ALBERT

Notes: Abstract Existing geochronological data are reviewed and new Rb-Sr, K-Ar and 39Ar–40Ar ages are presented, including a suite of 33 mica ages from a 20 km north–south tunnel section. These data are discussed in relation to the thermal history from the overthrusting of the Autroalpine nappes c. 65 Myr ago to the present. The earliest phase of metamorphism, involving lawsonite crystallization, is associated with emplacement of these nappes. Subsequently, temperatures in the rocks beneath rose, at a mean rate of 3–6°C/Myr, until the climax of metamorphism.At high structural levels, published data indicate an age 〉 35 Myr for the metamorphic climax. In contrast, a new 39Ar–40Ar step-heating age of 23.8 ± 0.8 Myr on amphibole, from near the base of Peripheral Schieferhülle, closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels. Following the climax, near-isothermal uplift and erosion reduced pressure to c. 1 kbar before white mica closure at 19 Myr; this implies uplift at 〉3 mm/yr.Along the tunnel section, white mica K-Ar ages vary systematically from 24 Myr to 16.5 Myr with position relative to a late 4 km amplitude dome whereas biotite Rb-Sr ages are uniform at 16.5 Myr across the whole profile; doming is thus dated at 16.5 Myr with transient uplift rates 〉5 mm/yr. At other times uplift rates were 〈1 mm/yr.

Notes: Abstract Granulites at Fyfe Hills in Enderby Land, Antarctica, crystallized at temperatures in excess of 850°C, and possibly as high as 1000°C, and at pressures of 8-10kbar during the mid to late Archaean. A number of features, including repeated retrograde metamorphism at 5.5-8kbar, retrograde reaction textures, and rimward zoning in pressure sensitive systems, suggest that following peak metamorphism the granulites stabilized at a depth of 18-26 km. After stabilization, the granulites cooled near-isobarically to temperatures of 600-700°C. Assuming a total crustal thickness of 35-40 km during this late Archaean interval of isobaric cooling, the peak metamorphic crustal thickness is estimated at 35-56 km. This estimate is significantly less than the 60-70 km obtained by summing the depths of the present levels of exposure (26-34 km) and the thickness of the crust presently beneath Fyfe Hills (approxi-mately 35km) and is, therefore, consistent with independent evidence for extensive post-Archaean thickening of the Enderby Land crust.

Notes: Abstract A Hercynian charnockite occurs within high-grade gneisses in the Agly Massif, French Pyrenees. Its thermal history has been evaluated using the Fe-Mg distribution coefticient (KD) between garnet and biotite. These minerals have different origins but similar compositions in the charnockites and host gneisses. In the charnockite, the Bi–Ga pairs are the retrograde products of Opx alteration. This Opx reaction with feldspar can be written. Opx + PI + Fluid 1(H2O + Al + K + Fe + Ti) = Bi + Ga + Q + Fluid 2(H2O + Na). The garnets are relatively Ca poor (4–2.5% grossular); they are automorphic and zoned in the gneisses and poikiloblastic in the charnockites. Both types show a retrograde rim (of few hundred microns’width) across which Fe and Mn increase as Mg decreases. The biotites show a good correlation between the octahedral cations (Ti4++ Fe2+) and (Mg2++ Al3+VI); Ti and Fe both increase, whereas Mg and AlVI decrease. There is an inverse linear correlation between Fe2+ and Mg2+ and the Fe/Mg ratio increases as Ti increases. The relation between Ti and KGa-BiDFe-Mg is less clear: it seems that KD slightly decreases as Ti increases. The equilibration temperatures of Ga–Bi pairs are discussed: the charnockite Ga-Bi pairs have equilibrated between 550°C and 600°C; whereas those of the gneisses have equilibrated between 550°C and 650°C. Two main thermal steps appear: one in the gneisses between 600-650°C and a second one in both the gneisses and the charnockites between 550°C and 600°C.

Notes: Abstract Whole-rock and mineral analyses of polydeformed mica-schist, quartzite, marble and amphibolite are presented from Signy Island, South Orkney Islands, part of the Scotia metamorphic complex. Whole-rock chemistry suggests that the amphibolites are the metamorphosed equivalent of enriched tholeiitic and alkali basalts of an oceanic intraplate basalt series. These, together with limestones and Mn-rich cherts of an oceanic island assemblage were tectonically mixed with trench or trench inner slope basin sediments in a subduction zone environment. Variation in mineral chemistry indicates an increase in temperature and decrease in pressure during metamorphism; pressures of 8 kbar and temperatures of approximately 545°C were reached during amphibolite facies metamorphism in the latter stages of deformation. These new data provide good evidence to support the previous interpretation of the Scotia metamorphic complex as a subduction complex.

Notes: Abstract The mid-Tertiary blueschists, eclogites and eclogitic gneisses of northern New Caledonia are the products of four phases of regional metamorphism and deformation (D1–D4). Omphacite, lawsonite and Mn-rich garnet isogradic surfaces were developed during the second deformation (D2) under prograde pressure and temperature conditions. Subsequent deformations (D3–D4) folded these D2 isogradic surfaces. However, within the P-retrograde, T-prograde metamorphic environment of the D4 phase, omphacite altered to albite and chlorite; as a result, a late-stage sub-horizontal isogradic surface developed for omphacite-out where this mineral preserved as relics within syn-D4 albite porphyroblasts. Other minerals that crystallized for the first time (epidote) or had rim additions (almandine phengite) during D4, also form nearly horizontal isogradic surfaces. Porphyroblastic garnet and albite contain inclusion trails, which allow their microstructural development and crystallization of the matrix to be traced from D2 to D4.Late syn-D4 the temperature increased markedly in association with an extensive exothermic decarbonation, even though the rocks were in a state of pressure retrogression. This caused considerable neocrystallization, recrystallization and growth of mattix and porphyroblasts such that, although S2 foliation crenulated by D3 and D4 is readily observable, almost all signs of stored strain due to D3 and D4 have been removed, and the deeper schists and eclogitic gneisses superficially appear to have undergone a drastic annealing recrystallization, post-dating deformation.

Notes: Abstract This, the second of two papers, represents the application of a least squares approach, discussed in the previous paper, to the generation of an internally consistent thermodynamic dataset involving 60 reactions among 43 phases, in the system K2O–Na2O–CaO–MgO–Al2O3–SiO2–H2O–CO2. We make the assumption that all the thermodynamic data, with the exception of enthalpies of formation of the phases, are well known, and solve for an internally consistent set of enthalpies which reproduces the 60, experimentally determined, phase equilibrium reactions. An important difference between our dataset and that of previous alternatives in the literature is that we are able to determine the uncertainties on, and correlations between, the enthalpies of formation for all phases in the set, and hence are able to apply simple error propagation techniques to determine the uncertainties in any phase equilibrium calculations performed using this dataset. Selection of reactions, for geothermometry and geobarometry, may be more readily made by choosing equilibria with small uncertainties in their thermodynamics. Our data are in reasonably close agreement with the high temperature molten oxide calorimetry results on silicate minerals where available, a fact which lends a degree of confidence to the results.

Notes: Abstract The Pennine rocks exposed in the south-east Tauern Window, Austria, contain mineral assemblages which crystallized in the mid-Tertiary ‘late Alpine’regional metamorphism. The pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers. The results are:(a) In the garnet+chlorite zone, 2–5 km structurally above the staurolite+biotite isograd: T= 490.50°C, P= 7° 1 kbar;(b) Within 0.5 km of the staurolite+biotite isograd: T= 560±300C, P=7.1 kbar;(c) In the staurolite+biotite zone, c. 2.5 km structurally below the staurolite+biotite isograd: T= 610±30°C, P=7.6±1.2 kbar;(d) In the staurolite+biotite zone, 3–4 km structurally below the staurolite+biotite isograd: T= 630±40°C, P= 6.6±1.2 kbar.The pressure estimates imply that the total thickness of overburden above the basement-cover interface in the mid-Tertiary was c. 26.4 km. This overburden can only be accounted for by the Austro-Alpine units currently exposed in the vicinity of the Tauern Window, if the Altkristallin (the ‘Middle Austro-Alpine’nappe) was itself buried beneath an ‘Upper Austro-Alpine’nappe or nappe-pile which was 7.4 km thick at that time.The occurrence of epidote + margarite + quartz pseudomorphs after lawsonite in garnet, indicates that part of the Mesozoic Pennine cover sequence in the south-east Tauern experienced blueschist-facies conditions (T〈450°C, P〈12 kbar) in early Alpine times. Evidence from the central Tauern is used to argue that the blueschist-facies imprint post-dated the main phase of tectonic thickening (D1A) and was thus a direct consequence of continental collision.Combined oxygen-isotope and fluid-inclusion studies on late-stage veins, thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation, suggest that they crystallized from aqueous fluids at 1.1±0.4 kbar and 420.20°C.Early Alpine, late Alpine and vein-formation P–T constraints have been used to construct a P–T path for the base of the Mesozoic cover sequence in the south-east Tauern Window. The prograde part of the P–T path, between early and late Alpine metamorphic imprints, is unlikely to have been a smooth curve and may well have had a low dP/dT overall; the decompression (presumably due to erosion) which occurred immediately before the thermal peak and possibly also earlier in the Tertiary, was probably partly or completely cancelled by the effects of early- to mid-Tertiary (D2A) tectonic thickening. The thermal peak of metamorphism was followed by a phase of almost isothermal decompression, which implies a period of rapid uplift in the middle Tertiary.The peak metamorphic P–T estimates are compared with the solutions of England's (1978) one-dimensional conductive thermal model of the Eastern Alps, and are shown to be consistent with the idea that the late Alpine metamorphism was caused by tectonic burial of the Pennine Zone beneath the Austro-Alpine nappes in the absence of extraneous heat sources, such as large intrusions, at depth.

