two mediums. The occurrence of viscous folding exponentially increased the contact area between the leucosome and the melanosome, eventually leading to enhanced diffusion and augmented mixing between the two mediums. Evidence of mixing through elemental diffusion is well documented by the compositions of amphibole and biotite occurring in the leucosome and melanosome. These minerals show substitution of magnesium and ferrous ion that show linear variation between the endmember compositions.

Description: The late Viséan anthracosauroid Eldeceeon rolfei from the East Kirkton Limestone of Scotland is re-described. Information from two originally described and two newly identified specimens broadens our knowledge of this tetrapod. A detailed account of individual skull bones and a revision of key axial and appendicular features are provided, alongside the first complete reconstructions of the skull and lower jaw and a revised reconstruction of the postcranial skeleton. In comparison to Silvanerpeton, the only other anthracosauroid from East Kirkton, Eldeceeon is characterised by a proportionally wider semi-elliptical skull, comparatively smaller nostrils set farther apart, smaller and more rounded orbits, a shorter skull table with gently convex lateral margins, and a deeper suspensorium with a straight posterior margin and a small dorsal embayment. The remarkably large hind feet and elongate toes of Eldeceeon presumably represent an adaptation for attaining high locomotory speed through increased stride length and reduced stride frequency. This would necessitate great muscle force but few muscle contractions. At the beginning of a new stride cycle, repositioning the pes anteriorly and lifting the toes off the ground would require a strong and large muscle to pull the femur upward and rotate it inward and forward. It is hypothesised that such muscle might correspond to the puboischiofemoralis internus 2, which would extend along the posterior half of the vertebral column, consistent with the occurrence of long, curved ribs in the anterior half of the trunk. Using maximum parsimony and Bayesian inference, cladistic analyses of all major groups of stem amniotes retrieve a sister group relationship between Eldeceeon and Silvanerpeton, either as the most plesiomorphic stem amniote clade or as a clade immediately crownward of anthracosauroids.

Description: Foraminifers, calcareous algae and incertae sedis Algospongia of late Asbian to late Brigantian age in limestones from East Fife, East Lothian and Northumberland, enable the base of the late Brigantian to be recognised in all these areas. Preservation of the late Asbian and early Brigantian limestones in cyclothemic successions is generally poor. The St Monans White Limestone (St Monans, Fife), First Abden Limestone (Kirkcaldy, Fife), Middle Longcraig Limestone (East Lothian) and Lower Bath-House Wood/Middle Bath-House Wood (Northumberland) were confidently correlated by their foraminiferal assemblages. These limestones are all assigned to the top of the Assemblage 6 in northern England (Single Post Limestone). The St Monans Brecciated/St Monans Little/Charlestown Main limestones (St Monans, Fife) and the Second Abden/Seafield Tower limestones (Kirkcaldy, Fife), Upper Longcraig/Lower Skateraw limestones (East Lothian), Upper Bath-House Wood/Shotto Wood limestones and Eelwell Limestone (Northumberland) are assigned to the Assemblage 7 in northern England (Scar Limestone and Five Yard Limestone). The paired Middle/Upper Skateraw limestones (East Lothian) and the Acre Limestone (Northumberland) contain representatives of the Assemblage 8 from northern England (Three Yard Limestone). Higher up in the succession, in Northumberland, the foraminiferal assemblage in the Sandbanks Limestone can be compared with Assemblage 9 in northern England (Four Fathom Limestone). Above the Great Limestone and Little Limestone, with their characteristic Pendleian assemblages, the Sugar Sands Limestone and Corbridge Limestone contain Arnsbergian foraminiferal assemblages, typical of the Lower Felltop Limestone in northern England. The Lower Foxton Limestone is correlated with the Upper Felltop Limestone, whereas the Thornbrough Limestone in Northumberland lacks diagnostic Arnsbergian taxa.

Description: The Kilmaluag Formation on the Isle of Skye, Scotland, provides one of the richest Mesozoic vertebrate fossil assemblages in the UK, and is among the richest globally for Middle Jurassic tetrapods. Since its discovery in 1971, this assemblage has predominantly yielded small-bodied tetrapods, including salamanders, choristoderes, lepidosaurs, turtles, crocodylomorphs, pterosaurs, dinosaurs, non-mammalian cynodonts and mammals, alongside abundant fish and invertebrates. It is protected as a Site of Special Scientific Interest and by Nature Conservancy Order. Unlike contemporaneous localities from England, this assemblage yields associated partial skeletons, providing unprecedented new data. We present a comprehensive updated overview of the Kilmaluag Formation, including its geology and the fossil collections made to date, with evidence of several species occurrences presented here for the first time. We place the vertebrate faunal assemblage in an international context through comparisons with relevant contemporaneous localities from the UK, Europe, Africa, Asia and the US. This wealth of material reveals the Kilmaluag Formation as a vertebrate fossil assemblage of global significance, both in terms of understanding Middle Jurassic faunal composition and the completeness of specimens, with implications for the early evolutionary histories of mammals, squamates and amphibians.

Description: The Carboniferous lungfish genus Sagenodus is reviewed from all available British specimens and described in detail for the first time. We identify two species exclusive to the UK: Sagenodusinaequalis, the type species, deriving from the late Carboniferous (=Pennsylvanian); and Sagenodus quinquecostatus derived from the early Carboniferous (=Mississippian). The genus is probably the most widespread of the known Carboniferous lungfish genera, but the British species have not been formally described since their discovery in the mid–late 19th Century. This work will provide data to help resolve existing questions about the position of Sagenodus in the phylogeny of Palaeozoic lungfishes, and provide a template for the recognition of isolated elements in museum collections and the finds from recent and future field work. The early Carboniferous species, S. quinquecostatus, shows a so far unique functional mechanism in which the lower tooth plates appear to rotate relative to the upper plates during jaw closure, implying a kinetic function at the symphysis or jaw joint.

Description: Silicic and minor intermediate and mafic pyroclastics, lavas, and dykes occupy a NW-trending zone through the Whitsunday, Cumberland and Northumberland Island groups, and locally areas on the adjacent mainland, over a distance of more than 300 km along the central Queensland coast. K-Ar and Rb-Sr data indicate an age range of 95–132 Ma, with the main activity approximately between 105–120 Ma; there is, however, evidence for easterly increasing ages. Comagmatic granites, some clearly intrusive into the volcanics, occur together with two localised areas of Triassic potassic granites (229 Ma), that form the immediate basement.The volcanics are dominantly rhyolitic to dacitic lithic ignimbrites, with intercalated surge and bedded tuffs, accretionary lapilli tuffs, and lag deposits. Associated rock types include isolated rhyolitic and dacitic domes, and volumetrically minor andesite and rare basalt flows. The sequence is cut by abundant dykes, especially in the northern region and adjacent mainland, ranging from dolerite through andesite, dacite and rhyolite. Dyke orientations show maxima between NW-NNE. Isotope data, similarities in petrography and mineralogy, and alteration patterns all suggest dyke intrusion to be broadly contemporaneous with volcanism. The thickness of the volcanics is unconstrained, although in the Whitsunday area, minimum thicknesses of 〉1 km are inferred. Eruptive centres are believed to occur throughout the region, and include at least two areas of caldera-style collapse. The sequences are thus considered as predominantly intracaldera.The phenocryst mineralogy is similar to modern “orogenic” volcanics. Phases include plagioclase, augite, hypersthene (uralitised), magnetite, ilmenite, with less common hornblende, and even rarer quartz, sanidine, and biotite. Fe-enriched compositions only develop in some high-silica rhyolites. The granites range from quartz diorite to granite s.s., and some contain spectacular concentrations of partially disaggregated dioritic inclusions.Chemically, the suite ranges continuously from basalt to high-silica rhyolite, with calc-alkali to high-K affinities, and geochemical signatures similar to modern subduction-related magmas. Only the high-silica rhyolites and granites exhibit evidence of extensive fractional crystallisation (e.g. pronounced Eu anomalies). Variation within the suite can only satisfactorily be modelled in terms of two component mixing, with superimposed crystal fractionation. Nd and Sr isotope compositions are relatively coherent, with εNd + 2·2 to +7·3, and ISr (calculated at 110 and 115 Ma) 0·7031-0·7044. These are relatively primitive, and imply mantle and/or newly accreted crustal magma sources.The two end-members proposed are within-plate tholeiitic melt, and ?low-silica rhyolitic melts generated by partial fusion of Permian (to ?Carboniferous) arc and arc basement. The arc-like geochemistry is thus considered to be source inherited. The tectonic setting for Cretaceous volcanism is correlated with updoming and basin rifting during the early stages of continental breakup, culminating in the opening of the Tasman Basin. Cretaceous volcanism is also recognised in the Maryborough Basin (S Queensland), the Lord Howe Rise, and New Caledonia, indicating the regional extent of volcanism associated with the complex breakup of the eastern Australasian continent margin.

Description: The Great Tonalite Sill (GTS) of southeastern Alaska and British Columbia (Brew & Ford 1981; Himmelberg et al. 1991) is one of the most remarkable intrusive bodies in the world: it extends for more than 800 km along strike and yet is only some 25 km or less in width. It consists of a belt of broadly tonalitic sheet-like plutons striking NW–SE and dipping steeply NE, and has been dated between 55 Ma and 81 Ma (J. L. Wooden, written communication to D. A. Brew, April 1990) (late Cretaceous to early Tertiary). The sill (it is steeply inclined and rather more like a “dyke”) is emplaced along the extreme western margin of the Coast Plutonic and Metamorphic Complex (CPMC), the high grade core of the Western Cordillera. The CPMC forms the western part of a group of tectonostratigraphic terranes including Stikine and Cache Creek, collectively known as the Intermontane Superterrane (Rubin et al. 1990). To the W of the GTS, rocks of the Insular Superterrane, including the Alexander and Wrangellia terranes and the Gravina belt, form generally lower metamorphic grade assemblages. The boundary between these two superterranes is obscure but it may lie close to, or be coincident with, the trace of the GTS.

Description: Understanding the controls on the evolution of natural feldspars is greatly assisted by coupling experimental determinations of feldspar/melt equilibria with thermodynamic modelling and the calculation of crystallisation paths. Such a combined approach permits the evaluation of the influence of intensive and extensive variables on feldspar compositions. Feldspar compositional paths are influenced only to a minor degree by pressure. The presence of H2O or other melt component incompatible in feldspar has a more major effect, not only in increasing the temperature interval over which feldspar crystallises, but also in decreasing the amount of Ab enrichment of the feldspar which occurs during crystallisation. The amount and behaviour of H2O in the magma has a pronounced influence on feldspar compositions when two feldspars are stable. Under conditions of high bulk H2O content or constant activity of H2O, plagioclase and alkali feldspar compositions evolve by increasing Ab content similar to the behaviour manifested in the simple binary systems. If the bulk H2O content is low, however, and the H2O content increases during crystallisation, plagioclase evolves by increasing Ab content until alkali feldspar is stabilised. From that point on, plagioclase compositions change mainly by decreasing Or content, while alkali feldspar evolves mainly by increasing Or content.

Description: It should be possible to infer the thermal state of the source terrane for granitic bodies, provided we have independent means to establish the chemical nature of this terrane. The chemical nature of the granitic rocks, including their degree of hydration, implies the solidus temperature. The concentration of the heat-producing radioactive elements in the granite (K, U, and Th) probably provides an upper estimate of their concentration in the source rock, which is an important thermal parameter. The depth and ambient temperature of the country rock into which the granite magma intruded provide useful boundary conditions for the thermal regime at the crustal level of anatexis. These constraints in turn form the bases for estimating the subcrustal thermal flux as well as the effective thermal interface for enhanced heat flow from below that resulted in anatexis. These inferences, in combination with other field-based parameters such as uplift rates and permissible time lapses for the geological events, permit realistic thermal modelling for the formation of granitic batholiths. The procedure is applied to the Late Cretaceous Pioneer and Boulder batholiths in southwestern Montana, U.S.A. The modelling results suggest that mantle upwelling, not subduction or thrust loading, caused anatexis. The isotopic chemistry of the granitic rocks rules out direct mixing of mantle magma, and field relations rule out crustal thinning as causes for partial melting.

Description: The Hidaka Metamorphic Belt (HMB) in Hokkaido, northern Japan, consists of tilted metamorphic layers of an island-arc type crust from lower (granulite facies) to upper (very low-grade metasedimentary) horizons. Abundant granitic rocks, mainly S-type tonalites of crustal origin, intrude various metamorphic layers and are classified into four depth types, namely upper, middle, lower and basal. The basal orthopyroxene-garnet (S-type) tonalities were intruded into granulite facies country rocks. Textural and compositional evidence from minerals in the basal tonalite indicates that the crystallisation sequence is Grt-Pl-Opx-Bt-Qtz-Crd-Kfs, and that crystallisation took place at about 600 MPa and 900°C-700°C.Some crystallisation experiments were carried out in an internally heated pressure vessel, using the basal tonalite, under the conditions of 300 and 600 MPa, 700-900°C, and with 0-20 wt% H2O, respectively. The results show that the primary S-type tonalite magma was at a temperature above 900°C and contained 3-4 wt% H2O at the beginning of crystallisation. In order to study the influence of normative orthoclase content on orthopyroxene crystallisation, some starting materials also included 15, 20 and 25% normative orthoclase, by adding KAlSi3O8 gel to the rock powder. Normative orthoclase content has an influence on the subliquidus crystallisation limit of orthopyroxene.The changes in P-T conditions and chemical composition of the magma during ascent would generate the sequence from the basal to upper S-type granite. Opx-free S-type granitic magma can be generated from lower crustal Grt-Opx S-type granitic magma, by differentiation with falling magmatic temperature.

Description: It is now generally accepted that British Tertiary granites contain crustal and mantle components. Genesis principally by differentiation of crustally contaminated basaltic magmas is widely held and silicic melts with some remarkable trace element similarities were generated within different upper crust along the St Kilda/Skye - Carlingford zone.New whole-rock (and mineral) O isotope data for the southern sector of the province (N Arran, Ailsa Craig, Mourne Mountains, Slieve Gullion, etc) reveal that δ18O lies in the range +5·1 to +9·7‰ for most of the analysed granites, meteoric water-rock interaction having been in general less intensive than at Skye and Mull. Nevertheless, highly 18O-depleted country rocks (with δ18O

Description: The Velay granite pluton (Massif Central, France) is the youngest (304 ± 5 Ma) and largest (∼6,900 km2) of the major Massif Central monzogranites/granodiorites and was formed nearly 50 Ma after the cessation of Hercynian continental collision (Pin & Duthou 1990). It is a highly heterogeneous pluton consisting of I-type, high-Sr granites (Sr = 500-900 ppm) with low (+35 to +41) and high (-3 to -5), at its centre, grading into S-type and mixed I-S-type heterogeneous granites of more normal Sr content (100–420 ppm) and higher (+40 to +210) and lower (-3·8 to -7.3) at its margins.The metasedimentary lower crust of the Massif Central was underplated/intruded by mafic mantle-derived magmas between 360 Ma and 300 Ma. From 300-280 Ma (Downes et al. 1991) underplating led to partial melting and granulite facies metamorphism of the underplated material (represented by felsic and mafic meta-igneous lower crustal xenoliths, = –11 to +112, = +2·2 to 8·2, Downes et al 1990). The partial melts assimilated mainly schist but also felsic gneiss and older granite country rock material ( = +100 to +300, = - 5 to -9) to produce the heterogeneous granites. Plagioclase and biotite were accumulated at the base of the intrusion which was intruded to high levels to form the high-Sr granites.

