ALBERT

Notes: Matlab scripts that apply the Bence & Albee (1968) matrix correction algorithm to X-ray intensity data collected as element maps on a Cameca SX-50 microprobe are used to produce two-dimensional maps of oxide weight percent and cation proportions for SiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O and K2O. Once generated, large data sets of mapped oxide weight percent values or cation numbers that retain spatial information can be used petrologically. The technique is used to evaluate the compositional range of barroisitic amphibole in an eclogite from New Caledonia, to examine aspects of equilibration during the partial hydration of the eclogite facies mineral assemblage.

Notes: The exceptional andalusite–kyanite–andalusite sequence occurs in Al-rich graphitic slates in a narrow pelite belt on the hangingwall of a ductile normal fault in NW Variscan Iberia. Early chiastolite is replaced by Ky–Ms–Pg aggregates, which are overgrown by pleochroic andalusite near granites intruded along the fault. Slates plot in AKFM above the chloritoid-chlorite tie-line. Their P–T grids are modelled with Thermocalc v2.7 and the 1998 databases in the NaKFMASH and KFMASH systems. The univariant reaction Ctd + And/Ky = St + Chl + Qtz + H2O ends at progressively lower pressure as F/FM increases and A/AFM decreases, shrinking the assemblage Cld–Ky–Chl, and opening a chlorite-free Cld–Ky trivariant field on the low temperature reaction side. This modelling matches the observed absence of chlorite in high F/FM rocks, which is restricted to low pressure in the andalusite stability field.The P–T path deduced from modelling shows a first prograde event in the andalusite field followed by retrogression into the kyanite field, most likely coupled with a slight pressure increase. The final prograde evolution into the andalusite field can be explained by two different prograde paths. Granite intrusion caused the first prograde part of the path with andalusite growth. The subsequent thermal relaxation, together with aH2O decrease, generated the retrograde andalusite–kyanite transformation, plus chlorite consumption and chloritoid growth. This transformation could have been related to folding in the beginning, and aided later by downthrowing due to normal faulting. Heat supplied by syntectonic granite intrusion explains the isobaric part of the path in the late stages of evolution, causing the prograde andalusite growth after the assemblage St–Ky–Chl. Near postectonic granites, a prograde path with pressure decrease originated the assemblage St–And–Chl.

Notes: Sm–Nd garnet-whole rock geochronology, phase equilibria, and thermobarometry results from Garnet Ledge, south-eastern Alaska, provide the first precisely constrained P–T–t path for garnet zone contact metamorphism. Garnet cores from two crystals and associated whole rocks yield a four point isochron age for initial garnet growth of 89.9 ± 3.6 Ma. Garnet rims and matrix minerals from the same samples yield a five point isochron age for final garnet growth of 89 ± 1 Ma. Six size fractions of zircon from the adjacent pluton yield a concordant U–Pb age of 91.6 ± 0.5 Ma. The garnet core and rim, and zircon ages are compatible with single-stage garnet growth during and/or after pluton emplacement. All garnet core–whole rock and garnet rim-matrix data from the two samples constrain garnet growth duration to ≤5.5 my. A garnet mid-point and the associated matrix from one of the two garnet crystals yield an age of 90.0 ± 1.0 Ma. This mid-point result is logically younger than the 90.7 ± 5.6 Ma core–whole rock age and older than the 88.4 ± 2.5 Ma rim-matrix age for this sample. A MnNaCaKFMASH phase diagram (P–T pseudosection) and the garnet core composition are used to predict that cores of garnet crystals grew at 610 ± 20 °C and 5 ± 1 kbar. This exceeds the temperature of the garnet-in reaction by c. 50 °C and is compatible with overstepping of the garnet growth reaction during contact metamorphism. Intersection of three reactions involving garnet-biotite-sillimanite-plagioclase-quartz calculated by THERMOCALC in average P–T mode, and exchange thermobarometry were used to estimate peak metamorphic conditions of 678 ± 58 °C at 6.1 ± 0.9 kbar and 685 ± 50 °C at 6.3 ± 1 kbar, respectively. Integration of pressure, temperature, and age estimates yields a pressure-temperature-time path compatible with near isobaric garnet growth over an interval of c. 70 °C and c. 2.3 my.

Notes: Metapelites and intercalated metapegmatites of the Saualpe crystalline basement, which forms part of the Austroalpine nappe complex in the Eastern Alps, display a polyphase tectonometamorphic history. Here, we focus on the evolution that these rocks underwent prior to Cretaceous (eo-Alpine) high-pressure metamorphism and related penetrative deformation. Geothermobarometry on coarse-grained porphyroclastic parageneses (garnet–biotite–muscovite–plagioclase–sillimanite–quartz), which occur as relics in kyanite–garnet, two-mica gneiss, yielded 600 °C/0.4 GPa. Results from a corundum-bearing lithology suggest that higher temperatures may have been reached in very restricted areas. The matrix of these rocks displays intense recrystallization during a pressure-dominated metamorphic overprint. Microstructures and mineral chemistry indicate that this low-pressure metamorphism was the first significant metamorphic imprint in these rocks. Mineral relics in all metapelitic rock types reflect low-pressure conditions for this interkinematic crystallization phase.The distribution, macroscopic and microscopic observations and the mineralogical composition of intercalated metapegmatites point to regionally elevated temperature conditions during their emplacement. Therefore, pegmatite formation is correlated with mineral formation in metapelites. Sm–Nd-dating of magmatic garnet from the pegmatite gneiss yielded 249 ± 3 Ma, which is interpreted to represent the age of pegmatite-emplacement and low-pressure metamorphism in the metapelites. Since the pegmatites are overprinted by mylonitisation and high-pressure metamorphism, this Permo–Triassic age also sets an upper age-limit to the eclogite facies metamorphic event, which affected considerable parts of the Saualpe crystalline basement.

Notes: A sequence of psammitic and pelitic metasedimentary rocks from the Mopunga Range region of the Arunta Inlier, central Australia, preserves evidence for unusually low pressure (c. 3 kbar), regional-scale, upper amphibolite and granulite facies metamorphism and partial melting. Upper amphibolite facies metapelites of the Cackleberry Metamorphics are characterised by cordierite-andalusite-K-feldspar assemblages and cordierite-bearing leucosomes with biotite-andalusite selvages, reflecting P–T conditions of c. 3 kbar and c. 650–680 °C. Late development of a sillimanite fabric is interpreted to reflect either an anticlockwise P–T evolution, or a later independent higher-P thermal event. Coexistence of andalusite with sillimanite in these rocks appears to reflect the sluggish kinematics of the Al2SiO5 polymorphic inversion. In the Deep Bore Metamorphics, 20 km to the east, dehydration melting reactions in granulite facies metapelites have produced migmatites with quartz-absent sillimanite-spinel-cordierite melanosomes, whilst in semipelitic migmatites, discontinuous leucosomes enclose cordierite-spinel intergrowths. Metapsammitic rocks are not migmatised, and contain garnet–orthopyroxene–cordierite–biotite–quartz assemblages. Reaction textures in the Deep Bore Metamorphics are consistent with a near-isobaric heating-cooling path, with peak metamorphism occurring at 2.6–4.0 kbar and c. 750–800 °C. SHRIMP U–Pb dating of metamorphic zircon rims in a cordierite-orthopyroxene migmatite from the Deep Bore Metamorphics yielded an age of 1730 ± 7 Ma, whilst detrital zircon cores define a homogeneous population at 1805 ± 7 Ma. The 1730 Ma age is interpreted to reflect the timing of high-T, low-P metamorphism, synchronous with the regional Late Strangways Event, whereas the 1805 Ma age provides a maximum age of deposition for the sedimentary precursor. The Mopunga Range region forms part of a more extensive low-pressure metamorphic terrane in which lateral temperature gradients are likely to have been induced by localised advection of heat by granitic and mafic intrusions. The near-isobaric Palaeoproterozoic P–T–t evolution of the Mopunga Range region is consistent with a relatively transient thermal event, due to advective processes that occurred synchronous with the regional Late Strangways tectonothermal event.

Notes: The Pinos terrane (Isle of Pines, W Cuba) is a coherent metamorphic complex that probably represents a portion of the continental margin of the Yucatan Block during the Mesozoic. Within the framework of other metamorphic terranes in the Greater Antilles, the Pinos terrane is characterized by the occurrence of high-grade kyanite-, sillimanite- and andalusite-bearing metapelites and migmatites. Assessment and modelling of phase relations in these high grade rocks indicate that they reached a peak temperature of c. 750 °C at 11–12 kbar, and then underwent strong decompression to c. 3 kbar at c. 600 °C. Decompression was contemporaneous with the main synmetamorphic deformation in the area (D2), and was accompanied by segregation of trondhjemitic partial melts formed by wet melting of metapelites. Metamorphism terminated in the Uppermost Cretaceous (68 ± 2 Ma; 40Ar/39Ar dates on biotite and muscovite). The P–T–t-deformation relations of the high-grade rocks suggest that crustal thickening (during collision of this portion of the Yucatan margin with the Great Volcanic Arc of the Caribbean?) was followed by decompression interpreted to reflect exhumation by extension, possibly related to the initial development of the Yucatan Basin in the uppermost Cretaceous.

Notes: Phengite occurring along with carpholite±lawsonite and/or chloritoid in HP–LT domains shows not only variable Si–(Mg+Fe) contents, but also variable interlayer contents (IC). To determine whether these chemical variations are coherently related to variation in P–T conditions on a regional scale, c. 100 rock samples were sampled in metapelites metamorphosed at conditions varying from 350 °C, 8 to 12 kbar to 450–500 °C, 18 to 20 kbar (Schistes Lustrés complex, franco-italian Western Alps). Based on microstructural and habit criteria, four types of phengite were differentiated that are related either to the rock mineralogy (carpholite vs chloritoid bearing samples) or correspond to various generations of phengite occurring in the same rock sample or thin section. Microprobe analyses reveal that each type of phengite is characterized by a specific composition and that phengite associated with carpholite has a lower interlayer content than phengite associated with chloritoid. The successive generations of retrograde phengite overgrowing carpholite point to a large decrease of interlayer content (c. 0.9–0.7 pfu) and (Fe+Mg) content (c. 0.25–0 pfu) with decreasing P–T conditions. This change is best accounted for by a gradual increase of the pyrophyllite component. In contrast, phengite from higher-temperature, chloritoid-bearing rock samples shows an almost constant interlayer content (c. 0.9–0.95 pfu) but a larger decrease of (Fe+Mg) content (c. 0.6–0.1 pfu). Hence, (1) the composition of the different phengite generations occurring (metastably) in the same rock sample may be used to retrieve points in P–T loops and (2) the pyrophyllitic substitution in phengite is large at low-temperature conditions and cannot be ignored. Thermobarometric estimates based on the Si-content alone will therefore result in pressure over-estimates. We propose a tentative location of the phengite Si and IC isopleths in P–T space which could allow a direct determination of the P–T conditions in carpholite-bearing rocks. Especially in some carpholite-bearing rocks, new thermodynamic models accounting for tschermak and pyrophyllitic substitution are also required prior to making reliable thermobarometric estimates in HP-LT metapelites.

Notes: High-MgAl rocks occur as xenoliths (up to 2 m in diameter) in mafic granulites at a newly discovered locality near Anakapalle. Following an early phase of deformation, ultrahigh-temperature (UHT) metamorphism and near-isothermal decompression, the rocks were intruded in a lit-par-lit manner by felsic melts (charnockite), which caused local-scale metasomatism. A subsequent deformation produced isoclinal folds and the distinct gneissic foliation of the charnockite still at granulite facies conditions.The sequence of multiphase reaction textures in the high-MgAl xenoliths reflects the changes of physico-chemical conditions during the polyphase evolution of the terrane; UHT metamorphism (stage 1, 〉 1000°C, c. 10 kbar) is documented by relics of extremely coarse grained domains with the assemblage orthopyroxene (opx)1 + garnet (grt)1 + sapphirine (spr)1 + spinel (spl)1 + rutile (rt). A subsequent phase of near-isothermal decompression in the order of 1–2 kbar (stage 2) resulted in extensive replacement of grt1 and opx1 megacrysts by lamellar (opx2 + spr2) symplectites. The intrusion of felsic melt (stage 3) led to the development of a narrow metasomatic black wall reaction zone (bt + sil + plg3 + opx2,3 + rt) at the immediate contact of the xenoliths and in melt infiltration zones to the partial replacement of (opx2 + spr2) symplectites by biotite and sillimanite and/or plg3, mainly at the expense of orthopyroxene, with concomitant coarsening of the intergrowth texture. The subsequent deformation (stage 4) further modified the symplectite textures through polygonization, recrystallization and grain-size coarsening. The deformation was followed by a period of cooling and decompression (stage 5, c. 800°C, 4–7 kbar) as indicated by local growth of late garnet (grt5) at the expense of (opx + spr + plg) domains at static conditions.Recently published isotope data suggest that the multistage evolution of the high-MgAl granulites at Anakapalle followed a discontinuous P–T trajectory that may be related to heating of the crust through magmatic accretion culminating in deep-crustal UHT metamorphism at 1.4 Ga (stage 1), fast uplift of the UHT granulites into mid-crustal levels as a consequence of extensional tectonics (stage 2), emplacement of felsic magmas in the Grenvillian (at c. 1 Ga, stage 3) resulting in reheating of the crust to high–T conditions followed by a phase of compressional tectonics (stage 4) and a period of cooling to the stable geotherm (stage 5) still in the Grenvillian.

Notes: The Flatraket Complex, a granulite facies low strain enclave within the Western Gneiss Region, provides an excellent example of metastability of plagioclase-bearing assemblages under eclogite facies conditions. Coesite eclogites are found 〈200 m structurally above and 〈1 km below the Flatraket Complex, and are separated from it by amphibolite facies gneisses related to pervasive late-orogenic deformation and overprinting. Granulites within the Flatraket Complex equilibrated at 9–11 kbar, 700–800°C. These predate eclogite facies metamorphism and were preserved metastably in dry undeformed zones under eclogite facies conditions. Approximately 5% of the complex was transformed to eclogite in zones of fluid infiltration and deformation, which were focused along lithological contacts in the margin of the complex. Eclogitisation proceeded by domainal re-equilibration and disequilibrium breakdown of plagioclase by predominantly hydration reactions. Both hydration and anhydrous plagioclase breakdown reactions were kinetically linked to input of fluid. More pervasive hydration of the complex occurred during exhumation, with fluid infiltration linked to dehydration of external gneisses. Eclogite facies shear zones within the complex equilibrated at 20–23 kbar, 650–800°C, consistent with the lack of coesite and with the equilibration conditions of external HP eclogites. If the complex experienced pressures equivalent to those of nearby coesite eclogites (〉 28 kbar), unprecedented metastability of plagioclase and quartz is implied. Alternatively, a tectonic break exists between the Flatraket Complex and UHP eclogites, supporting the concept of a tectonic boundary to the UHP zone of the Western Gneiss Region. The distribution of eclogite and amphibolite facies metamorphic overprints demonstrates that the reactivity of the crust during deep burial and exhumation is strongly controlled by fluid availability, and is a function of the protolith.