Notes: Abstract Activity-composition relations in oligoclase near the peristerite gap are investigated in pelites from the Central Menderes Massif. The pressure of metamorphism is estimated independently, from garnet-rutile-ilmenite-kyanite-quartz, as being in the range 4–7 kbar. In the temperature range, 450–600°C approximately, both the Newton-Haselton calibration of the garnet-plagioclase-kyanite-quartz geobarometer and a related simple treatment of garnet-plagioclase-muscovite-biotite give a wide range of apparent pressures, correlated with plagioclase composition and ranging up to 11–12 kbar where the plagioclase is most sodic. This effect is attributed to failure of the activity model for plagioclase used in the Newton-Haselton treatment. It is inferred that, in the present area, γplagAn decreases with increasing XplagAn in the range An15-An25. The data can be interpreted in terms of high γplagAn in the high-albite structure at these temperatures, modified to lower values by ‘e’ordering in the more calcic oligoclases. The ordering appears to be independent of the peristerite gap, and the data do not support the interpretation of the gap as a solvus. Garnet-plagioclase assemblages are unreliable as geobarometers where the plagioclase is more sodic than approximately An20 and T 〈 700°C, and should instead be used to investigate the γ-X behaviour of the plagioclase where independent geobarometry can be used as a constraint.

Notes: Abstract Precambrian granulites of the Aldan shield in southern Yakutia, USSR, form a massif of 200,000 km2 bounded by younger fold-belts to the south, west and east. The massif consists of several blocks that reflect a primary heterogeneity of composition and differences in structural and thermodynamic evolution of different parts of the area. According to structural and petrological data the massif can be divided into two megablocks: eastern Aldan and western Aldan. They are separated by a narrow meridional fold-belt. Structural evolution of this central zone was determined by the geodynamics of the mega-blocks and was completed in the late Archaean. Towards the south, this central zone is ‘transformed’into the relatively small Sutam block adjoining the Stanovoy fold-belt that bounds the Aldan shield on the south. The Sutam block is separated from the other structural units of the Aldan shield by a system of north trending grabens filled by post-Archaean sediments.The Aldan shield is composed of Archaean high-grade granulites, while the Stanovoy fold-belt, to the south, consists of highly foliated Proterozoic rocks metamorphosed under relatively lower-grade conditions. However, relics of the granulites are mapped within the fold-belt. They contain high-grade assemblages (e.g. Opx + Sil + Qz, Sap + Qz, Opx + Gr + Sil, etc.). One of the relics, the Tokskii block, which is only slightly touched by diaphthoresis, is located in the southeastern part of the Stanovoy fold-belt. Metamorphic conditions of the Tokskii block are compared with those of the Sutam block and a similar evolution of the units is revealed.Mineral assemblages and mineral compositions do not vary within each unit, but they change in a north-south direction. The Opx + Sil + Qz assemblage has been found only in Sutam and Tok, but not in eastern Aldan and western Aldan. The Sap + Qz assemblage has been found in the Tokskii block but has not yet been found in the Sutam block. The pyrope content in garnets, from metapelites of both blocks, is significantly higher than that from the Aldan (eastern and western blocks) rocks to the north. The most important assemblages from different units of the Aldan shield have been studied using the electron microprobe in order to unravel the metamorphic evolution of the granulites and thus to deduce the thermodynamic regime of this evolution. A geodynamic model for the Aldan shield is discussed in terms of Archaean island arc development.

Notes: Abstract The high-grade meta-plutonic rocks of this study lie entirely within the Jotun Nappe of the southern Norwegian Caledonides. They are divisible on the basis of metamorphic grade and petrographic character into three units, the Storadalen Complex (SCX), the Svartdalen Gneiss (SG), and the Mjølkedøla Purple Gabbro (MPG). The SCX is a differentiated series of ultrabasic to intermediate rocks now showing only tectonite fabrics. It has been metamorphosed to spinel-Iherzolite granulite facies grade. The broadly monzonitic SG is weakly tectonized and internally differentiated. Its metamorphic grade does not exceed plagioclase-lherzolite granulite facies grade. The mis-named MPG is also broadly of monzonitic composition but it retains a coarse ophitic texture, and is of amphibolite facies grade. A gradational boundary exists between the MPG and SG, but the contact between these two units and the SCX is the steeply dipping Tyin-Gjende Fault. The three units represent a comagmatic body of mid-Proterozoic age, metamorphosed during a Sveconorwegian event and finally dismembered and upthrust during the Caledonian Orogeny.The new trace element analyses reported here show that the three rock units have remarkably similar trace element abundances and trends. K-Rb covariation shows increasing K/Rb ratios with increasing K. These patterns were produced by magmatic fractionation processes acting at deep crustal levels, possibly in the presence of a non-aqueous fluid phase. With the exception of K and Sr, close similarities exist between the rocks of this study and present-day calc-alkaline basalts and andesites from island arcs. The high K content is regarded as a primary magmatic feature, but the available data are insufficient to indicate its origin. The Sr contents are abnormally high and are ascribed to metasomatism which occurred during either high-grade metamorphism or post-climactic cooling. There are no systematic geochemical variations with metamorphic grade or degree of deformation.

Notes: Abstract The calibration of geothermometers and geobarometers should involve not only the determination of the parameters in the equation used, but also the uncertainties on, and the correlations between, these parameters. This necessitates the use of a technique such as least squares. Given the poor performance of least squares in the presence of outliers in the data, techniques for identifying outliers for exclusion—regression diagnostics, and techniques for handling data which include outliers—robust regression and jackknifing, are essential. These techniques are summarized and their importance is emphasized, and they are applied to the calibration of the garnet-clinopyroxene Fe-Mg exchange geothermometer.The experimental data of Raheim & Green (1974) and Ellis & Green (1979) are explored using regression diagnostics to discover outliers in the data. After exclusion of the two influential outliers found, a new geothermometer equation for garnet-clinopyroxene Fe-Mg exchange is derived using robust regression and based on all the data: thus, T(K) = 2790 + 10P+ 3140xca,g/1.735 + In KD where T is in Kelvin and P is in kbar. This equation, as might be hoped, is essentially identical to that of Ellis & Green (1979). Equations for calculating the uncertainty in a calculated temperature, contributed by uncertainties in the calibration, are also derived.

Notes: Abstract Zircons have been studied from different layers of migmatites (from Arvika, western Sweden and Nelaug, southern Norway) and from a paragneiss (from Arvika) associated with one of the migmatites. The main purpose of the investigation is to establish whether or not information about zircons can help in the elucidation of the parentage and rock-forming processes of migmatites.The elongation ratio of zircons from all layers is small and characteristic of sedimentary zircons. Further, the absence of characteristic colours and the growth trends of the zircons (indicated by the reduced major axes) observed in the various samples both support a sedimentary parentage for these rocks. The zircons of all layers exhibit secondary growth (overgrowth, outgrowth and multiple growth) due to metamorphism. Compared with the zircons from the paragneiss, those of the migmatite layers are more clouded and less rounded, some of them becoming opaque or even skeletal; this is especially true of the zircons from the leucosomes. These observations indicate an alteration of the original sedimentary zircons in the migmatite, especially in the leucosomes, in response to the migmatization process, previously interpreted as partial melting.

Notes: Abstract Microprobe analysis of the continuous chemical evolution of coexisting biotite-garnet and biotite-garnet-staurolite has been undertaken from interbedded micaschists of the volcanodetrital group of the Vilaine. A thermobarometric study using pertinent mineralogical equilibria reveals a complex P-T evolution, continuous throughout time, from high pressure, medium temperature (kyanite zone) to medium pressure, high temperature (sillimanite zone), then low pressure, medium temperature (andalusite zone). The T, P, fH2o and XH2o variations have been calculated from coexisting biotite-garnet pairs, and from the equilibria: paragonite (in white mica) + quartz ± albite (in plagioclase) + Al silicate + H2O; and, 3 anorthite ± grossular + 2 Alsilicate + quartz. The P-T evolution is correlated with the continuous change in composition of minerals (using P–XMg and T–XMg diagrams) and with the evolution of assemblages. This continuous P-T-time evolution, correlated with the successive formation of S1-S2 foliations, allows us to propose a P-T-time-deformation path for the micaschists and to relate the growth of its mineral components to tectonic processes.

