ALBERT

Notes: Garnet-whole rock Sm-Nd data are presented for several samples from the Indian plate in the NW Himalaya. These dates, when combined with the P-T evolution of the Indian plate rocks, allow a thorough reconstruction of the prograde thermal evolution of this region (including the Nanga Parbat Haramosh Massif) during the early Cenozoic. Combining these data with Rb-Sr mineral separate ages, enables us to constrain the post-peak cooling history of this region of the Himalaya.The data presented here indicate that the upper structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, and similar rocks in the Kaghan Valley to the south-west, were buried to pressures of c. 10 kbar and heated to temperatures of c. 650 °C at 46–41 Ma. The burial of the lower structural levels of the cover rocks of the Nanga Parbat Haramosh Massif, to similar depths but at higher temperatures of c. 700 °C, occurred slightly later at 40–36 Ma, synchronous with the imbrication and exhumation of the amphibolite- and eclogite-grade rocks of the Kaghan Valley. In contrast, the cover rocks of the Nanga Parbat Haramosh Massif were not imbricated or exhumed at this time, remaining buried beneath the Kohistan-Ladakh Island Arc until the syntaxis-forming event that occurred in the last 10 Myr. The timing of tectonic events in the north-western Himalaya differs from that experienced by the rocks of the Central Himalaya in that the earliest stage of burial in the NW Himalaya predates that of the Central Himalaya by c. 6 Myr. This difference may result from the diachronous nature of the Indo-Asian collision or may simply be a reflection of differing timing at different structural levels.

Notes: SHRIMP U–Pb dating and laser ablation ICP-MS trace element analyses of zircon from four eclogite samples from the north-western Dabie Mountains, central China, provide evidence for two eclogite facies metamorphic events. Three samples from the Huwan shear zone yield indistinguishable late Carboniferous metamorphic ages of 312 ± 5, 307 ± 4 and 311 ± 17 Ma, with a mean age of 309 ± 3 Ma. One sample from the Hong'an Group, 1 km south of the shear zone yields a late Triassic age of 232 ± 10 Ma, similar to the age of ultra-high pressure (UHP) metamorphism in the east Qinling–Dabie orogenic belt. REE and other trace element compositions of the zircon from two of the Huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase, namely in the eclogite facies, an interpretation supported by the presence of garnet, omphacite and phengite inclusions. Zircon also grew during later retrogression. Zircon cores from the Huwan shear zone have Ordovician to Devonian (440–350 Ma) ages, flat to steep heavy-REE patterns, negative Eu anomalies, and in some cases plagioclase inclusions, indicative of derivation from North China Block igneous and low pressure metamorphic source rocks. Cores from Hong'an Group zircon are Neoproterozoic (780–610 Ma), consistent with derivation from the South China Block. In the western Dabie Mountains, the first stage of the collision between the North and South China Blocks took place in the Carboniferous along a suture north of the Huwan shear zone. The major Triassic continent–continent collision occurred along a suture at the southern boundary of the shear zone. The first collision produced local eclogite facies metamorphism in the Huwan shear zone. The second produced widespread eclogite facies metamorphism throughout the Dabie Mountains–Sulu terrane and a lower grade overprint in the shear zone.

Notes: Sodic metapelites with jadeite, chloritoid, glaucophane and lawsonite form a coherent regional metamorphic sequence, several tens of square kilometres in size, and over a kilometre thick, in the Orhaneli region of northwest Turkey. The low-variance mineral assemblage in the sodic metapelites is quartz + phengite + jadeite + glaucophane + chloritoid + lawsonite. The associated metabasites are characterized by sodic amphibole + lawsonite ± garnet paragenesis. The stable coexistence of jadeite + chloritoid + glaucophane + lawsonite, not reported before, indicates metamorphic pressures of 24 ± 3 kbar and temperatures of 430 ± 30  °C for the peak blueschist facies conditions. These P–T conditions correspond to a geotherm of 5  °C km−1, one of the lowest recorded in continental crustal rocks. The low geotherm, and the known rate of convergence during the Cretaceous subduction suggest low shear stresses at the top of the downgoing continental slab.