Description: A new temnospondyl amphibian Balanerpeton woodi gen. et sp. nov. is represented by over 30 complete or partial skeletons from the Viséan limestones, shales and tuffs in East Kirkton Quarry, Bathgate, near Edinburgh, Scotland. It is the commonest tetrapod represented in the East Kirkton assemblage and grew to about half a metre in length. Although superficially like the later Dendrerpeton, it is more advanced in possessing small premaxillaries each bearing a pronounced alary process, large external nares, large rounded interpterygoid vacuities, broadly bordered by the vomers anteriorly, a narrow vomer-pterygoid suture and a rod-like stapes. It is characterised by an unusual dental configuration in which each dentary bears a smaller number of larger teeth than the corresponding upper jaw ramus. A second probable temnospondyl is represented by two straight ribs of a much larger form.The relationships of basal temnospondyls and other amphibian groups are discussed and it is proposed that the sister-group of the temnospondyls is the Microsauria and that neither colosteids nor Caerorhachis can be considered to be temnospondyls, as both fall outside the temnospondyl-microsaur clade. A preliminary study of character distribution across a selection of primitive temnospondyls, including Balanerpeton, suggests that it is more advanced than the long-snouted Edopoidea and the Dendrerpetontidae despite its Viséan age. This implies that by the Viséan, significant diversification of temnospondyls had taken place.

Description: Fluid dynamic modelling of crystallising calc-alkalic magma bodies has predicted that differentiated liquids will ascend as boundary layers and that accumulation of these buoyant liquids near chamber roofs will result in compositionally stratified magma chambers. This paper reports physical features in La Gloria Pluton that can be interpreted as trapped ascending differentiated liquids. Leucogranitic layers decimetres thick, which are locally stratified, are trapped beneath overhanging wall contacts. The same felsic magmas were also preserved where they were injected into the wall rocks as dykes and as large sill complexes. These rocks do not represent differentiated magmas produced by crystallisation along the exposed walls because the felsic layers occur at the wall rock contact, not inboard of it. Rather, we speculate that evolved felsic liquids are generated by crystallisation all across the deep levels of chambers and that initial melt segregation occurs by flowage of melt into tension fractures. Melt bodies so formed may be large enough to have significant ascent velocities as diapirs and/or dykes. The other way in which the leucogranite occurrence is at variance with the convective fractionation model is that the ascending liquids did not feed a highly differentiated cap to the chamber, as the composition at the roof, although the most felsic in this vertically and concentrically zoned pluton, is considerably more mafic than the trapped leucogranitic liquids. This suggests that these evolved liquids were usually mixed back into the main body of the chamber. Backmixing may be general in continental-margin calc-alkalic magmatic systems, which, in contrast to those in intracontinental settings, rarely produce volcanic rocks more silicic than rhyodacite. That the highly differentiated liquids are preserved at all at La Gloria is a result of the unusual stepped nature of the contact and the entirely passive mode of emplacement of the pluton, which, in contrast to ballooning in place, does not result in wall zones being “scoured”.

Description: Using zircons taken from two granite plutons, Strontian (Caledonian, northwestern Scotland) and Kameruka (Bega Batholith, southeastern Australia), this study presents observations that have a bearing on refractory zircons as provenance indicators. Two broad textural types of refractory zircon were identified: (1) those which show simple two-stage growth histories; and (2) those which have apparently undergone repeated periods of growth, resorption, mechanical abrasion, fracturing and fracture-healing. SHRIMP U-Pb ages obtained from the Kameruka zircons indicate that the cores are the textural manifestation of inheritance. The shapes of refractory cores are not unambiguously indicative of their ultimate origin, since they may also be modified by processes that occur before and after incorporation into the magma. The cores within the two populations show a great diversity in types and styles of zoning, and in composition, implying that they have not chemically equilibrated internally, or externally with their host melt.

Description: Of all the localities that have yielded a diversity of Carboniferous tetrapods, the fossil assemblage at East Kirkton most closely resembles that of the Joggins locality in Nova Scotia. Both assemblages are dominated by dendrerpetontid temnospondyls and a smaller number of small anthracosaurs, which are thought to have been primarily terrestrial in habits. Both localities lack adelogyrinids and lysorophids, and such presumably deep water genera as Crassigyrinusand large embolomeres. The East Kirkton Limestone differs in the presence of aïstopods and a possible nectridean, which are associated with a shallow-water environment in other localities. The absence of amniotes and microsaurs may be explained by the later evolution of these groups, their limited geographical distribution, or the lack of any aspects of the depositional environment that would preferentially select primarily terrestrial animals.

Description: Coprolites are most common in the transition zone between the East Kirkton Limestone and the Little Cliff Shale. One hundred and twenty five samples are classified in five groups on the basis of size and shape. Within these groups distinctive subgroups are described. Many of the coprolites are believed to have been produced by fish, but some could have been produced by eurypterids and aquatic tetrapods.

Description: One of the rarest tetrapods in the East Kirkton fauna is an aïstopod represented by very fragmentary material of five individuals. It is described as a new species of the genus Ophiderpeton which is redefined and restricted to broad-snouted forms with large, robust teeth from the late Viséan and early Westphalian. Later Westphalian species are referred to the genus Oestocephalus.

Description: Several specimens of myriapodous arthropods have been discovered at the early Carboniferous East Kirkton site near Bathgate, West Lothian, Scotland. None is particularly well preserved, but they are the earliest known Carboniferous myriapods, filling the time gap between the Old Red Sandstone of the early Devonian and the abundant myriapod faunas of the late Carboniferous (Pennsylvanian). One of the specimens, a milliped, provides the earliest evidence for both ozopores (repugnatorial gland openings) and spiracles. A second milliped specimen has some characteristics of the living Order Glomeridesmida, and hence of Enghoff's (1990) ‘ground plan’ of chilognathan millipeds. Aspects of these forms and a third suggest a novel early Carboniferous fauna clearly different from both earlier and later ones. The taxon name ‘Myriapoda’ should be abandoned, since it covers a group now recognised as paraphyletic. ‘Archipolypoda’ is probably synonymous with Order Euphoberiida, Class Diplopoda.

Description: Thirteen fragments of fossil elasmobranchs can be identified with certainty from East Kirkton. Those collected in situ range from Units 32 to 37. The remains appear to come from two different families of sharks: spines which show features typical of the Lower Carboniferous hybodont Tristychius arcuatus Agassiz; teeth from a xenacanth which fall within the size range of those found in the Lower Carboniferous xenacanth Diplodoselache woodi Dick. Both these genera are found in other Oil-Shale assemblages in the Lothians. These rare shark fossils reinforce the evidence that the East Kirkton Limestone was fresh water in origin.

Description: Volcanic eruptions and their deposits provide paleobiologists with an array of depositional environments in which to investigate the conditions in which exceptionally preserved flora and fauna are preserved. Studies of vegetation patterns before and after eruptions have shown that tropical vegetation makes a very rapid recovery at the vegetational level (proportion of devastated land covered). The recolonisation of the rare elements of a diversified flora, however, is slow, and so is the rebound of floristic richness, assembled over centuries from surrounding patches of vegetation and from in situ speciation.Two major volcanic events that occurred in the past 15 years were studied in an attempt to understand the processes and complex patterns of plant deposition in volcanic landscapes. Both volcanoes gave rise to terrestrial, andesitic, explosive eruptions that gave little warning of their absolute magnitude or duration. In both eruptions, sediment-dammed lakes were formed in which a large quantity of plant material was trapped. In both instances, forests were killed and both standing and fallen trunks record the composition of the pre-eruption flora. The vegetation present in the vicinity of the volcanoes was, in the case of Mount St Helens (Washington, U.S.A.), dense coniferous forest living in a cool temperate climate and, in the case of El Chichón (Chiapas, Mexico), remnants of paratropical rainforest alternating with patches of agricultural land.Litter layers are present under the tephra at both volcanic sites, yet the pattern of deposition and quality of the plant material differs dramatically between the two, in part because of differences in the types of eruptions and in part because of the nature of the plants available for burial. One of the most significant styles of burial, unexpected in the air-fall ash deposits, is the presence of more than one eruptive layer generated by eruptions only hours apart. These separate eruption layers have different lithological characteristics and the plant deposits buried in the different layers are different in taxonomic composition. Significantly, leaves in the upland volcanic-ash deposits are preserved thus far for 10 years, even in the tropical settings where root growth might be expected to have obliterated all signs of depositional stratigraphy. These impressions and compressions have a high likelihood of entering the fossil record and provide an excellent example of upland deposition and preservation.

Description: Stable isotope data from the East Kirkton succession are used to elucidate the extent of hot-spring influence in the palaeoenvironment by constraining conditions of deposition of the silica and the formation of sulphides.Petrographically silica occurs as chert laminae thought to be primary, and as patchy chert considered as replacive. No evidence for biogenic silica was observed. For 20 silica samples δ18O was measured for structural oxygen and δD for bound water. δ18O(SMOW) varied between +21 and +27‰ with no sample groupings related to petrography. The range in δD(SMOW) was from −50 to −90‰ with lower values characterising replacive or altered silica; water contents of both petrographic groups were similar. A plot of δ18O versus δD for the laminated primary silica defines a grouping about the line defined by Scottish agates (Fallick et al. 1985). This suggests for the unaltered silica a formation temperature of about 60°C and a fluid containing a strong component of meteoric water. The data imply a Lower Carboniferous meteoric water δ18O composition of −3‰ and δD of −15‰, consistent with the known palaeolatitude.The only sulphide observed was pyrite; 34 samples were selected from a wide variety of lithological and textural occurrences. δ34S(CDT) ranges widely and continuously between +8 and −34‰ with no strong mode. The sulphur appears to be derived from several sources, and pyrite formation from a variety of conditions as indicated by such wide ranging data, but for the samples with the lowest δ34S the involvement of bacteria in sulphate reduction is inferred.

Description: The Stephanian Konservat-Lagerstätte of Hamilton, Kansas, deposited in a marine-estuarine environment preserves a mixture of terrestrial, fresh-water, and marine fossil organisms. The marine component is the most diverse taxonomically, whereas one ostracod species, commonly interpreted as a fresh-water form, together with vascular plant debris dominates volumetrically. Well-preserved terrestrial and aquatic vertebrates and arthropods were embedded in rapidly deposited calcareous mud conducive to microbial early-diagenesis of vertebrate soft tissues in a tidal estuarine setting. Many vertebrate fossils show no evidence of preburial decay or disarticulation. Dark-coloured body silhouettes (‘skin preservation’) are composed of calcitic bacteria, calcite crystals and organic material, and have been interpreted to reflect preservation under saline conditions. The aquatic vertebrates had a broader tolerance of salinity than today. The fishes were perhaps migratory (anadromous or catadromous), and some used the estuarine environment for spawning. The tetrapods (dissorophid amphibians) retained their tolerance to salinity from their marine ancestors and were able to spawn in near-shore environments. The terrestrial biota was dominated by the conifer Walchia and was subjected to forest fires, as evidenced by preserved charcoal fragments.

Description: Westlothiana lizziae is known from the Brigantian of East Kirkton, Scotland. The skull resembles that of later amniotes in the large size of the parietal, the apparent loss of the intertemporal, and the absence of a squamosal notch, palatal fangs and labyrinthine infolding of the marginal teeth, but is primitive in the absence of a transverse flange of the pterygoid. The individual trunk vertebrae resemble those of amniotes; large intercentra are retained, but the neural arch is fused to the centrum. A surprising feature is the presence of 36 presacral vertebrae, as is the relative size of the very small but highly ossified limbs. The humerus is much shorter than the femur, but similar in configuration to that of early amniotes. There are three proximal tarsals as in primitive tetrapods, but an amniote phalangeal count. The presence of massive dorsal as well as ventral scales is a more primitive feature than that of most anthracosaurs.Westlothiana is ‘reptiliomorph’, and is judged to be a stem-group amniote on features of the skull roof, the absence of an otic notch, the gastrocentrous vertebrae and the pedal phalangeal formula. It has not, however, reached the amniote condition in the structure of the tarsus, and the palate is more primitive than that of both early amniotes and the ‘diadectomorphs’.

Description: Scorpions from East Kirkton Quarry are represented by abundant cuticle fragments and rarer articulated specimens. Cuticles isolated from their matrix are exquisitely preserved, permitting this fauna to be described in more detail than other Carboniferous scorpion faunas. Most of the material is attributed to Pulmonoscorpius kirktonensis n. gen. n. sp. Specimens possibly indicating the presence of two additional Pulmonoscorpius species are referred to under open nomenclature. Rare fragments of an aquatic ‘archaeoctonoid’, and an orthostern scorpion, also occur. Most specimens of Pulmonoscorpius are juveniles. The range of taphonomic effects observed in these and larger individuals suggests that, as a consequence of poor preservation, the morphology of some Upper Palaeozoic scorpions has been misinterpreted by previous workers. Within the infraorder Mesoscorpionina two groups are recognised. These are distinguished by the position of the posterior pair of coxae. Pulmonoscorpius n. gen. belongs to group A, in which the posterior coxae abut the sternum. This group includes the known Lower Carboniferous mesoscorpions and ranges from the Upper Devonian to the Upper Carboniferous. All group-A mesoscorpions are reviewed here. In group-B mesoscorpions the posterior pair of coxae apparently abut the genital opercula, but confirmation of this derived character and formal taxonomic recognition of these groupings must await a restudy of the group-B mesoscorpions, which are known from the Upper Carboniferous and Triassic.

Description: The East Kirkton Limestone is typically a carbonate/organic laminite characterised at many levels by abundant radial-fibrous calcite (RFC) spherules and by less common larger stromatolite-like accretions of laminated botryoidal RFC. The spherules are mostly c. 1 mm in diameter and have cyanophyte and chlorophyte inclusions. Some spherules enclose parallel bundles of complete cyanophyte fibres and probably grew within a living cyanophyte mat. The botryoidal accretions were commonly seeded upon wood and other exposed organic remains such as bone, and they completely enclose twigs and branches where these were held above the sediment surface. Botryoidal accretions commonly contain the remains of a benthos of cyanophytes, chlorophytes and ostracods.Both types of calcite have carbon and oxygen stable isotope values similar to those of known fresh-water precipitates. Their stable isotope and trace element geochemistries are consistent with precipitation on the floor of a tropical fresh-water lake within a volcanic setting, but removed from the influence of any hot-spring activity. Spherules and botroids are mineralogically closely similar and, whilst precipitation may have been biogenically mediated, they are regarded as passive lake floor cements.The carbonate laminae are dominated by rhombohedral calcite. Many of these laminae may have originated as calcite suspensoids which settled to the lake floor during relatively brief precipitation events, blanketing the normally richly organic substrate, smothering the cyanophyte mats, and leading to the preservation of individual organic laminae. Crystals later became enlarged and intergrown within the sediment, but this occurred early and prior to significant compaction, because detail of fragile and degradable organic constituents is commonly preserved. The likely source of the carbonate is through leaching of the local basic volcanic terrain. The precipitation of two types of calcite implies regular fluctuations in the chemistry of the lake waters, or in the factors controlling precipitation, which may have been a biogenic and/or seasonal effect.