Notes: Abstract Chemical analysis (including H2, F2, FeO, Fe2O3) of a Mg-vesuvianite from Georgetown, Calif., USA, yields a formula, Ca18.92Mg1.88Fe3+0.40Al10.97Si17.81- O69.0.1(OH)8.84F0.14, in good agreement on a cation basis with the analysis reported by Pabst (1936). X-ray and electron diffraction reveal sharp reflections violating the space group P4/nnc as consistent with domains having space groups P4/n and P4nc. Refinement of the average crystal structure in space group P4/nnc is consistent with occupancy of the A site with Al, of the half-occupied B site by 0.8 Mg and 0.2 Fe, of the half-occupied C site by Ca, of the Ca (1,2,3) sites by Ca, and the OH and O(10) sites by OH and O. We infer an idealized formula for Mg-vesuvianite to be Ca19Mg(MgAl7)Al4Si18O69(OH)9, which is related to Fe3+-vesuvianite by the substitutions Mg + OH = Fe3++ O in the B and O(10) sites and Fe3+= Al in the AlFe site.Thermodynamic calculations using this formula for Mg-vesuvianite are consistent with the phase equilibria of Hochella, Liou, Keskinen & Kim (1982) but inconsistent with those of Olesch (1978). Further work is needed in determining the composition and entropy of synthetic vs natural vesuvianite before quantitative phase equilibria can be dependably generated. A qualitative analysis of reactions in the system CaO-MgO-Al2O3-SiO2-H2O-CO2 shows that assemblages with Mg-vesuvianite are stable to high T in the absence of quartz and require water-rich conditions (XH2O 〉 0.8). In the presence of wollastonite, Mg-vesuvianite requires very water-rich conditions (XH2O 〉 0.97).

Notes: Abstract Part of the augite in the Artfjället gabbro consists of symplectitic intergrowths between augite and blebs or lamellae of orthopyroxene. Mineral compositions are consistent with formation of these symplectites by exsolution of orthopyroxene from magmatic augite at a temperature of ca. 900–1000°C. The microstructures indicate that the exsolution mechanism is discontinuous precipitation, whereby the boundary of an augite grain sweeps through a neighbouring augite, leaving the symplectite in its wake. The formation of this symplectitic augite is catalysed by the presence of an intergranular water-rich fluid phase, which promotes grain boundary mobility.

Notes: Abstract Petrological data from intercalated pelitic schists and greenstones are used to construct a pressure–temperature path followed by the Upper Schieferhülle (USH) series during progressive metamorphism and uplift in the south-west Tauern Window, Italy. Pseudomorphs of Al–epidote + Fe-epidote + albite + oligoclase + chlorite after lawsonite and data on amphibole crystal chemistry indicate early metamorphism in the lawsonite-albite-chlorite subfacies of the blueschist facies at P± 7–8 kbar. Geothermometry and geobarometry yield conditions of final equilibration of the matrix assemblage of 475±25°C, 5–6 kbar; calculations with plagioclase and phengite inclusions in garnet indicate early garnet growth at pressures of ∼ 7.5 kbar. Garnet zoning patterns are complex and reversals in zoning can be correlated between samples. Thermodynamic modelling of these zoning profiles implies garnet growth in response to four distinct phases of tectonic activity. Fluid inclusion data from coexisting immiscible H2O–CO2–NaCl fluids constrain the uplift path to have passed through temperatures of 380 + 30°C at 1.3 + 0.2 kbar.There is no evidence for metamorphism of USH at pressures greater than ∼ 7.5 kbar in this area of the Tauern Window. This is in contrast to pressures of ± 10 kbar recorded in the Lower Schieferhülle only 2–3 km across strike. A history of differential uplift and thinning of the intervening section during metamorphism is necessary to reconcile the P–T data obtained from these adjacent tectonic units.

Notes: Abstract In pelites of the central Menderes Massif, albite and oligoclase with only slight chemical zoning coexist in apparent textural equilibrium in the garnet zone, staurolite zone, and staurolite + kyanite transition zone. The metamorphic temperature range is estimated as approximately 440–550°C (from the Hodges-Spear calibration of the garnet-biotite geo-thermometer), or 440–500°C (Ganguly-Saxena calibration). While oligoclase composition at the peristerite gap changes from An22 to An14, albite also becomes more sodic (An1,5–An0.6). The slope of the albite limb is thus the reverse of that reported in other areas, and may not be a true equilibrium feature. Occurrence of kyanite, at temperatures below the crest of the gap, is due to low water activity in the presence of graphite: aH2o is estimated at approximately 0.1–0.2 from the Na content of muscovite coexisting with albite + kyanite + quartz.

Notes: Abstract The Kvamsøy pyroxenite complex consists of olivine websterite, olivine gabbro and leucogabbro-norite which have been subjected to regional high P-T (HPT) metamorphism. The metamorphism has resulted in a range of disequilibrium textures with the development of coronas and pseudomorphism of the igneous phases. Reactions between felsic and mafic mineral domains have been controlled by variable and selective diffusion of elements, resulting in a variety of local plagioclase-breakdown reactions and in significant compositional variations for the product garnet. Restricted diffusion favours transient reaction stages with garnet ± spinel ± corundum ± zoisite after calcic plagioclase in olivine gabbro and olivine websterite and garnet ± spinel ± kyanite ± quartz + sodic plagioclase in leucogabbro-norite. Complete HPT reaction has produced garnet pyroxenite which consists of garnet + diopside + hornblende + zoisite in gabbroic rocks, while amphibolitization continued during the cooling and uplift history. Grt + Ky + Pl + Qtz geobarometry suggests pressures in the range 13-16 kbar for T= 750°C, comparable with the regional eclogite-forming metamorphism.

Notes: Abstract This, the first two papers, sets out the philosophy and methods of determining an internally consistent thermodynamic dataset for minerals using the least squares method. The applicability of the least squares method is discussed, and it is applied to a small set of experimental equilibria in the system Na2O–Al2O3–SiO2–H2O. The importance is stressed of defining not only the enthalpies of formation of minerals, but also the uncertainties and the correlations among them. The system which has been used as an illustration for this paper serves as a visual guide to the method, as it is small enough to represent graphically in two dimensions. In the paper which follows, we extend the method to a system of 60 equations (experimentally determined equilibria) involving 34 unknowns (enthalpies of formation of mineral end-members).

Notes: Abstract New occurrences of crossite and jadeitic pyroxene are described from a thick metabasite unit within the upper levels of the Peripheral Schieferhülle in the Tauern Window, Austria. Unusual textures are preserved which provide evidence for the reactions and mechanisms involved in the breakdown of crossite and jadeitic pyroxene. Zones of albite and chlorite, produced by reaction between crossite and paragonite, have been preserved due to sluggish reaction kinetics during decompression from the blueschist to the greenschist facies. The zonal sequence is interpreted in terms of chemical potential gradients in Na, Mg and Al, which have been established by overstepping the equilibrium boundary. Breakdown textures of jadeite-acmite pyroxene to a symplectite of albite + hematite + actinolite, and of crossite to talc and actinolite are also described.The occurrence of crossite and jadeitic pyroxene at high levels within the Peripheral Schieferhülle implies that even upper levels of the structural sequence have undergone blueschist facies metamorphism with pressures in excess of 8 kbar during the Alpine collisional event.

Notes: Abstract The chemical evolution of garnets from pelitic rocks of probable Palaeozoic age corresponds to a complex metamorphic evolution of the host rocks.Among the almandine-rich garnets (Alm60–80), two main types of evolution can be distinguished. Early Mn-rich garnets coexisting with kyanite may be replaced by plagioclase and then, during a late stage, by biotite and/or sillimanite. The second type of evolution corresponds to an overgrowth of Mn-poor late-stage garnet on older Mn-rich garnets which corresponds to a thermal peak with sillimanite-type of metamorphism. This new garnet may appear either as an overgrowth with a strong discontinuity, or as small, new euhedral garnet or as skeletal garnet.This chemical evolution of garnet corresponds to an early collisional stage of metamorphism (of high pressure type with high Mn values) of probable Ordovician age followed by uplift and a thermal peak (low Mn values) in Devonian times.

Notes: Abstract Small unexploited copper-lead-zinc deposits, characterized by a distinctive wall-rock association of cordierite quartzite, silica-undersaturated rocks, calc-silicate rocks and impure marbles, occur in quartzofeldspathic gneisses and mafic granulites of the Strangways Metamorphic Complex, central Arunta Block, central Australia. Available data support the hypothesis that these are metamorphosed volcanogenic ore bodies. The chemical compositions of the quartzofeldspathic gneisses are comparable with those of less metamorphosed felsic igneous rocks, particularly the felsic igneous rocks emplaced in the North Australian Orogenic Province in the interval 1880–1800 Ma; and the mafic granulites are chemically similar to basalts (olivine-normative tholeiites). The wall-rock suite can be correlated from chemistry and lithological association with the suites of wall rocks found in unmetamorphosed volcanogenic ore deposits. That the protolith of the cordierite quartzites may well have been leached tuff, similar to the illite-chlorite-quartz tuff found in volcanogenic ore deposits, is also shown by retrogression of the granulitefacies assemblage: cordierite-garnet-ortho-pyroxene-biotite-quartz in the cordierite quartzites to cordierite-anthophyllite-bearing assemblages and thence to chlorite-muscovite-quartz assemblages. Lenses of silica-undersaturated rocks with spinel and, less commonly, sapphirine are interpreted as the metamorphosed equivalents of chlorite-rich pods found within leached tuffs in volcanogenic ore deposits. The wall rocks form sheet-like bodies; this suggests that they were deposited in relatively shallow water, thus precluding the formation of massive sulphides.