Notes: SHRIMP U–Pb ages have been obtained for zircon in granitic gneisses from the aureole of the Rogaland anorthosite–norite intrusive complex, both from the ultrahigh temperature (UHT; 〉900 °C pigeonite-in) zone and from outside the hypersthene-in isograd. Magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis. A sample from outside the UHT zone has magmatic cores with an age of 1034 ± 7 Ma (2σ, n = 8) and 1052 ± 5 Ma (1σ, n = 1) overgrown by M1 metamorphic rims giving ages between 1020 ± 7 and 1007 ± 5 Ma. In contrast, samples from the UHT zone exhibit four major age groups: (1) magmatic cores yielding ages over 1500 Ma (2) magmatic cores giving ages of 1034 ± 13 Ma (2σ, n = 4) and 1056 ± 10 Ma (1σ, n = 1) (3) metamorphic overgrowths ranging in age between 1017 ± 6 Ma and 992 ± 7 Ma (1σ) corresponding to the regional M1 Sveconorwegian granulite facies metamorphism, and (4) overgrowths corresponding to M2 UHT contact metamorphism giving values of 922 ± 14 Ma (2σ, n = 6). Recrystallized areas in zircon from both areas define a further age group at 974 ± 13 Ma (2σ, n = 4). This study presents the first evidence from Rogaland for new growth of zircon resulting from UHT contact metamorphism. More importantly, it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c. 950 °C for at least 1 Myr. Magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information, a result inconsistent with some experimental data on Pb diffusion in zircon which predict measurable Pb diffusion under such conditions. The implication is that resetting of zircon ages by diffusion during M2 was negligible in these dry granulite facies rocks. Imaging and Th/U–Y systematics indicate that the main processes affecting zircon were dissolution-reprecipitation in a closed system and solid-state recrystallization during and soon after M1.

Notes: O, Sr and C isotopes from east-central Vermont are used to provide information on the timing and volume of metamorphic fluid flow. The results are then used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenised on a metre scale; comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during dewatering and diagenesis in addition to the high temperature alteration recorded by strontium. Sr isotope distributions are consistent with cross-layer fluid fluxes of 104−106 moles m−2; absolute values depend on the Sr fluid-rock distribution coefficient which is poorly known; however, reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ13C values observed at lithological boundaries cannot be explained by volume loss or closed system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO2 and CH4-bearing fluids. Mass balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO2 released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models.

Notes: Prograde P–T paths recorded by the chemistry of minerals of subduction-related metamorphic rocks allow inference of tectonic processes at convergent margins. This paper elucidates the changing P–T conditions during garnet growth in pelitic schists of the Sambagawa metamorphic belt, which is a subduction related metamorphic belt in the south-western part of Japan. Three types of chemical zoning patterns were observed in garnet: Ca-rich normal zoning, Ca-poor normal zoning and intrasectoral zoning. Petrological studies indicate that normally-zoned garnet grains grew keeping surface chemical equilibrium with the matrix, in the stable mineral assemblage of garnet + muscovite + chlorite + plagioclase + paragonite + epidote + quartz ± biotite. Pressure and temperature histories were inversely calculated from the normally-zoned garnet in this assemblage, applying the differential thermodynamic method (Gibbs' method) with the latest available thermodynamic data set for minerals. The deduced P–T paths indicate slight increase of temperature with increasing pressure throughout garnet growth, having an average dP/dT of 0.4–0.5 GPa/100 °C. Garnet started growing at around 470 °C and 0.6 GPa to achieve the thermal and baric peak condition near the rim (520 °C, 0.9 GPa). The high-temperature condition at relatively low pressure (for subduction related metamorphism) suggests that heating occurred before or simultaneously with subduction.

Notes: The Schistes Lustrés (SL) suture zone occupies a key position in the Alpine chain between the high-pressure (HP) Brianconnais domain and the ultrahigh-pressure (UHP) Dora Maira massif, and reached subduction depths ranging from c. 40–65 km (Cottian Alps). In order to constrain the timing of HP metamorphism and subsequent exhumation, several phengite generations were differentiated, on the basis of habit, texture, paragenesis and chemistry, as belonging to the first or second exhumation episode, respectively, D2 or D3, or to earlier stages of the tectono-metamorphic evolution. Ten carefully selected samples showing D2, D3 (D2 + D3), or earlier (mostly peak temperature) phengite population(s) were subjected to laser probe 40Ar/39Ar analysis. The data support the results of the petrostructural study with two distinct age groups (crystallization ages) for D2 and D3 phengite, at 51–45 and 38–35 Ma, respectively. The data also reveal a coherent age cluster, at 62–55 Ma, for peak temperature phengite associated with chloritoid which were preserved in low strain domains. The age of the D3 event in the SL complex appears very similar to ages recently obtained for greenschist facies deformation on the border of most internal crystalline massifs. Exhumation rates of the order of 1–2 mm yr−1 are obtained for the SL complex, which are compatible with velocities documented for accretionary wedge settings. Similarly, cooling velocities are only moderate (c.5 °C Myr−1), which is at variance with recent estimates in the nearby UHP massifs.