Notes: One of the currently popular theories on magma ascent is that it mainly occurs by propagating hydrofractures (dykes) and that magma viscosity is the primary rate-controlling factor. This theory is based on mathematical models for single hydrofractures under idealised conditions. We simulated magma ascent with air ascending through gelatine and observed that the air ascended in batches, following paths made by their predecessors. Multiple batches accumulate at obstacles along the path. Although magma viscosity may control ascent rate during movement, obstacles ultimately control the size and average ascent velocity of ascending batches. We propose that step-wise movement of magma batches is the mechanism of primary accumulation and ascent from the partially molten source rock of a magma to its first emplacement site and therefore the main ascent mechanism for granitic magmas. ‘Classical’ dyking is the mechanism for secondary ascent from a magma chamber.

Notes: Generally, P–T pseudosections for reduced compositional systems, such as K2O–FeO–MgO–Al2O3–SiO2–H2O, Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O and MnO–K2O–FeO–MgO–Al2O3–SiO2–H2O, are well suited for inferring detailed P–T paths, comparing mineral assemblages observed in natural rocks with those calculated. Examples are provided by P–T paths inferred for four metapelitic samples from a 1 m2 wide outcrop of the Herbert Mountains in the Shackleton Range, Antarctica. The method works well if the bulk composition used is reconstituted from average mineral modes and mineral compositions (AMC) or when X-ray fluorescence (XRF) data are corrected for Al2O3 and FeO. A plagioclase correction is suitable for Al2O3. Correction for FeO is dependent on additional microscopic observations, e.g. the kind and amount of opaque minerals. In some cases, all iron can be treated as FeOtot, whereas in others a magnetite or hematite correction yields much better results. Comparison between calculated and observed mineral modes and mineral compositions shows that the AMC bulk composition is best suited to the interpretation of rock textures using P–T pseudosections, whereas corrected XRF data yield good results only when the investigated sample has few opaque minerals. The results indicate that metapelitic rocks from the Herbert Mountains of the Northern Shackleton Range underwent a prograde P–T evolution from about 600 °C/5.5 kbar to 660 °C/7 kbar, followed by nearly adiabatic cooling to about 600 °C at 4.5 kbar.

Notes: A major problem with the current use of porphyroblast–matrix microstructural relationships to infer orogenic histories, such as multiple orthogonal orogenic events, is that other evidence for these events is typically lacking. For example, a comparison of regional relationships and local structures formed in and adjacent to porphyroblasts present in contact aureoles in the Foothills Terrane, Sierra Nevada, California, shows that: (1) except in shear zones, contact aureoles and local zones along lithological contacts, the Foothills Terrane has a single regional cleavage, although locally formed by multiple processes; (2) the regional cleavage and locally developed porphyroblast inclusion trails have variable orientations, and neither dataset supports the formation of dominantly subhorizontal and subvertical cleavages in this orogen; (3) structural and metamorphic heterogeneities occur at all scales and can markedly affect inclusion trail patterns in porphyroblasts; (4) complex porphyroblast growth features and internal inclusion trail patterns can form in porphyroblasts that grow during short time intervals in contact aureoles, indicating that local complexity in porphyroblasts does not imply regional complexity. Because of these conclusions, multiple datasets, rather than data acquired only from porphyroblasts, should be considered when attempting to understand the evolution of orogens. Furthermore, using microstructural information preserved only in porphyroblasts to infer orogenic processes and plate motions is generally unjustified.

Notes: An extensive humite-bearing marble horizon within a supracrustal sequence at Ambasamudram, southern India, was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics. At peak metamorphic temperatures of 775±73°C, based on calcite-graphite carbon isotope thermometry, the mineral assemblages suggest layer-by-layer control of fluid compositions. Clinohumite + calcite-bearing assemblages suggest XCO2 〈 0.4 (at 700°C and 5 kbar), calcite + forsterite + K-feldspar-bearing assemblages suggest XCO2〉0.9 (at 790°C); and local wollastonite + scapolite + grossular-bearing zones formed at XCO2 of c. 0.3. Retrograde reaction textures such as scapolite + quartz symplectites after feldspar and calcite and replacement of dolomite + diopside or tremolite+dolomite after calcite+forsterite or calcite+clinohumite are indicative of retrogression under high XCO2 conditions. Calcite preserves late Proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration, while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting. Isotopic zonation of calcite and graphite grains was likely produced by localized CO2 fluid infiltration during retrogression. Contrary to the widespread occurrence of humite-marbles related to retrograde aqueous fluid infiltration, the Ambasamudram humite-marbles record a prograde-to-peak metamorphic humite formation and retrogression under conditions of low XH2O.

Notes: The Central Anatolian Crystalline Complex (CACC) is a microcontinent in the Alpine–Himalayan belt. It has previously been considered as a coherent structural entity, but, although the entire CACC is comprised of similar rocks (primarily metasedimentary rocks and granitoids), it consists of at least four tectonic blocks characterized by different P–T–t paths. These blocks are the Kırşehir (north-west), Akdağ (north-east), Niğde (south) and Aksaray (west) massifs. The northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion; metamorphic rocks are characterized by clockwise P–T paths at moderate P–T and local low-P–high-T (LP–HT) overprinting in the highest grade rocks. Apatite fission track ages are Eocene to Oligocene (47–32 Ma). The Aksaray block represents the hot, shallow mid-crust of a Late Cretaceous–early Tertiary arc. It is dominated by intrusions; rare metapelitic rocks record low-P (〈 4 kbar) regional metamorphism overprinted by LP–HT contact metamorphism. Apatite fission track ages are 50–45 Ma. The Niğde massif is different from the other CACC blocks because it evolved as a core complex in a wrench-dominated setting. It is characterized by clockwise P–T paths at moderate P–T followed by widespread LP–HT metamorphism. Apatite fission track ages are Miocene (12–9 Ma), significantly younger than those in the northern massifs. Niğde rocks resided in the mid-crust at a time when the rest of the CACC was at or near the Earth's surface. Variations in P–T–t and tectonic histories — especially timing of exhumation — between the northern and southern CACC reflect the difference between head-on collision vs. mid-crustal wrenching.

Notes: Granulite facies rocks from the northernmost Harts Range Complex (Arunta Inlier, central Australia) have previously been interpreted as recording a single clockwise cycle of presumed Palaeoproterozoic metamorphism (800–875 °C and 〉9–10 kbar) and subsequent decompression in a kilometre-scale, E-W striking zone of noncoaxial, high-grade (c. 700–735 °C and 5.8–6.4 kbar) deformation. However, new SHRIMP U-Pb age determinations of zircon, monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the Proterozoic, but in the Ordovician (c. 470 Ma).The youngest metamorphic zircon overgrowths from two metabasites (probably meta-volcaniclastics) yield 206Pb/238U ages of 478±4 Ma and 471±7 Ma, whereas those from two metapelites yield ages of 463±5 Ma and 461±4 Ma. Monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock (457±5 Ma and 462±5 Ma, respectively). Zircon, and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes. In contrast, titanite from the two metabasites yield 206Pb/238U ages that are much younger (411±5 Ma & 417±7 Ma, respectively) than those of coexisting zircon, which might indicate that the terrane cooled slowly following final melt crystallization. One metabasite has a second titanite population with an age of 384±7 Ma, which reflects titanite growth and/or recrystallization during the 400–300 Ma Alice Springs Orogeny. The c. 380 Ma titanite age is indistinguishable from the age of magmatic zircon from a small, late and weakly deformed plug of biotite granite that intruded the granulites at 387±4 Ma. These data suggest that the northern Harts Range has been subject to at least two periods of reworking (475–460 Ma & 400–300 Ma) during the Palaeozoic.Detrital zircon from the metapelites and metabasites, and inherited zircon from the granite, yield similar ranges of Proterozoic ages, with distinct age clusters at c. 1300–1000 and c. 650 Ma. These data imply that the deposition ages of the protoliths to the Harts Range Complex are late Neoproterozoic or early Palaeozoic, not Palaeoproterozoic as previously assumed.

Notes: Seven eclogite facies samples from lithologically different units which structurally underlie the Semail ophiolite were dated by the 40Ar/39Ar and Rb–Sr methods. Despite extensive efforts, phengite dated by the 40Ar/39Ar method yielded saddle, hump or irregularly shaped spectra with uninterpretable isochrons. The total gas ages for the phengite ranged from 136 to 85 Ma. Clinopyroxene–phengite, epidote–phengite and whole-rock–phengite Rb–Sr isochrons for the same samples yielded ages of 78 ± 2 Ma. We therefore conclude that the eclogite facies rocks cooled through 500 °C at c. 78 ± 2 Ma, and that the 40Ar/39Ar dates can only constrain maximum ages due to the occurrence of excess Ar inhomogeneously distributed in different sites.Our new results lead us to conclude that high-pressure metamorphism of the Oman margin took place in the Late Cretaceous, contemporaneous with ophiolite emplacement. Previously published structural and petrological data lead us to suggest that this metamorphism resulted from intracontinental subduction and crustal thickening along a NE-dipping zone. Choking of this subduction zone followed by ductile thinning of a crustal mass wedged between deeply subducted continental material and overthrust shelf and slope units facilitated the exhumation of the eclogite facies rocks from depths of c. 50 km to 10–15 km within c. 10 Ma, and led to their juxtaposition against overlying lower grade rocks. Final exhumation of all high-pressure rocks was driven primarily by erosion and assisted by normal faulting in the upper plate.

Notes: Antitaxial non-deforming strain fringes from Lourdes, France, show complex quartz, calcite and chlorite fibre patterns that grew around pyrite in a slate during non-coaxial progressive deformation. Development of these fringes was modelled using a computer program ‘Fringe Growth 2.0’ which can simulate incremental growth of crystal fibres around core-objects of variable shape. It uses object-centre paths as input, which are obtained from fibre patterns in thin section. The numerical experiments produced fibre patterns that show complex intergrowth of displacement-controlled, face-controlled and intermediate fibres similar to those in the natural examples. The direction of displacement-controlled growth is only dependent on the relative movement between core-object and fringe, so that core-object rotation with respect to the fringe influences the fibre patterns and produces characteristic asymmetric fibre curvature. Object-centre paths should be used for kinematic analysis of strain fringes instead of single fibres since these paths represent the fringe as a whole. The length along the path can be interpreted in terms of finite strain and path curvature in terms of rigid body rotation of fringes with respect to an external reference frame.

Notes: A sharp line delimitating the distribution of tourmaline (termed as a ‘tourmaline-out isograd’) is defined in the migmatite zone of the Ryoke metamorphic belt, Japan. The trend of the tourmaline-out isograd closely matches that of the isograds formed through the regional metamorphism, suggesting that it represents the breakdown front of tourmaline during regional metamorphism. This is confirmed by the presence of the reaction textures of tourmaline to sillimanite and cordierite near the tourmaline-out isograd. The breakdown of tourmaline would release boron into associated melts or fluids and be an important factor in controlling the behaviour of boron in tourmaline-bearing high-temperature metamorphic rocks.Near the tourmaline-out isograd, large tourmaline crystals occur in the centre of interboudin partitions containing leucosome. In the melanosome of the intervening matrix, reaction textures involving tourmaline are locally observed. These observations imply that tourmaline breakdown is related to a melting reaction and that the boron in the leucosome is derived from the breakdown of tourmaline in the melanosome during prograde metamorphism.Boron released by tourmaline breakdown lowers both the solidus temperature of the rock and the viscosity of any associated melt. Considering that the tourmaline-out isograd lies close to the schist–migmatite boundary, these effects might have enhanced melt generation and segregation in the migmatite zone of the Ryoke belt.The evidence for the breakdown of tourmaline and the almost complete absence of any borosilicates throughout the migmatite zone suggest that boron was effectively removed from this region by the movement of melt and/or fluid. This implies that the tourmaline-out isograd can reflect a significant amount of mass transfer in the anatectic zones.

Notes: A sequence of prograde isograds is recognized within the Dalradian Inzie Head gneisses where pelitic compositions have undergone variable degrees of partial melting via incongruent melting reactions consuming biotite. Three leucosome types are identified. At the lowest grades, granitic leucosomes containing porphyroblasts of cordierite (CRD-melt) are abundant. At intermediate grades, CRD-melt mingles with garnetiferous leucosomes (GT-melt). At the highest grades, CRD-melt coexists with orthopyroxene-bearing leucosomes (OPX-melt), while garnet is conspicuously absent. The prograde metamorphic field gradient is constrained to pressures of 2–3 kbar below the CRD-melt isograd, and no greater than 4.5 kbar at the highest grade around Inzie Head.A petrogenetic grid, calculated using thermocalc, is presented for the K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH) system for the phases orthopyroxene, garnet, cordierite, biotite, sillimanite, H2O and melt with quartz and K-feldspar in excess. For the implied field gradient, the reaction sequence predicted by the grid is consistent with the successive prograde development of each leucosome type. Compatibility diagrams suggest that, as anatexis proceeded, bulk compositions may have been displaced towards higher MgO content by the removal of (relatively) ferroan granitic leucosome. An isobaric (P = 4 kbar) T–aH2O diagram shows that premigmatization fluids must have been water-rich (aH2O 〉 0.85) and suggests that, following the formation of small volumes of CRD-melt, the system became fluid-absent and melting reactions buffered aH2O to lower values as temperatures rose. GT- and OPX-melt formed by fluid-absent melting reactions, but a maximum of 7–11% CRD-melt fraction can be generated under fluid-absent conditions, much less than the large volumes observed in the field. There is strong evidence that the CRD-melt leucosomes could not have been derived by buoyantly aided upwards migration from levels beneath the migmatites. Their formation therefore required a significant influx of H2O-rich fluid, but in a quantity insufficient to have exhausted the buffering capacity of the solid assemblage plus melt. Fluid : rock ratios cannot have exceeded 1 : 30. The fluid was channelled through a regionally extensive shear zone network following melt-induced failure. Such an influx of fluid at such depths has obvious consequences for localized crustal magma production and possibly for cordierite-bearing granitoids in general.