Notes: Abstract Polymetamorphic orthoamphibole-bearing gneisses from the vicinity of shear zones in Casey Bay, Enderby Land, Antarctica, record both the overprinting of Archaean granulite lithologies by Proterozoic metamorphism and the subsequent evolution of the latter episode during localized deformation.Mineral chemistry and zoning relationships in orthoamphibole-garnet-kyanite-quartz and later orthoamphibole-garnet-cordierite-quartz assemblages are used together with interpretation of reaction and corona textures to constrain the Proterozoic pressure-temperature path experienced by the rocks. Consideration of reaction topologies, P-T-X(Fe-Mg-A1) relationships in orthoamphibole-bearing assemblages, and standard geothermobarometry indicate that the gneisses underwent a near-isothermal decompression P-T history (steep positive dP/dT) from ± 8 kbar and 700°C to 〈5.5kbar and 650°C. This uplift path is correlated with the general effects of Rayner Complex metamorphism and deformation which occurred after 1100 Ma in a major erogenic belt south of Casey Bay.

Notes: Abstract This contribution discusses the formation of stromatic high-grade migmatites. Volume considerations require that most of the leucosome material is not added from outside the system. A segregation mechanism is necessary except in those cases where the protolith of the migmatite already had a banded structure. Although partial melting is most often advocated to provide the segregation mechanism, several arguments can be raised against high degrees of melting: mineral compositions and even zoning patterns are similar in both mesosomes and leucosomes; sufficient degrees of melting at reasonable temperatures require more than the available amounts of water; the leucosomes do not always approximate to a minimum melt composition; high degrees of melting cannot occur without an appreciable volume increase; etc. Diffusion works as a segregation mechanism at low temperatures. As diffusion rates increase exponentially with temperature diffusion must become still more important as a segregation mechanism at high temperatures. A model is suggested based on the diffusion of components in response to the gradient δσ/δx, where σ= 1/3∑3i=1 σi is the mean pressure. In homogeneously strained rocks, σ3 is larger in rock parts rich in incompetent phases than in rock parts depleted in incompetent phases. Accordingly, mechanically competent but chemically incompetent high-volume phases like quartz and feldspars stressed in micadominated parts of a rock (high σσ) migrate to parts of the rock that are depleted in mica (low σ¯). It is suggested that hornblende occurring in many leucosomes may be premigmatitic or early syn-migmatitic and due to its mechanical competency it initiates the segregation. Diffusion occurs along grain boundaries and is enhanced by small amounts of ‘intergranular fluid’;. At the best, semiquantitative estimates of diffusion rates and distances indicate that the process should work over geological times.

Notes: Abstract Two Archaean synvolcanic stocks with contact aureoles occur in the Wawa greenstone belt near Wawa, Ontario, Canada. The Gutcher Lake and Jubilee stocks consist mainly of granitoid trondhjemite with feldspar laths mottled by white mica + calcite + epidote and rimmed by clear albite. Biotite is partly or wholly pseudomorphosed by chlorite + sphene; some epidote is partly altered to calcite + chlorite. The granitoid phase grades into a foliated phase of quartz + albite + white mica + calcite + chlorite near fracture zones traversing the stocks.The alteration of the Gutcher Lake stock along its foliated margin involved addition of K2O, H2O + CO2, MnO, plus Rb; loss of CaO plus Sr; and a shift in Fe+2/Fet from 0.66 to 0.81. The alteration of the Jubilee stock along the Darwin Shear involved addition of H2O + CO2; loss of Sr; and no significant shift in Fe+2/Fet. The greenschist alteration also modified the contact aureoles bordering both stocks.One interpretation is that regional metamorphism in the Archaean overprinted a greenschist assemblage on both stocks. The alteration was intense near fracture zones and sporadic remote from fractures. Lower integrated water to rock ratios along the Darwin Shear compared to the margin of the Gutcher Lake stock may explain the comparatively lower perturbation of the element abundances and redox state of iron.

Notes: Abstract Most porphyroblasts never rotate during ductile deformation, provided they do not internally deform during subsequent events, with the exception of relatively uncommon but spectacular examples of spiralling garnets. Instead, the surrounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast. Consequently, porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails, even where these structures have been rotated or obliterated in the matrix due to subsequent deformation. These relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subsequent deformation. They can also be used to determine the deformation history, as porphyroblasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component.

Notes: Abstract. A new method of measuring susceptibility to poaching is described, based on the concept that poaching is caused by a progressive loss of soil strength during repeated treading in wet weather. Susceptibility was measured by the rate of loss of strength in response to concurrent treading and irrigation at standard rates. The pressures exerted on the ground by a walking dairy cow were simulated by a purpose-built penetrometer, whilst water was applied via a network of plastic pipes fitted with syringe needles. Measurements were performed on four pasture soils having a range of clay contents and compared in relation to a mechanism proposed for the process. The results show susceptibility to be a property not wholly determined by the clay content of the soil, but suggest that it is influenced by bulk density and the strength of the sward, which will van, according to weather and pasture management.

Notes: IT IS now almost two years since the Royal Society published its authoritative study group report, The Nitrogen Cycle of the UK, the first comprehensive account of the nitrate issue. For the first time a complete picture was revealed of the nitrogen cycle in the UK and the Study Group was able to make a wide-ranging series of recommendations for future research.

Notes: Abstract. Sugarcane yields in the Herbert Valley in North Queensland have been declining over the past 15 years. Better yields are obtained where crops are grown on previously unused land. Soils under cane are more compacted, more acid, contain less organic matter and are lower in cation exchange capacity and exchangeable cations. These differences reflect soil degradation caused by intensive cultivation.Contributing factors to the degradation of soils include soil compaction and structural breakdown occurring during harvest and cultivation operations, losses of organic matter due to burning of crop residues and acidification of soils due to large applications of nitrogen fertilizers.Soil management practices should aim to increase soil organic matter levels, provide a more favourable biological environment, reduce physical damage to soils during harvesting and cultivation, reduce soil acidity and improve the effectiveness of fertilizing practices.

Notes: Abstract. Information on rainfall erosivity, soil erodibility and land capability is combined to produce a map of England and Wales showing areas with a risk of soil erosion at rates above the soil loss tolerance level. About 20 500 km2 or 37% of the arable area is at risk. Given the shallow soils and current rates of erosion, sustained use of this area for cereal, sugar beet and vegetable production beyond the first quarter of the next century is threatened. A further 4000 km2 is at risk in non-arable areas, mainly associated with blanket peat in the uplands and with coastal sand dunes.

Notes: Abstract. Data on lime loss and soil acidification obtained from a range of ADAS experiments are reviewed. The trials, which include drainage and lysimeter studies and long-term liming, manuring and soil management experiments, indicate a wide range of annual lime losses, with maximum rates in excess of 1000 kg ha−1 CaCO3.

Notes: Abstract. Survey information on the use of lime in England and Wales between 1974 and 1983 shows year-to-year fluctutions but no marked trend. Areas limed per year are compared for different types of region and cropping, and estimates given of the percentages of agricultural soils by pH according to rotation type. There was no general change in soil acidity between 1969–73 and 1974–78 but recent data show some reductions in grassland pH.

Notes: Abstract. The pH of soil surface horizons in Wales ranges from 3.5 to 7.5 and is significantly higher on agricultural land than under either rough grazing, unenclosed grassland or woodland. Sufficient information exists to map broad classes of soil pH. Rough grazing and woodland sites are concentrated on soil types which are naturally very acid. In Wales, such soils are found on the main mountain ranges and show up clearly on the map of pH. Their acidity is the result of an interrelationship between soil, climate and vegetation. However, afforestation, particularly with coniferous species, appears to lower the pH of the underlying soil. There is a trend in agricultural soils towards lower pH under a moister climate.

Notes: Abstract. A review of recent data shows that (i) dissolved CO2 has its greatest acidifying effect in soils with pH values above about 6.5, (ii) fertilizers containing NH−1+ ions or urea will acidify soil whether the ions are taken up directly by plants or are first nitrified, (iii) oxidation of nitrogen and sulphur in soil organic matter causes acidification especially after deforestation, and (iv) the acidifying effect of rainfall and dry deposition is due to sulphuric and nitric acids, SO2 and NH−1+ ions. A table is given showing the order of magnitude of each source of acidification.

Notes: Abstract. A careful study of the etiology and symptoms of the decline phenomena in stands of silver fir (Abies alba Mill.), Scots pine (Pinus sylv L.), European beech (Fagus silv. L.) and Norway spruce (Picea abies Karst.) in southern Germany leads to the conclusion that all these diseases, although exhibiting some common features (e.g. premature senescence and shedding of leaves, formation of transparent crowns), vary considerably between species and, within one particular species, between forest regions. It therefore seems plausible to assume, as a first approach, that we have to deal with different types of disease or decline, and consequently also with varying sets of causes or stress factors. This approach can be demonstrated best by reviewing the present knowledge of diseases in Norway spruce.

Notes: Abstract. The effects of ditch spacing (10, 20 and 40 m) and depth (60 and 90 cm) on watertable depth were measured in a Sitka spruce plantation before and after drainage and finally after part of the plantation had been clearfelled. No significant differences in watertable depth were recorded between drainage treatments mainly because the ditch spacings were too large but also because of inadequate calibration of the site before the drainage treatments were applied. By the time of felling, the site had been thoroughly calibrated for the behaviour of the watertable, enabling sensitive comparisons to be made, and a significant rise in the watertable was recorded after felling.