Description: The hibbertopteroid eurypterid genera Hibbertopterus, Dunsopterus, and Cyrtoctenus occur in the East Kirkton Limestone of Bathgate, West Lothian. Most specimens are fragmentary and appear to have been washed into the depositional area with plant debris and tuffaceous sediment. Nearly all of the identifiable material can be attributed to Hibbertopterus scouleri (Hibbert), but two isolated Cyrtoctenus combs, and a femur comparable with Dunsopterus have also been recognised.New material of Hibbertopterus scouleri (Hibbert) reveals that the posterior legs and telson resemble those of the cyrtoctenids more closely than was previously thought. It is possible that Hibbertopterus, Dunsopterus, and Cyrtoctenus are indistinguishable except by relatively minor characteristics, and that all of the material from East Kirkton Quarry might be derived from a single eurypterid species. However, associations of the diagnostic sclerites which would demonstrate that these taxa are either cogeneric or distinct have not yet been found.

Description: The southern Bathgate Hills, in the eastern part of the Midland Valley basin of Scotland, were the site of a volcanic rise during late Dinantian to early Silesian times and a sequence of basaltic lavas and tuffs up to 600 m thick accumulated. The volcanic pile interrupted the regional sedimentary deposition, which involved a cyclical sequence of marine limestones and mudstones followed by estuarine, lagoonal and deltaic clastic deposits. During the Brigantian Stage of the Dinantian, freshwater terrestrial environments developed locally on the volcanic rise between eruptive phases, but later in the Brigantian the rise was transgressed by marine limestones. Intermittent basaltic eruptions continued into the Amsbergian Stage of the Silesian, accompanied by intrusion of high-level alkaline doleritic sills and associated with strata-bound Zn—Pb mineralisation. Folding later in the Silesian was followed by the intrusion of a suite of quartz-dolerite sills and dykes. These latter were commonly intruded along penecontemporaneous E—W trending faults. The intrusion of the quartz-dolerites may have resulted in remobilisation of earlier strata-bound mineralisation into epigenetic veins.

Description: The East Kirkton Limestone is one of a number of horizons within the Scottish Carboniferous sequence which have commonly been referred to as ‘fresh-water’ limestones. The stratigraphy and distribution of these non-marine carbonates is reviewed and discussed in terms both of Carboniferous palaeogeography and of the interaction between sedimentation, volcanism and tectonics within the Midland Valley graben. Particular attention is given to late Viséan horizons of broadly similar age to the East Kirkton Limestone. The range of carbonate facies and faunas found in these limestones is described and their environmental significance is discussed.

Description: Magnetic and resistivity geophysical surveys conducted across the only known exposure of the East Kirkton Limestone have produced new information upon its extent. This is important to determine because of its unique faunal assemblage and possible hot spring deposition, suggesting a potential for precious metal mineralisation. Magnetic anomalies are attributed to basalts within the Bathgate Hills Volcanic Formation. Modelling of the magnetic data demonstrates a general dip to the west of about 25°, and the presence of significant local faulting. Modelling of vertical electrical sounding data shows the East Kirkton sequence (the limestone and associated beds) to be a low resistivity layer within the more highly resistive volcanic sequence. The East Kirkton sequence is seen to deepen to the west, and also to the north probably by faulting. Therefore the present exposure is the only near surface occurrence of the East Kirkton Limestone locally, but within the area of the survey no lateral limits to the formation are observed.

Description: Volcanogenic sediments form a significant part of the East Kirkton Limestone, with thin tuff units occurring at several levels and pyroclastic fragments being an important constituent of the coarser clastic limestone units.The tuffs have been extensively altered during diagenesis but recognisable pseudomorphs after olivine and plagioclase phenocrysts confirm the basaltic nature of the volcanism. The considerable lateral variations in thickness of the tuff horizons in conjunction with the poorly sorted and lithologically heterogeneous nature of the tuffs indicate an epiclastic origin for the volcanogenic sediments. Well-rounded volcanic rock fragments—products of erosion—occur with angular fragments within the tuffs. Blocky tuffs in the lower part of the formation contain charred wood fragments, rip-up clasts of limestone and disarticulated amphibian bones. Graded bedding at several horizons and the presence of ostracods within some tuffs confirms subaqueous deposition.The findings are consistent with the usual, dominantly epiclastic products of basaltic volcanism, in an equatorial, continental, humid environment, with assorted debris being washed from the flanks of a volcano into a shallow lake.

Description: Forty-one specimens of acanthodians and actinopterygians were examined from Units 26 to 38 of the Geikie Tuff, Little Cliff Shale and East Kirkton Limestone of the Viséan East Kirkton Limestone sequence. The results yielded six actinopterygian species including a platysomid and two probable juveniles of uncertain affinities, and three acanthodians including two acanthodidids and a climatiid-like denticle. Most specimens consist of isolated bones and scales, but articulated remains of an acanthodian and actinopterygians were found in Units 37 and 38 of the East Kirkton Limestone. The faunal composition is characteristically Oil-Shale in aspect and resembles that of Broxburn (Pumpherston). The presence of deep-bodied and juvenile fishes in the same strata combined with the mode of preservation indicate a palaeohabitat with limited current action and a soft substrate.

Description: The Viséan sequence at East Kirkton contains abundant plant fossils which show a wide range of preservation states. Most of the plant fragments are allochthonous, but stigmarian rootlets are found in situ at the top of the sequence and form mats near the base, where they are preserved in cherts. Axes have commonly been reworked within tuffs at the base. The majority of the plants are preserved as fragmentary compressions, although mineral replacement of the organic matter has occurred in some places. A number of woody axes which have been permineralised by phases of calcite and silica are found in the limestone and tuffs of the sequence. These axes often show complex mineralisation patterns and can occur at the centre of stromatolitic nodules. Some are well preserved and appear to have been permineralised rapidly whereas others show evidence of decay prior to calcite growth or degradation after stromatolite developed. Fusain (fossil charcoal) is abundant in the sequence, in addition to fusain transition fossils caused by partial charring, which suggests the occurrence of palaeowildfires in the area. The plant fossils have been assigned to a number of categories (some of which are new), based on their varied preservation states.

Description: In the early Carboniferous, the portion of continental crust that now constitutes Scotland lay within the hinterland of a large continent that extended westwards to what is now the western parts of North America, eastwards to what is now the Urals and northwards towards what is now Arctic Canada, Greenland, Scandinavia and Russia. Open ocean probably lay at between 600 and 1000 km to the south. Whereas mountainous terrane lay to the north of the Highland Boundary fault, the Scottish Midland Valley, like the Northumberland Trough further south, was a region of low relief subject to periodic marine incursions.A period of block faulting and concomitant basaltic volcanism commenced at the beginning of the Carboniferous at c. 350 Ma. This had manifestations in various regions of the British Isles from the south-west of England to the west of Ireland and as far north as the Midland Valley (Francis 1978, 1991; Upton 1982; Cameron and Stephenson 1985).

Description: A laminated, partly peloidal lacustrine limestone from the Lower Permian intermontane Döhlen basin in Saxony, Germany, contains one of the most diverse late Palaeozoic tetrapod faunas in Europe associated with a marine higher algal flora of Tethyan character. The surprising co-occurrence of these organisms and the lack of fishes is explained by the special position of this basin above the Elbe lineament, the influence of strong volcanism, of differentiated salinity in the lake and of the palaeowind systems, as well as by the action of stratigraphic, palaeogeographic and palaeoecological filters.

Description: Plants of gymnospermous affinities are the most important component of the flora at East Kirkton. Four genera of anatomically preserved gymnosperm stems with well developed secondary xylem are interpreted as arborescent. The largest specimens (trunks up to 50 cm in diameter) are attributed to the genus Pitus. Features of the wood, including ray size, are characteristic of the species Pitus withamii Lindley & Hutton which has long been described from the Strathclyde (former Oil-Shale) Group of Scotland. Decorticated axes of Eristophyton fasciculare are more common; their study has enlarged our concept of the species with regard to maximum diameter, internode length and phloem organisation. Similarly, the decorticated specimens of Bilignea solida Kidston found at East Kirkton exceed in diameter the original material described from Ayrshire. The fourth taxon is Stanwoodia recently described by Galtier and Scott (1991). In all these plants, features of leaf traces suggest that leaves were relatively large and densely borne on ultimate branches. These leaves were shed ultimately, prior to a later phase of wood development; they certainly correspond to (? most of) the compression foliage commonly found in association: Sphenopteridium, Adiantites and Spathulopteris.

Description: Granites and related volcanic rocks of the Lachlan Fold Belt can be grouped into suites using chemical and petrographic data. The distinctive characteristics of suites reflect source-rock features. The first-order subdivision within the suites is between those derived from igneous and from sedimentary source rocks, the I- and S-types. Differences between the two types of source rocks and their derived granites are due to the sedimentary source material having been previously weathered at the Earth's surface. Chemically, the S-type granites are lower in Na, Ca, Sr and Fe3+/Fe2+, and higher in Cr and Ni. As a consequence, the S-types are always peraluminous and contain Al-rich minerals. A little over 50% of the I-type granites are metaluminous and these more mafic rocks contain hornblende. In the absence of associated mafic rocks, the more felsic and slightly peraluminous I-type granites may be difficult to distinguish from felsic S-type granites. This overlap in composition is to be expected and results from the restricted chemical composition of the lowest temperature felsic melts. The compositions of more mafic I- and S-type granites diverge, as a result of the incorporation of more mafic components from the source, either as restite or a component of higher temperature melt. There is no overlap in composition between the most mafic I- and S-type granites, whose compositions are closest to those of their respective source rocks. Likewise, the enclaves present in the more mafic granites have compositions reflecting those of their host rocks, and probably in most cases, the source rocks.S-type granites have higher δ18O values and more evolved Sr and Nd isotopic compositions, although the radiogenic isotope compositions overlap with I-types. Although the isotopic compositions lie close to a mixing curve, it is thought that the amount of mixing in the source rocks was restricted, and occurred prior to partial melting. I-type granites are thought to have been derived from deep crust formed by underplating and thus are infracrustal, in contrast to the supracrustal S-type source rocks.Crystallisation of feldspars from felsic granite melts leads to distinctive changes in the trace element compositions of more evolved I- and S-type granites. Most notably, P increases in abundance with fractionation of crystals from the more strongly peraluminous S-type felsic melts, while it decreases in abundance in the analogous, but weakly peraluminous, I-type melts.

Description: The Lower Devonian plant- and arthropod-bearing cherts of the Rhynie area of Aberdeenshire, NE Scotland, were deposited from silica-rich waters emanating from the hot-springs of a precious-metal (Au) bearing epithermal system. Cherts were deposited at temperatures up to 100°C. The hot-springs were active in the waning phase of local volcanism and reworked volcanic debris is associated with the hot-spring system. Plant and animal communities inhabited a low energy alluvial plain with small ponds. Hot-springs deposited surficial sinter and silicified standing plants and underlying plant litter in a generally terrestrial setting, but aquatic organisms were present in low temperature pools within areas of sinter deposition. Silicification also affected plants and sediment in the shallow subsurface. The cherts display massive, vuggy, laminated, lenticular, nodular and brecciated textures in laterally impersistent beds. Faunal and floral variation between beds is of local significance, possibly reflecting general water availability. Variations in preservation of plants reflect not only degrees of imperfection in the permineralisation process, but also silicification at different times in the cycle of plant growth and decay.

Description: Plant fossils are a common and important element in the East Kirkton biota of Brigantian (late Viséan age). The most important taxa are preserved as compressions or anatomically preserved as permineralisations. The basis of the quantitative study of the flora and the distribution of individual plant species was the trenched section excavated for the East Kirkton Project. The largest diversity of compressions have been recorded from loose blocks. In the trenched section, the uppermost ashes contain only lycopsid compressions including Stigmaria. Nodules in the underlying shales yield mainly lycopsid leaf and sporophyll compressions. The uppermost limestones (Units 39-52) contain drifted fragments of pteridosperm fronds mainly Sphenopteridium crassum, S. pachyrrhachis, Spathulopteris obovata and Adiantites antiquus. Permineralised Lyginorachis spp. occur at this level. Large permineralised woody gymnosperm axes have been found loose (including Pitus, 50 cm in diameter). Permineralised axes, mainly reworked, including the gymnosperms Bilignea, Eristophyton, Stanwoodia and possibly Protopitys, have been found in Units 72-88. Poorly preserved permineralised lycopsids are rare, but include Lepidophloios. Loose chert blocks contain root mats of permineralised Stigmaria, together with Lepidocarpon, the sphenopsid Archaeocalamites and the fern Botryopteris. Similar material is found in Unit 83 of the Limestone sequence. Unit 82, the black shale containing many of the articulated vertebrates, contains predominantly pteridosperm frond and pinnule material including Spathulopteris obovata. The distinctive changes in the flora from the base to the top of the trenched sequence reflect mainly ecological and taphonomic controls upon plant distribution and preservation. Evidence suggests a close relationship between climate, fire, erosion, deposition and vegetation type through the sequence and a climatic change, from a drier to a wetter environment, is suggested at the top of the East Kirkton Limestone sequence.

Description: Syenogranites and monzogranites of Edward VII Peninsula, Marie Byrd Land, represent magmatism associated with continental rifting and the separation of New Zealand from W Antarctica in the mid-Cretaceous. These coarse-grained, leucocratic, subsolvus biotite granites occur as five small plutons cutting Lower Palaeozoic metasediments. Petrographic features include the predominance of microcline perthite over albite, bipyramidal smoky quartz, red-brown biotite and accessory ilmenite, zircon, apatite, monazite and fluorite. Enclaves are absent and miarolitic cavites are rare.The granites are a weakly peraluminous, potassic, and highly fractionated suite with high concentrations of Rb, Nb, Y, HREE and F in the most evolved compositions. REE patterns vary from LREE-enriched (CeN/YbN = 8·4), to flat REE patterns (CeN/YbN = 1·1) with large negative Eu anomalies (Eu/Eu* = 0·02). Initial 87Sr/86Sr ratios are 0·7116-0·7206 and initial εNd values are −5·5 to −7·7. Generalised fractionation trends for the suite are explicable in terms of the modal mineralogy. Monazite crystallisation exerted a predominant control on LREE concentrations.The geochemistry of the Edward VII Peninsula granites suggests an infracrustal I-type source, and regionally available Devonian-Carboniferous I-type granodiorites and tonalites satisfy the isotopic constraints. The granites classify as A-type (preferred term A-subtype) and Within-Plate Granites on standard diagrams, but the least fractionated rocks clearly indicate the I-type, Volcanic Arc Granite geochemical signatures of their inferred crustal sources.