Notes: The South Karakorum margin, east of the Himalayan syntaxis, consist of an E–W elongated zone of young (10–3 Ma) high-grade metamorphic rocks (M2) and related migmatitic domes. This late tectono-metamorphic event post-dates the Palaeogene (55–37 Ma) phase of thickening of the belt featured by NW–SE structures and associated M1 amphibolite facies metamorphism (0.7 GPa, 700 °C). This M2 metamorphism is characterised by low-pressure, high-temperature conditions coeval with migmatite formation in response to a thermal increase of c. 150 °C compared to M1, culminating at a temperature of c. 770 °C and a pressure of 0.5–0.6 GPa. Rapid exhumation of migmatitic domes, at a rate of 5 mm yr−1, was accommodated by vertical extrusion, in the core of E–W crustal-scale folds. These crustal-scale folds formed in response to N–S syn-collisional shortening and were enhanced by thermal weakening of the migmatised continental crust.M2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity, firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid-crustal level. Such relationships between a mantle-related magmatism and a high-temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted Indian slab since 20 Ma.

Notes: High-P/low-T metamorphic rocks of the Hammondvale metamorphic suite (HMS) are exposed in an area of 10 km2 on the NW margin of the Caledonian (Avalon) terrane in southern New Brunswick, Canada. The HMS is in faulted contact on the SE with c. 560–550 Ma volcanic and sedimentary rocks and co-magmatic plutonic units of the Caledonian terrane. The HMS consists of albite- and garnet-porphyroblastic mica schist, with minor marble, calc-silicate rocks and quartzite. Pressure and temperature estimates from metamorphic assemblages in the mica schist and calc-silicate rocks using TWQ indicate that peak pressure conditions were 12.4 kbar at 430 °C. Peak temperature conditions were 580 °C at 9.0 kbar. 40Ar/39Ar muscovite ages from three samples range up to 618–615 Ma, a minimum age for high-P/low-T metamorphism in this unit. These ages indicate that the HMS is related to the c. 625–600 Ma subduction-generated volcanic and plutonic units exposed to the SE in the Caledonian terrane. The ages are also similar to those obtained from detrital muscovite in a Neoproterozoic-Cambrian sedimentary sequence in the Caledonian terrane, suggesting that the HMS was exposed by latest Neoproterozoic time and supplied detritus to the sedimentary units. The HMS is interpreted to represent a fragment of an accretionary complex, similar to the Sanbagawa Belt in Japan. It confirms the presence of a major cryptic suture between the Avalon terrane sensu stricto and the now-adjacent Brookville terrane.

Notes: The Sanddal mafic-ultramafic complex (SMUK) is a cluster of variably eclogitised mafic and ultramafic bodies that comprise the westernmost known eclogite facies locality in the North-East Greenland eclogite province (NEGEP). Although there are no true eclogites in the SMUK, we interpret three distinct textural types of plagioclase replacement to record sequential stages in adjustment of SMUK olivine gabbro-norites to eclogite facies conditions. The earliest stage, in which plagioclase was replaced by omphacite/spinel symplectite before nucleation of garnet (Type 1A & 1B) has not previously been described. Documentation of this texture provides clear evidence that, at least in some cases, garnet nucleation is delayed relative to nucleation of omphacite and is a rate-limiting step for eclogitisation. Type 1C domains were produced by scattered nucleation of garnet in the same sample. In Type 2 domains, plagioclase was replaced by a layered corona with an outer layer of garnet, an inner layer of omphacite and an interior of inclusion-rich plagioclase. In Type 3 domains, the omphacite layer was overgrown by the garnet rim, and omphacite is preserved only as inclusions in garnet. In more coarse grained leucogabbros, recrystallization was more complete, plagioclase replacement textures were less localised, and could not be divided into distinct stages. Plagioclase replacement in SMUK samples was not isochemical, and required diffusion of at least Mg and Fe from replacement of mafic phases in the surroundings. Strong compositional gradients in garnet reflect disequilibrium and were controlled by the different diffusion rates of Mg/Fe and Ca, different local chemical environments, and progress of the plagioclase breakdown reaction. The presence of small amounts of hydrous minerals (amphibole, phlogopite and clinozoisite) in local equilibrium in plagioclase domains of most SMUK samples indicates that a small amount of H2O was present during high pressure metamorphism.

Notes: Kyanite and staurolite occur in the Tananao Metamorphic Complex as submicron inclusions in almandine-rich garnet from a metamorphosed palaeosol weathering horizon, near Hoping, eastern Taiwan. Quartz, rutile/brookite and zircon are also found as associated submicron inclusions in garnet. Employing the reaction ilmenite+kyanite+quartz=almandine+rutile, and the breakdown of staurolite and quartz as thermobarometers, these submicron-scale minerals formed at 〉8.3–8.8 kbar and 〈 660–690 °C. This P–T estimate is different from that (i.e. 5–7 kbar and 530–550 °C) derived from matrix minerals, which include almandine-rich garnet, muscovite, chlorite, chloritoid, plagioclase, quartz and ilmenite. These results suggest that submicron inclusions in garnet-like materials may record portions of the otherwise undocumented prograde path or provide information about previous metamorphic events and thus yield new insights into orogenic belts.

Notes: A hydrothermally metamorphosed/altered greenstone complex capped by bedded cherts exposed in the North Pole, Pilbara Carton, Western Australia, is interpreted as an accretionary complex. It is distinctive in being characterised by both duplex structure and an oceanic crust stratigraphy. This complex is shown to represent an Archaean upper oceanic crust with a mid-ocean ridge hydrothermal metamorphism that increases in grade stratigraphically downward. Three mineral zones have been defined; Zone A of the zeolite facies, the prehnite-pumpellyite facies or the lower-greenschist facies at high-XCO2 condition, Zone B of the greenschist facies, and Zone C of the greenschist/amphibolite transition facies. In Zone A metabasites, Ca-Al silicates including Ca-zeolites, prehnite and pumpellyite are absent and epidote/clinozoisite is extremely rare. Instead, abundant carbonates are present with chlorite suggesting high-XCO2 composition in the fluid. On the other hand, in Zones B and C metabasites, where Ca-amphibole + epidote/clinozoisite + chlorite + Ca-Na plagioclase are the dominant assemblages, carbonate is not identified. The metamorphic conditions boundary of Zones B/C were estimated to be about 350 °C at a pressure of 〈0.5 kbar.Fluid compositions coexisting with Archaean greenstones at the transition between Zones B and C were estimated by thermodynamic calculation in the CaFMASCH system (T = 350–370 °C, P = 150–1000 bar) at XCO2 of 0.012–0.140, such values are higher than present-day vent fluids collected near mid-ocean ridges with low-XCO2 values, up to 0.005. The Archaean seawater depth at the mid-ocean ridge was estimated to be 1600 m at XCO2 = 0.06 using a depth-to-boiling point curve for a fluid. The carbonation due to high-XCO2 hydrothermal fluids occurred near the ridge-axis before or was coincident with ridge metamorphism.

Notes: Metapelitic rocks from the Marble Hall Fragment, enclosed in the granites of the magmatic Bushveld Complex, record a two-stage, low-pressure, high-temperature metamorphism. An early paragenesis containing chiastolitic andalusite, cordierite, biotite and quartz ± garnet crystallized in most rocks and equilibrated at 550–600 °C, 0.2 GPa. It was transformed during the second, peak event into various parageneses that commonly coexist within a single thin section. These include garnet–cordierite–biotite–K-feldspar–quartz, sillimanite–cordierite–K-feldspar–quartz and spectacular quartz-undersaturated cordierite–spinel symplectites replacing the chiastolite porphyroblasts.Based on a detailed phase diagram analysis, we argue that these parageneses result from rapid heating at an approximately constant pressure to temperatures of more than about 720 °C. At these temperatures, the internally buffered activity of water was reduced by incipient water-saturated partial melting, while only minor quantities of melt were produced. Subsequent dry conditions inhibited large-scale equilibration and, together with local inhomogeneities in mineral distribution, led to the development of contrasting parageneses and symplectite textures. No signs of widespread fluid-absent melting of biotite were found, and so the temperature probably did not exceed 760 °C. The peak metamorphic event is attributed to the emplacement of the hot Nebo granite, whereas the early metamorphism was probably caused by the intrusion of one of the phases of the Rustenburg Layered Suite.We infer the conditions of development of the cordierite–spinel intergrowths and we show that, although symplectites are commonly associated with retrograde processes (cooling and/or decompression), they can record a prograde metamorphic evolution. Furthermore, our contribution emphasizes the importance of the concept of reduced equilibration volume for the understanding and interpretation of some particular textures and parageneses in common rocks.

Notes: Two types of garnet porphyroblast occur in the Schneeberg Complex of the Italian Alps. Type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz, decussate mica and small garnet grains, and a margin containing large garnet grains. Orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains. Individual garnet grains without subdomains are small (〈 50 µm), faceted and idioblastic, and have simple zoning profiles with Ca-rich cores and Ca-poor rims. Subdomains of larger garnet grains are similar in size to the individual, small garnet grains. Type 2 porphyroblasts comprise only ellipsoidal garnet, with small subdomains in the centre and larger subdomains at the margin. Each subdomain has its own Ca high, Ca dropping towards subdomain boundaries. Garnet grains, with or without subdomains, all have the same Ca-poor composition at rims in contact with other minerals. The compositional zonation patterns are best explained by simultaneous, multiple nucleation, followed by growth and amalgamation of individual garnet grains. The range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre. The difference between Type 1 and Type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast.Electron backscatter diffraction shows that small, individual garnet grains are randomly oriented. Large marginal garnet grains and subdomain-bearing garnet grains have a strong preferred orientation, clustering around a single garnet orientation. Misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations. The only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other. This process was driven by the reduction of subdomain boundary energy associated with misorientation loss. Rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals (quartz and mica) around the garnet. An analytical model, in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz, suggests that, at the conditions of metamorphism, the rotation required to give a strong preferred orientation can occur on a similar time-scale to that of porphyroblast growth.

Notes: The late Mesozoic and Cenozoic metamorphic evolution of the western North American continental margin is recorded in a belt of homogeneous metapelitic rocks, the Kluane metamorphic assemblage (KMA), in the northern Coast Belt of Yukon Territory. A record of Late Cretaceous medium-pressure and -temperature (c. 7 kbar, 500 °C) metamorphism, M1, is preserved in Ca-rich garnet and Na-rich plagioclase cores in rocks that were little affected by later events. M1 was synchronous with mylonitization and is attributed to accretion of the KMA to the ancient continental margin. Isothermal decompression during rapid uplift was followed by early Eocene emplacement of the Ruby Range Batholith (RRB), part of a magmatic arc produced by subduction of the Kula plate. The intrusion of the RRB led to a contact metamorphic overprint, M2, producing a 5–6 km wide aureole in which the grade ranges from subgarnet zone to garnet–cordierite–K-feldspar zone. Pressure and temperature estimates for M2, calculated from mineral equilibria, are 3.5–4.5 kbar and 530–720 °C, generally consistent with the stability limits of the observed mineral assemblages. Comparison of mineral assemblages and P–T conditions in the KMA with those in the Mclaren Glacier metamorphic belt in Alaska does not support the correlation of the two metamorphic sequences. This weakens the hypothesis proposing 400 km of dextral slip along the Denali fault zone.

Notes: Primary multiphase brine fluid inclusions in omphacite and garnet from low- to medium-temperature eclogites have been analysed for Cl, Br, I, F, Li and SO4. Halogen contents and ratios provide information about trapped lower crustal fluids, even though the major element (Na, K, Ca) contents of inclusion fluids have been modified by fluid–mineral interactions and (step-) daughter-crystal formation after trapping. Halogens in the inclusion fluids were analysed with crush–leach techniques. Cl/Br and Cl/I mass ratios of eclogite fluids are in the range 31–395 and 5000–33 000, respectively. Most fluids have a Cl/Br ratio lower than modern seawater and a Cl/I ratio one order of magnitude lower than modern seawater. Fluids with the lowest Cl/Br and highest Cl/I ratios come from an eclogite that formed by hydration of granulite facies rocks, and may indicate that Br and I are fractionated into hydrous minerals. Reconstructions indicate that the inclusion fluids originally contained 500–4000 ppm Br, 1–14 ppm I and 33–438 ppm Li. Electron microprobe analyses of eclogite facies amphibole, biotite, phengite and apatite indicate that F and Cl fractionate most strongly between phengite (F/Cl mass ratio of 1469 ± 1048) and fluid (F/Cl mass ratio of 0.008), and the least between amphibole and fluid. The chemical evolution of Cl and Br in pore fluids during hydration reactions is in many ways analogous to Cl and Br in seawater during evaporation: the Cl/Br ratio remains constant until the aH2O value is sufficiently lowered for Cl to be removed from solution by incorporation into hydrous minerals.

Notes: A thermodynamic model for haplogranitic melts in the system Na2O–CaO–K2O–Al2O3–SiO2–H2O (NCKASH) is extended by the addition of FeO and MgO, with the data for the additional end-members of the liquid incorporated in the Holland & Powell (1998) internally consistent thermodynamic dataset. The resulting dataset, with the software thermocalc, is then used to calculate melting relationships for metapelitic rock compositions. The main forms for this are P–T and T–X pseudosections calculated for particular rock compositions and composition ranges. The relationships in these full-system pseudosections are controlled by the low-variance equilibria in subsystems of NCKFMASH. In particular, the solidus relationships are controlled by the solidus relationships in NKASH, and the ferromagnesian mineral relationships are controlled by those in KFMASH. However, calculations in NCKFMASH allow the relationships between the common metapelitic minerals and silicate melt to be determined. In particular, the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks, particularly relating to open-system behaviour of rocks under high-grade conditions.

Notes: A detailed analysis of chemical zoning in two garnet crystals from Harpswell Neck, Maine, forms the basis of an interpretation of garnet nucleation and growth mechanisms. Garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation, giving rise to complex two-dimensional zoning patterns depending on the orientation of the thin section cut. Contours of Ca zoning cross those of Mn, Fe and Mg, indicating a lack of equilibrium among these major garnet constituents. Zoning of Fe, Mg and Mn is interpreted to reflect equilibrium with the rock matrix, whereas Ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal.Image analysis reveals that the growth of garnet is more rapid along triple-grain intersections than along double-grain boundaries. Moreover, different minerals are replaced by garnet at different rates. The relative rate of replacement by garnet along double-grain boundaries is ordered as muscovite 〉 chlorite 〉 plagioclase 〉 quartz. Flux calculations reveal that replacement is limited by diffusion of Si along double-grain boundaries to or from the local reaction site. It is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet, with Si and Al transport being rate limiting in these samples.