Notes: Abstract. Two hill pastures in north Dyfed, Wales, were each treated at reseeding in 1971 with 2.25, 4.5 and 9.0 kg ha−1 cobalt sulphate. Herbage samples for analysis of Co content were taken in summer at each site from 1971 to 1976 and also at site 1 from 1977 to 1983. Acetic acid extractable Co was measured in soil samples taken each winter for the same period at both sites. At site 1, on a peat, the treatments continued to give worthwhile increases in herbage and soil Co after 13 years. At site 2, on a mineral soil, the residual effects were small and lasted no more than four years. It is suggested that me lower response and residual value at site 2 is due to higher levels of exchangeable and easily reducible manganese.

Notes: Abstract. The reasons for bracken encroachment in Scottish hill land are examined. The cost effectiveness of bracken control methods are discussed and it is shown how the real cost of aerial spraying, the most practical method, has increased in the last decade. The waiving of the follow-up requirements under the DAFS grant schemes may alter this cost situation in the future. The need for more accurate estimates of the extent of the bracken problem is highlighted by the possible link between bracken and cancer in humans. Recent surveys utilizing remote sensing techniques are described and the cost of a full bracken eradication programme is estimated to be c.£80 million which is contrasted with the current level of grant assistance of c.£135 000 a−1. The use of bracken as biofuel is considered as an alternative to eradication.

Notes: Abstract. Correlation analysis was used to determine the main factors related to soil pH and to yield of white clover in a range of hill soils. Results for 109 Northern Ireland pasture soils showed that pH (H2O) was significantly correlated with exchangeable Ca, total exchangeable bases, base saturation, P, exchangeable Al and Al saturation, but not with exchangeable Mn. Clover yield (dry weight of shoots) in 12 acid soils from Northern Ireland, Scotland and the Falkland Islands was significantly correlated with exchangeable Ca, total exchangeable bases and Al saturation. The results support the use of Al saturation rather than exchangeable Al, soil solution Al or pH when calculating lime requirements to overcome these limiting factors in hill soils.

Notes: Abstract. Effects on soil physical properties in a trial which compared establishing an apple orchard on grassed and cultivated soil and of maintaining soil with or without a vegetative cover post-planting are discussed. On a fine sandy loam soil (Fyfield series) prone to erosion, bulk density, water filled porosity and soil erosion, measured at intervals after the establishment year, were all unaffected by the use of grass. Infiltration rate was much higher on grassed than on herbicide treated soil as was the apparent ability to accept heavy rainfall.

Notes: Abstract. This paper reports the growth and yield of grain and the utilization of fertilizer nitrogen applied on either one or two occasions in spring to a crop of winter barley established by direct drilling on a chalk soil in southern England. Nitrogen, as ammonium nitrate, was applied at rates of 0 to 140 kg N ha−1 in a range of proportions on two occasions (March and April 1981); nitrogen-15 was used to facilitate study of the nitrogen utilization by the crop.When sampled before the second top-dressing in April, the greatest number of tillers were found on plants treated with 70 and 100 kg N ha−1 in March. The total above ground dry matter production at harvest was greatest when the split nitrogen dressing totalled more than 100 kg N ha−1, although the apparent efficiency of nitrogen usage (kg DM per kg N applied) was greatest when 60 kg N ha−1 was divided equally between the two application dates. Grain yield was heaviest (6.471 ha−1) at the largest rate of nitrogen applied (140 kg N ha−1); the lightest yield from the nitrogen treated crops was recorded from 100 kg N ha−1 applied as a single dressing in April that stimulated shoot production and decreased individual grain weight. The recovery in grain and straw of labelled fertilizer nitrogen applied only in March averaged 42.2% and was 49.8% when the nitrogen was applied only in April. The recovery of nitrogen applied in both March and April at the total rate of 100 kg N ha−1 but split 30/70 or 70/30 was 44.5% and 42.5% respectively. Non-fertilizer sources of nitrogen contributed 60.7–71.7% of the total nitrogen uptake by the crop at harvest.

Notes: Abstract. The factors influencing inorganic nitrogen inputs in wet deposition in two upland catchments in northeast Scotland are discussed. Seasonal trends in nitrate-nitrogen concentrations in water draining from the catchments, and in monthly nitrate-nitrogen outputs, are reported and explained. The inputs in rain exceeded the output in the rivers in the two catchments by 3.9–9.4 kg ha−1a−1. Retention by vegetation probably plays a crucial role in nitrogen cycling in the uplands.

Notes: Abstract. Inputs of acidity to the ground arise through two distinct routes: wet deposition which includes all acidity deposited in rain and snow and dry deposition, the direct sorption of SO2, NO2 or HNO3 gases by vegetation or soil surfaces. The acidity from dry deposition of SO2 and NO2 is created during the oxidation of deposited SO2 and NO2 to SO24 and NO3− respectively. The areas of Britain experiencing the largest wet deposition of acidity are the high rainfall areas of the west and north, in particular the west central highlands of Scotland, Galloway and Cumbria where inputs exceed 1 kp H+ ha−1 annually. Wet deposited acidity in the east coast regions of Britain is in the range 0.3–0.6 kg H+ ha−1 a−1. Monitoring data for rainfall acidity at rural sites throughout northern Britain show a decline in deposited acidity of about 50% during the last six years. Dry deposition is largest in the industrial midlands and southeast England and in the central lowlands of Scotland, where concentrations of SO2 are largest. In these regions the dry deposition of SO2 following oxidation may lead to acid inputs approaching 3 kg H+ ha−1 a−1 and greatly exceeding wet deposition.

Notes: Abstract. Natural acidification processes result in increasing solubility of aluminium as soils become more acid. Exchangeable aluminium provides a large reserve that can be mobilized by percolating acids or salts, with solution pH determining the upper limit of its solubility. Aluminium can also be mobilized within soils and into drainage waters in soluble complexes with silica or fluoride, and in organically complexed forms.

Notes: Abstract. An example is given of urban fringe farming from Freetown, Sierra Leone, where immigrants practise intensive cultivation in an environmentally marginal situation. Great reliance is placed on farming experience, generally gained from rural areas, before migration to Freetown. Two main problems result; declining soil fertility and increased erosion hazards. Lack of government recognition of these farmers means that indigenous, innovative solutions to overcome these problems are being formulated.

Notes: Abstract. Recent progress in the techniques for improving the quality and quantity of herbage produced from indigenous hill pasture is described. There is general agreement on the main technical requirements for most situations. Knowledge of hill soils and vegetation and of the proposed grazing strategies for hill sheep are required initially so that the most economical and biologically appropriate method can be selected.In brief, soil pH must be raised by liming to at least 5.5; for each hectare, between 40–60 kg P and 80–100 kg K must be added plus a starter dressing of between 50–100 kg N after which a seeds mixture of grasses and white clover (25–30 kg seed ha−1) should be sown. Inoculation of clover seed with rhizobia is advised for all hill soil types but is essential for white clover sown in deep peat. Seeds must be sown in April or May, cultivation should be limited as far as possible for both technical and financial reasons, and new pastures should be grazed lightly initially, with subsequent rest periods to aid the persistence of white clover. Maintenance dressings of lime and fertilizer are required, more so in wetter areas. Careful monitoring of stock grazing recently improved hill pasture is advised to check for the occurrence of trace element problems.It is clear that the key to more efficient livestock rearing in the hills and uplands lies in pasture improvement and optimum utilization and maintenance of the upgraded pastures.

Notes: Abstract. The approximate time-scales for serious lowering of the base status of acidic upland soils in northeast Scotland have been based on assessments of geochemical weathering rates in two upland catchments. Periods of 1100 and 12000 years are obtained for soils evolved primarily from granite and quartz-biotite-norite respectively. Factors regulating the rate of removal of base cations in drainage water are discussed, to elucidate those which significantly influence long-term rates of soil acidification. The relationship between base cation leaching and river water acidity is briefly considered.

Notes: Abstract. Plaster of Paris (CaSO4½H2O) infiltration was used (i) to study the continuity of cracks and pores and the variation of macroporosity and crack width with depth and (ii) to maintain an undisturbed seedbed for subsequent resin impregnation. Examples are also given in which the remains of gaps between and at the bottom of the furrow slice can be clearly seen. The method is a useful qualitative visual technique, limited to the larger soil pores. Due to this limitation, it is more useful for showing pore continuity than for quantifying porosity.

Notes: Abstract. The impact of isolated trees and natural forest vegetation on soil acidity is discussed. There is a considerable variation in impact between species on similar soils and between sites for any given species. The effect of coniferous plantations on soil acidity is reviewed and the causes of any increased acidity discussed. Crop species, initial soil conditions, silvicultural practices and the proportion of the tree removed at felling are all important factors influencing the long-term impact of plantations on soil acidity.

Notes: IN 1984, there was no more body debated scientific issue than ‘acid rain’—the somewhat amorphous term covering a number of industrial-based airborne pollutants that chemically alter the pH of precipitation and, thus eventually, of soil and water resources.

Notes: Abstract. Agricultural soil erosion is serious in developed and developing countries alike. Soil runoff can diminish long-term land productivity and accompanying sedimentation of waterways contributes to flooding and substantially reduces both water quality and the useful life of reservoirs and irrigation works. To design effective erosion control policies, planners need to be able to evaluate conservation efforts by fanners. The research reported here develops comparative measures of conservation effectiveness using the management factors of the Universal Soil Loss Equation. These factors measure the effectiveness of farmers' existing conservation practices and can help policymakers identify the regions and types of farms which are not using effective erosion control measures, enabling them to direct scarce personnel and funds to areas where they are most needed.