Notes: Three periods of mineral growth and three generations of spiral-shaped inclusion trails have been distinguished within folded rocks of the Qinling-Dabie Orogen, China, using the development of three successive and differently trending sets of foliation intersection axes preserved in porphyroblasts (FIAs). This progression is revealed by the consistent relative sequence of changes in FIA trends from the core to rim of garnet porphyroblasts in samples with multiple FIAs. The first and second formed sets of FIAs trend oblique to the axial planes of macroscopic folds that dominate the outcrop pattern in this region. The porphyroblasts containing these FIAs grew prior to the development of the macroscopic folds, yet the FIAs do not change orientation across the fold hinges. The youngest formed FIAs (set 3) lie subparallel to the axial planes of these folds and the porphyroblasts containing these FIAs formed in part as the folds developed. The deformation associated with all three generations of spiral-shaped inclusion trails in garnet porphyroblasts involved the formation of subhorizontal and subvertical foliations against porphyroblast rims accompanied by periods of garnet growth; pervasive structures have not necessarily formed in the matrix away from the porphyroblasts. The macroscopic folds are heterogeneously strained from limb to limb, doubly plunging and have moderately dipping axial planes. The consistent orientation of Set 1 FIAs indicates that the development of spiral-shaped inclusion trails in porphyroblasts with FIAs belonging to Set 2 did not involve rotation of the previously formed porphyroblasts. The consistent orientation of Sets 1 and 2 FIAs indicate that the development of spiral-shaped inclusion trails in porphyroblasts with FIAs belonging to Set 3 did not involve rotation of the previously formed porphyroblasts during folding. This requires a fold mechanism of progressive bulk inhomogeneous shortening and demonstrates that spiral-shaped inclusion trails can form outside of shear zones.

Notes: The grain-scale spatial arrangement of melt in layer-parallel leucosomes in two anatectic rocks from two different contact aureoles located in central Maine, USA, is documented and used to constrain the controls on grain-scale melt localization. The spatial distribution of grain-scale melt is inferred from microstructural criteria for recognition of mineral pseudomorphs after melt and mineral grains of the solid matrix that hosted the melt. In both rocks, feldspar mimics the grain-scale distribution of melt, and quartz is the major constituent of the solid matrix. The feldspar pockets consist of individual feldspar grains or aggregates of feldspar grains that show cuspate outlines. They have low average width/length ratios (0.54 and 0.55, respectively), and are interstitial between more rounded and equant (width/length ratios 0.65 for both samples) quartz grains. In two dimensions, the feldspar pockets extend over distances equivalent to multiple quartz grain diameters, possibly forming a connected three-dimensional intergranular network. Both samples show similar mesoscopic structural elements and in both samples the feldspar pockets have a shape-preferred orientation. In one sample, feldspar inferred to replace melt is aligned subparallel to the shape-preferred orientation of quartz, indicating that pre- or syn-anatectic strain controlled the grain-scale distribution of melt. In the other sample, the preferred orientation of feldspar inferred to replace melt is different from the orientations of all other mesoscopic or microscopic structures in the rock, indicating that differential stress controlled grain-scale melt localization. This is probably facilitated by conditions of higher differential stress, which may have promoted microfracturing. Grain-scale melt distribution and inferred melt localization controls give insight into possible grain-scale deformation mechanisms in melt-bearing rocks. Application of these results to the interpretation of deep crustal anatectic rocks suggests that grain-scale melt distribution should be controlled primarily by pre- or syn-anatectic deformation. Feedback relations between melt localization and deformation are to be expected, with important implications for deformation and tectonic evolution of melt-bearing rocks.