Notes: Due to the retrograde cation exchange problems experienced by conventional geothermobarometers above their closure temperatures, petrogenetic grids are a potentially powerful alternative to unravelling the P–T evolution of ultrahigh-T granulite terranes. A new qualitative KFMASH (K2O–FeO–MgO–Al2O3–SiO2–H2O) petrogenetic grid for Mg–Al rich metapelites containing K-feldspar, sillimanite and quartzofeldspathic melt that successfully accounts for the majority of assemblages composed of variations of sapphirine, spinel, garnet, orthopyroxene, cordierite, biotite and quartz is developed. Univariant reactions are predicted utilizing a newly derived ‘melt projection’ and these reactions are entirely consistent with algebraically calculated reaction coefficients obtained using a set of standard phase compositions. Based upon observations of commonly associated mineral assemblages in natural lithologies the [Spr, Spl], [Qtz, Spl], [Bt, Spl], [Opx, Spr], [Opx, Qtz] and [Bt, Opx] invariant points are assumed to be stable, whilst the [Grt, Spr], [Grt, Qtz], [Spr, Qtz] and [Crd, Qtz] are assumed to be metastable. Biotite-bearing assemblages are confined to the lowest temperatures, and sapphirine + quartz to the highest temperatures. Orthopyroxene + sillimanite ± quartz assemblages are confined to the highest pressures, whilst spinel-bearing assemblages are stabilized by lower pressures. The alternative choice of invariant point stability leads to significant differences between this grid and previously proposed topologies. Spinel cannot be stable along with the orthopyroxene and sillimanite assemblage as previously proposed. Further, more subtle differences in topology result from the treatment of H2O in the chemographic projection used to deduce univariant reactions, and projecting from a water-bearing quartzofeldspathic melt does not yield the same reaction coefficients as projection from H2O. The new grid allows reinterpretation of previously proposed evolutionary P–T paths for Mg–Al rich granulites from the Napier Complex and Rauer Group, East Antarctica, and In Ouzzal, Algeria.

Notes: Sm–Nd (garnet), U–Pb (monazite) and Rb–Sr (biotite) ages from a composite migmatite sample (Damara orogen, Namibia) constrain the time of high-grade regional metamorphism and the duration of regional metamorphic events. Sm–Nd garnet whole-rock ages for a strongly restitic melanosome and an adjacent intrusive leucosome yield ages of 534±5, 528±11 and 539±8 Ma. These results provide substantial evidence for pre-500 Ma Pan-African regional metamorphism and melting for this segment of the orogen. Other parts of the migmatite yield younger Sm–Nd ages of 488±9 Ma for melanosome and 496±10, 492±5 and 511±16 Ma for the corresponding leucosomes. Garnet from one xenolith from the leucosomes yields an age of 497±2 Ma. Major element compostions of garnet are different in terms of absolute abundances of pyrope and spessartine components, but the flat shape of the elemental patterns suggests late-stage retrograde equilibration. Rare earth element compositions of the garnet from the different layers are similar except for garnet from the intrusive leucosome suggesting that they grew in different environments. Monazite from the leucosomes is reversely discordant and records 207Pb/235U ages between 536 and 529 Ma, indicating that this monazite represents incorporated residual material from the first melting event. Monazite from the mesosome MES 2 and the melanosome MEL 3 gives 207Pb/235U ages of 523 and 526 Ma, and 529 and 531 Ma, respectively, which probably indicates another thermal event. Previously published 207Pb/235U monazite data give ages between 525 and 521 Ma for composite migmatites, and 521 and 518 Ma for monazite from neosomes. Monazite from granitic to granodioritic veins indicates another thermal event at 507–505 Ma. These ages are also recorded in 207Pb/235U monazite data of 508 Ma from the metasediment MET 1 from the migmatite and also in the Sm–Nd garnet ages obtained in this study. Taken together, these ages indicate that high-grade metamorphism started at c. 535 Ma (or earlier) and was followed by thermal events at c. 520 Ma and c. 505 Ma. The latter event is probably connected with the intrusion of a large igneous body (Donkerhoek granite) for which so far only imprecise Rb–Sr whole-rock data of 520±15 Ma are available. Rb–Sr biotite ages from the different layers of the migmatite are 488, 469 and 473 Ma. These different ages indicate late-stage disturbance of the Rb–Sr isotopic system on the sub-sample scale. Nevertheless, these ages are close to the youngest Sm–Nd garnet ages, indicating rapid cooling rates between 13 and 20°C Ma−1 and fast uplift of this segment of the crust. Similar Sm–Nd garnet and U–Pb monazite ages suggest that the closure temperatures for both isotopic systems are not very different in this case and are probably similar or higher than the previously estimated peak metamorphic temperatures of 730±30°C. The preservation of restitic monazite in leucosomes indicates that dissolution of monazite in felsic water-undersaturated peraluminous melts can be sluggish. This study shows that geochronological data from migmatites can record polymetamorphic episodes in high-grade terranes that often contain cryptic evidence for the nature and timing of early metamorphic events.

Notes: A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well-preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P–T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N2-bearing NaCl-rich solutions, whereas it changed into CO2-dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low-salinity fluids were involved. In situ UV-laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (δ18OVSMOW = c. 6.7‰) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid–rock interactions. Unusual MORB-like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra-high-pressure (UHP) eclogites in the Dabie-Sulu area. However, the age-corrected initial εNd(t) is − 2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N2 content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism.

Notes: Fluid inclusions in coesite-bearing eclogites and jadeite quartzite at Shuanghe in Dabie Shan, East-central China, have preserved remnants of early, prograde and/or peak metamorphic fluids, reset during post-UHP (ultrahigh-pressure) metamorphic uplift. Inclusions occur in several minerals (e.g. omphacite & epidote), notably as isolated, primary inclusions in quartz included in various host minerals. Two major fluid types have been identified: non-polar fluid species (N2 or CO2) and aqueous, the latter is by far the most predominant. Aqueous fluids cover a wide range of salinity, from halite-bearing brines to low salinity fluids. For non-polar fluids, few N2 inclusions occur in undeformed eclogite, whereas a number of CO2-rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences.The primary character of N2 and high-salinity aqueous inclusions indicates that they are remnants from UHP metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre-metamorphic fluids. This conclusion is supported by the preservation, in some samples, of microdomains containing synchronous inclusions of variable salinities, which tend to relate to the chemical composition of the host crystal. Carbonic fluids may be derived from neighbouring rocks, notably marble and carbonate-bearing metasediments, during post-metamorphic uplift. During post-UHP exhumation, a limited decrease of the fluid density has occurred, with formation of new sets of fluid inclusions. Fluid movements, however, remained exceedingly limited, at the scale of the enclosing crystal.

Notes: Granulite facies gabbroic and dioritic gneisses in the Pembroke Valley, Milford Sound, New Zealand, are cut by vertical and planar garnet reaction zones in rectilinear patterns. In gabbroic gneiss, narrow dykes of anorthositic leucosome are surrounded by fine-grained garnet granulite that replaced the host two-pyroxene hornblende granulite at conditions of 750 °C and 14 kbar. Major and trace element whole-rock geochemical data indicate that recrystallization was mostly isochemical. The anorthositic veins cut contacts between gabbroic gneiss and dioritic gneiss, but change in morphology at the contacts, from the anorthositic vein surrounded by a garnet granulite reaction zone in the gabbroic gneiss, to zones with a septum of coarse-grained garnet surrounded by anorthositic leucosome in the dioritic gneiss. The dioritic gneiss also contains isolated garnet grains enclosed by leucosome, and short planar trains of garnet grains linked by leucosome. Partial melting of the dioritic gneiss, mostly controlled by hornblende breakdown at water-undersaturated conditions, is inferred to have generated the leucosomes. The form of the leucosomes is consistent with melt segregation and transport aided by fracture propagation; limited retrogression suggests considerable melt escape. Dyking and melt escape from the dioritic gneiss are inferred to have propagated fractures into the gabbroic gneiss. The migrating melt scavenged water from the surrounding gabbroic gneiss and induced the limited replacement by garnet granulite.

Notes: This paper examines the spatial statistics of matrix minerals and complex patterned cordierite porphyroblasts in the low-pressure, high-temperature (low P/T) Tsukuba metamorphic rocks from central Japan, using a density correlation function. The cordierite-producing reaction is sillimanite + biotite + quartz = K-feldspar + cordierite + water. The density correlation function shows that quartz is distributed randomly. However, the density correlation functions of biotite, plagioclase and K-feldspar show that their spatial distributions are clearly affected by the formation of cordierite porphyroblasts. These observations suggest that cordierite growth occurred through a selective growth mechanism: quartz adjacent to cordierite has a tendency to prevent the growth of cordierite, whereas other matrix minerals adjacent to cordierite have a tendency to enhance the growth of cordierite. The density correlation functions of complex patterned cordierite porphyroblasts show power-law behaviour. A selective growth mechanism alone cannot explain the origin of the power-law behaviour. Comparison of the morphology and fractal dimension of cordierite with two-dimensional sections from a three-dimensional diffusion-limited aggregation (DLA) suggests that the formation of cordierite porphyroblasts can be modelled as a DLA process. DLA is the simple statistical model for the universal fractal pattern developed in a macroscopic diffusion field. Diffusion-controlled growth interacting with a random field is essential to the formation of a DLA-like pattern. The selective growth mechanism will provide a random noise for the growth of cordierite due to random distribution of quartz. Therefore, a selective growth mechanism coupled with diffusion-controlled growth is proposed to explain the power-law behaviour of the density correlation function of complex patterned cordierite. The results in this paper suggest that not only the growth kinetics but also the spatial distribution of matrix minerals affect the progress of the metamorphic reaction and pattern formation of metamorphic rocks.

Notes: Alpine metamorphism, related to the development of a metamorphic core complex during Cretaceous orogenic events, has been recognized in the Veporic unit, Western Carpathians (Slovakia). Three metamorphic zones have been distinguished in the metapelites: 1, chloritoid + chlorite + garnet; 2, garnet + staurolite + chlorite; 3, staurolite + biotite + kyanite. The isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH). The isograds are roughly parallel to the north-east-dipping foliation related to extensional updoming along low-angle normal faults. Thermobarometric data document increasing P–T conditions from c. 500 °C and 7–8 kbar to c. 620 °C and 9–10 kbar, reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies. 40Ar/39Ar data obtained by high spatial resolution in situ ultraviolet (UV) laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the Late Cretaceous. Mean dates are between 77 and 72 Ma; however, individual white mica grains record a range of apparent 40Ar/39Ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous. The reconstructed metamorphic P–T–t path is ‘clockwise’, reflecting post-burial decompression and cooling during a single Alpine orogenic cycle. The presented data suggest that the Veporic unit evolved as a metamorphic core complex during the Cretaceous growth of the Western Carpathian orogenic wedge. Metamorphism was related to collisional crustal shortening and stacking, following closure of the Meliata Ocean. Exhumation was accomplished by synorogenic (orogen-parallel) extension and unroofing in an overall compressive regime.

Notes: Models of fluid/rock interaction in and adjacent to the Alpine Fault in the Hokitika area, South Island, New Zealand, were investigated using hydrogen and other stable isotope studies, together with field and petrographic observations. All analysed samples from the study area have similar whole-rock δD values (δDWR = −56 to −30‰, average = −45‰, n = 20), irrespective of rock type, degree of chloritization, location along the fault, or across-strike distance from the fault in the garnet zone. The green, chlorite-rich fault rocks, which probably formed from Australian Plate precursors, record nearly isothermal fluid/rock interaction with a schist-derived metamorphic fluid at high temperatures near 450–500°C (δD of water in equilibrium with the green fault rocks (δDH2O, green) ≈ −18‰; δD of water in equilibrium with the greyschists and greyschist-derived mylonites (δDH2O, grey) ≈ −19‰ at 500°C; δDH2O, green ≈ −17‰; δDH2O, grey ≈ −14‰ at 450°C). There is no indication of an influx of a meteoric or mantle-derived fluid in the Alpine Fault Zone in the study area. The Alpine Fault Zone at the surface shows little evidence of late-stage retrogression or veining, which might be attributed to down-temperature fluid flow. It is probable that prograde metamorphism in the root zone of the Southern Alps releases metamorphic fluids that at some region rise vertically rather than following the trace of the Alpine Fault up to the surface, owing to the combined effects of the fault, the disturbed isotherms under the Southern Alps, and the brittle–ductile transition. Such fluids could mix with meteoric fluids to deposit quartz-rich, possibly gold-bearing veins in the region c. 5–10 km back from the fault trace. These results and interpretations are consistent with interpretations of magnetotelluric data obtained in the South Island GeopHysical Transects (SIGHT) programme.

Notes: Metagranodiorite samples from the Brossasco-Isasca Unit, Dora-Maira Massif, western Alps, show pseudomorphous and coronitic textures where igneous minerals were partially replaced by ultra-high pressure (UHP) metamorphic assemblages. The original magmatic paragenesis consisted of quartz, plagioclase, K-feldspar, biotite and minor phases. During UHP metamorphism, the plagioclase (site P) was replaced by zoisite, jadeite, quartz, K-feldspar and kyanite, and coronitic reactions developed between biotite and adjacent minerals. At the original igneous biotite–quartz contact (site A), a single corona of poorly zoned garnet is developed, whereas at the biotite–K-feldspar (site B) and biotite–plagioclase (site C) contacts, composite coronas are formed. Integration of results from petrographic observations, calculations of mineral stoichiometry and thermodynamic calculations of mineral stability has allowed the determination of the metamorphic reactions involved and the estimation of the metamorphic conditions, which reached as high as 24 kbar and 650 °C. Accurate microanalysis by energy-dispersive spectroscopy (EDS) and statistical analysis of the data allowed us to identify, for the first time in a natural Na-pyroxene of metagranitoid rocks, the end-member Ca-Eskola.

Notes: The preservation of mineral assemblages that were fluid-present during their prograde history is primarily related to the consumption of the fluid by growth of more hydrous minerals as the retrograde history begins. The range of behaviour relating to the preservation of mineral assemblages is examined using calculated phase diagrams for fluid-saturated conditions, contoured for the H2O content of the mineral assemblage. At equilibrium, as a mineral assemblage crosses contours of decreasing H2O content along a pressure–temperature path, it dehydrates, the fluid being lost from the rock. If the assemblage crosses contours of increasing H2O content, the mineral assemblage starts to rehydrate using any fluid on its grain boundaries. When the rock has consumed its fluid, the resulting mineral assemblage is that preserved in the rock. Conditions relating to the preservation of mineral assemblages are discussed, and examples of the consequences of different pressure–temperature paths on preservation in a metapelitic and a metabasic rock composition are considered on phase diagrams calculated with thermocalc.