Notes: Abstract. Soil and crop responses to traffic with vehicles having an axle load of 10 tonnes were studied in 9 field experiments. The clay content of the soils ranged from 6 to 85%. The traffic resulted in increased soil bulk density and strength to a depth of 50 cm. Compaction effects persisted below plough depth 7–8 years after traffic. Crop response was negative and increased with clay content of the soil and with traffic intensity and decreased with time. The results indicate that maximum axle loads on arable fields should be less than 10 tonnes, especially on clay soils.

Notes: Abstract. After satisfactory results during the mid-1970s, winter cereal yields and profitability were disappointing during 1979–81 on a Buckinghamshire farm with Ragdale series stagnogley soil. Poor soil physical conditions were diagnosed and then improved by soil loosening and mole drainage. Other inputs and management remained intensive but essentially constant. Three-year average winter wheat and barley yields rose from 5.6 and 4.9 t ha for 1979–81 to 7.4 and 6.8 t ha respectively for 1982–84. A large part of this increase could be attributed to improved soil management. The observations were made as a farm case study and not as a replicated field trial. They may nevertheless be of interest to others and of national relevance as similar soils occupy some 30% of the cereal area in England.

Notes: Abstract. Losses of soil and fertilizer nitrogen by leaching and denitritication from a clay soil in southern England have been measured over four years. Nitrate losses in drainage water from direct-drilled land averaged 20–30 kg N ha ‘a’ with wide seasonal variation. Ploughing and conventional cultivations increased this loss. Denitritication from direct-drilled land averaged 5–10 kg N ha ‘a’ with wide seasonal variation. Ploughing and drainage both diminished denitritication losses but cultivation had the greater effect. These nitrogen losses occurred mainly in autumn and spring.Nitrogen losses, in drainage water or by denitritication after spring fertilizer applications, were related to the rainfall in the 28 days following top dressing. Approximately 40 mm rain was needed to cause a loss of 10% of the nitrogen applied but in practice losses were quite variable.

Notes: Abstract. Urea and ammonium were compared with and without nitrification inhibitors (nitrapyrin and dicyandiamide) as a possible means of reducing the nitrate concentration in winter lettuce grown in the glasshouse. Neither inhibitor had a significant effect on nitrate concentrations at the lower rate of applied nitrogen (138 kg ha−1 N). At the higher rate of urea (414 kg ha−1 N) dicyandiamide significantly reduced the nitrate concentration but this was accompanied by an unacceptable loss in yield and quality thought to be due to phytotoxic effects of the high level of residual ammonium. Nitrapyrin had no effect on the nitrate concentrations in lettuce.

Notes: Abstract. Lime was applied in summer 1981 at rates up to 201 ha−1 prior to reseeding an unimproved peaty hill soil. A marked pH gradient with depth developed showing that 3 years after application lime had very little effect below a depth of 5 cm. Soil pH values for 0–7.5 cm samples were: nil lime-4.2; 1 t ha−1-pH 4.3; 2 tha−1-pH 4.6; 4 t ha−1-pH 5.0; 6 t ha−1-pH 5.6. In the 0–2.5 cm layer pH values were much higher.In all years at least 80% of maximum yield was achieved from an initial application of 21 ha−1 lime. Botanical analysis showed that maximum persistence of sown species, perennial ryegrass and timothy, occurred from 2 t ha−1 lime; 6 t ha−1 lime was necessary for maximum persistence of clover. Lime application had only small effects on the mineral composition of the herbage.

Notes: Abstract. The bracken fern (Pteridium aquilinum (L.) Kuhn) is emerging as the most successful of international weeds. Tolerant, yet aggressive and opportunist, it follows characteristically in the wake of evacuated settlement, deforestation or reduced biotic pressures. It is hostile to many other plants and to animals, and generates toxins including some carcinogens. It appears to be extending its range into wet and exposed habitats and at its climatic limits. Estimated encroachment rates in the UK average 1%, sometimes 3% per annum, which appears to be unprecedented. Its historical use as an occasional resource, e.g. for litter, bedding, roofing, etc, has mostly ceased. It is now a major source of land loss and land pollution. More work is needed (and is pending) to calibrate bracken spread more precisely, e.g. from satellite imagery. The reclamation of bracken-infested land is probably more cost-beneficial per hectare than the reclamation of wetland or heathland, taking any time-scale.

Notes: Abstract. Rainfall has become less acid at Rothamsted and Saxmundham over the period 1969–83. The pH of rain at these two sites has increased from 4.4–4.6 to about 4.8–4.9; at Woburn it has remained approximately constant at 4.4–4.6. Amounts of NH4-N and NO3-N deposited at present are 10–15 and 5–10 kg ha−1 a−1 respectively. They have been increasing at Rothamsted and Woburn. Some 50–60 kg ha−1 a−1 of Cl and 25–35 kg ha−1 a−1 of SO4-S are presently deposited. Deposition of non-sea Cl and SO4-S has been increasing markedly at all three sites. Non-sea salts comprise 35% of the total salt deposition near the coast at Saxmundham, 58% inland at Rothamsted and Woburn.

Notes: The increase in the number of geophone groups in production records during recent years and the requirement for accurate basic static corrections for high resolution records have made it necessary to develop sufficiently accurate automatic techniques for the determination of static corrections.A fully automatic method is presented which makes use of the delay-time method in order to compute static corrections at each shot position. Delay times, weathering and subweathering velocities are determined from automatic picks of the first arrivals on common-offset trace collections.It is assumed that the weathering is a single layer and that the dip of the subweathering layer under the geophone groups is small.The picking routine is fully automatic and successful in most cases, provided the signal-to-noise ratio is sufficiently high.The subsequent filtering of erroneous values for picked times is performed by means of statistical techniques, using curves of picked times on common-offset trace collections. If the distance between receivers and shot-points on the profile is sufficiently short, one can expect only little change in the picked times of two contiguous traces.The method is well adapted to end-on spreads with a great number of traces, where distances between geophone groups are short.Examples are presented showing the possibilities of the method for the determination of long wavelength as well as short wavelength components of static corrections.

Notes: A new deterministic technique for estimating a wavelet suggested by Loewenthal and Jakubowicz requires measurement of both pressure and vertical particle velocity. Through construction of the impedance function a deterministic estimation of the wavelet and the reflectivity can be obtained.This idea is tested for a one-dimensional model. The test is carried out by forming a synthetic seismogram of both pressure and particle velocity and checking the formulas for obtaining the estimated wavelet under noisy conditions.

Notes: Four methods for the determination of Q in marine sediments are compared: two traditional methods, i.e. the risetime and the spectral ratio method, and two newly established ones, the spectrum modeling and the wavelet modeling method. In the latter one Q and the reflection time T are determined simultaneously, which gives a much better accuracy for T than reading it from the seismogram. The risetime and the spectral ratio methods are used for obtaining Q directly from the data. The principle of the modeling methods is to calculate the effect of absorption and dispersion on a reference wavelet or its spectrum for various values of Q, and the best fit between the observed and the calculated data leads to the optimum result. Numerical tests on synthetic data show that a precision of more than 25% for data containing noise or superposed arrivals can hardly be achieved; in any case, wavelet modeling is the superior method. Application to data from a vertical reflection profile in the Baltic Sea yields Q in the range of 15–100 for different layers, which is to be expected in the sedimentary environment of this area.The computations were performed in the Computer Center of Kiel University. The authors thank R. Meissner for his comments on the manuscript.

Notes: Small offsets in hard coal seams can be detected with the aid of seam (channel) waves. Transmission and reflection of seam waves depend, among other parameters, upon the symmetry properties of the sequence rock/coal/rock. Two typical unsymmetrical sequences are found in European coal deposits: (i) coal seams with roof and floor of differing acoustic impedance and (ii) coal seams interlayered with rock and soil.Two-dimensional analog models with appropriate impedance contrasts are used to study the effect of the unsymmetrical layers upon the propagation of Rayleigh seam waves. Data analysis is based upon amplitude measurements both parallel and perpendicular to the layers and dispersion curves.The effect of unsymmetrical roof (rock 1) and floor (rock 2) was studied with models containing homogeneous coal seams. Leaky mode wave groups with phase velocities (cR) in the range between the SV-wave velocities (βr1, 2) of the two rock materials, i.e. βr1≥cR 〉 βr2, form a characteristic part of the Rayleigh seam wave signal. Using Knott's energy coefficient calculations it is shown that in that range energy leakage into the surrounding rock by refracted SV-waves is restricted to only one of the two interfaces, namely coal/rock 2. At the other interface, coal/rock 1, all waves are totally reflected. Thus, the high amplitudes of these leaky mode wave groups are explained by “quasi-normal mode” features.The influence of a dirt bed on wave propagation was studied in models where the roof and the floor have the same elastic properties. The maximum thickness of the dirt bed did not exceed 20% of the total seam thickness. The effect of the bed's location within the seam was also investigated.For all recorded normal-mode wave groups either the total seam or the coal layers could be regarded as wave guides. This was shown by the fact that the phases could be associated with the phase velocity dispersion curves calculated for the symmetrical sequence rock/coal/rock. These curves are relevant under the condition that the thickness of the coal layer assumed under the calculation coincides with the thickness of the effective wave guide of the respective wave groups.Wave groups guided in the total seam are not influenced by either the thickness or the position of the dirt bed. On the other hand, for wave groups guided in the coal layers, the quotient of signal amplitudes in the coal layers is influenced by the position of the dirt bed.