Description: In situ, microscale, U-Pb isotopic analyses of zircon using the SHRIMP ion microprobe demonstrate both the potential and the limitations of zircon U-Pb geochronology. Most zircons, whether from igneous or metamorphic rocks, need to be considered as mixed isotopic systems. In simple, young igneous rocks the mixing is principally between isotopically disturbed and undisturbed zircon. In polymetamorphic rocks, several generations of zircon growth can coexist, each with a different pattern of discordance. A similar situation exists for igneous rocks rich in inherited zircon, as these contain both melt-precipitated zircon and inherited components of several different ages. Microscale analysis by ion probe makes it possible to sample the record of provenance, age and metamorphic history commonly preserved within a single zircon population. It also indicates how the interpretation of conventionallymeasured bulk zircon isotopic compositions might be improved.

Description: Temporal and spatial variations in the Nd isotopic compositions of Tertiary caldera-forming rhyolite tuffs, and Cretaceous and Tertiary granites of the western U.S.A. are used as a basis for a model that accounts for the observed proportions of crustal versus mantle contributions to silicic magmas in terms of two parameters: the ambient crustal temperature and the rate of supply of basaltic magma from the mantle. The crustal contribution to silicic igneous rocks is measured in terms of the Neodymium Crustal Index (NCI). The relationships between crustal temperature, basalt supply and NCI are quantified using a model of a magma chamber undergoing continuous recharge, wall-rock assimilation and fractional crystallisation. From the model, a critical value of the ratio of basalt recharge-to-assimilation, (r/a)c, is deduced, which increases with decreasing crustal temperature. The r/a value must exceed (r/a)c to allow the volume of differentiated magma to increase, a prerequisite for developing large volumes of silicic magma. Strongly peraluminous (or S-type) magmas (NCI = 0·8–1), form under conditions of high crustal temperature and low basalt supply. Metaluminous or I-type granites form over a wide range of conditions (NCI = 0·1–1), generally where basalt supply is substantial. In individual long-lived volcanic centres, the large-volume high-silica ignimbrites are associated with the highest r/a and lowest NCI values, indicating that these magmas are typically differentiates of mantle-derived basaltic parents.

Description: Igneous charnockites are characterised by distinctively high abundances of K2O, TiO2, P2O5 and LIL elements and low CaO at a given SiO2 level compared to metamorphic charnockites, and I-, S- and A-type granites. They form a distinctive type of intrusive igneous rocks, the Charnockite Magma Type (CMT or C-type), which generally lack hornblende and consist of pyroxene, alkali feldspar, plagioclase, quartz, biotite, apatite, ilmenite and titanomagnetite. Although this mineral assemblage superficially resembles that of metamorphic charnockites, magmatic charnockites are characterised by inverted pigeonite, exceptionally calcic alkali feldspar, potassic plagioclase, and coexisting opaque oxides, all with crystallisation temperatures of 950-1050°C. Apatite is a ubiquitous phase which, together with the very high concentrations of Zr and TiO2 over a wide silica range, is consistent with the derivation of the Charnockite Magma Type by very high temperature partial melting and fractionation.The credibility of intrusive charnockites as a magmatic type has historically foundered because of their apparent restriction to granulite belts and the absence of any reported extrusive equivalents. We report examples of volcanic rocks, of various ages, with the same distinctive major and trace element compositions, mineral assemblages and high temperatures of crystallisation as intrusive chamockites.The Charnockite Magma Type is considered to be derived by melting of a hornblende-free or poor, LILE-enriched fertile granulite source which had not been geochemically depleted by a previous partial melting event but which was dehydrated in an earlier metamorphism. Whereas H2O-saturated melting produces migmatites or "failed" granites, and vapour-absent melting of an amphibolite can produce I-type granites, according to this model the vapour-absent melting of a hornblende-free or hornblende-poor granulite at even higher temperatures produces charnockites.

Description: Thermal, mechanical and chemical exchange occurs between felsic and mafic magmas in dynamic magma systems. The occurrence and efficiency of such exchanges are constrained mainly by the intensive parameters, the compositions, and the mass fractions of the coexisting magmas. As these interacting parameters do not change simultaneously during the evolution of the granite systems, the exchanges appear sequentially, and affect magmatic systems at different structural levels, i.e. in magma chambers at depth, in the conduits, or after emplacement. Hybridisation processes are especially effective in the plutonic environment because contrasting magmas can interact over a long time-span before cooling. The different exchanges are complementary and tend to reduce the contrasts between the coexisting magmas. They can be extensive or limited in space and time; they are either combined into mixing processes which produce homogeneous rocks, or only into mingling processes which produce rocks with heterogeneities of various size-scales. Mafic microgranular enclaves represent the most common heterogeneities present in the granite plutons. The composite enclaves and the many types of mafic microgranular enclaves commonly associated in a single pluton, or in polygenic enclave swarms, are produced by the sequential occurrence of various exchanges between coexisting magmas with constantly changing intensive parameters and mass fractions. The complex succession and repetition of exchanges, and the resulting partial chemical and complete isotopic equilibration, mask the original identities of the initial components.

Description: Felsic I-type granites and associated volcanic rocks of Carboniferous age are extensively developed over an area of 15,000 km2 in northern Queensland. These granites have been subdivided into four supersuites: Almaden, Claret Creek, Ootann and O'Briens Creek.Granites of the Almaden Supersuite are intermediate to felsic (56-72% SiO2) and are characterised by high K2O, K/K(K + Na), Rb, Rb/Sr, Th, U and relatively low Ba and Sr. The Claret Creek Supersuite granites are a little more felsic (65-77% SiO2), and are chemically distinctive, having higher A12O3, CaO, Na2O and Sr, and lower K2O, Rb, Th and U than granites of the Almaden Supersuite.Granites of the Ootann and O'Briens Creek supersuites all contain more than 70% SiO2 and these comprise more than 90% of the total area of granites. These two supersuites are characterised by low Sr, Sr/Y and large negative Eu/Eu*, with the more evolved rocks becoming strongly depleted in TiO2, FeO* MgO, CaO, Ba, Sr, Sc, V, Cr, Ni, Eu, CeN/YN and K/Rb, and enriched in Rb, Pb, Th, U and Rb/Sr. Granites belonging to the O'Briens Creek Supersuite contain significantly higher abundances of HFSE, HREE and F (0·2-0·5 wt%) than those of the Ootann Supersuite, and as such have developed some characteristics of A-type granites.Geochemical and isotopic properties suggest that all granites are of crustal derivation. The granites of all supersuites have very similar initial 87Sr/86Sr and εNd of 0·710 and −7·0–−8·0, respectively, except where they outcrop within Proterozoic country rocks, when they have more evolved εNd (−8·0–−11·0). Depleted-mantle model ages cluster around 1·5 Ga. The isotope systematics and geochemistry indicate that these granites were not derived from the equivalents of any exposed country rocks.Models for the petrogenesis of these granites all appear to require the involvement of a long-lived and isotopically homogeneous crustal protolith, that most probably underplated the crust in the Proterozoic. Granites of the two more felsic supersuites were either derived by varying degrees of partial melting from this protolith of andesitic to dacitic composition, and/or were produced by a two-stage process by remelting of intermediate rocks similar in composition to the mafic end-members of the Almaden Supersuite. The resulting primary partial melts for the Ootann and O'Briens Creek supersuites underwent extensive, high-level, feldspar-dominated, crystal fractionation.

Description: The ore-element associations of granite-related ore deposits in the eastern Australian Palaeozoic fold belts can be related to the inferred relative oxidation state, halogen content and degree of fractional crystallisation within the associated granite suites. Sn mineralisation is associated with both S- and I-type granites that are reduced and have undergone fractional crystallisation. Cu and Au are associated with magnetite- and/or sphene-bearing, oxidised, intermediate I-type suites. Mo is associated with similar granites that are more fractionated and oxidised. W is associated with a variety of granite types and shows little dependence on inferred magma redox state. The observed ore deposit-granite type distribution in eastern Australia, and the behaviour of ore elements during fractionation, is consistent with models of ore element sequestering by sulphides and Fe-Ti phases (e.g. pyrrhotite, ilmenite, sphene, magnetite) whose stability is nominally fO2-dependent. Fractional crystallisation acts to amplify this process through the progressive removal of compatible elements and the concentration of incompatible elements into decreasing melt volumes. The halogen content is also important. S-type granites are poorer in Cl than I-types. Cl decreases and F increases in both S- and I-type granites with fractional crystallisation. Low Cl contents combined with low magma fO2 in themselves seem to provide an adequate explanation for the rarity of Mo, Cu, Pb and Zn type mineralisation with S-type granites. Although such properties of granite suites seem adequately to predict the associated ore-element assemblage to be expected in associated mineral deposits, additional factors determine whether or not there is associated economic mineralisation.

Description: Early Proterozoic rapakivi intrusions in S Greenland occur as thick sheets which have ramp–flat geometry and were intruded along the median planes of active ductile extensional shear zones. These shear zones and their intrusions were linked via transfer zones in a major three-dimensional framework. At high structural levels (c. 6 km) the rapakivi intrusions developed thermal aureoles which overprint the regional assemblages, whereas at deeper levels in the regional structure they are contemporaneous with regional metamorphism. Thermobarometry on the regional and contact assemblages indicates low pressure granulite facies conditions (200–400 MPa, 650°-800°C) suggesting very high thermal gradients. The rapakivi suite and associated norites have low initial 87Sr/86Sr together with positive εNd values, indicating the involvement of predominantly young crust and/or mantle component in the generation of the igneous suite. It is considered that the voluminous norites are closely related to the mafic melts which underplated the juvenile crust to trigger the generation of the monzonitic rapakivi suite. Taken together, the data are consistent with a model of Proterozoic lithospheric extension, thinning of relatively juvenile continental crust and compression of mantle isotherms, resulting in high crustal heat flow, mafic underplating, and crustal melting with emplacement of magmas along a linked network of extensional shear zones.

Description: Size and composition (bulk metal ratios) of magmatic hydrothermal mineral deposits are affected by a number of chemical and physical processes including the nature of the source region and mode of emplacement. At shallow levels, rising plumes of vapour bubbles + melt, and the advection of water through interconnected vapour bubbles, allows access of the magmatic aqueous phase to the upper reaches of a magma chamber. These processes are operative at shallow levels where low water solubility and high molar volume for water make these processes more efficient.Partitioning experiments suggest that oxygen fugacity-dependent crystal/melt partitioning of ore metals leads to different efficiencies of removal of Cu, W, and Mo from silicate melts into ore-forming aqueous fluids. For example, the Mo/W ratio in magmatic hydrothermal deposits should increase as the oxygen fugacity of the magma increases. Further, Cu should behave as a crystal-compatible element in H2O-undersaturated, sulfide-saturated felsic magmas with fO2 NNO + 1 due to the strong partitioning of Cu from the melt into pyrrhotite.Cycling of oxidised, hydrated, sulfidised and Cl-enriched oceanic crust into mantle can give rise to magmas that contain S but are oxidised (≥NNO). The combination of high oxidation state, relatively hydrous but shallow conditions and a high Cl/H2O ratio leads to saturation with respect to H2O early during crystallisation, and loss of a large proportion of magmatic Cu to the aqueous phase. Ores formed from these oxidised magmas also possess high Mo/W ratios due to the effect of oxygen fugacity on the sequestering of Mo vs W.In less oxidised magmas, Cu and Mo are partitioned into sulfides and Ti-bearing phases, respectively, resulting in lower efficiencies of removal of Cu and Mo from melts into aqueous fluids. Further, the partitioning of W into crystallising phases is reduced, producing a more efficient removal of W into ore-forming fluids. This ultimately leads to mineral deposits with higher W/(Mo + Cu) ratios relative to deposits associated with more oxidised systems. Silicic, high-F magmas with fO2 = NNO can be found in tensional environments (e.g. rocks associated with the Climax-type deposits of the Colorado Mineral Belt). High HF/H2O activity ratios in the source regions yield melts that evolve an aqueous phase late during crystallisation, leading to relatively low ratios of compatible/incompatible elements in the melt at H2O saturation.

Description: Late Archaean granitic rocks from the southern Yilgarn Craton of Western Australia have a close temporal relationship to the basaltic and komatiitic volcanism which occurs within spatially associated greenstone belts. Greenstone volcanism apparently began ∼2715 Ma ago, whereas voluminous felsic magmatism (both extrusive and intrusive) began about 2690 Ma ago. A brief but voluminous episode of crust-derived magmatism ∼2690-2685 Ma ago resulted in the emplacement of a diverse assemblage of plutons having granodioritic, monzogranitic and tonalitic compositions. This early felsic episode was followed immediately by the emplacement of mafic sills, and, after a further time delay, by a second episode of voluminous crust-derived magmatism dominated by monzogranite but containing plutons covering a wide compositional range, including diorite, granodiorite and tonalite. The products of this 2665–2660 Ma magmatic episode now form a significant fraction of the exposed southern Yilgarn Craton. Later magmatism, which continued to at least 2600 Ma ago, appears largely restricted to rocks having unusually fractionated compositions.The magmatic sequence basalt-voluminous crust-derived magmatism-later diverse magmatism, is interpreted in terms of a dynamically-based model for the ascent of the head of a new mantle plume. In this model basalts and komatiites are derived by decompression melting of rising plume material, and the crust-derived magmas result after conductive transport of heat from the top of the plume head into overlying continental crust. This type of magmatic evolution, the fundamentally bimodal nature of the magmatism, the presence of high-Mg volcanics (komatiites), and the areal extent of the late Archaean magmatic event, are all suggested to be characteristic of crustal reworking above mantle plumes rather than resulting from other processes, such as those related to subduction.

Description: Liquidus phase relationships at H2O-saturated and -undersaturated conditions and 2 kbar in the systems Qz-Or-Ab (SiO2-KAlSi3O8-NaAlSi3O8), Qz-Or-Ab-Al2O3, and subsystems are compared and discussed. In the peraluminous systems (i.e. when melts are saturated with respect to mullite) the liquidus temperatures are lowered by 40-55°C for compositions in the quartz primary field and by 15-25°C for cotectic compositions. The composition of the Qz-Ab eutectic and of the minimum are slightly shifted towards more Qz-rich compositions (minimum composition at P(H2O) = 2 kbar in the system Qz-Or-Ab-A12O3, saturated with respect to mullite: Qz40Or23Ab37). In melts saturated with sillimanite or mullite, the effect of high Al content may be lower for the Qz-Or than for the Qz-Ab eutectic.The depression of the liquidus temperatures may be partly related to the higher H2O solubility in melts saturated with respect to mullite. The solubility of H2O in a melt with a composition of Qz28Or34Ab38 at 2 kbar and 800°C is 5·77 ± 0·15 wt% H2O and 6·36 ± 0·30 wt% H2O in a melt with the same Qz/Or/Ab proportions but saturated with respect to mullite.The effect of high Al contents on the Mg and Fe contents of Ca-free granite melts was investigated at 775°C-3 kbar (melts coexisting with phlogopite), and at 820°C-2 kbar (melts coexisting with biotite and spinel), under NNO buffer conditions. Less than 0·15 wt% MgO is incorporated in subaluminous melts coexisting with phlogopite, whereas peraluminous melts (2·9 wt% normative corundum) contain 0·6–0·7 wt% MgO. A similar behaviour of the MgO content is observed for melts coexisting with biotite. In contrast, no significant effect of high Al contents on the FeO content of melt coexisting with biotite was observed. This suggests that the Fe/Mg ratio may be significantly lower in peraluminous than in subaluminous granitic melts.