Notes: A metamorphic field gradient has been investigated in the Moldanubian zone of the central European Variscides encompassing, from base to the top, a staurolite–kyanite zone, a muscovite–sillimanite zone, a K-feldspar–sillimanite zone, and a K-feldspar–cordierite zone, respectively. The observed reaction textures in the anatectic metapsammopelites of the higher grade zones are fully compatible with experimental data and petrogenetic grids that are based on fluid-absent melting reactions. From structural and microstructural observations it can be concluded that the boundary between the kyanite–staurolite zone and the muscovite- and K-feldspar–sillimanite zones coincides with an important switch in deformation mechanism(s). Besides minor syn-anatectic shearing (melt-enhanced deformation), microstructural criteria point (a) to a switch in deformation mechanism from rotation recrystallization (climb-accommodated dislocation creep) to prism slip and high-temperature (fast) grain boundary migration in quartz (b) to the activity of diffusion creep in quartz–feldspar layers, and (c) to accommodation of strain by intense shearing in fibrolite–biotite layers. It is suggested that any combination of these deformation mechanisms will profoundly affect the rheological characteristics of high-grade metamorphic rocks and significantly lower rock strength. Hence, the boundary between these zones marks a major rheological barrier in the investigated cross section and probably also in other low- to medium-pressure/high-temperature areas. At still higher metamorphic grades (K-feldspar-cordierite zone), where the rheologically critical melt percentage is reached, rock rheology is mainly governed by the melt and other deformation mechanisms are of minor importance. In the study area, the switch in deformation mechanism(s) is responsible for large-scale strain partitioning and concentration of deformation within the higher-temperature hanging wall during top-to-the-S thrusting, thus preserving a more complete petrostructural record within the rocks of the footwall including indications for a ?Devonian high- to medium-pressure/medium-temperature metamorphic event. Thrusting is accompanied by diapiric ascent of diatexites of the K-feldspar-cordierite zone and infolding of the footwall, suggesting local crustal overturn in this part of the Moldanubian zone.

Notes: This paper presents the results of numerical modelling to investigate the regional occurrence of prehnite-bearing metamorphic rocks at shallow levels in subduction zones. The modelling assumes a simple geometrical configuration in which the thermal structure in a prism is controlled by boundary conditions at the top and base of the prism. It is expected that the predominant metamorphic facies in a prism will change with decreasing age of the descending slab. The results of thermal modelling show that the facies boundary between pumpellyite–actinolite and prehnite–actinolite facies (including prehnite–pumpellyite facies) overlaps with an array of P–T conditions in the prism when the age of a descending slab is younger than 10 Myr. This implies that the change of the predominant metamorphic facies from pumpellyite–actinolite to prehnite–actinolite facies will switch drastically. The critical age of the switch depends on subduction parameters. In particular, the critical age of the descending slab is 〈5 Myr in the case of no shear heating, with a subduction rate of v=75–200 mm y−1 and subduction angle of θ=5–15°. For shear heating (constant shear stress=30 MPa) with a subduction rate of v=75 mm y−1 and subduction angle of θ=10° the critical age is 7 Myr. To test this switching behaviour in the development of prehnite–actinolite facies in the prism, petrologic data from the Cretaceous Shimanto Accretionary Complex (CSAC) in Kyushu, Japan were compiled. The regional occurrence and mineral assemblages of prehnite-bearing metamorphic rocks suggest that the most of CSAC was metamorphosed under prehnite–actinolite facies. This conclusion is consistent with subduction of a young, hot slab, as has been proposed based on other geological observations. This suggests that the regional extent of the prehnite–actinolite facies metamorphic rocks may be a unique evidence for the subduction of a young, hot slab.

Notes: Fluid compositions and bedding-scale patterns of fluid flow during contact metamorphism of the Weeks Formation in the Notch Peak aureole, Utah, were determined from mineralogy and stable isotope compositions. The Weeks Formation contains calc-silicate and nearly pure carbonate layers that are interbedded on centimetre to decimetre scales. The prograde metamorphic sequence is characterized by the appearance of phlogopite, diopside, and wollastonite. By accounting for the solution properties of Fe, it is shown that the tremolite stability field was very narrow and perhaps absent in the prograde sequence. Unshifted oxygen and carbon isotopic ratios in calcite and silicate minerals at all grades, except above the wollastonite isograd, show that there was little to no infiltration of disequilibrium fluids. The fluid composition is poorly constrained, but X(CO2)fluid must have been 〉0.1, as indicated by the absence of talc, and has probably increased with progress of decarbonation reactions.The occurrence of scapolite and oxidation of graphite in calc-silicate beds of the upper diopside zone provide the first evidence for limited infiltration of external aqueous fluids. Significantly larger amounts of aqueous fluid infiltrated the wollastonite zone. The aqueous fluids are recorded by the presence of vesuvianite, large decreases in δ18O values of silicate minerals from c. 16‰ in the diopside zone to c. 10‰ in the wollastonite zone, and extensive oxidation of graphite. The carbonate beds interacted with the fluids only along margins where graphite was destroyed, calcite coarsened, and isotopic ratios shifted.The wollastonite isograd represents a boundary between a high aqueous fluid-flux region on its higher-grade side and a low fluid-flux region on its lower-grade side. Preferential flow of aqueous fluids within the wollastonite zone was promoted by permeability created by the wollastonite-forming reaction and the natural tendency of fluids to flow upward and down-temperature near the intrusion-wall rock contact.