Notes: Shotpoint gathers from conventional reflection seismic surveys contain both reflected and refracted waves. In this study shot records were processed and analyzed, and the data were modeled with reflected, refracted, and reflected-refracted waves to fit the recorded data. The result is a detailed velocity model. The inverse problem for refracted waves was solved by using the Wiechert-Herglotz inversion.A 500-km-long 26-fold reflection seismic line from the Barents Sea, north of Norway, has been investigated. The data show high velocities, multiple reflections, and various types of noise. To test the method a total of 34 shot gathers were analyzed along this line. The aim of the interpretation was to determine the velocity in the seafloor and the near-surface sediments. It is possible to map the vertical as well as the lateral velocity distribution in detail. Depending on the length of the streamer and the velocity gradient in the sediments, the calculated depth varies between 300 and 500 m below the seafloor. These velocities were also compared to the stacking velocities obtained from the reflection seismic data to see how the velocities determined by different methods were related.The velocity distribution in the sediments is one of the key factors in seismic interpretation. The technique discussed in this paper can contribute to velocity information both in the processing and interpretation of seismic data.

Notes: In the course of investigations concerning disposal of radioactive waste, DC-geoelectric soundings were performed in the salt mine Asse in 1982. The survey resulted in the determination of resistivities of various salt formations. A comparison of various resistivities obtained in salt formations in the mine shows that it is possible to estimate the content of free water in salt using Archie's equation.The significant result of this survey is that salt formations in the mine can be divided into two categories according to their resistivities:1. Salt with resistivity between 107 and 108Ωm (particularly Na2Sp and Na3β). The particularly pure halitic formations are to be found within this resistivity range.2. Salt with resistivity between 103 and 105Ωm (Na2Tl, K2, transition salt). The salt formations with thin layers of anhydrite and a high content of hygroscopic salts are classified in the paper.

Notes: Various exact methods of inverting the complete waveform of vertical seismic reflection data to produce acoustic impedance profiles have been suggested. These inverse methods generally remain valid for nonvertical, plane-wave data, provided total reflection does not occur. Thus, in principle, the “seismogram” at each ray parameter in a slant stack can be interpreted separately.Rather than invert each plane-wave seismogram separately, they can all be interpreted simultaneously and an “average” model thus obtained. Inversion for both the velocity and the density also becomes possible when two or more plane-wave seismograms are simultaneously inverted. The theory for a noniterative inversion method, based on the time-domain Riccati equation, is discussed. Numerical examples of inversions using this technique on synthetic data demonstrate its numerical stability and the advantage of simultaneous inversion of several seismograms to reduce the effect of noise in the data and increase the stability of the inversion process.

Notes: The geophysical data processor today has on offer a great variety of tools for the inversion of seismic reflection data to estimate geological structure. The major subset of these comprises migration procedures, which span a wide range of sophistication and cost in terms both of computation time and manual effort on the part of interpreters and processing staff. The choice of an over-powerful process can be very wasteful, but on the other hand too naive a migration procedure can lead to wrong interpretations which are much more costly still.Complete inversion procedures which aim to delineate all changes in rock densities and elastic properties in the subsurface are still in the imaginative stages of research. Not even the most sophisticated migration procedure in current use with real data, however, provides a complete inversion, but all depend in some measure on prior knowledge of the velocity structure of the section of the earth traversed by the seismic energy. Such knowledge may be very approximate at first, but each inversion should, through the skill of the interpreter, allow him to revise his velocity model and, up to some limit imposed by the quality and ambiguity of the original data, to improve the next inversion. Paradoxically, he can often be helped by using forward modeling procedures to check the implications of his ideas in the data domain, both in deciding how to update the velocity model and in selecting the most appropriate migration process to use next.We review here the currently available toolkit of migration and modeling processes and make suggestions as to how each process can fit into a learning strategy which can improve the interpretation as economically as possible and in as many iterative steps as the complexity of the earth's velocity structure makes necessary. An example is shown of the strategy being used in a complex overthrust region.The authors wish to thank the Chairman and Board of Directors of BP Exploration Co. for permission to publish this paper, and also make acknowledgment to our colleagues whose labours in research and development have made available to our use many of the essential tools required to implement the strategies we describe.

Notes: The time-domain induced polarization (IP) of saturated Sherwood Sandstone correlates significantly with the intergranular permeability and the matrix conductivity but only at low electrolyte concentrations (〈 500 p.p.m. NaCl). An increase in the magnitude of sandstone IP with increase in the valence of the electrolyte cation is pronounced but occurs only at intermediate concentrations, i.e., between 100 and 2500 p.p.m. Surface IP and resistivity depth sounding measurements, supplemented by data from laboratory measurements, can be used to estimate the groundwater conductivity and hence the salinity in a moderate to strongly saline sandstone aquifer.

Notes: The linear filter is used extensively in exploration geophysics, and is usually computed using the least squares normal equations. In the general field of time series, the inverse problem is often solved through eigenvalue expansion solutions to integral equations.The normal equations can be solved in terms of the eigenvalues and eigenvectors of the autocorrelation matrix. It has been suggested that a spectral expansion technique should be used which computes the inverse directly without explicit use of the normal equations. If all possible spiking positions are calculated using the normal equations, the spiking operator matrix is obtained. The matrix operator obtained from the spectral expansion is closely related to the spiking operator matrix. Thus, it is possible to compute the spectral expansion filter using the normal equations. Therefore, it is possible to use the best features of both methods, i.e. obtaining the optimum filter with the normal equations, and discarding the poorly determined parts of the solution based on spectral expansion.

Notes: The advent of signal energy on a VSP or check-shot trace may be defined as the first break. An accurate pick of this first break would be possible in the absence of noise. However, real data traces are inevitably corrupted by noise and this leads to difficulty in identifying a break because the signal-to-noise ratio is low in its neighbourhood.Under such conditions, an obvious alternative is to pick “troughs” where the local signal-to-noise ratio is likely to be much higher. Although trough picking is an effective way to minimize the noise problem, it is sensitive to signal properties (such as absorption and multiple reflections) which have no effect upon the accuracy of break picks. Thus, trough picking is signal-sensitive and break picking is noise-sensitive.Clearly, an ideal first-arrival picking scheme would combine the noise-tolerant features of trough picking with the signal-tolerant features of break picking. This ideal may be approached by exploiting known properties of the VSP trace using conventional signal processing techniques. The result of such processing is to reduce the problem to that of picking a trough correctly centered about the true break time.

Notes: A new method for suppressing multiple reflections in seismograms is developed. It is based on a downward continuation procedure which uses the full acoustic wave equation (hyperbolic form) as a downward continuation operator. We demonstrate that the downward continuation of the recorded wave field maps a reflectivity function without multiply reflected events. The method is applied successfully to individual traces of plane-wave decomposed (slant-stacked) synthetic and field data.

Notes: Gradient measurements in a homogeneous electrical primary field can easily be interpreted for simple models. The simplified solution (conducting or resistant body in a homogeneous space in a homogeneous electrical field) is often sufficiently accurate, as comparisons with the exact solution (body of finite resistivity in a homogeneous half-space in a quasihomogeneous electrical field) show. The exact geometry of the body cannot be determined by gradient measurements; the same anomaly of apparent resistivity can be caused by different bodies. In particular, the similarity between a sphere and a cube of the same volume is very high.There is a distinct influence of the resistivity of the overburden: the higher this resistivity is, the stronger is the effect caused by a buried body.If a deviation of 10% of the apparent resistivity is assumed as the lower boundary at which a buried body can be detected by gradient measurements, the depth of investigation for a three-dimensional body is approximately equal to its width; in the two-dimensional case the thickness of the overburden can be twice the width. If the overburden has a resistivity which is higher than the resistivity of the substratum, these depths are greater. The greatest possible depth is approximately three times the width of the body.

Notes: Deterministic deconvolution of seismic data recorded with a non-minimum phase source, such as a sparker, requires an estimate of the source signature. Present methods of deterministic signature estimation and deconvolution require additional field equipment (near- or far-field hydrophones), or else make a deterministic estimate of the effective source signature (the free-field source signature convolved with source and receiver ghosts). By analyzing the direct arrival signal to normal hydrophone groups it is shown that extraction of the free-field source signature from this signal is possible for a spherically symmetric source, and it is demonstrated that the use of this signature for a preliminary deterministic deconvolution gives better results on sparker data than minimum-phase whitening deconvolution applied on its own. The applicability of the method to non-spherically symmetric sources, such as arrays, is also discussed.This paper is published with the permission of the Director, Bureau of Mineral Resources, Geology and Geophysics, Canberra, Australia.

Notes: Data quality assessments have been made on time-domain induced polarization decay curves taken over sulphide ore bodies of Cyprus. The data were taken with the dipole-dipole, pole-dipole and symmetrical quadripole arrays. The results indicate that at larger array separations decay curves taken with the dipole-dipole and pole-dipole arrays are often seriously affected by noise, but that curves taken with the symmetrical quadripole array are not so affected. Optimum pseudo-sections designed to minimize the noise show that the noise results in spurious highs and lows.This work was carried out as part of a NERC research studentship at the University of Leicester.