Description: Rare garnet phenocrysts and garnet-bearing xenoliths occur in high-silica, metaluminous to peraluminous andesites and dacites (and their high-level intrusive quartz diorite equivalents) from a Miocene calc-alkaline province in Northland, New Zealand. These garnets are among the most Ca-rich (17–28 mol% grossular) garnets of igneous origin so far recorded in calc-alkaline suite rocks. Associated minerals are dominant hornblende and plagioclase and minor augite, occurring as phenocrysts in xenoliths and as inclusions in the garnet. This mineralogy points to the I-type character of the garnet-bearing host magma compositions, and contrasts this garnet occurrence with the more frequently recorded grossular-poor (3–10 mol%) garnets with hypersthene, plagioclase, biotite and cordierite, found in S-type volcanic and intrusive host rocks.Detailed experimental work on a glass prepared from one of the garnet-bearing dacites closely constrains the conditions under which the natural phenocryst and xenolith mineral assemblages formed. This work was conducted over a pressure-temperature range of 8–20 kbar, 800–1050°C with 3–10 wt% of added H2O, defining overall phase relationships for these conditions. Importantly, amphibole only appears at temperatures of 900°C or less and clinopyroxene at 〉900°C (with 3wt% H2O). Orthopyroxene occurs with garnet at lower pressure (∼15 kbar with 3wt% H2O; ∼〉10kbar with 5wt% H2O). Absence of orthopyroxene from the natural garnet-bearing assemblages indicates pressures above these limits during crystallisation. Plagioclase is markedly suppressed (with respect to temperature) with increasing H2O content, and for pressures of 10–15 kbar, the maximum H2O content possible in the magma with retention of clinopyroxene and plagioclase together (as evident in xenoliths) is 5–6 wt%. Finally, the lack of quartz in any of the xenoliths suggests magma H2O content higher than 3% (where quartz appears with amphibole at 900°C), since the quartz liquidus temperature decreases with increasing H2O content, and with decreasing pressure. In experiments with 5wt% H2O, a quartz-free field of crystallisation of garnet-clinopyroxene-amphibole-plagioclase occurs between 10 and 15 kbar and temperatures between 850 and 900°C. In addition, detailed experimentally-determined garnet compositional trends, together with ferromagnesian mineral compositional data for specific experiments with 5 wt% H2O added and run at 10-13 kbar and ∼900°C, suggest that the natural assemblages formed at these conditions. This implies that the parental dacitic magma must have been derived at mantle depths (the Northland crust is ∼25 km thick), and any basaltic or basaltic andesite precursor must have contained ∼2–3 wt% H2O.The unique nature of the Northland volcanics and high-level intrusives, preserving evidence of relatively grossular-rich garnet fractionation in the high-pressure crystallisation history of an originally mantle-derived magma, is attributed to a combination of unusually hydrous conditions in the source region, complex tectonic history involving obduction and subduction, possible incorporation of crustal slivers in a mantle-crust interaction zone, and relatively thin (∼25 km) crust.

Description: Stable isotopic ratios (mainly 18O/16O, but also D/H) have been measured for the three most important types of late-Hercynian granites, and their hosts, in the western area of the Central Iberian Massif (CIM), Spain. These granites are amphibole-bearing biotite granites, biotite granites and cordierite-bearing biotite granites. No intrusive relationships have been observed among them; the contact of each granite with the others is always gradational. Host-rocks are Precambrian/Cambrian metasediments, ranging from low-grade schists to migmatites (nebulites).Whole-rock δ18OSMOW values are as follows: amphibole-bearing biotite granites 8·9 ± 0·58% (1σ, n = 17); biotite granites 9·0 ± 0·35% (1σ, n = 11); cordierite-bearing biotite granites 9·6 ± 0·24% (1σ, n = 21). δ18O values for nebulites, into which some of these granites were emplaced, are significantly higher, at 11·1 ± 0·58‰ (1σ, n = 13). The Precambrian to Cambrian shales gave an average value of δ18O = 11·9 ± l·23‰ (lδ, n = 5). Whole-rock oxygen isotope ratios indicate that the origin of the granites was in neither purely sedimentary/metasedimentary rocks nor pristine mantle melts. δ18O values close to 9·0‰ require a crustal protolith, having an important recycled component.Oxygen isotope results are compatible with the cordierite-bearing granites being generated by assimilation of nebulite-like material by a biotite granite magma. However, 18O/16O of mineral separates obtained from the three different granites and the nebulite indicate that isotopic equilibrium, if ever reached, has not been preserved. The modified isotopic equilibrium is attributed to fluid activity, but mineral-pair δ-δ plots suggest that the granite system behaved as a closed system, and that the fluid was deuteric (magmatic) in origin. This implies that if assimilation did happen, it occurred at a temperature higher than the closure temperature of the different minerals to isotopic exchange. In a δ18O vs δD plot, hornblende and biotite separates from the granites plot within the igneous field. A simple mesocrustal anatectic origin for the peraluminous late Hercynian granites of the western area of the CIM is difficult to sustain on the basis of the stable isotope data, consistent with other field, petrographic and geochemical evidence. Cordierite in the cordierite-bearing granites is not “restitic” from a deep source area, but rather is xenocrystic from the high-grade metamorphic country rock (nebulites).

Description: The Layos Granite forms elongated massifs within the Toledo Complex of central Spain. It is late-tectonic with respect to the F2 regional phase and simultaneous with the metamorphic peak of the region, which reached a maximum temperature of 800–850°C and pressures of 400–600 MPa. Field studies indicate that this intrusion belongs to the “regional migmatite terrane granite” type. This granite is typically interlayered with sill-like veins and elongated bodies of cordierite/garnet-bearing leucogranites. Enclaves are widespread and comprise restitic types (quartz lumps, biotite, cordierite and sillimanite-rich enclaves) and refractory metamorphic country-rocks including orthogneisses, amphibolites, quartzites, conglomerates and calc-silicate rocks.These granites vary from quartz-rich tonalites to melamonzogranites and define a S-type trend on a QAP plot. Cordierite and biotite are the mafic phases of the rocks. The particularly high percentage of cordierite (10%–30%) varies inversely with the silica content. Sillimanite is a common accessory mineral, always included in cordierite, suggesting a restitic origin. The mineral chemistry of the Layos Granite is similar to that of the leucogranites and country-rock peraluminous granulites (kinzigites), indicating a close approach to equilibrium. The uniform composition of plagioclase (An25), the high albitic content of the K-feldspar, the continuous variation in the Fe/Mg ratios of the mafic minerals, and the high Ti content of the biotites (2.5–6.5%) suggest a genetic relationship.Geochemically, the Layos Granite is strongly peraluminous. Normative corundum lies between 4% and 10% and varies inversely with increase in SiO2. The CaO content is typically low (

Description: Cretaceous and Cainozoic granites and rhyolites in the northwestern U.S.A. provide a record of silicic magmatism related to diverse tectonic settings and large-scale variations in crustal structure. The Late Cretaceous Idaho Batholith is a tonalitic to granitic Cordilleran batholith that was produced during plate convergence. Rocks of the batholith tend to be sodic (Na2O 〉 K2O), with fractionated HREE, negligible Eu anomalies, and high Sr contents, suggesting their generation from relatively mafic sources at a depth sufficient to stabilise garnet. In contrast, Neogene rhyolites of the Snake River Plain, which erupted in an extensional environment, are potassic (K2O 〉 Na2O), with unfractionated HREE patterns, negative Eu anomalies, and low Sr contents, suggesting a shallower, more feldspathic source with abundant plagioclase. Eocene age volcanic and plutonic rocks have compositions transi- tional between those of the Cretaceous batholith and the Neogene rhyolites. These data are consistent with a progressively shallowing locus of silicic magma generation as the tectonic regime changed from convergence to extension.

Description: A review of granite emplacement mechanisms in transcurrent, extensional and contractional (thrust sense) shear zones reveals that in all three tectonic settings the plutons have been constructed by multiple granite sheeting parallel to the shear zone walls and deformation fabrics. The sheets and plutons are non-Andersonian in type and were emplaced obliquely to the principal stress directions. Their shape and orientation is more likely to reflect the exploitation of faults and shear zones which were active during emplacement. Sheeting (dyking) is therefore also likely to be the mechanism of ascent along fault zones in the crust.

Description: Granites and their associated comagmatic felsic volcanic rocks occur in most Proterozoic provinces of Australia. Using multi-element, primordial-mantle-normalised abundance diagrams and various petrological characteristics, Australian Proterozoic granites can be subdivided into five groups: (i) I-type, Sr-depleted, Y-undepleted, restite-dominated, (ii) I- type, Sr-depleted, Y-undepleted, fractionated, low in incompatible elements, (iii) I-type Sr-depleted, Y-undepleted, enriched in incompatible elements (anorogenic granites), (iv) I-type, Sr-undepleted, Y-depleted, (v) S-type, Sr-depleted, Y-undepleted. The four Sr-depleted groups dominate, and group (iv) is of very limited extent. A comparison of these Proterozoic granites with Australian and Papua New Guinean granites of other time periods shows that these characteristic Sr-depleted Y-undepleted patterns are also dominant in early Palaeozoic granites. They are significantly different from those of granites in modern island arcs associated with subduction, and with most granites from Archaean terranes, where the multi-element diagrams are dominated by Sr-undepleted, Y-depleted patterns.The Sr-depleted, Y-undepleted patterns are thought to indicate source regions that contained plagioclase but not garnet, whilst the Sr-undepleted, Y-depleted patterns are taken to correspond with the presence of garnet, but not plagioclase, in the source rocks. The Sr-depleted, Y-undepleted patterns also only occur in regions where the lower crustal structure is dominated by an underplated mafic layer with a P-wave velocity of 7·2-7·-4 km/s. In contrast, in regions where the granites are dominated by Sr-undepleted, Y-depleted patterns, such as in the Archaean and in Cainozoic island arcs, this intermediate velocity layer is not present, and the crust-mantle boundary is very sharp.Two other distinctive compositional changes have been noted among the I-type granites of different age. Firstly, Na is highest in Archaean and Cainozoic granites, and lowest in early Proterozoic granites; Palaeozoic and Mesozoic granites have intermediate values. Secondly, late Archaean and Proterozoic granites are the most enriched in K, Th and U, while the Cainozoic and early Archaean tonalites are the most depleted; Palaeozoic and Mesozoic granites again contain intermediate amounts of those elements.

Description: Using the ion microprobe SHRIMP we have analysed zircons from the Ben Vuirich, Glen Kyllachy, Inchbae and Vagastie Bridge granites from the Scottish Caledonides, in an attempt to resolve the ages of inherited zircons shown to be present in these granites by previous conventional multigrain analyses. Middle Proterozoic age components were found in inherited zircons from all four granites. Late Proterozoic (900–1,100 Ma) components have been identified in zircons from the Glen Kyllachy and Ben Vuirich granites in the Grampian Highlands. A Late Archaean age has only been detected in one zircon from the Glen Kyllachy granite. The distribution of inherited components in the granite zircon populations could reflect fundamental divisions in the age composition of granite source rocks; however, detailed assessment of this possibility must await further ion microprobe analyses on zircons from many more granites.SHRIMP isotopic and U, Th and Pb analyses were made on successive shells of zoned zircon surrounding inherited cores from the Glen Kyllachy granite to monitor chemical changes during magmatic zircon growth. Results show that zircon shells have characteristic but significantly different Th, U and Pb concentrations. Magmatic zircon from the Vagastie Bridge granite also forms as clearly defined oscillatory zoned shells around unzoned nuclei of inherited zircon. However, the distinction between magmatic and inherited zircon in zircons from the Inchbae granite is less clear. Zircons from the Ben Vuirich granite occur as euhedral, magmatic zircons, or as rounded, subhedral, inherited zircon grains. A SHRIMP age of 597 ± 11 (2σ) Ma for euhedral magmatic zircon from this granite is identical, within the uncertainty, to the conventional multigrain zircon age of 590 ± 2 (2σ) Ma reported by Rogers et al. (1989) and confirms the conclusions of those authors that sedimentation of the Dalradian sequence took place in the Precambrian.

Description: Melting experiments with plagioclases were performed in the systems Ab-An, Ab-An-H2O, Qz-Ab-An-H2O, and Qz-Or-Ab-An-H2O-CO2. The experimental products were analysed by electron microprobe, and the kinetics of the reactions were studied qualitatively.Melting of the plagioclase in the system Ab-An (P = 1 atm, T = 1420°C) is very fast in the first minutes but becomes slower with increasing run duration and is incomplete even after 1000 hours. The Ab/An fractionation between melt and residual plagioclase is similar to that described by Bowen (1913).Melting kinetics of plagioclase in the system Ab-An-H2O ( = 5 kbar, T = 1000°C) is controlled by the diffusion of water into the plagioclase structure. Melting is especially fast parallel to the a-axis. The experimental products show separation of melts and crystals.In the tonalite system Qz-Ab-An-H2O, equilibrium melting could be observed down to 830°C ( = 2 kbar) but not a lower temperatures. The kinetics of the reaction is enhanced by deficiency or excess of alumina in the aluminosilicate melt surrounding the plagioclase crystals. The fractionation of Ab and An between melt and plagioclase crystals is more pronounced in the presence of quartz than in the Ab-An-H2O system. The ratio An/An + Ab is approximately 0·35 in the melt and 0·85 in the coexisting plagioclase T = 880°C).In the haplogranodiorite system Qz-Or-Ab-An-H2O–CO2, melting reactions were performed at P = 0·5 kbar, T = 880°C, and of approximately 0·5. It is assumed that near equilibrium compositions of melt and coexisting residual plagioclase could be obtained in long duration runs (run time = 60 days). The distribution of Ab and An between melt and minerals is similar to that observed in the tonalite system. The partial melt coexisting with an An-rich plagioclase and Or-rich K-feldspar is relatively poor in An.