Notes: Reactions producing Al-rich index minerals in the south-eastern part of the Lepontine Dome (Central Alps, Switzerland) are investigated using mineral distribution maps, microstructural observations and equilibrium phase diagrams. The apparent staurolite mineral zone boundary corresponds to the paragonite breakdown reaction Pg + Grt + Qtz = Pl + Al2O3 + W. Equilibrium phase diagrams show that most natural metapelites do not contain staurolite or alumosilicates as long as univalent cations are predominantly accommodated in white mica. For a wide range of metapelitic compositions the paragonite breakdown releases sufficient Al for the formation of these minerals. Rare occurrences of staurolite and kyanite, north of the formerly mapped mineral zone boundaries, coexist with paragonite and are restricted to extremely Al-rich bulk compositions. The stable branch of the kyanite-forming paragonite breakdown reaction above 660 °C yields an additional mapable isograd. The second set of Al-releasing reactions is biotite-producing phengite breakdown. However, these reactions are less suitable to produce well defined reaction isograds in the field as they are more continuous and their progress is strongly dependent on bulk composition. Well developed fibrolite in metapelites does not appear until staurolite starts to breakdown. We conclude that amphibolite facies conditions in the study area were attained by decompression, without substantial heating at low pressures.

Notes: The granitic mylonite zone in the Cretaceous Ryoke metamorphic belt contains deformed amphibolites as thin layers. The amphibolite layers do not exhibit pinch-and-swell or boudinage structures, even when contained in a high-strain granitic mylonite. This mode of occurrence suggests that they were deformed as much as the surrounding granite mylonite. In the highly deformed zone, strongly foliated amphibolites contain Ti-rich brown amphibole porphyroclasts rimmed by Ti-poor green amphibole, titanite and chlorite. These porphyroclasts are elongated, forming shear surfaces defined by preferential distribution of the chlorite and titanite. Porphyroclastic plagioclase in the strongly foliated amphibolites consists of two components: an anorthite-rich core and an anorthite-poor rim. Based on these observations, the mass-balanced reaction occurring during deformation is defined as 〈inlineGraphic alt="inline image" href="urn:x-wiley:02634929:JMG367:JMG_367_mu1" location="equation/JMG_367_mu1.gif"/〉 As the reaction products form a weak interconnected matrix, the strain rate of the amphibolites may be controlled by the rate of dissolution–precipitation through fluids. Weakly foliated amphibolites in the low-strain zone exhibit cataclastic microstructures, whereas the strongly foliated amphibolites do not exhibit such features. These microstructural and chemical changes suggest that high-strain amphibolites were initially deformed by cataclasis, followed by deformation through metamorphic reactions. During the metamorphism/deformation, old plagioclase grains with high Xan were not stable and dissolved, and new plagioclase grains with low Xan crystallized at the old plagioclase rim. Dissolution of old plagioclase and precipitation of new plagioclase occurred normal to and parallel to the foliation, respectively, reflecting incongruent pressure solution due to differential stress and changes in P–T–H2O conditions. The development of incongruent pressure solution is attributed to increased fluid flux in the strongly foliated amphibolites, as evidenced by the greater abundance of hydration-reaction products in the strongly foliated amphibolites than in the weakly foliated ones.

Notes: This paper describes a kinetic study on reaction textures in eclogitic rocks from the Sulu region, eastern China. Some of the eclogitic rocks display a decompressional reaction texture, whereby kyanite grains are surrounded by plagioclase coronas and are never in contact with quartz. The change in mineral parageneses with progress of the reaction was predicted by constructing chemical potential diagrams in a model system. The chemical potential diagrams indicated that the chemical potential of 2Na2O + CaO (2µNa2O + µCaO) in intergranular regions between kyanite and quartz should decrease with decreasing pressure, whereas 2µNa2O + µCaO in intergranular regions between garnet and omphacite should increase with decreasing pressure. Thus, upon decompression, an inequality in chemical potential arises in the rock. To reduce this inequality, garnet and omphacite react to produce amphibole and plagioclase and release Na2O and CaO. Then, the released Na2O and CaO components diffuse into the regions between kyanite and quartz grains and react to produce plagioclase between them. This model also indicates that the chemical potential of SiO2 should decrease around kyanite grains during the progress of the decompressional reaction, and Si-undersaturated conditions should have formed around kyanite grains in spite of the presence of quartz in these eclogitic rocks. Thus, spinel or corundum that are not stable in the system with excess quartz can form as a metastable phase, as observed in eclogitic rocks from the study areas. Phase diagrams in the system with excess quartz should be carefully applied for analysis of such reaction textures.