Notes: This work supports a growing body of evidence that the Ashe Metamorphic Suite (AMS) of the eastern Blue Ridge province in North Carolina has an ensimatic origin and is part of a subduction-related accretionary mélange, marking the Taconic suture between the North American craton and the Inner Piedmont. In a palinspastic reconstruction, the thrust fault at the base of the AMS appears to have intercepted the greatest depths (i.e. highest-P metamorphic rocks) beneath parts of the AMS now exposed adjacent to the Grandfather Mountain window. The greatest volume of mafic rock is found in these same areas. We suggest that the nascent, subduction-related, basal thrust fault was deflected downward by an obstacle in the form of an isolated, mafic volcanic edifice on the oceanic crust–a sea mount.Pelitic and mafic rocks dominate the AMS. North of the Grandfather Mountain window, retrograded eclogite occurs in the amphibolite near the base of the AMS. Textures and mineralogy indicate that an original eclogite assemblage was subjected to the following sequence of parageneses:(a) Eclogite(I) facies: omphacite+garnet+quartz,(b) Eclogite(II) facies: omphacite+garnet+epidote+quartz,(c) Symplectic (diopside+plagioclase)+garnet+epidote+quartz,(d) Amphibolite facies: (diopside+plagioclase)+garnet+epidote+hornblende+quartz,(e) Amphibolite facies: plagioclase+garnet+epidote+hornblende+quartz. P–T conditions, estimated from geothermobarometry applied to relevant mineral compositions, are c.720 °C and c.16 kbar for (b) eclogite(II) facies; c.655 °C and c.8.5 kbar for (e) amphibolite facies.

Notes: X-ray composition maps and quantitative analyses for Mn, Ca and Cr have been made for six pelitic and calc-pelitic garnet crystals and Al, Fe and Cr analyses maps have been made for two kyanite crystals, from lower and mid/upper amphibolite facies rocks from the Grenville Province of western Labrador, using an electron microprobe analyser and a laser ablation ICP-MS. Garnet with spiral (‘snowball’) internal fabrics (Si) has spiral zoning in major elements, implying that growth was concentrated in discrete regions of the crystal at any one time (spiral zoning). Cr zoning is parallel to Si in low amphibolite facies garnet with both straight and spiral internal fabrics, indicating that the garnet overprinted a fabric defined by Cr-rich (mica±chlorite±epidote) and Cr-poor (quartz±plagioclase) layers during growth (overprint zoning) and that Cr was effectively immobile. In contrast, in mid/upper amphibolite facies garnet porphyroblasts lacking Si, Cr zoning is concentric, implying that Cr diffusion occurred. Cr zoning in kyanite porphyroblasts appears superficially similar to oscillatory zoning, with up to three or four annuli of Cr enrichment and/or depletion present in a single grain. However, the variable width, continuity, Cr concentration and local bifurcation of individual annuli suggest that an origin by overprint zoning may be more likely. The results of this study explain previously observed nonsystematic Cr zoning in garnet and irregular partitioning of Cr between coexisting metamorphic mineral pairs. In addition, this study points to the important role of crystal growth rate in determining the presence or absence of inclusions and the type of zoning exhibited by both major and trace elements. During fast growth, inclusions are preferentially incorporated into the growing porphyroblast and slow diffusing elements such as Cr are effectively immobile, whereas during slow growth, inclusions are not generally included in the porphyroblast and Cr zoning is concentric.

Notes: The grain- and outcrop-scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths. At the grain scale, anatectic melt is pervasively distributed in the grain boundaries and in small pools; consequently, most melt is located parallel to the principal fabric in the rock, typically a foliation. Short, branched arrays of linked, melt-bearing grain boundaries connect melt-depleted parts of the matrix to diffuse zones of melt accumulation (protoleucosomes), where magmatic flow and alignment of euhedral crystals grown from the melt developed.The distribution of melt (leucosome) and residual rocks (normally melanocratic) in outcrop provides different, but complementary, information. The residual rocks show where the melt came from, and the leucosomes preserve some of the channels through which the melt moved, or sites where it pooled. Different stages of the melt segregation process are recorded in the leucosome–melanosome arrays. Regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin, branching leucosomes with little melanosome. A more advanced stage of melting and segregation is marked by the development of residual rocks around extensive, branched leucosome arrays, generally oriented along the foliation or melting layer. Places where melting had stopped, or slowed down, before crystallization began are marked by a high ratio of melanosome to leucosome; because most of the melt has drained away, very few leucosomes remain to mark the melt escape path — this is common in melt-depleted granulite terranes. Many migmatites contain abundant leucosomes oriented parallel to the foliation; mostly, these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel (leucosome) arrays collected. Melt collected in the foliation planes was partially, or fully, expelled later, when discordant leucosomes formed. Leucosomes (or veins) oriented at high angles to the foliation/layering formed last and commonly lack melanocratic borders; hence they were not involved in draining the matrix of the melting layer. Discordant leucosomes represent the channels through which melt flowed out of the melting layer.

Notes: The Southern Marginal Zone of the late Archean Limpopo Belt of southern Africa is an example of a high-grade gneiss terrane in which both upper and lower crustal deformational processes can be studied. This marginal zone consists of large thrust sheets of complexly folded low-strain gneisses, bound by an imbricate system of kilometre-wide deep crustal shear zones characterized by the presence of high-strain gneisses (‘primary straight gneisses’). These shear zones developed during the decompression stage of this high-grade terrane. Low- and high-strain gneisses both contain similar reaction textures that formed under different kinematic conditions during decompression. Evidence for the early M1/D1 metamorphic phase (〉 2690 Ma) is rarely preserved in low-strain gneisses as a uniform orientation of relict Al-rich orthopyroxene in the matrix and quartz and plagioclase inclusions in the cores of early (M1) Mg-rich garnet porphyroblasts. This rare fabric formed at 〉 820 °C and 〉 7.5 kbar. The retrograde M2/D2 metamorphic fabric (2630–2670 Ma) is well developed in high-strain gneisses from deep crustal shear zones and is microscopically recognized by the presence of reaction textures that formed synkinematically during shear deformation: M2 sigmoid-shaped reaction textures with oriented cordierite–orthopyroxene symplectites formed after the early M1 Mg-rich garnet porphyroblasts, and syn-decompression M2 pencil-shaped garnet with oriented inclusions of sillimanite and quartz formed after cordierite under conditions of near-isobaric cooling at 750–630 °C and 6–5 kbar. The symplectites and pencil-shaped garnet are oriented parallel to the shear fabric and in the stretching direction. Low-strain gneisses from thrust sheets show similar M2 decompression cooling and near-isobaric cooling reaction textures that formed within the same P–T range, but under low-strain conditions, as shown by their pseudo-idioblastic shapes that reflect the contours of completely replaced M1 garnet and randomly oriented cordierite–orthopyroxene symplectites. The presence of similar reaction textures reflecting low-strain conditions in gneisses from thrust sheets and high-strain conditions in primary straight gneisses suggests that most of the strain during decompression was partitioned into the bounding shear zones. A younger M3/D3 mylonitic fabric (〈 2637 Ma) in unhydrated mylonites is characterized by brittle deformation of garnet porphyroclasts and ductile deformation of the quartz–plagioclase–biotite matrix developed at 〈 600 °C, as the result of post-decompression shearing under epidote–amphibolite facies conditions.

Notes: Abstract. 15N labelled NH4NO3 (fertilizer N) was applied at a rate of 50 kg N ha–1 to an Ando-Humic Nitisol and two maize crops grown on it. About 20 months later, soil cores were taken to a depth of 2.5 m. Leached fertilizer N was found between 1.4 m and 1.8 m deep and was delayed relative to net drainage by between 4.2 and 4.9 pore volumes. Anion exchange capacity (AEC) increased ten-fold down the profile, up to 2.9 cmolckg–1. The delay to fertilizer N leaching was predicted to be between 4.1 and 5.3 pore volumes when calculated from the AEC and from an equation relating delay due to AEC in laboratory columns of repacked soil obtained by Wong et al. (1990b). It was concluded that the nitrate leaching delay equation was also valid in undisturbed field profiles. Two concentration maxima for mineral N were found, which did not usually coincide with the fertilizer N and were thought to result from mineralization of soil organic matter and plant residues at the end of each season. The delay equation overestimated their leaching delay but the results were considered close enough to support the hypothesis for their formation.

Notes: Abstract. Regions in the Po Valley, Northern Italy, are characterized by intensive crop-livestock farming systems. A simulation model has been chosen for an inter-regional project, which should help in defining groundwater vulnerability and pollution risk on a regional scale, in relation to agricultural land use, by allowing the prediction of nitrate leaching under different climate, soil, crop and management scenarios. The model derives from the coupling of a hydrological model, MACRO, simulating water flow and solute transport in structured soils, with a model simulating soil N dynamics, SOILN. The aim of this work was to test the model's ability to simulate nitrate leaching through soil after land spreading of pig slurries. A dataset obtained from lysimeter experiments which had been carried out in the period 1976–1981 was used for this purpose. Four soil types were compared (silty clay, sandy loam, loam and sand) in factorial combination with four rates of pig slurry (0, 142, 284, 426 g of N m–2, accumulated values from 1976 to 1979) for a seven crop sequence. The efficiency of the MACRO model ranged from 0.96, in the sandy-loam soil, to 0.81, in the sand. Percolation was usually under-estimated, the relative error ranging from 0.7 to 14.6, depending on the soil. The low efficiency of the SOILN model in simulating nitrate leaching is attributed to the lack of knowledge of the mechanisms regulating N transformation processes and especially the mineralization of pig slurry N. This lack of knowledge hampers the correct setting of the N transformation parameter values. A remarkable improvement of the model's performance was obtained by changing a few coefficients which control the mineralization-immobilization turnover of the faeces-organic N. The model efficiency, following this recalibration, ranged from –0.62 to 0.84, and the relative error ranged from –56 to 35, depending on soil and treatment. N leaching was under-estimated at the low pig slurry N application rates and over-estimated at the high ones.

Notes: Abstract. The effectiveness of contour grass strips in erosion control was investigated in a field experiment involving two grass treatments (Festuca ovina and Poa pratensis) and a bare soil control on an erodible sandy loam soil on a 5° slope using simulated rainstorms of 40 mm h–1 for 45 minutes duration. The grass strips resulted in significantly (P 〈 0.05) lower runoff and soil loss than the bare soil but there was no significant difference in the performance of the two grasses, despite their differences in density, height and leaf size. The effect of the lower density of the Poa pratensis was offset by its larger stem diameter so that the surface area facing the flow was similar for both grasses. Instead of acting as a filter with sedimentation occurring within the barrier, the grass strips operated by ponding water upslope of the barriers. Deposition then occurred in the ponded area above the barrier.

Notes: Abstract. Since the 1980s, land use in rural areas of China has changed greatly as the result of political initiatives. These changes have caused soil nutrient changes which are examined in this paper for Zunhua County, northern China from 1980 to 1999. The areas of farmland, grassland, and paddy decreased greatly and were replaced by increases in forest and residential land. The soils under forest in 1999 transformed from farmland in 1980 increased in organic matter by 21%, total nitrogen by 18%, available nitrogen by 65%, available phosphorus by 17% and available potassium by 17%. Similarly, in the area which was converted from farmland in 1980 to grassland in 1999, soil organic matter, total nitrogen, available nitrogen, available phosphorus, and available potassium increased by 38%, 37%, 71%, 2% and 28%, respectively. Changes from farmland to forest and grassland not only changed land cover but also improved soil fertility and probably reduced soil nutrient losses.

Notes: Abstract. Much of the low-lying farmland around the coastline of south-east England was once inter-tidal salt marsh, which was subsequently reclaimed from the sea and converted to farmland. It is becoming increasingly uneconomic to maintain the embankments which protect this land from the sea. ‘Managed retreat’ involves relocating the embankments further inland and recreating inter-tidal habitat in front of them. Salt marsh not only provides a protective buffer for these sea walls by dissipating wave energy, but is also important as a habitat for birds and as a source of organic matter for fish and inter-tidal fauna. When ‘managed retreat’ takes place, the creation of inter-tidal habitat occurs on soils that have undergone physical and chemical changes, some of which are irreversible. However, the indications are that rapid sedimentation creates conditions in which salt marsh plants germinate and become established; soil salinity rises quickly to a level which restricts competition from terrestrial plants, and deposited sediment is relatively rich in available phosphorus. The physical properties of the old agricultural soil influence the subsequent development of creeks.

Notes: Abstract. When the farmers of the Highlands of Tigray (northern Ethiopia) consider rock fragment cover in their fields to be excessive, they remove some of them. In addition, large amounts of rock fragments of all sizes are removed from fields for building stone bunds. Semi-structured interviews indicate that the farmers are often reluctant to take away the smaller rock fragments (i.e. 〈 5 cm across) from their fields, since they believe these benefit soil moisture conservation and protect topsoil from erosion. A field experiment was carried out on a Vertic Cambisol (average slope: 0.125 m m–1), 2 km east of Hagere Selam (subhumid climate). Rock fragments were totally, partially or not removed from the 12 runoff plots (5 m × 6 m) before the beginning of the 1999 cropping season, during which a local mixture of wheat varieties (Triticum spp.) was sown. After harvest, erosion rates were assessed by measuring deposited sediment volume in trenches at the lower side of each subplot, and grain and straw yields were assessed. We found a significant negative relationship between rock fragment cover and soil loss by water erosion. However, the resulting positive relationship between rock fragment cover and grain and straw yield was weak. This might be explained by the fact that the plot did not suffer from drought due to soil and climatic conditions. Detailed analysis showed that cover by medium and large rock fragments (〉 2 cm diameter) showed an optimum percentage cover above which crop yields decrease. A recommendation resulting from this study is to rely on the farmers’ experience: smaller rock fragments should never be removed from the surface of fields during soil and water conservation works; instead rock fragment rich soil can be used to top the stone bunds.

Notes: Abstract. The fertilizer nitrogen requirement of winter wheat was assessed in sixteen experiments on marine silt soils in Eastern England. Eight experimental sites followed potatoes (Solanum tuberosum), six vining peas (Pisum sativum) and two wheat (Triticum aestivum). The yield response to nitrogen fertilizer was much less following peas than potatoes or wheat, five sites following peas showed little response to more than 30 kg N ha–1. Previous crop explained some 79.7% of the variation in nitrogen optima. When autumn soil mineral nitrogen was also taken into account 81.9% of the variation in optimum nitrogen rate was explained (P〈0.001). The study revealed noticeably higher levels of autumn soil mineral nitrogen following vining peas on some sites than those found elsewhere in the UK and as assumed in the standard national fertilizer recommendation system.