Description: The granites of Hong Kong comprise a variety of assemblages dominated by chemically evolved compositions. They are divided into two suites based on petrographic, geochemical, and age criteria. The oldest and most primitive intrusive units are deformed biotite-hornblende granodiorites and monzogranites of the Lamma Suite. These rocks are characterised by high CaO (1·4-2·7%), and low Nb and Y contents. The Lion Rock Suite (LRS) is dominated by relatively undeformed monzogranite with subordinate quartz syenite and comprises three subgroups. Granites of subgroup I are separated into coarse- and fine- to medium-grained lithologies. The fine- to medium-grained granites are predominantly fluorite-bearing with silica contents ranging from 75·5-78%. They are characterised by high total REE, Ga, F, Rb, Nb, and Y contents and yield a Rb-Sr whole-rock isochron age of 155 ± 6 Ma with an initial 87Sr/86Sr ratio of 0·7101 ± 0·0060 (MSWD = 4·6). Granites of subgroup II comprise a diverse range of compositions (SiO2 = 63–77%) and are characterised by highly variable trace element abundances. Coarse-grained granites yield an age of 148 ± 9 Ma with an initial 87Sr/86Sr ratio of 0·7060 ± 0·0006 (MSWD = 0·1). Granites of subgroup III are moderately to highly evolved (SiO2 = 72·5-77·9%) and the silica-rich compositions are marked by enrichment in Y, Nb, Rb and depletion in Ba and Sr. Rb-Sr whole-rock isochron ages for individual plutons vary from 138 ± 1 to 136 ± 1 and corresponding initial 87Sr/86Sr ratios are 0·7080 ± 0·0002 (MSWD = 1·2) and 0·7092 ± 0·0006 (MSWD = 0·4). Granites of the Lamma Suite and coarse-grained granites of LRS subgroup I are interpreted as synorogenic I-types, whereas those of LRS subgroups II and III are interpreted as late-orogenic to postorogenic, fractionated I-types. Fineto medium-grained granites of LRS subgroup I have distinctive A-type affinities and together with their association with quartz syenite indicate a transition from compressional to tensional tectonics.

Description: Geochemical and isotopic data obtained from three bimodal basalt-rhyolite fields in west-central Arizona point to significant variation in the sources of the siliceous products despite petrological similarities between them. The studied fields, which straddle the boundary between the Basin and Range and Colorado Plateau physiographic provinces, include Castaneda Hills (CH) in the Basin and Range, Kaiser Spring (KS) in the Transition Zone, and Mount Floyd (MF) in the Colorado Plateau. Two types of rhyolite (high-silica [HSR] and low-silica [LSR]) occur as lavas in the KS and MF fields, whereas all analysed CH samples are HSR. These lavas generally post-date low-angle extension of the Basin and Range crust and become generally younger towards the Colorado Plateau. Our isotopic data illustrate that the CH rhyolites require a source with comparatively radiogenic Sr, that most rhyolites require a source with comparatively unradiogenic 206Pb/204Pb, and that the MF-HSR require a source with comparatively radiogenic Nd and 206Pb/204Pb. The isotopic data clearly indicate that the western Arizona rhyolites contain a large crustal component. Importantly, the Pb isotopic compositions of the rhyolites illustrate the transition between two crustal provinces identified by other workers on the basis of Nd and Pb isotopic studies of Proterozoic granites. The Sr, Nd, and Pb isotopic compositions of our rhyolites can be modelled by mixing a basaltic component with three hypothetical crustal end-members which themselves may be formed by mixing two crustal components. One crustal component, which is characterised by unradiogenic Pb and Sr, may be similar to the mafic gneiss xenoliths of Tule Tank on the Colorado Plateau. The second crustal component, which has more radiogenic Sr and Pb, may be similar to the Proterozoic Fenner Gneiss of southeastern California. This conceptual model indicates an apparent increase in the contribution of the depleted Tule Tank source from the Basin and Range onto the Colorado Plateau and accommodates the notion that there is an underlying consistency to the petrogeneses of the western Arizona rhyolites as suggested by their chemistry and mineralogy. Although the CH and KS lavas require only one crustal end-member, the MF-HSR and LSR require two isotopically distinct sources. This difference may be attributed to the homogenisation of diverse crustal lithologies by ductile stretching during crustal extension.

Description: The Criffell pluton in southwestern Scotland (397 Ma, a Newer Granite of late Caledonian age) is concentrically zoned with outer granodiorites of typically I-type aspect passing into inner granite with more evolved characteristics. The zonation is examined in terms of the compositional surfaces of bulk parameters such as SiO2 and Rb/Sr and compositional variation is best modelled as multi-pulse, there being greater variation in bulk composition between pulses than within pulse. Published variations in Sr, Nd and O isotopes reflect the derivation of the pulses from separate and isotopically distinct sources. Other evidence for open-system behaviour includes mingling with mafic magmas to form enclaves, whereas closed-system behaviour is indicated by restite separation in the early granodiorites, and fractional crystallisation in the late granites. A dominant infracrustal I-type magma formed the first pulse followed by magma derived from more evolved crustal rocks (mainly metasediments of varying ages and maturities). Experimental fluid-absent melting of amphibolite and metapelite at about 900°C has shown that significant quantities of melt can be generated, respectively with I-type and S-type characteristics. Despite having similar bulk compositions, these melts have very different viscosities and densities for the same H2O contents (ηS-type〉ηI-type and ρS-type≤ρI-type). It is argued that the rheological controls on magma escape from the source region along complex and tortuous pathways favour the more fluid I-type melts over the more viscous (and only slightly less dense) S-type melts. This constraint could have the effect of reversing the expected buoyancy-driven emplacement sequence, and may represent an alternative rheological differentiation mechanism for the formation of some zoned plutons.

Description: Most zoned plutons described in the geological literature have mafic rims and felsic cores and are referred to as “normally zoned”, whereas relatively few “reversely zoned” intrusions (felsic rims and mafic cores) have been described. That unusual zonation pattern has been variously attributed to in situ processes or to the reordering of an underlying, vertically stratified, magma chamber either by intrusion through an orifice or by emplacement of composite diapirs. The Turtle Pluton is an early Cretaceous, reversely zoned, intrusion that is divided into four facies: a Rim Sequence that is graditionally zoned from bt + ilm + muse monzogranite to hb + bt + mt + sph granodiorite; a Core Facies of more homogeneous hb + bt + mt + sph granodiorite to quartz monzodiorite; between these two facies, a structural discontinuity termed the Schlieren Zone; and an Eastern Facies of monzogranite to granodiorite. Field relationships, distribution of strain, and geochemical and isotopic studies (including a range of initial87Sr/86Sr from 0·7085–0·7065) suggest that the reverse zonation of the Turtle Pluton is the result of sequential emplacement of two diapirs each derived from the same underlying, vertically stratified, magma chamber, and that the Rim Sequence zonation is chiefly the result of mixing of intermediate and felsic magmas from distinct sources accompanied by minor fractional crystallisation.

Description: Approximately 10-15 vol% of the Neogene Hoyazo dacite consists of Al-rich restite rock inclusions (A12O3 = 20–45%) and monocrystal inclusions derived therefrom. Restite material and dacitic melt were formed syngenetically from a (semi-)pelitic rock sequence by means of anatexis. Restite rock fragments and dacite show similar high δ18O values (13–16‰) corresponding to those found for sedimentary material. Striking monocrystal restite inclusions in the dacite rock are graphite crystals measuring a few hundred μm, 0.5–10 mm blue cordierite crystals and 2–10 mm ruby red crystals of almandine-rich garnet (1.1 ± 0.2 vol%). Although the almandine crystals are perfectly euhedral, they are identical in every respect to the crystals found in the Al-rich restite rock inclusions and cannot be crystallisation products of the magmatic melt. The dacite also contains many inclusions of quartz gabbroic and basaltoid material which contains inclusions identical to the restite material found in the dacitic glass base. Many basaltoid inclusions show well-developed chilled borders. These inclusions may represent a more mafic magma of deeper origin which mixed with some dacite magma before mingling into it.

Description: The Cooma Complex of southeastern New South Wales comprises an andalusite-bearing S-type granodiorite surrounded by migmatites and low-pressure metamorphosed pelitic and psammitic sediments. The migmatite formed by the melting reaction:Biotite + Andalusite + K-feldspar + Quartz + V = Cordierite + Liquidat about 350–400 MPa , 670-730°C.The melanosome consists of biotite + cordierite + andalusite + K-feldspar + plagioclase + quartz + ilmenite, whereas the leucosome consists of cordierite + K-feldspar + quartz with extremely rare biotite and plagioclase. In a closed system, freezing of the leucosome melt patches should have resulted in cordierite back-reaction with melt to produce biotite and andalusite. The virtually anhydrous mineralogy of the leucosome patches, lack of cordierite reaction and the absence of biotite selvedges at the leucosome-melanosome contacts, indicates that the melt did not completely solidify in situ. These observations can be explained by an initial peritectic melting reaction in the migmatite being arrested from back-reaction upon cooling because of the removal of hydrous melt, enabling leucosome cordierite to escape back-reaction. We propose that the melanosome is the residue of partial melting but that the leucosome patches do not represent frozen melt segregations but rather the liquidus minerals (cumulates) which precipitated from the melt.In the restite-rich granodiorite from the core of the Cooma Complex, cordierite of similar composition to that in the migmatite has reaction rims of biotite and andalusite and there are coexisting biotite and andalusite in the matrix. The granodiorite consisted of about 50 wt% melt together with resite biotite, quartz and plagioclase, which can possibly be identified in the surrounding migmatite. Previous work suggested that the Cooma Granodiorite can be derived from a mixture of the surrounding metasediments which are of similar composition in the high and low-grade areas surrounding the granodiorite. Re-examinatibn of those data shows that the high-grade metasediments are more An-rich than the low-grade rocks. The Cooma Granodiorite is very similar to the high-grade rocks in terms of Or-Ab-An ratio. This suggests derivation of the Cooma Granodiorite from the high-grade rocks and not from the relatively An-poor low-grade rocks which are typical of exposed sediments in the Lachlan Fold Belt. It is most likely that the granodiorite and envelope of high-grade rocks have been emplaced into the compositionally different lower grade rocks from slightly greater depths.

Description: Blocks of medium-grained granodiorite to 4 m, and minor diabase, quartz diorite, granite, aplite and granophyre, are common in ejecta of the ∼6,900 yrBP calderaforming eruption of Mount Mazama. The blocks show degrees of melting from 0–50 vol%. Because very few have adhering juvenile magma, it is thought that the blocks are fragments of the Holocene magma chamber's walls. Primary crystallisation of granodiorite produced phenocrystic pl + hyp + aug + mt + il + ap + zc, followed by qz + hb + bt + alkali feldspar (af). Presence of fluid inclusions in all samples implies complete crystallisation before melting. Subsolidus exchange with meteoric hydrothermal fluids before melting is evident in δ18O values of −3·4+4·9‰ for quartz and plagioclase in partially melted granodiorites (fresh lavas from the region have δ18O values of +5·8−+7·0‰); δ18O values of unmelted granodiorites from preclimatic eruptive units suggest hydrothermal exchange began between ∼70 and 24 ka. Before eruption, the granitic rocks equilibrated at temperatures, estimated from Fe-Ti oxide compositions, of up to ∼1000°C for c. 102–104 years at a minimum pressure of 100-180 MPa. Heating caused progressive breakdown or dissolution of hb, af, bt, and qz, so that samples with the highest melt fractions have residual pl + qz and new or re-equilibrated af + hyp + aug + mt + il in high-silica rhyolitic glass (75-77% SiO2). Mineral compositions vary systematically with increasing temperature. Hornblende is absent in rocks with Fe-Ti oxide temperatures 〉870°C, and bt above 970°C. Oxygen isotope fractionation between qz, pl, and glass in partially fused granodiorite also is consistent with equilibration at T≥900°C (Δ18Oqz.pl = +0·7 ± 0·5‰). Element partitioning between glass and crystals reflects the large fraction of refractory pl, re-equilibration of af and isolation or incomplete dissolution of accessory phases. Ba and REE contents of analysed glass separates can be successfully modelled by observed degrees of partial melting of granodiorite, but Rb, Sr and Sc concentrations cannot. Several samples have veins of microlite-free glass 1–5 mm thick that are compositionally and physically continuous with intergranular melt and which apparently formed after the climactic eruption began. Whole-rock H2O content, microprobe glass analysis sums near 100% and evidence for high temperature suggest liquids in the hotter samples were nearly anhydrous. The occurrence of similar granodiorite blocks at all azimuths around the 8 × 10 km caldera implies derivation from one pluton. Compositional similarity between granodiorite and pre-Mazama rhyodacites suggests that the pluton may have crystallised as recently as 0·4 Ma; compositional data preclude crystallisation from the Holocene chamber. The history of crystallisation, hydrothermal alteration, and remelting of the granitic rocks may be characteristic of shallow igneous systems in which the balance between hydrothermal cooling and magmatic input changes repeatedly over intervals of 104-106 years.

Description: The 1·65–1·54 Ga rapakivi granites of southeastern Fennoscandia represent the silicic members of a bimodal magmatic association in which the mafic members are tholeiitic diabase dykes and minor gabbroic-anorthositic bodies. They are metaluminous to slightly peraluminous A-type granites and occur as high-level batholiths and stocks in an E-W-trending belt extending from Soviet Karelia to southwestern Finland. The Soviet Karelian granites were emplaced into the contact zone between Archaean craton and Svecofennian juvenile 1·9Ga-old crust, while the Finnish granites were intruded into the Svecofennian crust. Deep seismic soundings show that the rapakivi granites and the contemporaneous, mainly WNW or NW-trending diabase dyke swarms are situated in a zone of relatively thin crust. Below the Wiborg Batholith there exists a domal structure in the lithosphere in which a transitional zone (mafic underplate) occurs between the crust and the mantle.The Nd isotopic evolution of the rapakivi granites (εNd(T) −3·1—−0·2) corresponds to the evolution of the 1·9Ga-old Svecofennian crust, as do their Pb isotopic compositions. This implies that the Finnish granites represent anatectic melts of the Svecofennian crust. In contrast, the Soviet Karelian granites show isotopic composition indicative of substantial incorporation of Archaean lower crust material. Petrochemical modelling of one of the Finnish batholiths shows that its parental magma could have been generated by c. 20% melting of a granodioritic source and that fractional crystallisation was important during the subsequent evolution of this magma.The rapakivi granites are redefined as A-type granites that show the rapakivi texture at least in larger batholiths. The field, geochemical, and seismic data indicate that the classical Finnish rapakivi granites were generated in an anorogenic extensional regime by partial melting of the lower/middle crust. The melting, and possibly also the extensional tectonics, were related to upwellings of hot mantle material which led to intrusion of mafic magmas at the base and into the crust.