Notes: Porphyroblastic schists in the thermal aureole of the Victor Harbor Granite at Petrel Cove, in the southern Adelaide Fold Belt, South Australia, preserve a record of sequential cordierite, andalusite, staurolite, fibrolite, chlorite and muscovite growth (along with biotite+plagioclase+quartz+ilmenite) during progressive deformation. A P–T pseudo-section appropriate to biotite-saturated assemblages in KFMASH shows that the sequence of mineral reactions records increasing pressure of at least 1 kbar (from c. 3 to c. 4 kbar) during cooling from around 580 °C. Heating at pressures below c. 3 kbar is inferred for growth of early formed cordierite porphyroblasts, and is attributed in part to the thermal effects of granite emplacement, while the pressure increase is attributed to tectonic burial accruing from ongoing deformation. The ‘anticlockwise’P–T path is consistent with convergent deformation being focussed as a consequence of heating, as to be expected for a lithospheric rheology that is strongly temperature dependent.

Notes: Nine marble horizons from the granulite facies terrane of southern India were examined in detail for stable carbon and oxygen isotopes in calcite and carbon isotopes in graphite. The marbles in Trivandrum Block show coupled lowering of δ13C and δ18O values in calcite and heterogeneous single crystal δ13C values (− 1 to − 10‰) for graphite indicating varying carbon isotope fractionation between calcite and graphite, despite the granulite facies regional metamorphic conditions. The stable isotope patterns suggest alteration of δ13C and δ18O values in marbles by infiltration of low δ13C–δ18O-bearing fluids, the extent of alteration being a direct function of the fluid-rock ratio. The carbon isotope zonation preserved in graphite suggests that the graphite crystals precipitated/recrystallized in the presence of an externally derived CO2-rich fluid, and that the infiltration had occurred under high temperature and low fO2 conditions during metamorphism. The onset of graphite precipitation resulted in a depletion of the carbon isotope values of the remaining fluid+calcite carbon reservoir, following a Rayleigh-type distillation process within fluid-rich pockets/pathways in marbles resulting in the observed zonation. The results suggest that calcite–graphite thermometry cannot be applied in marbles that are affected by external carbonic fluid infiltration. However, marble horizons in the Madurai Block, where the effect of fluid infiltration is not detected, record clear imprints of ultrahigh temperature metamorphism (800–1000 °C), with fractionations reaching 〈2‰. Zonation studies on graphite show a nominal rimward lowering δ13C on the order of 1 to 2‰. The zonation carries the imprint of fluid deficient/absent UHT metamorphism. Commonly, calculated core temperatures are  〉 1000 °C and would be consistent with UHT metamorphism.

Notes: The frequency of occurrence of minerals in 1876 samples of Sanbagawa pelitic schist in central Shikoku is summarized on the basis of microscopic observation accompanied, in part, by use of an electron microprobe. All samples contain quartz, plagioclase, phengite, chlorite and graphite. More than 90% of samples contain clinozoisite, titanite and apatite. Garnet is present in 95% of samples from the garnet zone, and biotite is present in 64% of samples from the albite-biotite zone. Calcite is found in about 40% of samples of the pelitic schist collected from outcrop, but occurs in 95% of the pelitic schist from drill cores. Calcite was apparently ubiquitous in the pelitic schist during the Sanbagawa metamorphism, but must have been dissolved recently by the action of surface or ground water. The mineral assemblages of the Sanbagawa pelitic schist have to be analyzed in the system with excess calcite, quartz, albite (or oligoclase), clinozoisite, graphite and fluid that is composed mainly of H2O, CO2 and CH4. In the presence of calcite, reactions that produce garnet, rutile, oligoclase, biotite and hornblende, some of which define isograds of the metamorphic belt, should be written as mixed volatile equilibria that tend to take place at lower temperature than the dehydration reactions that have been proposed. The presence of calcite in pelitic schist suggests that fluid composition is a variable as important in determining mineral assemblages as pressure and temperature. Thus Ca-bearing phases must be taken into account to analyze the phase relations of calcite-bearing pelitic schist, even if CaO content of Sanbagawa pelitic schist is low. As calcite is a common phase, the mineral assemblages of the biotite zone pelitic schist may contravene the mineralogical phase rule and warrant further study.