Notes: Abstract. The aim of this study was to investigate the effects of water submergence depth on radial oxygen loss (ROL), soil solution chemistry and rice growth performance in acid sulphate soils in southern Vietnam. ROL was measured in a solution culture. In a separate pot experiment the impact of water submergence depth on rice growth and soil solution chemistry was studied. Three submergence depths were used in the two experiments (5, 10 and 15 cm). ROL declined with submergence depth and was significantly greater in young roots (with no root hairs) than in older roots. In the pot experiment rice growth and soil solution chemistry were clearly affected by the submergence depth. During the first crop at 5 cm submergence, there was a significantly higher yield and a higher oxidation state (pe+pH) compared to 10 or 15 cm submergence. The Fe concentration was significantly greater at the 5 cm depth compared to the 10 or 15 cm depth. SO42– reduction was delayed at the 5 cm depth. Rice yield was c. 25% less at the 15 cm than at the 5 cm depth. During a second crop, there was a substantial SO42- reduction and H2S formation and almost no significant effects of submergence depth on either soil solution chemistry or crop yield. In a field experiment with a dry-season rice crop, yield and Fe, Al and SO42– concentrations were higher at a shallow submergence depth than at greater depths in the same field, showing similar depth trends to those found during the first crop in the pot experiment. Farmers should be advised to use a shallow submergence depth and, if possible, avoid deep-rooted rice varieties. A conceptual model is suggested, which summarizes the relationships between ROL and soil solution chemistry.

Notes: Abstract. Tillage displaces large amounts of soil from upper slopes and deposits soil in lower landscape positions, greatly affecting productivity in these areas. The long-term effect of tillage on soil erosion was studied in four field sites growing mainly rainfed wheat. The soil loss from landscape positions with slopes, ranging from 3 to 28%, was estimated by: (a) comparing data of horizon thickness described at the same position at different times; and (b) using soil movement tracers added to the soil. Existing empirical relationships were used for estimating soil loss by tillage and runoff water, and loss in wheat biomass production. The experimental data showed soil losses of 0.4 to 1.4 cm yr–1 depending on slope gradient, plough depth, and tillage direction. In two of the sites, soil depth has been reduced by 24–30 cm in a period of 63 years. The mean soil displacement of the plough layer (30 cm thick), measured by soil movement tracers, ranged from 31 to 95 cm yr–1 depending mainly on slope gradient, corresponding to a rate of soil loss of 0.3 cm to 1.4 cm yr–1. Soil eroded from the upper slopes was deposited on the lower slopes increasing soil thickness by 0.4 cm to 1.4 cm yr–1. The application of empirical relationships, estimating soil loss by tillage and water runoff, showed that soil erosion at the field sites can be mainly attributed to tillage. The loss in wheat biomass production due to erosion was estimated at 26% on upper slopes for a period of 63 years, while a 14.5% increase in wheat production was estimated due to deposition of soil material in the lower landscape.

Notes: Abstract. The most common way of assessing soil organic matter content is by loss on ignition, which is both simple and inexpensive. This method tends to overestimate organic matter content because additional weight losses occur during ignition. An alternative, more expensive and time-consuming method for determining soil organic matter content is by an acid dichromate oxidation. This paper compares the results of applying these methods to soil on different parent materials in two arable fields. Summary statistics and correlation coefficients showed that there were consistent relationships between the two sets of values: the stronger was for the sandy soil and the weaker was for the clay loam. This relationship can be used to improve the accuracy with which soil organic matter content is known while using fewer of the expensive measurements and more of the inexpensive ones. Two approaches to prediction were compared: the geostatistical method of cokriging, and simple linear regression. These were used to predict organic matter determined by an acid dichromate oxidation from the loss on ignition. The estimates from cokriging were more accurate but the method requires the spatial correlation to be modelled reliably. The regression results showed it to be a valuable and practical approach. Using the information from nine carefully selected sampling sites a regression line could be fitted that was representative of the full data.

Notes: Abstract. In 1983, an annual Survey of Fertiliser Practice in England and Wales was extended to Scotland, to provide comprehensive information on inorganic fertilizer, lime and also organic manure use in mainland Britain. It was based on an annual sample of about 1500 farms, selected from the Agricultural Census and stratified by farm type and size. Results from the first fifteen years (1983–97) show that fertilizer nitrogen (N) rates on both tillage crops and grassland peaked at 157 and 132 kg ha–1, respectively, in the mid 1980s and subsequently decreased by c.10%. The majority of N was applied in straight form (without P or K) to tillage crops and in compound form (containing two or more nutrients e.g. NPK; NK) to grassland. Total N use on cereals showed little change but autumn-applied N decreased on both winter cereals and winter oilseed rape. Total N rates decreased on oilseed rape and, to a smaller extent, on maincrop potatoes and sugarbeet. Between 1983–87 and 1993–97, mean phosphate (P2O5) rates declined by almost 10% on both tillage crops (from 58 to 53 kg ha–1) and on grassland (from 25 to 23kg ha–1). The corresponding mean potash (K2O) rates decreased slightly on both tillage crops (from 64 to 62 kg ha–1), and on grassland (from 32 to 31 kg ha–1), although annual usage was more variable on grassland. Sulphur use increased appreciably on cereal and oilseed rape crops between 1993, when S data were first recorded in the survey, and 1997 when 13% and 30%, respectively, of these crop areas received S-fertilizer. However, on grassland, S use remained very low. Average lime use increased on both tillage crops and grassland between the mid 1980s and mid 1990s, from 10 to 12% and 4 to 7% of the total area, respectively. The proportion of land receiving organic manures remained at c. 16% for tillage cropping but increased slightly for grassland, from a mean of 40% in 1983–87 to 44% in 1993–97. Manures were applied throughout the year but about half the applications to tillage land, and a quarter of those to grassland, were made in autumn when the risk of subsequent nitrate leaching loss is greatest.

Notes: Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%.

Notes: Abstract. Cashew soils of South Eastern Tanzania become acidified due to sulphur used for controlling powdery mildew disease (Oidium anacardii Noack). The buffering capacity of surface and subsurface horizons of 35 soil profiles of major cashew growing areas –- the Makonde plateau, its piedmont and inland plains –- was studied. The buffering capacity of surface and subsurface horizons was strongly correlated with clay content and weakly with organic carbon content. In addition, it was only weakly correlated with total exchangeable bases and available P of the surface horizon, but strongly with soil pH, base saturation and cation exchange capacity of the clay fraction of the subsurface horizon. Highly weathered sandy soils, dominant on the Makonde plateau and common on the Piedmont, had the lowest buffering capacity. Soils from the inland plains had better buffering capacities as they are generally more clayey or are less weathered. The risk of severe acidification and of a decline in productivity of cashew and of food crops is highest on the Makonde plateau. Further development and dissemination of methods which can reduce the use of sulphur are required.

Notes: Abstract. Biomass productivity and soil microbial responses to long-term CO2 enrichment have been investigated in a Mediterranean natural forest ecosystem. Several biochemical parameters have been measured on soil samples taken from six open top chambers (OTCs), enclosing clumps of natural Mediterranean woody vegetation including: Quercus ilex L., Phillyrea angustifolia L., Pistacia lentiscus L. and Myrtus communis L. The CO2 concentration of the air inside the OTCs was either ambient or ambient plus 350 μmol mol–1 (c. 710 ppm as mean daily value). Microbial C biomass, microbial respiration, dehydrogenase, β-glucosidase, acid phosphatase and protease activities, inorganic N and soluble P, were tested in order to evaluate soil microbial size and activity. Statistically correlated seasonal patterns have been identified in some biochemical parameters in response to climatic conditions, soil nutritional status and the physiology of the vegetative cover. In situ soil respiration and above- and below-ground productivity were also measured. Microbial responses to CO2 enrichment were observed only at the beginning of the study and a general progressive reduction of the CO2 effect was recorded as monitoring continued. These results are in agreement with data from literature regarding similar studies on natural complex communities.

Notes: Abstract. The Century model was used for estimating soil carbon levels under grassland at the regional scale in the Pampean Region of Argentina. Predicted values were compared with observed soil carbon contents obtained from soil surveys and the differences considered to be the results of cropping on soil organic matter. The Pampean Region was divided into five major sub-regions and carbon in the top 20 cm of each estimated by Century using aggregated soil and climatic data. In four of the sub-regions small differences between predicted and observed carbon contents were obtained which suggested little land use effect on soils. In the Rolling Pampa, a northern portion of the Pampean Region, observed carbon content was about half of Century prediction. In this sub-region, the main agricultural area of the country, cropping intensity, rainfall and temperature are higher than in the rest of the Pampas. A degradation index constructed by a multiplicative approach, taking into account percentage of surface cropped, rainfall and temperature was 2–5 times higher in the Rolling Pampa than in the other pampean sub-region. The difference between predicted C and observed C in the Rolling Pampa was attributed to carbon losses by cropping in a warm and wet climate.

Notes: Abstract. Recent developments in in situγ ray spectrometry offer a new approach to measuring the activity of radionuclides such as 137Cs and 40K in soils, and thus estimating erosion or deposition rates and field moist bulk density (ρm). Such estimates would be rapid and involve minimal site disturbance, especially important where archaeological remains are present. This paper presents the results of a pilot investigation of an eroded field in Scotland in which a portable hyper pure germanium (HPGe) detector was used to measure γ ray spectra in situ. The gamma (γ) photon flux observed at the soil surface is a function of the 137Cs inventory, its depth distribution characteristics and ρm. A coefficient, QCs, derived from the forward scattering of 137Cs γ ray photons within the soil profile relative to the 137Cs full energy peak (662 keV), was used to correct the in situ calibration for changes in the 137Cs vertical distribution in the ploughed field, a function of tillage, soil accumulation and ρm. Based on only 8 measurements, the agreement between in situγ ray spectrometry and soil sample measurements of 137Cs inventories improved from a non significant r2=0.05 to a significant r2=0.62 (P〈0.05). Erosion and deposition rates calculated from the corrected in situ137Cs measurements had a similarly good agreement with those calculated from soil cores. Mean soil bulk density was also calculated using a separate coefficient, QK, derived from the forward scattering γ photons from 40K within the soil relative to the 40K full energy peak (1460 keV). Again there was good agreement with soil core measurements (r2=0.64; P〈0.05). The precision of the in situ137Cs measurement was limited by the precision with which QCs can be estimated, a function of the low 137Cs deposition levels associated with the weapons testing fallout and relatively low detector efficiency (35%). In contrast, the precision of the in situ ρm determination was only limited by the spatial variability associated with soil sampling.

Notes: Books Reviewed in this Article: Fertiliser recommendations for agricultural and horticultural crops (RB209) Published with the permission of MAFF by HMSO, 7th edition 2000.

Notes: Abstract. Soil management studies show that intensive arable agriculture can lead to a decline in both organic matter levels and the stability of the soil structure. It is a priority to understand how soil structure responds when fresh organic materials are added to poor quality degraded arable soils. This is of particular interest because of its implication for carbon sequestration. We investigate whether the addition of organic materials can form stable aggregates in a degraded soil. Grass or peat residues were added to samples of soil obtained from the continuous grassland and arable plots of the long-term experiment at highfield, IACR-Rothamsted (UK) and incubated at 2° and 24°C, for upto 8 weeks at -5 kPa. At 1 day and at 2, 4 and 8 weeks the soil was slaked in de-ionised water and the aggregate size distributions were measured. The data was used to calculate mean weight diameters (MWD). The treatments with added grass showed increased aggregated relative to the control; the treatments with added peat did not. At 24°C the value of MWD increased with the incubation period, but at 2°C there was no further aggregation beyond week two. Respiration measurements were made and the samples that released the most CO2 were also those which re-aggregated the most. This suggests that the process of aggregation is microbiologically mediated. The results are discussed within the broader context of the implications of soil organic matter content on soil management.

Notes: Abstract. By comparing field measurements from 1989, 1997, and 1998, the differences between farmland (sloping farmland, sloping farmland with contour cultivation, terraced farmland) and orchard (terraced orchard, unterraced orchard), in the Three Gorges Reservoir Area, were significant for runoff (P〈0.01), erosion (P〈0.05) and nutrient loss (P〈0.05). Taking into account economic costs and environmental influences, reasonable and sustainable land use on slopes of 25° in the Three Gorges Reservoir Area should be unterraced orchard.

Notes: Abstract. Paper sludge composted or stored in static piles for six months was compared to raw and lime-stabilized sludge in a three-year pot experiment (loam) and a four-year field experiment (silt loam) at rates of up to 40 t DM ha-l. The original sludge contained equal amounts of fibre sludge and biological sludge, mixed with bark in 1:1 ratio to improve the structure. The N content in composted sludge (1.30%) was markedly lower than that of the uncomposted piles (1.98%), indicating significant loss during composting. The yield results were generally inversely proportionate to the C:N ratios of the sludges applied. Sludge from the uncomposted piles gave significant grain yield increases in the year following sludge application, while the other sludge types gave variable results. In the residual years there was, generally, a small but positive effect on yield from all the sludge types. The N and P content in grain generally increased with sludge application, but only the higher rates gave statistically significant increases. Sludge application also increased the Zn content in grain, while Mn, B and Cu was less affected. The increase in Cd content was very small. The 40 t ha-l sludge rate tended to increase the residual mineral N in soil at the field site and thus the risk of nitrate leaching.

Notes: Abstract. An increasing number of breeding sows is kept outdoors in Europe. Outdoor pig production has benefits in terms of animalwelfare but may have hidden costs through nutrient losses. We investigated the distribution of nutrients in sow paddocks and the consequence for losses and utilization in the succeeding crop. Significant correlation between soil inorganicNand the distance to feeding sites was observed after the paddocks had been used by lactating sows for 6 months (P〈0.01). Near to feeders inorganic N levels became extremely high whereas 30–40m from feeders some patches hadN levels in the topsoil corresponding to the levels in the reference area without sows. In the following spring only a minor part of inorganic N was still present in the top 0–40 cm. Similarly, extractable P and exchangeable K in topsoil were significantly affected by distance to feeders with the highest values close to the feeders (P〈0.001). In addition there were significant effects of the distance to huts with increasing nutrient content closer to huts. Although huge variations in dry matter production and nutrient content occurred in the succeeding potato crop, these were only weakly related to the distribution of nutrients (N, P and K) in the previous year, which explained 17%of the total variation in dry matter production. To increase nutrient efficiency in outdoor pig production a uniformdistribution of nutrients should be obtained by manipulating the excretory behaviour of the sows and stocking densities must be adjusted to locally acceptable nutrient surpluses.

Notes: Abstract. A survey of cattle manure management was undertaken in England and Wales, in 1997, by postal questionnaire sent out to a stratified sample (by unit size) of 1750 dairy and 1750 beef producers. The level of response obtained, with 471 dairy farmers (27%) and 515 beef farmers (29%) returning questionnaires, reflects well on the interest shown by the industry and on the survey design. The survey provided information on manure production and storage, when and how applied and nutrient value. Dairy farms are estimated to produce manures in the form of c. 65% slurry and 35% farmyard manures (FYM) and, beef units, 80%FYM and 20%slurry (based on survey response data, animal numbers and calculations of undiluted outputs of excreta). Slurry storage within both dairy and beef systems is typically up to 3–6 months capacity, although there is no storage for an estimated 16% of dairy and 25% of beef slurry. Autumn and winter spreading is common practice, with 40–50% of slurry and 50–60% of FYM applied at that time. Although some evidence suggests that farmers make little allowance for the nutrient content of manures in planning fertilizer inputs, the results of this survey suggest that many farmers do make some effort to utilize manure nutrients. However, they currently fail to be assured by the advice available to them or they lack confidence in manures as nutrient sources for a number of technical reasons. Information provided by the survey may be important to policy makers, researchers and consultants, as well as farmers.