Description: The thermodynamic relations embodied in the Quasicrystalline Model of Burnham and Nekvasil (1986), as recently extended by the author, have been used to quantitatively assess the feldspar-quartz liquidus relations in two I-type (Jindabyne and Moruya) and two S-type (Bullenbalong and Dalgety) suites of Australian granites, using analytical data provided by B. W. Chappell and co-workers. Among the more notable results obtained from these calculations at a constant pressure of 5·0kbar and = 0·30 (≍2·8 wt% H2O), for purposes of comparison, are that: (1) felsic melts of remarkably uniform, but distinctive composition can be extracted from each suite, leaving solid residues in amounts up to 65 mol%; (2) all melts from both S-type suites have two feldspars plus quartz on their liquidii, whereas both I-type suites have only plagioclase plus quartz on their liquidii; (3) the total solid residue ranges from 27-63% in the Jindabyne suite, from 15–62% in the Moruya suite, from 30–65% in the Bullenbalong suite, and from 27–65% in the Dalgety suite; (4) liquidus temperatures of the S-type Bullenbalong and Dalgety melts are similar (856° and 860°C), reflecting similar feldspar compositions of An53, Or75 and An60, Or77, respectively; (5) liquidus temperatures of the I-type Jindabyne and Moruya melts, however, are distinctly different (950° and 894°C), reflecting correspondingly different plagioclase compositions of An80 and An52; (6) the calculated liquidus plagioclase composition throughout a given suite is very uniform (±1%) and amounts to as much as 46% of the total rock; and (7) these calculated liquidus and residual plagioclase compositions are also the same, within the uncertainty of measurement, as those of the plagioclase crystal-cores determined optically by A. J. R. White. The only plausible explanation for this remarkable consanguinity in plagioclase liquidus, residue, and crystal-core compositions, hence liquidus temperatures, is that the bulk of the residue is restite, in accordance with the model of White and Chappell (1977). This explanation is corroborated by the very systematic variations in the amounts of individual restite minerals with respect to total restite contents. Accordingly, those members of each suite that contain more than 60% total restite probably closely represent the bulk composition of the source rock, which is dioritic or andesitic for the Jindabyne suite, tonalitic or dacitic for the Moruya suite, pelitic metagreywacke for the Bullenbalong suite, and feldspathic metagreywacke for the Dalgety suite. As a corollary, those members with less than 60% restite must have undergone melt-restite segregation (unmixing), probably during ascent and emplacement.

Description: Two models for the heating responsible for granite generation during convergent deformation may be distinguished on the basis of the length- and time-scales associated with the thermal perturbation, namely: (1) long-lived, lithospheric-scale heating as a conductive response to the deformation, and (2) transient, localised heating as a response to advective heat sources such as mantle-derived melts. The strong temperature dependence of lithospheric rheology implies that the heat advected within rising granites may affect the distribution and rates of deformation within the developing orogen in a way that reflects the thermal regime attendant on granite formation; this contention is supported by numerical models of lithospheric deformation based on the thin-sheet approximation. The model results are compared with geological and isotopic constraints on granite genesis in the southern Adelaide Fold Belt where intrusion spans a 25 Ma convergent deformation cycle, from about 516 to 490 Ma, resulting in crustal thickening to 50–55 km. High-T metamorphism in this belt is spatially restricted to an axis of magmatic activity where the intensity and complexity of deformation is significantly greater, and may have started earlier, than in adjacent low-grade areas. The implication is that granite generation and emplacement is a causative factor in localising deformation, and on the basis of the results of the mechanical models suggests that granite formation occurred in response to localised, transient crustal heating by mantle melts. This is consistent with the Nd- and Sr-isotopic composition of the granites which seems to reflect mixed sources with components derived both from the depleted contemporary mantle and the older crust.

Description: A two-parameter Margules method has been developed for modelling the thermodynamic mixing properties and hypersolidus phase relations of albite-water (ab-w) melts. The method is based largely on phase-equilibrium and calorimetric data that are either currently available or readily obtainable; P-V-T data are not required.The new modelling method has been applied to calculate: (1) thermodynamic mixing properties for ab-w melts at 2-5 kbar, 815°C; and (2) hypersolidus phase relations for the ab-w system at 2·5 kbar. Results are uniformly positive—activity-composition relations are similar to those predicted by equations based on P-V-T data, excess enthalpies are in good agreement with data obtained from calorimetry, and calculated phase relations are fully compatible with phase-equilibrium data for ab-w melts acquired at 2·5 kbar.It is concluded that the Margules method for thermodynamic modelling of ab-w melts is a practical alternative to the P-V-T modelling method.

Description: Granites of the Batholith of Central Patagonia were emplaced into late Precambrian metamorphic basement rocks and Palaeozoic orthogneisses (here dated by Rb–Sr whole-rock errorchrons at 346 ±35 Ma and 267 ±27 Ma), and are in fault-contact with younger volcanic rocks, mostly andesites. Two main suites of granites are recognised: both are much younger than their previously-supposed Late Palaeozoic age. The Gastre Suite is composed predominantly of hornblende-biotite granodiorite and monzogranite, often slightly foliated, and has yielded a Rb-Sr whole-rock isochron age of 220 ±3 Ma. The Lipetrén Suite includes biotite monzogranite and leucogranite, grading into quartz-feldspar porphyries and felsites, and has been dated at 208 ±1 Ma. A minor granodioritic unit yields an apparently Middle Jurassic age of 172 ±15 Ma. Textural evidence and hornblende geobarometry confirm that these are high-level sub-volcanic intrusions. Metaluminous compositions are common in the Gastre Suite, but are subordinate to highly siliceous (〉70% SiO2) and peraluminous varieties in the Lipetrén Suite. Despite this compositional bias, the granites are almost entirely calcalkaline and I-type, and have volcanic-arc rather than intraplate or collisional trace element characteristics. Initial87Sr/86Sr ratios of 0·706 and –2·5 are also relatively primitive and are thought to indicate a juvenile crustal contribution (Nd “depleted mantle” model ages are less than 1,000 Ma).The Triassic “Gondwana” magmatic episode is thus not an expression of Permo-Triassic collision of an allochthonous Patagonian terrane with the rest of southern S America, but may be related to the initial stages of supercontinent rifting.

Description: Like many granites, the Late Cretaceous intrusives of the eastern Mojave Desert, California, have heretofore provided useful but poorly focused images of their source regions. New studies of lower crustal xenoliths and inherited accessory minerals are sharpening these images.Xenoliths in Tertiary dykes in this region are the residues of an extensive partial melting event. Great diversity in their composition reflects initial heterogeneity (both igneous and sedimentary protoliths) and varying amounts of melt extraction (from 70%). Mineral assemblages and thermobarometry suggest that the melting event occurred at T ≥ 750°C at a depth of about 40 km. Present-day Sr, Nd, and Pb isotopic ratios indicate a Mojave Proterozoic heritage, but unrealistic model ages demonstrate the late Phanerozoic adjustment of parent/daughter ratios. A link between these xenoliths and the Late Cretaceous granites, though not fully documented, is probable; in any case, they provide invaluable clues concerning a crustal melting event, recording information about nature of source material (heterogeneous, supracrustal-rich), conditions of melting (moderately deep, moderately high T, accompanied by partial dehydration), and melt extraction (highly variable, locally extensive).The Old Woman-Piute granites contain a large fraction of inherited zircon and monazite. A SHRIMP ion probe investigation shows that these zircons record a Proterozoic history similar to that which affected the Mojave region. Zonation patterns in zircons, and to a lesser extent monazites and xenotimes, document multiple phases of igneous, metamorphic, and sedimentary growth and degradation, commonly several in a single grain. Low Y in portions of the cores of inherited zircons and monazites and in monazites and outer portions of zircons from the xenoliths appear to indicate growth in equilibrium with abundant garnet.

Description: One of the most outstanding apparent examples in N America of a forcibly emplaced pluton is the Papoose Flat Pluton of eastern California. Sideways expansion of this granitic pluton, during emplacement into a series of Cambrian shelf strata, has been regarded by early workers as resulting in the observed intense crystal plastic deformation of the pluton's mylonitic border facies and surrounding country rocks. This deformation is evidenced by up to 90% thinning of individual stratigraphic layers within the pluton's metamorphic aureole, although such intense penetrative deformation of the country rocks is not observed outside the aureole.Previously published quartz c-axis fabrics associated with this deformation (and presented on projection planes oriented perpendicular to lineation) were interpreted as being symmetrical with respect to foliation and lineation, implying almost coaxial deformation histories. Such fabrics could be interpreted as indicating that the pluton evolved by “ballooning” as a result of new magma being intruded into its core during emplacement. However, a major problem with applying the strict ballooning model to the Papoose Flat Pluton is that while oblate strains would be expected to develop in association with a ballooning mechanism, the mylonitic rocks of this elongate WNW-ESE-trending pluton and its aureole are characterised by both a strongly developed foliation, which is concordant with the pluton's margin, and an intense, NW-SE trending, shallow plunging stretching lineation.Previously published fabrics from the Papoose Flat Pluton and its metamorphic aureole have been rotated on to a projection plane oriented parallel to lineation and perpendicular to foliation. Examination of the fabrics in this projection plane has revealed that they are in fact dominantly asymmetric, and that a constant sense of asymmetry is detected across the pluton, suggesting a consistent (top-to-the-SE) shear-sense. This new interpretation is strongly supported by microstructural and petrofabric analysis of additional L-S tectonites collected, during recent fieldwork, from both the aureole and quartz veins within the pluton's gneissic border facies. Thus mylonite formation around the Papoose Flat Pluton could have involved large-scale consistently oriented translation and associated shearing, rather than passive “blister-like” coaxial deformation associated with pluton ballooning. It should be noted that mylonitic deformation is restricted to the western half of the pluton, features indicative of a more “permitted” emplacement mechanism being found in the eastern portion of the pluton.The detected top-to-the-SE shear-sense could be interpreted as indicating that the granitic material forming the western part of the pluton was forcibly intruded in a northwestward direction from the pluton source as a nearly solidified wedge beneath a static cover of sedimentary rocks. Alternatively, the detected shear sense could also be interpreted as indicating SE-directed thrusting of the cover rocks over the underlying pluton, the western margin of the pluton suffering intense mylonitic deformation, while the eastern margin was located in a “stress-shadow” region. If this alternative interpretation is correct, then the deformation temperatures indicated by the pattern of quartz c-axis fabrics dictate that thrusting must either be synchronous with pluton emplacement, or at least have commenced during the early stages of pluton cooling.

Description: A brief history of research into the unusual laminated and spherulitic East Kirkton Limestone (Brigantian, Viséan) is given. It documents the paucity of fossil finds until 1984, when S. P. Wood discovered a previously unsuspected terrestrial biota. Some early finds, such as stromatolites, have since been overlooked, while others were misinterpreted, e.g. a ‘fish-bone’ collected before 1870 proves to be amphibian. A formal lithostratigraphic description is given of the three beds that comprise the c. 15 m sequence in East Kirkton Quarry: the East Kirkton Limestone, overlain by Little Cliff Shale and Geikie Tuff, the latter two being here formally named. Lithological descriptions and a unit-by-unit distribution of major elements of the biota are provided for a measured section comprising 88 units. This is based on bed-by-bed excavations carried out 1985-92, supplemented by nine boreholes. Two 3 m-thick massive limestones lenses are recorded from the quarry and a probable third was proved in a borehole. Brief reports are given on the ‘stromatolites’ (by M. R. Walter), bivalve molluscs (R. M. C. Eagar and R. B. Wilson), ostracods (J. Pollard) and gypsum pseudomorphs.

Description: Eldeceeon rolfei gen. et sp. nov. a primitive anthracosaur from the Brigantian of East Kirkton, Scotland, is described. Uniquely among non-mammalian tetrapods, its ribs are restricted to the anterior half of the presacral column. Eldeceeon lacks the diagnostic features of the two suborders of anthracosaur, the Anthracosauroideae and Seymouriamorpha, and may represent their sister group.

Description: Silvanerpeton miripedes gen. et sp. nov. is a small gracile anthracosauroid. The holotype is an almost complete articulated specimen in black shale. Its anthracosaur characters include tabular-parietial contact, with a tabular horn and a moderate surangular crest indicating relationship with the embolomeres. It has gastrocentrous vertebrae with poorly ossified centra and neural arches, and the presacral vertebral count is estimated to be over 30. There are a number of apparently primitive characters as found in other anthracosauroids include a closed palate, mobile basal articulation, and an intertemporal. It differs from the other recognised species of anthracosaur at East Kirkton, Eldeceeon rolfei, in vertebral count, number of ribs, interclavicle shape, relative limb length, and in having an unossified tarsus, and a pedal phalangeal count of 23455.Disarticulated bones from East Kirkton including large limb and vertebral elements may belong to this taxon, to Eldeceeon rolfei or to as yet unidentified taxa.

Description: The Viséan sequence at East Kirkton was deposited in a shallow lake, set within a richly vegetated landscape formed of volcanic cones a few hundred metres high. There was little volcanic activity, however, while the lake existed, and the many tuff horizons within the sequence were washed in during weathering. The lake may have been generally cool, though of unusual water chemistry, as a result of which the spherulitic East Kirkton Limestone precipitated. At times, however, water temperatures may have risen sharply through localised hot-spring activity; both factors deterred ‘normal’ aquatic life.The bulk of the preserved biota consists of plants (permineralisations and compressions) and dominantly land-living animals, including the oldest terrestrial tetrapods (amphibians and reptiliomorphs), large terrestrial-aquatic eurypterids, the first harvestman and rare millipedes. All these animals lived close to the lake, in a fire-prone forest dominated by gymnosperms and pteridosperms.At a late stage in the history of the lake, deposition of spherulitic limestones was replaced by black shales, bearing a ‘standard’ Oil-Shale fish fauna, suggesting that the isolated lake had linked with a larger fish-bearing water body. This is coupled with a shift to a lycopod-dominated flora and may indicate a climatic change to wetter conditions. Finally the lake silted up with tuff, ending an existence of only a few tens of thousands of years.

Description: The Late Triassic fauna of the Lossiemouth Sandstone Formation (LSF) from the Elgin area, Scotland, has been pivotal in expanding our understanding of Triassic terrestrial tetrapods. Frustratingly, due to their odd preservation, interpretations of the Elgin Triassic specimens have relied on destructive moulding techniques, which only provide incomplete, and potentially distorted, information. Here, we show that micro-computed tomography (μCT) could revitalise the study of this important assemblage. We describe a long-neglected specimen that was originally identified as a pseudosuchian archosaur, Ornithosuchus woodwardi. μCT scans revealed dozens of bones belonging to at least two taxa: a small-bodied pseudosuchian and a specimen of the procolophonid Leptopleuron lacertinum. The pseudosuchian skeleton possesses a combination of characters that are unique to the clade Erpetosuchidae. As a basis for investigating the phylogenetic relationships of this new specimen, we reviewed the anatomy, taxonomy and systematics of other erpetosuchid specimens from the LSF (all previously referred to Erpetosuchus). Unfortunately, due to the differing representation of the skeleton in the available Erpetosuchus specimens, we cannot determine whether the erpetosuchid specimen we describe here belongs to Erpetosuchus granti (to which we show it is closely related) or if it represents a distinct new taxon. Nevertheless, our results shed light on rarely preserved details of erpetosuchid anatomy. Finally, the unanticipated new information extracted from both previously studied and neglected specimens suggests that fossil remains may be much more widely distributed in the Elgin quarries than previously recognised, and that the richness of the LSF might have been underestimated.