Notes: The high grade rocks (metapelites and metabasites) of Clavering Ø represent the easternmost exposures of granulites in the Palaeozoic Caledonian Orogen of East Greenland. Mafic granulites which occur as sheet-like bodies and lenses within metapelitic migmatites and orthogneiss complexes have experienced migmatisation and mineral equilibria which define a clockwise P–T path incorporating a near-isothermal decompression segment. Textures demonstrate the existence of early garnet-clinopyroxene-melt assemblages which equilibrated at 〉8–11 kbar and 850–915 °C. Subsequently, decompression melting led to formation of orthopyroxene-plagioclase-melt assemblages at conditions below 〉8–11 kbar. Continued syn-deformational decompression is indicated by a combination of both static and syn-deformational recrystallization textures which generated finer grained orthopyroxene-plagioclase assemblages. P–T constraints indicate these assemblages equilibrated at c. 5.0–6.5 kbar at 850–915 °C. These data are consistent with the rocks undergoing a stage of rapid tectonic-induced exhumation involving some 3.0–4.5 kbar (c.10–12 km) uplift as part of a clockwise P–T path in a collisional setting.

Notes: Metre to tens-of-metre wide, steeply dipping, greenschist facies shear zones that cut blueschists and eclogites of the Combin and Zermatt–Saas Zones at Täschalp and in adjacent areas of the western Alps were sites of extensive recrystallization driven by fluid flow and deformation. Rb–Sr data imply that these shear zones formed at 42–37 Ma with a systematic younging of structures northward toward, and into, the hangingwall of the Mischabel Structure. Shearing commenced at 400–475 °C and 400–500 MPa and continued as pressures and temperatures fell to 300–350 °C and 300–350 MPa. Individual shear zones were active for 2–3 Myr with later lower grade stages of shearing concentrated into narrow zones. Fluids that infiltrated the shear zones were water rich (XH2O 〉 0.9). Alteration zones around albite veins and at the margins of serpentinite bodies are penecontemporaneous with these shear zones and formed at approximately the same conditions. The eclogites were exhumed from c. 64 km at 44 Ma to 14–16 km at 42–41 Ma implying exhumation rates of 2–5 cm yr−1. Rapid exhumation was probably achieved by extension aided by buoyancy, following subduction of continental crust, and rapid erosion. The shear zones form part of a regional-scale extensional system responsible for a significant portion of the exhumation of the subducted oceanic crust.

Notes: High-T, low-P metamorphic rocks of the Palaeoproterozoic central Halls Creek Orogen in northern Australia are characterised by low radiogenic heat production, high upper crustal thermal gradients (locally exceeding 40 °C km−1) sustained for over 30 Myr, and a large number of layered mafic-ultramafic intrusions with mantle-related geochemical signatures. In order to account for this combination of geological and thermal characteristics, we model the middle crustal response to a transient mantle-related heat pulse resulting from a temporary reduction in the thickness of the mantle lithosphere. This mechanism has the potential to raise mid-crustal temperatures by 150–400 °C within 10–20 Myr following initiation of the mantle temperature anomaly, via conductive dissipation through the crust. The magnitude and timing of maximum temperatures attained depend strongly on the proximity, duration and lateral extent of the thermal anomaly in the mantle lithosphere, and decrease sharply in response to anomalies that are seated deeper than 50–60 km, maintained for 〈5 Myr in duration and/or have half-widths 〈100 km. Maximum temperatures are also intimately linked to the thermal properties of the model crust, primarily due to their influence on the steady-state (background) thermal gradient. The amplitudes of temperature increases in the crust are principally a function of depth, and are broadly independent of crustal thermal parameters. Mid-crustal felsic and mafic plutonism is a predictable consequence of perturbed thermal regimes in the mantle and the lowermost crust, and the advection of voluminous magmas has the potential to raise temperatures in the middle crust very quickly. Although pluton-related thermal signatures significantly dissipate within 〈10 Myr (even for very large, high-temperature intrusive bodies), the interaction of pluton- and mantle-related thermal effects has the potential to maintain host rock temperatures in excess of 400–450 °C for up to 30 Myr in some parts of the mid-crust. The numerical models presented here support the notion that transient mantle-related heat sources have the capacity to contribute significantly to the thermal budget of metamorphism in high-T, low-P metamorphic belts, especially in those characterised by low surface heat flow, very high peak metamorphic geothermal gradients and abundant mafic intrusions.