Notes: Abstract. Demand for water from catchments dominated by upland peat as a source of drinking water supplies in the UK is likely to increase in the future as demand per capita continues to rise (Thomsen 1990) and/or summer droughts increase in frequency (Arnell 1992). Concern has been expressed in recent years over rising colour levels (related to dissolved organic carbon (DOC) and iron (Fe)) from such catchments (e.g. Kay et al. 1989) causing reduced drinking water quality. One of the major causes of increased DOC concentrations is rewetting following periods of relative drought (Mitchell & McDonald 1992). Experimental rewetting of a naturally drained wetland in Mid-Wales over four years was found to substantially increase the concentrations of DOC, and Fe in the pore-water, with peak values of 〉60 mg dm–3 (Fe) and 〉300 mg dm–3 (DOC) after rewetting, compared with typical values of 〈1 mgdm–3 (Fe) and 〈15 mg dm–3 (DOC) under the drained conditions. Seasonal peak concentrations of Fe and DOC have since remained at these higher levels. Rewetting produced a selective enrichment of the 〉5000 to 〈90 000 apparent molecular weight (AMW) material and this fraction was found to yield peak Fe concentrations. Two additional peaks of DOC were also found in the experimental wetland (not present in the control wetland), of 〉90 000 to 〈200 000 AMW and 〉200 000 AMW material. The AMW spectrum of DOC in the experimental wetland changed with season, and the 〉90 000 to 〈200 000 AMW fraction could only be seen in spring, representing a transient pool of carbon that is rapidly transformed in or transported from the wetland. These findings suggest that rewetting of peatland following drought (e.g. due to climate change) has the potential to reduce water quality. Moreover, recent interest in restoration (rewetting) of drained peatlands (Wheeler & Shaw 1995) could create an additional source of DOC rich water.

Notes: Abstract. The hierarchial concept of land use planning becomes less relevant in a society with continuous interactions between stakeholders, researchers, planners and politicians. In this context, land use negotiation rather than land use planning appears to be the most appropriate concept. In the negotiation process, good quality data about the land is important as land properties are, obviously, key elements to be considered. Case studies at farm and regional level have been analysed to explore answers to a number of questions. How can soil data be presented most effectively? What are the research needs? How can the large existing body of data be mobilized most effectively? Studies on regional land use in Costa Rica used methods in a logical sequence including projections, explorations and predictions of land use patterns. The work involved upscaling of data, obtained at farm level, to the regional level. Work at farm level focussed on prototyping procedures in which farming systems were ‘designed’ by close interaction between farmers and scientists, including applications of precision agriculture. Soil data demands were analysed, emphasizing the effects of using data with different degrees of detail together with the application of pedotransfer functions which effectively transform existing data into parameters that are difficult or expensive to measure directly. This not only facilitated interactions with stakeholders but also with colleague scientists in interdisciplinary teams. In addition, use of Geographical Information Systems allowed visual presentations of alternative geographical land use patterns that were associated with various scenarios, thereby facilitating the interaction processes. A plea is made to increase interaction of stakeholders and researchers by considering research programmes as vehicles for joint learning.

Notes: Abstract. Topsoil (0–15 cm) bulk density, aggregate stability, soil dispersibility, water retention and infiltration were measured between 1989 and 1996 on an Alfisol under rehabilitation in southwestern Nigeria. The planted leguminous species were Pueraria phaseoloides, Senna siamea, Leucaena leucocephala, Acacia leptocarpa and A. auriculiformis. Also, plots with natural fallow and maize/cassava intercropping were included. Level (minimum) and mound tillage with hoes was adopted for the cultivated areas under study after 4 and 6 year fallow periods. Under fallow, the soil bulk density decreased from1.56 to 1.11 t m73.The continuously cropped treatment (level tillage) had significantly higher bulk density than the fallowed subplots after 6 years. Mean soil penetrometer resistance ranged from 75 to 157 kPa for fallowed plots and from 192 to 295 kPa for the continuously cropped (level tillage) subplot. Surface soilwater contentswere similar for all the treatments during the soil strength measurements. Although soil aggregates were generally of low stability and not well formed, they were improved by fallowing.Soil structural improvement by planted fallows was similar to that by natural fallow, but the trees were more promising for long-term fallow (〉6 years) than the herbaceous P. phaseoloides. However, the improvement in soil structure after 4 or 6 year fallow could not be maintained in subsequent cropping. Furthermore, the significant improvement in soil bulk density caused by A. auriculiformis and natural fallow was more rapidly lost on the cultivated subplots compared with other fallow treatments. Thus, soil structure recovery under a fallow does not imply a sustained improvement when stress is applied to this soil. Post-fallow soil management options such as residue incorporation and tillage to ameliorate compaction or soil strength will be necessary to enhance the improvements by fallow species.

Notes: Abstract. Changes in particulate organic carbon (POC) relative to total organic carbon (TOC) were measured in soils from five agronomic trial sites in New South Wales, Australia. These sites covered a wide range of different land use and management practices. POC made up 42–74% of TOC and tended to be greater under pasture and more conservative management than traditional cropping regimes. It was the form of organic carbon preferentially lost when soils under long-term pasture were brought under cultivation. It was also the dominant form of organic carbon accumulating under more conservative management practices (direct drilling, stubble retained and organic farming). Across all sites, changes in POC accounted for 81.2% (range 69–94%) of the changes in total organic carbon caused by differences in land use and management. Significant differences were found between pasture and cropped soils in the carbon content in the 〈53 μm fraction, particularly for hardsetting soils. However, even with these, POC was a more sensitive indicator of change caused by land use and management practices than TOC. The current method for measuring POC involves dispersion using sodium hexametaphosphate. The dispersing agent was found to extract 4–19 % of the TOC, leading to a significant under-estimation of POC.

Notes: Abstract. An estimate of organic carbon stored in French soils to a depth of 30 cm was made using data from geo-referenced databases. We produced statistics on carbon stocks in soils according to land use, different land uses and soil type. Then, using a combination of maps of soil and land use we were able to estimate regional and national carbon stocks. This soil carbon map of France allowed us to identify the main controlling factors of the carbon distribution: land use, soil type in some cases, clay content, and elevation. Carbon stocks in French soils were found to be about 3.1 Pg (1015g).

Notes: Abstract. The problem of soil erosion is particularly evident in New Zealand, given the combination of coarse-textured soils, steep relief, high rainfall, and intensification of agriculture. A study was undertaken to assess the effects of land use change on soil erosion and sediment transport for the Ngongotaha catchment in New Zealand's North Island, using a GIS based decision support and modelling system. Model simulations considered the effect of increased catchment area under deer farming and forestry on the amount of sediment delivered to the catchment outlet, averaged over a period of six years. The simulations predicted that sediment loss from land under deer farming was considerably greater than from land under other livestock or forestry. Further model simulations testing best management practices demonstrated that sediment yield could be halved if deer farming was restricted to slopes under 20%.

Notes: Abstract. Measures to reduce ammonia (NH3) emissions by incorporating livestock manures into the soil may increase the potential for nitrate (NO3-) leaching. The Manure Evaluation Routine (MANNER) model estimates the amount of N available to crops following livestock manure applications after calculating losses due to NH3 volatilization and NO3- leaching. The main objective of this study was to use the MANNER model to quantify the impact on NO3- leaching of introducing measures to reduce NH3 emissions, following application of livestock manures. The data produced were also used to make preliminary estimates of the likely effect of selected NH3 abatement techniques on the potential for nitrous oxide (N2O) emissions. At typical UK rates of application, the potential for increased NO3- leaching following either injection of slurry or rapid incorporation of solid manures was greatest for broiler/turkey manure (22–58 kg N ha–1) and least for straw-based cattle manure (6–10 kg N ha–1). The results suggest that in order to avoid substantially increasing the potential for NO3- leaching as a consequence of NH3 abatement, livestock manures should not be applied by low NH3 emission techniques prior to autumn-sown crops in the UK. Instead, low-emission applications should be made from October onwards to grassland and where possible, late autumn-sown combinable crops or to arable land which will be planted in the spring. However, in several areas of England and Wales there is currently insufficient land planted to spring crops on which to incorporate the livestock manures produced in those areas.

Notes: Abstract. A survey of manure management practice was undertaken in 1996, by postal questionnaire submitted to a stratified sample of egg and broiler producers in England and Wales. Out of a target of 500 laying hen and 500 broiler (chickens produced for meat) production units in the survey sample, 356 (36%) returned questionnaires. The survey provided information on amount and type of manure production, manure storage and land application strategies (timing, techniques and awareness of nutrient content). Within the survey, no attempt was made to differentiate between organic and conventional production systems. About 45% of manure production was estimated to come from layer holdings, 55% from broiler litter. It was estimated that 70% of the national manure production is litter-based and about 30% are droppings collected without litter. Sawdust/shavings are the most popular bedding material, with an average final depth of 100 mm for broilers and 140 mm on litter-based layer units. Commonly, storage is available within housing for at least the length of the cropping cycle (6 weeks in broiler production, or 12 months in deep pit laying houses), around 60% of poultry manure is stored for a period following removal from the house, most commonly for 3-6 months. Overall, autumn was the peak period for manure spreading, with over 40% of laying hen manure and 50% of broiler manure applied at that time. On grassland, spreading was reasonably evenly distributed throughout the year but autumn application was favoured for arable crops, especially before the establishment of cereals and root crops, overall, almost 50% of layer and broiler manure was applied in the autumn. In the survey, up to 10% of manures were claimed to be incorporated within a day of application and about 60% within a week of application, presumably because of concern about odour nuisance. Around 25% of poultry manure was applied by contractors. A high proportion of farmers (c. 40% with layers, c. 60% with broilers) exported manures from their holdings, the proportion removed amounting to almost 90% on these farms. Although evidence elsewhere indicates that farmers make little allowance for manures in planning crop fertilizer inputs, the survey responses suggested that farmers do make an effort to allow for manures but that their confidence in the advice available to them is lacking, or they may have other technical reasons for not taking advantage of the manurial value. Information provided by the survey is of significant importance to policy makers (e.g. for the construction of environmental emissions inventories), researchers, consultants and farmers.

Notes: Abstract. The phosphorus (P) sorption and desorption dynamics of eleven major agricultural grassland soil types in Ireland were examined using laboratory techniques, so that soils vulnerable to P loss might be identified. Desorption of P from soil using the iron-oxide paper strip test (Pfeo), water extractable P (Pw) and calcium chloride extractable P (Pcacl2) depended on soil P status in all soils. However, soil types with high organic matter levels (OM), namely peat soils (%OM 〉30), had lower Pfeo and Pw but higher Pcacl2 values compared to mineral soils at similar soil test P levels. Phosphorus sorption capacity remaining (PSCr) was measured using a single addition of P to soils and used to calculate total P sorption capacities (PSCt) and degree of P saturation (DPS). Phosphorus sorption capacities correlated negatively with % OM in soils indicating that OM may inhibit P sorption from solution to soil. High organic matter soils exhibited low P sorption capacities and poor P reserves (total P, oxalate extractable P) compared to mineral soils. Low P sorption capacities (PSCt) in peat soils were attributed to OM, which blocked or eliminated sorption sites with organic acids, therefore, P remained in the soil solution phase (Pcacl2). In this work, peat and high organic matter soils exhibited P sorption and desorption characteristics which suggest that these soils may not be suitable for heavy applications of manure or fertilizer P owing to their low capacities for P sorption and storage.

Notes: Abstract. Field peas (Pisum sativum L.) were grown in sequence with winter wheat (Triticum aestivum L.) or spring barley (Hordeum vulgare L.) in large outdoor lysimeters. The pea crop was harvested either in a green immature state or at physiological maturity and residues returned to the lysimeters after pea harvest. After harvest of the pea crop in 1993, pea crop residues (pods and straw) were replaced with corresponding amounts of 15N-labelled pea residues grown in an adjacent field plot. Reference lysimeters grew sequences of cereals (spring barley/spring barley and spring barley/winter wheat) with the straw removed. Leaching and crop offtake of 15N and total N were measured for the following two years. These treatments were tested on two soils: a coarse sand and a sandy loam. Nitrate concentrations were greatest in percolate from lysimeters with immature peas. Peas harvested at maturity also raised the nitrate concentrations above those recorded for continuous cereal growing. The cumulative nitrate loss was 9–12 g NO3-N m–2 after immature peas and 5–7 g NO3-N m–2 after mature peas. Autumn sown winter wheat did not significantly reduce leaching losses after field peas compared with spring sown barley. 15N derived from above-ground pea residues accounted for 18–25% of the total nitrate leaching losses after immature peas and 12–17% after mature peas. When compared with leaching losses from the cereals, the extra leaching loss of N from roots and rhizodeposits of mature peas were estimated to be similar to losses of 15N from the above-ground pea residues. Only winter wheat yield on the coarse sand was increased by a previous crop of peas compared to wheat following barley. Differences between barley grown after peas and after barley were not statistically significant. 15N lost by leaching in the first winter after incorporation accounted for 11–19% of 15N applied in immature pea residues and 10–15% of 15N in mature residues. Another 2–5% were lost in the second winter. The 15N recovery in the two crops succeeding the peas was 3–6% in the first crop and 1–3% in the second crop. The winter wheat did not significantly improve the utilization of 15N from the pea residues compared with spring barley.

Notes: Abstract. In view of the increasing wheel loads of agricultural vehicles, the question arises as to whether soil can recover from the mechanical impact of traffic. The damage to soil quality depends also on the soils resilience. This paper presents a new approach to monitoring vertical soil movement in situ. We assessed the effects of trafficking the soil with excavators and sugarbeet harvesters by monitoring surface and subsurface levels. The caterpillar loads of the crawlers varied from 13 to 19 t, the wheel loads of the sugarbeet harvesters from 6 to 11 t. Classical geodetic levelling was used to record soil surface movement and a hydrostatic settlement meter measured deformation at three depths within the soil profile. The results of three field tests prove the importance of wheel load and soil moisture for soil compaction. Trafficking very dry soil with an excavator did not cause significant plastic deformation in 30 cm depth. Conversely, trafficking wet soil with a sugarbeet harvester led to soil sinkage of 1 to 2 cm even at 60 cm depth. Increased wheel load in subsequent passes led to greater subsidence than during the first pass. Settlement decreased from the soil surface to deeper layers, but it remained throughout the monitoring period of up to 12 days. No soil recovery from plastic deformation was recorded within this time. The measuring system has the potential for long-term monitoring of the mechanical recovery of the soil. Additionally, it can contribute to the validation of mechanical impact models, which are based on soil stresses.