Description: We present the bat assemblage from the early Miocene (MN4, 16.9–15.95 MY) basin of Ribesalbes-Alcora, which has yielded the remains of ten chiropteran taxa. Bat assemblages are rarely recovered in the fluvio-lacustrine fossil record. A bat species described in this work, Cuvierimops penalveri sp. nov., is a new form of a typically Oligocene free-tailed bat. In addition, the other molossids Hydromops helveticus, Rhizomops cf. brasiliensis, Chaerephon sp., Tadarida sp., and the vespertilionids Myotis cf. intermedius and Miostrellus aff. petersbuchensis, as well as undetermined fossils ascribed to the genera Submyotodon, Plecotus, and Rhinolophus are described. This is the first record of the genus Rhizomops in the early Miocene; the genus Cuvierimops is the first recording from the Neogene, while the ‘Lazarus taxon’ Chaerephon is the first fossil record of this genus, registered previously only in Holocene deposits. This bat assemblage with a high abundance of molossids is typical from the early Oligocene of western Europe, while in the early Miocene from Europe the molossids are scarce. The abundance of these bats is consistent with the presence of a tropical forest surrounding a paleolake. The fossils from the Ribesalbes-Alcora Basin represent the most complete bat assemblage of the Iberian Peninsula during this age, and significantly increase our knowledge about the early Miocene bats of Europe.

Description: A better understanding of the role of Quaternary-era climate change in the development of regional hydrology in the Loess Plateau and the impact on regional ecosystems is needed. In particular, a thorough examination of the permeability and recharge under different conditions in the fifth loess–palaeosol layer is required. The fifth loess–palaeosol layer is located at the southern edge of the Jinghe River in the Guanzhong Basin, and was examined to better understand these conditions. A constant head permeability test was conducted at 11 points that covered different stratum of loess–palaeosol, and 55 corresponding undisturbed soil samples were analysed for porosity, magnetic susceptibility, and grain size. Results showed that: (1) with an increase in hydraulic gradient, the permeability coefficient of the upper part of the loess and the lower part of the palaeosol showed contrasting characteristics – this phenomenon was closely related to climatic conditions during the sedimentary period, post-sedimentary microbial activity, and to certain properties relating to permeability in the strata under similar monsoon effects; (2) the Loess Plateau, alternately dominated by the East Asian summer and winter monsoons, exhibited different grain-size compositions in the sedimentary layer, which, in turn, made the permeability in the loess noticeably more stable than that in the palaeosol; and (3) different aquifer characteristics and recharge conditions between the loess–palaeosol layers can be primarily explained by the intensity of the pedogenesis, which depended on extreme dry-old glacial climates and relatively humid-warm interglacial climates. These findings show that climate change played an important role in influencing hydrological systems in the loess–palaeosol sequence.

Description: Hydrocarbon migration mechanism into a reservoir is one of the most controversial in oil and gas geology. The research aimed to study the effect of supercritical carbon dioxide (СО2) on the permeability of sedimentary rocks (carbonates, argillite, oil shale), which was assessed by the yield of chloroform extracts and gas permeability (carbonate, argillite) before and after the treatment of rocks with supercritical СО2. An increase in the permeability of dense potentially oil-source rocks has been noted, which is explained by the dissolution of carbonates to bicarbonates due to the high chemical activity of supercritical СО2 and water dissolved in it. Similarly, in geological processes, the introduction of deep supercritical fluid into sedimentary rocks can increase the permeability and, possibly, the porosity of rocks, which will facilitate the primary migration of hydrocarbons and improve the reservoir properties of the rocks. The considered mechanism of hydrocarbon migration in the flow of deep supercritical fluid makes it possible to revise the time and duration of the formation of gas–oil deposits decreasingly, as well as to explain features in the formation of various sources of hydrocarbons and observed inflow of oil into operating and exhausted wells.

Description: Pareiasaurs were globally distributed, abundant, herbivorous parareptiles with the basal-most members found only in the mid-Permian of South Africa. These basal forms form a monophyletic group and were locally abundant and became extinct at the top of the Tapinocephalus Assemblage Zone at the end of the Guadalupian. Four species of basal pareiasaurs are currently recognised: Bradysaurus baini, B. seeleyi, Embrithosaurus schwarzi and Nochelesaurus alexanderi, but they are all poorly understood and there remains historic uncertainty as to their validity. In this paper, our second contribution designed to improve understanding of the basal group, we present the first detailed cranial description and updated diagnosis for Nochelesaurus alexanderi and demonstrate that it is a distinct taxon based on one cranial autapomorphy, a large transversely wide postparietal, and a combination of cranial characters. Within the local group of mid-Permian pareiasaurs, we recognise new dental features of Nochelesaurus alexanderi: non-symmetrical marginal cusp arrangements on upper and lower teeth resulting from an extra basal mesial cusp; an incipient horizontal cingulum on lower jaw teeth, sometimes with one or two tiny medial cingular cusps; and up to ten marginal cusps. Our study demonstrates that tooth morphology and orientation, cranial ornamentation, morphology of the cheek bosses, shape of the postfrontal and postparietal, and morphology of the distal paroccipital process of the opisthotic are the most useful to identify South African mid-Permian pareiasaurs.

Description: Herein, we present a synthetic study combining iron (Fe) speciation and biomarkers in sediment samples from Luguhu Lake to investigate their relationship and the environmental significance thereof. Mössbauer spectroscopy and gas chromatography–mass spectrometry were used for these measurements. The results suggest that (a) there is a strong negative correlation between Fe2+/Fe3+ and the ratio of pristane to phytane (Pr/Ph), indicating that both Fe2+/Fe3+ and Pr/Ph effectively present the inorganic and organic aspects, respectively, of the oxidation–deoxidation environment in Luguhu Lake; (b) palaeotemperature may be a factor, in addition to the redox conditions, that affects the Fe2+/Fe3+ ratio, and it might play a favourable role in studies of palaeotemperature; and (c) the relative abundance of Fe in Luguhu Lake is affected by the palaeoclimate and the environment in which the palaeosediment was deposited. The mechanism of change in the total area (the total absorption area of Mössbauer spectrum) with the palaeoenvironment seems to be explained by the loss of Fe, which occurs as the water drains out of the lake, and the increase in Fe loss from the sediment as rainfall levels increase.

Description: During the Upper Ordovician–Lower Silurian, chert was widely distributed in the Zhongbao Formation in the eastern part of the North Qilian Orogen. The origin and the tectonic setting of these chert were largely unknown. In order to analyse the material provenance, sedimentary environment, their formation and the tectonic setting, we present petrology and geochemical research on chert samples collected from Shihuigou Section. The evidence provided by radiolarite occurrences, Aluminium (Al)–iron (Fe)–manganese diagram and the silicon(Si)/Si + Al + Fe + calcium ratios suggesting a non-hydrothermal input and the biogenic origin chert. The geochemical features and the petrographic signatures have shown that the chert was also influenced by a terrigenous origin. It is considered that the deposition of the Late Ordovician chert is mainly affected by tectonic collision and volcanic ash events. During the Late Ordovician–Early Silurian transition, huge amounts of volcanic ash were released by massive volcanic activity that fell into the ocean, triggering the proliferation of radiolarians. Finally, in the Late Ordovician–Lower Silurian the tectonic setting of the North Qilian Orogen was not a typical deep-water basin, nor a typical continental margin, but a multi-island deep-water basin, which is closed to the mainland.

Description: Echimyidae is the most widely diversified family among hystricognath rodents, both in the number of species and variety of lifestyles. In the Patagonian Subregion of southern South America, extinct echimyids related to living arboreal species (Echimyini) are recorded up to the middle Miocene, whereas all the known southern fossils since the late Miocene are linked to terrestrial and fossorial lineages currently inhabiting the Chacoan open biome in eastern South America. In this work, we describe a new genus of echimyid rodent, Paralonchothrix gen. nov., from the late Miocene of northwestern Argentina and western Brazil. Its single recognised species, Paralonchothrix ponderosus comb. nov., is represented by two hemimandibles. One of them comes from a level of Loma de Las Tapias Formation, underlying a tuff dated at 7.0 ± 0.9 Ma (Huayquerian age, late Miocene); the other specimen comes from the ‘Araucanense’ of Valle de Santa María (type locality, Huayquerian age, late Miocene). A phylogenetic analysis linked Paralonchothrix to Lonchothrix, both being the sister group to Mesomys. Thereby, for the first time, an echimyid linked to living Amazonian arboreal clades is recognised for the late Miocene of southern South America. Paralonchothrix gen. nov. thus represents an exceptional record that raises the need to review the postulated evolutionary pattern for echimyids recorded at high latitudes since the late Miocene. The new genus provides a minimum age (ca.7 Ma) in the fossil record for the divergence between Mesomys and Lonchothrix. The palaeoenvironmental conditions inferred for the late Miocene in western and northwestern Argentina suggest savanna-type environments, with areas with more closed woodlands in peri-Andean valleys. The record of Paralonchothrix gen. nov. supports the hypothesis that this area would have maintained connections with tropical biomes of northern South America during the late Miocene.

Description: Moradisaurine captorhinid eureptiles were a successful group of high-fibre herbivores that lived in the arid low latitudes of Pangaea during the Permian. Here we describe a palaeoassemblage from the Permian of Menorca (Balearic Islands, western Mediterranean), consisting of ichnites of small captorhinomorph eureptiles, probably moradisaurines (Hyloidichnus), and parareptiles (cf. Erpetopus), and bones of two different taxa of moradisaurines. The smallest of the two is not diagnostic beyond Moradisaurinae incertae sedis. The largest one, on the other hand, shows characters that are not present in any other known species of moradisaurine (densely ornamented maxillar teeth), and it is therefore described as Balearosaurus bombardensis gen. et sp. nov. Other remains found in the same outcrop are identified as cf. Balearosaurus bombardensis gen. et sp. nov., as they could also belong to the newly described taxon. This species is sister to the moradisaurine from the lower Permian of the neighbouring island of Mallorca, and is also closely related to the North American genus Rothianiscus. This makes it possible to suggest the hypothesis that the Variscan mountains, which separated North America from southern Europe during the Permian, were not a very important palaeobiogeographical barrier to the dispersion of moradisaurines. In fact, mapping all moradisaurine occurrences known so far, it is shown that their distribution area encompassed both sides of the Variscan mountains, essentially being restricted to the arid belt of palaeoequatorial Pangaea, where they probably outcompeted other herbivorous clades until they died out in the late Permian.

Description: While the external infiltration of water has been identified from modern geothermal and/or fossil hydrothermal systems through stable isotopes, the physicochemical boundary conditions like the initial oxygen isotopes of water $( {{ m delta }^{ 18}{ m O}_{ m W}^{ m i} } ) $ and rock as well as alteration temperature were implicitly presumed or empirically estimated by the conventional forward modelling. In terms of a novel procedure proposed to deal with partial re-equilibration of oxygen isotopes between constituent minerals and water, the externally infiltrated meteoric and magmatic water are theoretically inverted from the early Cretaceous post-collisional granitoid and intruded Triassic gneissic country rock across the Dabie orogen in central-eastern China. The meteoric water with a $ {{ m delta }^{ 18}{ m O}_{ m W}^{ m i} } $ value of −11.01 ‰ was externally infiltrated with a granitoid and thermodynamically re-equilibrated with rock-forming minerals at 140°C with a minimum water/rock (W/R)o ratio around 1.10 for an open system. The lifetime of this meteoric hydrothermal system is kinetically constrained less than 0.7 million years (Myr) via modelling of surface reaction oxygen exchange. A gneissic country rock, however, was externally infiltrated by a magmatic water with $ {{ m delta }^{ 18}{ m O}_{ m W}^{ m i} } $ value of 4.21 ‰ at 340°C with a (W/R)o ratio of 1.23, and this magmatic hydrothermal system could last no more than 12 thousand years (Kyr) to rapidly re-equilibrate with rock-forming minerals. Nevertheless, the external infiltration of water can be theoretically inverted with oxygen isotopes of re-equilibrated rock-forming minerals, and the ancient hydrothermal systems driven by magmatism or metamorphism within continental orogens worldwide can be reliably quantified.

Description: Groundwater is widely used in the semi-arid region of Remila plain (Khenchela, Algeria) for urban and agricultural supplies. An integrated statistical and hydro-geochemical approach was performed with 70 water samples in order to identify the main processes and the origin of water salinisation. The results have suggested the dominance of three chemical facies: Sulphato cloruro calcic (SO4–Cl–Ca) in the northeastern part, Sulphato cloruro calci magnisian (SO–4Cl–Ca–Mg) in most of the waters andalkali-earth bicarbonate (HCO3–Ca–Mg) in the southeastern part. Although based on principal component analysis and hierarchical clustering analysis, the statistical approach identified three water groups: (1) saline water (17 %; total dissolved solids 〉1000 mg l−1 with the dominance of Sulphate (SO42−)); (2) moderately saline water (17 %) with a dominance of bicarbonate (HCO3−); and (3) moderately saline water (66 %) with mixed facies. The binary diagrams confirmed the predominance of three processes: evaporite dissolution and/or precipitation, combined by ionic exchange. In the northeastern part of the area, however, another process was detected – the saline intrusion of Sabkha water, favoured by extensive groundwater use.

Description: The integration of biostratigraphical, wireline log, geophysical and available geochronological ages has identified two principal periods of volcanism in the Faroe–Shetland and Rockall basins. The first is pre-breakup, upper Danian to lower Thanetian: in the Rockall and Faroe–Shetland basins, isolated volcanic activity from 62 Ma to 58.7 Ma is identified in areas closely linked to the SSW–NNE structural fabric of the continental margin. Volcanic activity was concentrated at basin flank fissures and localised point sources. This rift-flank volcanism led to widespread volcanic ash deposition, localised lava flow fields and the formation of igneous centres. Some of the Hebridean and onshore central complexes (e.g., Rum) were uplifted and rapidly eroded during the later pre-breakup period, while additional accommodation space was developed in the adjacent offshore basins. Onset and termination of pre-breakup volcanism is correlated to intra-plate stress regimes in Europe, following the cessation of convergence of Africa and Europe in the Danian. The second is syn-breakup, upper Thanetian to Ypresian, initiated at ca.57 Ma in the Rockall and Faroe–Shetland basins. Initial high-volume extrusive igneous successions were focussed to the W in the Faroe–Shetland Basin. In the centre and E of the Faroe–Shetland and Rockall basins, separate eruption loci developed along pre-existing lineaments either as fissure or point-sourced lava fields. Short-term cessation of eruption at ~55.8 Ma was followed by resumption of flood basalt eruptions and a shift in focus to the NW. Fluctuations in the syn-breakup eruption tempo are reflected in the formation and subsequent rejuvenation of prominent unconformities, only previously recognised as a single erosive event. The W and northward shift of eruption focus, and the eruption of mid ocean ridge basalt-type lavas in the syn-breakup period reflect the onset of lithospheric thinning in the nascent North Atlantic Rift prior to flooding of the rift and eruption of the widespread lower Ypresian Balder Formation tephras.