Notes: Theoretical model study shows that when an earth model is composed of two (Cole-Cole) polarizable media, its normalized complex resistivity spectrum is approximately a multiplicative combination of the contributions of the two media. This also applies on inversion, but the two dispersions thus obtained are apparent rather than intrinsic dispersions.In models consisting of two media, either a multiplicative or an additive combination of Cole-Cole functions fits the complex apparent resistivity spectrum. On inversion each combination gives similar parameters except for the apparent chargeability of the component with the shorter time constant. However, this can be compensated simply. In this sense the two representations are almost equivalent.We show that the apparent spectrum due to a finite polarizable body is actually a true Cole-Cole dispersion, as is usually assumed in practice.The behavior of a complex apparent resistivity spectrum and its corresponding apparent Cole-Cole dispersion parameters is influenced by the variation of the dilution factor with frequency. Hence when estimating intrinsic parameters from the nomogram, based on constant (frequency-independent) dilution factors, particular care is required to correctly relate apparent parameters to intrinsic parameters.

Notes: We present dispersion curves, and amplitude-depth distributions of the fundamental and first higher mode of Love seam waves for two characteristic seam models. The first model consists of four layers, representing a coal seam underlain by a root clay of variable thickness. The second model consists of five layers, representing coal seams containing a dirt band with variable position and thickness. The simple three-layer model is used for reference.It is shown that at higher frequencies, depending on the thickness of the root clay and the dirt band, the coal layers alone act as a wave guide, whereas at low frequencies all layers act together as a channel. Depending on the thickness, and position of the dirt band and the root clay, in the dispersion curves of the group velocity, secondary minima grow in addition to the absolute minima. Furthermore, the dispersion curves of the group velocity of the two modes can overlap. In all these cases, wave groups in addition to the Airy phase of the fundamental mode (propagating with minimum group velocity) occur on the seismograms recorded in in-seam seismic surveys, thus impeding their interpretation. Hence, we suggest the estimation of the dispersion characteristics of Love seam waves in coal seams under investigation preceding actual field surveys.All numerical calculations were performed using a fast and stable phase recursion algorithm.

Notes: The deconvolution equation is solved in the z-transform domain directly for an impluse response. The principal assumption is the odd-depth model: two-way traveltimes to the boundaries are constrained to be odd integers only. It is further assumed that the length of the wavelet sequence is known to be less than half the length of the data sequence.An inverse of the impulse response is constrained by the zero samples of the source function. The resulting underdetermined set of equations is supplemented with the equations provided by the odd-depth model. The impulse response is found from the inverse by polynomial division.

Notes: A series of gravity measurements were taken over a period of time (c. 150 days each) above two adjacent working coal faces. Precise levelling and gravity measurements were taken along the same profile before, during, and after seam extraction. The observed change in gravity agrees well with the levelling data. The combined data sets illustrate the validity of a simple Bouguer relationship for the gravity gradient.The results of two-dimensional modelling are used to estimate the gravitational effect of the extracted material. A local feature detected only on the gravity signal may be due to an outcropping limestone layer.This controlled experiment demonstrates the possibility of using high-precision gravity measurements as a substitute for levelling, particularly in surveys of large areal extent where the cost of obtaining comprehensive coverage by levelling may be prohibitive.

Notes: In dealing with the problem of large amplitude multiple reflections arising from a hard water-bottom, it has been found that the use of extended source array techniques resulted in a considerably better penetration than that obtained using either computer simulated long arrays or the conventional air-gun array systems. The purpose of this paper is to use the concept of the array directivity factor in discussing the reason for the improvement in penetration achieved by using extended marine source arrays.Examples are given showing that the low frequency power radiated within the so called “penetration window” can be increased by a factor of two by choosing the correct spacing of the point sources forming the extended array. It is concluded that to ensure that most of the low frequency energy is concentrated within the penetration window to achieve deep penetration, a source array with spacing comparable with the wavelength is required.

Notes: This paper investigates the form of the nonwhiteness found in the reflection coefficients from a wide variety of rock sequences around the world. In all but one case densities are taken as constant due to the paucity of suitable density data. The reflection sequences are pseudo-white only above a corner frequency, below which their power spectrum falls away according to a power law fβ, where β is between 0.5 and 1.5. This spectrum can be adequately modelled in practice very simply with an ARMA (1, 1) process which acts on a white innovation sequence. The corollary of this is that before wavelet estimation methods are applied (all of which-except those based on synthetic seismograms—presuppose white reflection sequences) or deconvolution filters estimated, seismic traces should be filtered with the inverse of this process.Interestingly, the estimated ARMA processes group themselves into two clearly differentiated categories, having very different indices of predictability (or, strictly, indices of linear determinism). The two categories apparently correlate precisely with two kinds of sedimentation: one which consists largely of sequences of rocks with repeating properties, called “repetitive” in this paper but perhaps loosely describable as “cyclic”, and the other which is randomly bedded with no apparent pattern of components. The former has indices of predictability which are two to four times as great as those of the latter. Another, probably related, property is that β for the repetitive sequences tends to be greater than that for non-repetitive rock columns.The observed power spectra are shown to be consistent with a simple model for the logarithm of acoustic impedance consisting of a mixture of processes where the distribution of (time) scale parameters is reciprocal.Detailed effects of block-averaging and sampling the logs are shown to depend on the type of sequence under examination.

Notes: Anomalies in self potential (SP) are usually explained in terms of geochemical activity. However, there are other sources of current which cause complications in the interpretation. In particular, DC telluric currents can be generated outside the survey region. Contrasts in resistivity cause current channelling and secondary voltages can be induced by leakage. The effect can be demonstrated using network theory and internal sources can be emphasized by subtraction. Joint surveys are required to demonstrate correlations with apparent resistivity.

Notes: A main problem in computing reflection coefficients from seismograms is the instability of the inversion procedure due to noise. This problem is attacked for two well-known inversion schemes for normal-incidence reflection seismograms. The crustal model consists of a stack of elastic, laterally homogeneous layers between two elastic half-spaces. The first method, which directly computes the reflection coefficients from the seismogram is called “Dynamic Deconvolution”. The second method, here called “Inversion Filtering”, is a two-stage procedure. The first stage is the construction of a causal filter by factorization of the spectral function via Levinson-recursion. Filtering the seismogram is the second stage. The filtered seismogram is a good approximation for the reflection coefficients sequence (unless the coefficients are too large).In the non-linear terms of dynamic deconvolution and Levinson-recursion the noise could play havoc with the computation. In order to stabilize the algorithms, the bias of these terms is estimated and removed. Additionally incorporated is a statistical test for the reflection coefficients in dynamic deconvolution and the partial correlation coefficients in Levinson-recursion, which are set to zero if they are not significantly different from noise.The result of stabilization is demonstrated on synthetic seismograms. For unit spike source pulse and white noise, dynamic deconvolution outperforms inversion filtering due to its exact nature and lesser computational burden. On the other hand, especially in the more realistic bandlimited case, inversion filtering has the great advantage that the second stage acts linearly on the seismogram, which allows the calculation of the effect of the inversion procedure on the wavelet shape and the noise spectrum.

Notes: Wavenumber domain expressions for bodies with elliptical cross-section and of ellipsoidal shape have been developed both for homogeneous bodies and for certain bodies of density/magnetization varying linearly with depth or, more generally, according to a polynomial with depth. The simple expressions thus obtained lend themselves to an easy analysis, especially for long and short wavelengths. At the long-wavelength end of the spectra their decay is governed by an exponential with a decay “depth” equal to the depth to the center of mass. At the short-wavelength end this depth is replaced by the depth to the upper focus of the ellipsoid (or the elliptic cross-section). For vertically inhomogeneous ellipsoids the decay rate is also dependent on the product of the vertical gradient of density/magnetization and their semi-axes.

Notes: The Cole-Cole relaxation model has been found to provide good fits to multifrequency IP data and is derivable mathematically from a reasonable, albeit greatly simplified, physical model of conduction in porous rocks. However, the Cole-Cole model is used to represent the mutual impedance due to inductive or electromagnetic coupling on an empirical basis: this use has not been similarly justified by derivation from any simple physical representation of, say, a half-space, layered or uniform.A uniform conductive half-space can be represented as a simple subsurface loop with particular resistive and inductive properties. Based upon this, a mathematical expression for the mutual impedance between the two pairs of electrodes of a dipole-dipole array is derived and designated “model I”. It is seen that a degenerate case of model I is the Cole-Cole model with frequency exponent c= 1. Model I is thus more general than the Cole-Cole expression and must provide at least as good a fit to a set of field data. Provision for variation of c from unity could be made in model I equally well as for the Cole-Cole model although, at present, this would be a purely empirical alteration.Model I contains four parameters, one of which is, in effect, the resistivity of the half-space. Therefore only three parameters are involved in the model I expressions for normalized amplitude and for phase of the EM-coupling mutual impedance. Model I is compared with previously published “standard” values for two different dipole separations. Under particular constraints, model I is shown to provide better fits than the Cole-Cole model (with c= 1) over particular frequency ranges, specifically at very low frequencies and at moderately high frequencies where the model I phase curve follows the standard phase curve across the axis to positive values (negative coupling).