Notes: Abstract. Two case studies on Danish sandy loams investigated the long-term effects of fertilization and crop rotation. Case Study 1 compared a diversely cropped organically farmed soil (DFG(1)) with a conventionally farmed soil predominantly growing annual crops (DFA), both receiving animal manure. In Case Study 2, a diversely cropped organically managed soil (DFG(2)) receiving animal manure was compared with an almost exclusively cereal cropped conventionally farmed soil receiving no animal manure (CCC). A multi-level experimental strategy was followed to compare integrating field methods with specialized laboratory methods. Ease of tillage was described in the field and characterized using a drop shatter field test and by measuring aggregate tensile strength. Fitness as a seedbed was characterised visually in the field and from the drop shatter test. Impedance to seedling emergence and root penetration was evaluated by measuring bulk soil shear strength. For Case Study 1, soil tilth was better for the DFA soil than for the DFG(1) soil (i.e. lower soil strength and higher ease of fragmentation and friability index for DFA). However, a crumbly structure and a moderate bulk density suggested that the DFG(1) soil was also a favourable medium for plant growth. For Case Study 2, the CCC soil had a lower organic matter content, higher bulk density, higher soil strength, and lower ease of fragmentation in comparison with the DFG(2) soil.

Notes: Abstract. A two year field study was conducted to evaluate the effects of straw management and tillage on the soil profile (1.5m) water storage, nature of the moisture profile, infiltration and sorptivity as influenced by rainfall, evaporativity (E0) and soil texture. The straw mulch treatment stored more moisture under low E0 rainy conditions in three coarse to medium textured soils. Straw incorporation treatment was better under low E0 rain free conditions, as well as under high E0 rainy conditions in the two coarser textured soils. In the coarsest textured soil, tillage and straw mulching were not effective in maintaining greater soil water storage under high E0 because of the very open nature of the soil. The soil moisture profiles showed a sharper increase in water content below the tilled layer in the tillage and straw- incorporation treatments than the untreated and straw mulch treatments. Tillage and straw incorporation treatments increased the sorptivity of the soil compared with untreated and straw mulch treatments respectively. The results of this study suggest that when selecting a suitable soil water conservation practice to increase water storage in the soil profile, information on soil texture and weather (rain and evaporativity) must be considered.

Notes: Abstract. Phosphorus (P) use in UK agriculture is reviewed and a P balance sheet presented. The productive grassland and arable area has accumulated an average P surplus of c. 1000 kg ha–1 over the last 65 years. Over the period 1935–1970, the annual P surplus more than doubled due to an increase in animal numbers and associated requirements for inorganic fertilizers and livestock feeds. Since 1970, surplus P has declined by c. 40% as crop yields and P offtake have continued to increase while fertilizer and manure P inputs have remained relatively constant. In 1993, P use efficiency (P imports/P exports) in UK agriculture was estimated at 25% leading to an average annual surplus of 15 kg P ha–1 yr–1, although the latter has since decreased slightly due to reduced fertilizer use. Intensification and specialization of agriculture has also increased the range in P surpluses that are likely between livestock and arable dominated systems. The largest P surpluses occur in the relatively limited areas of arable soils which receive manure from intensive pig and poultry units, whilst farms without manure inputs generate only small surpluses, or are in balance. The cumulative P surplus has led to a build-up of soil total and easily-exchangeable P, especially in areas receiving both fertilizers and manures. Fundamental differences in P use efficiency, surplus P accumulation and the potential for P loss to water, exist between arable and grassland farms and it is important to separate these, due to the marked regionalization of UK agriculture. More judicial use of feeds and fertilizers is required to further reduce the P surplus and minimize the long-term risk of water eutrophication.

Notes: Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.

Notes: Abstract. Nitrate leaching and soil mineral N status under grassland were measured on three contrasting soils, spanning winters 1995/96, 1996/97 and 1997/98, in Western England. The soils investigated were a freely draining silty clay loam (Rosemaund), a well drained loam (IGER 1) and a poorly drained clay loam (IGER 2). The effects of reseeding (ploughing and resowing grass) at IGER 1 and IGER 2 in autumn 1995 or 1996 were compared with undisturbed pasture. Reseeding at Rosemaund, in autumns 1995 or 1996, or spring 1996 was compared with undisturbed pasture of 3 sward ages (2, 5, 〉50 years).Nitrate-N leaching losses during the winter immediately following autumn reseeding ranged between 60 and 350 kg N ha–1 in 1995/96, depending on soil type, sward management history and rainfall. Losses were much less in the following winter when treatments were repeated (10–107 kg N ha–1).Reseeding in spring had little effect on soil mineral N content or leaching losses in the following autumn, compared with undisturbed pasture. Similarly, leaching losses from autumn reseeds in the second winter after cultivation were the same as undisturbed pasture (1-19 kg N ha–1). The effect of ploughing grassland for reseeding was relatively short-term, in contrast to the effect of repeated annual cultivation associated with arable rotations.

Notes: Abstract. Intensively managed grasslands are potentially a large source of N2O in the North Coast of Spain because of the large N input, the wet soil conditions and mild temperatures. To quantify the effect of fertilizer type and management practices carried out by farmers in this area, field N2O losses were measured over a year using the closed chamber technique. Plots received two types of fertilizer: cattle slurry (536 kg N ha–1) and calcium ammonium nitrate (140 kg N ha–1). N2O losses were less in the slurry treatment than after mineral fertilizer. This was probably due to high, short-lived peaks of N2O encountered immediately following mineral N addition. In contrast, the seasonal distribution of N2O losses from the slurry amended plot was more uniform over the year. The greater N2O losses in the mineral treatment might have been enhanced by the combined effect of mineral fertilizer and past organic residues present from previous organic amendments. Weak relationships were found between N2O emission rates and soil nitrate, soil ammonium, soil water content and temperature. Better relationships were obtained in the mineral treatment than in the slurry plots, because of the wider range in soil mineral N. Water filled pore space (WFPS) was a key factor controlling N2O emissions. In the 〉 90% WFPS range no relationships were found. The best regressions were found for the mineral treatment in the 40–65% WFPS range, 49% of the variance being explained by soil nitrate and ammonium content. In the 65–90% WFPS range, 43% of the variance was explained by nitrate only, but the inclusion of soil ammonium did not improve the model as it did in the 40–65% WFPS range. This fact indicates that nitrification is likely to be an important process involved in N2O emissions at the 40–65% WFPS.

Notes: Abstract. Boreholes have been constructed at eight sites on the Permo-Triassic Sandstone and Chalk aquifers to assess the extent of chemical and microbiological contamination emanating from unlined farm manure stores. Slurry along fracture faces in the Chalk was found on cores taken from beneath two stores. Porewaters from the Chalk sites and one of the Sandstone sites were discoloured and showed high concentrations of nitrate, ammonium and organic carbon to depths in excess of 10 m. Although Cryptosporidia and Escherichia coli O157 were found in many of the cattle slurry lagoons, neither were found in the aquifer material beneath. The self-sealing of unlined slurry stores is seen as a crucial step in minimizing leakage. A simple mass balance shows farm boreholes near to contaminant sources are at greater risk than public supply wells. Contaminant modelling shows discontinuing use of an unlined farm manure store will lead to little difference in solute concentrations over the short to medium term. Groundwater is most at risk where the water table is shallow since direct hydraulic connection between the lagoon base and the water table considerably increases the rate of vertical migration. This is of greatest significance for pathogens that are thought to be relatively short lived in the subsurface. Under the majority of situations minimal threat is posed to potable groundwater drinking supplies.

Notes: Classification of soil based on structure is useful for conveying information about physical properties and soil processes. The distance transform is an image analysis technique suitable for quantifying soil structure. An analysis of distance transform data, in the form of cumulative area distribution curves for previously published images of soil structures of various types, is presented. The images were used to derive a quantitative classification of structure using maximum distance of solid from a macropore (Dmax, measured), the distance from macropore space containing 50% of the solid area (k, derived by fitting a sigmoidal function to the cumulative area distribution curve), the total interface length between pore and solid per area of sample (IA, measured), the porosity or the proportion of pores per area of sample (PA, measured) and the pore distribution characteristic (n, derived by fitting a sigmoidal function to the cumulative area distribution curve) which is related to the number, continuity and distribution of pores. The influence of image resolution was investigated, and within limits found to be fairly small. The final classification of soil structure was based on the hypothesized relations between the descriptors and structure-forming processes.

Notes: To investigate the effect of soil physical conditions and land use on emissions of nitrous oxide (N2O) to the atmosphere, soil cores of an imperfectly drained gleysol were taken from adjacent fields under perennial ryegrass and winter wheat. The cores were fertilized with ammonium nitrate and incubated at three different temperatures and water-filled pore space (WFPS) values, and N2O emissions were measured by gas chromatography. Emissions showed a very large response to temperature. Apparent values of Q10 (emission rate at (T + 10)°C/emission rate at T°C) for the arable soil were about 50 for the 5–12°C interval and 8.9 for 12–18°C; the corresponding Q10s for the grassland soil were 3.7 and 2.3. Emissions from the grassland soil were always greater than those from the arable soil, although the ratio narrowed with increasing temperature. Changes in soil WFPS also had a profound effect on emissions. Those from the arable soil increased about 30-fold as the WFPS increased from 60 to 80%, while that from the grassland soil increased 12-fold. This latter response was similar to earlier field measurements. The N2O emissions were considered to be produced primarily by denitrification. We concluded that the impacts of temperature and WFPS on emissions could both be explained on the basis of existing models relating increasing respiration or decreased oxygen diffusivity, or both, to the development of anaerobic zones within the soil.

Notes: The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC.The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P 〈 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water-soluble P than either the Olsen or Morgan tests for P in soil.

Notes: This study tested the hypothesis that, like dissolved organic nitrogen (N), dissolved organic phosphorus (P) and sulphur (S) are more mobile in soil than is organic carbon (C). To do so, I compared the sorption of organic P and S to subsoil materials with that of organic C. Soil samples were equilibrated with water-soluble organic matter from the forest floor at pH 4 and in the equilibrium solutions organic C, P, and S, and their distributions between the hydrophilic and hydrophobic fraction were determined. Sorption of C within the organic matter did not differ from that of P and S. However, the hydrophilic fraction contained the vast majority of P and S and sorbed far less than the hydrophobic fraction. So the overall retention of organic P and S was smaller than that of organic C. This result suggested that dissolved organic matter is more important in the loss of plant nutrients than in the release of C from soil.

Notes: Despite decades of research to define optimal chamber design and deployment protocol for measuring gas exchange between the Earth's surface and the atmosphere, controversy still surrounds the procedures for applying this method. Using a numerical simulation model we demonstrated that (i) all non-steady-state chambers should include a properly sized and properly located vent tube; (ii) even seemingly trivial leakiness of the seals between elements of a multiple-component chamber results in significant risk of measurement error; (iii) a leaking seal is a poor substitute for a properly designed vent tube, because the shorter path length through the seal supports much greater diffusive gas loss per unit of conductance to mass flow; (iv) the depth to which chamber walls must be inserted to minimize gas loss by lateral diffusion is smaller than is customary in fine-textured, wet or compact soil, but much larger than is customary in highly porous soils, and (v) repetitive sampling at the same location is not a major source of error when using non-steady-state chambers. Finally, we discuss problems associated with computing the flux of a gas from the non-linear increase in its concentration in the headspace of a non-steady-state chamber.

Notes: The structural condition of swelling soils can be assessed from their shrinkage curves. We re-evaluated data on six British swelling soils using modern methods to model the void ratio, e, as a function of the moisture ratio, ϑ. The points on the e–ϑ curve were fitted with a constitutive shrinkage equation using an unbiased least-squares, curve-fitting program. The shrinkage curves were then differentiated to obtain their slopes, σ(ϑ), which were used to calculate the overburden potentials, Ω. The slope functions were subsequently differentiated to obtain the curvatures, κ(ϑ), from which the maximum curvature at the wet end was used to separate the structural shrinkage, Sc, from the proportional (unsaturated) shrinkage. At the point of maximum curvature, Sc and the volumetric air content, θac, were calculated and found to correspond closely to those reported previously. Water retention curves were constructed and fitted using the van Genuchten equation, from which the α coefficient appears an important structural parameter. The structural condition of a swelling soil appears to be well described by its air content at the point of maximum curvature, its van Genuchten α coefficient, and a parameter describing the effect of the overburden potential.

Notes: It is essential that important field processes are taken into account to model water flow and chemical transport accurately in agricultural fields. Recent field studies indicate that transport through macropores can play a major role in the export of solutes and particulates from drained agricultural land into surface water. Non-ideal drain behaviour may further modify the flow and transport. We extended an existing two-dimensional flow and transport model for variably saturated soils (SWMS_2D) by adding a macropore domain and an additional Hooghoudt drain boundary condition. The Hooghoudt boundary condition accounts for an entrance head needed to initiate flow into the drains. This paper presents the application of the new model (M-2D) to an agricultural field in Switzerland. To understand interactions between macropore flow and drains better we simulated water flow and bromide transport for four different field scenarios. We considered both collector drains only with an ideal drain boundary condition (with and without macropores) and collectors and laterals with a Hooghoudt boundary condition (also with and without macropores). For each scenario, inverse modelling was used to identify model parameters using 150 days of data on observed cumulative discharge, water table depth, and tracer concentration. The models were subsequently tested against a 390-day validation data set. We found that the two additional components (macropore flow, drain entrance head) of the M-2D model were essential to describe adequately the flow regime and the tracer transport data in the field.

Notes: The processes controlling the solid–solution partitioning of organic matter in soils are central to understanding carbon cycling in terrestrial ecosystems, yet are poorly understood at present. We studied the partitioning of soil organic matter between solid and solution in batch titrations of 12 soil samples from three European forests in a range of climates. We also examined the release of soil organic matter on repeated leaching. The partitioning was simulated using a model that pictures the pool of potentially mobile organic matter to consist of fractions of differing solubilities. Desorption of organic matter was then effected by an increase in the electrical charge of the organic molecules due to their chemical reactions with other soil components.The model could simulate the partitioning of organic matter in all the soils using two parameters describing the amounts of soil organic matter in each fraction. The release of organic matter on repeated leaching was reasonably well described. The model predicted that dissolved organic matter should have become more hydrophilic with depth in the soil, due to the retention of more hydrophobic components in the upper horizons. This accorded with observed compositions of the soil organic matter. The model also showed that at the ambient pH of the soils, only a small proportion of the potentially mobile organic matter (comprising fulvic acids and hydrophilic moieties) was involved in partitioning to the solution.