Notes: The late Palaeozoic western Tianshan high-pressure /low-temperature belt extends for about 200 km along the south-central Tianshan suture zone and is composed mainly of blueschist, eclogite and epidote amphibolite/greenschist facies rocks. P–T conditions of mafic garnet omphacite and garnet–omphacite blueschist, which are interlayered with eclogite, were investigated in order to establish an exhumation path for these high-pressure rocks. Maximum pressure conditions are represented by the assemblage garnet–omphacite–paragonite–phengite–glaucophane–quartz–rutile. Estimated maximum pressures range between 18 and 21 kbar at temperatures between 490 and 570 °C. Decompression caused the destabilization of omphacite, garnet and glaucophane to albite, Ca-amphibole and chlorite. The post-eclogite facies metamorphic conditions between 9 and 14 kbar at 480–570 °C suggest an almost isothermal decompression from eclogite to epidote–amphibolite facies conditions. Prograde growth zoning and mineral inclusions in garnet as well as post-eclogite facies conditions are evidence for a clockwise P–T path. Analysis of phase diagrams constrains the P–T path to more or less isothermal cooling which is well corroborated by the results of geothermobarometry and mineral textures. This implies that the high-pressure rocks from the western Tianshan Orogen formed in a tectonic regime similar to ‘Alpine-type’ tectonics. This contradicts previous models which favour ‘Franciscan-type’ tectonics for the southern Tianshan high-pressure rocks.

Notes: Garnet-mica schists from the Scottish Highlands provide new insight into an important mechanism of phyllosilicate growth, termed ‘crack-fill porphyroblastesis’. It is shown that grain boundary dilatancy, microcracking and porphyroblast-matrix decoupling all play a significant role in facilitating growth in regimes of noncoaxial shear. With respect to chlorite porphyroblasts, there are three growth stages. Following nucleation, the initial phase of growth is by progressive matrix replacement, to preserve inclusion trails of fine carbonaceous material. The second growth stage produced new optically continuous inclusion-free chlorite on the {001} margins of those crystals at a high angle to the schistosity. This growth results from decoupling at the porphyroblast–matrix contact on those margins at a high angle to the principal axis of extension. The development of dilatant cracks at porphyroblast margins provides a sink for material migrating down Pf and chemical potential gradients. This causes precipitation of new optically continuous ‘clear’ chlorite on the pre-existing, heavily included core. The porphyroblast–matrix boundary continues to dilate after porphyroblast growth had terminated, producing plano-convex quartz-rich strain shadows. Similar growth behaviour is recognised in biotite porphyroblasts, indicating that ‘crack-fill porphyroblastesis’ is an important growth mechanism for phyllosilicates in actively deforming metamorphic rocks. It also indicates that decoupling and crack-fill development at porphyroblast margins could be important in controlling the pattern of material transfer, and may have significant implications for matrix permeability and fluid-flow characteristics.

Notes: Cordierite H2O and CO2 volatile saturation surfaces derived from recent experimental studies are presented for P–T conditions relevant to high-grade metamorphism and used to evaluate fluid conditions attending partial melting and granulite formation. The volatile saturation surfaces and saturation isopleths for both H2O and CO2 in cordierite are strongly pressure dependent. In contrast, the uptake of H2O by cordierite in equilibrium with melts formed through biotite dehydration melting, controlled by the distribution of H2O between granitic melt and cordierite, Dw[Dw = wt% H2O (melt)/wt% H2O(Crd)], is mainly temperature dependent. Dw = 2.5–6.0 for the H2O contents (0.4–1.6 wt percentage) typical of cordierite formed through biotite dehydration melting at 3–7 kbar and 725–900 °C. This range in Dw causes a 15–30% relative decrease in the total wt% of melt produced from pelites. Cordierite in S-type granites are H2O-rich (1.3–1.9 wt%) and close to or saturated in total volatiles, signifying equilibration with crystallizing melts that achieved saturation in H2O. In contrast, the lower H2O contents (0.6–1.2 wt percentage) preserved in cordierite from many granulite and contact migmatite terranes are consistent with fluid-absent conditions during anatexis. In several cases, including the Cooma migmatites and Broken Hill granulites, the cordierite volatile compositions yield aH2O values (0.15–0.4) and melt H2O contents (2.2–4.4 wt%) compatible with model dehydration melting reactions. In contrast, H2O leakage is indicated for cordierite from Prydz Bay, Antarctica that preserve H2O contents (0.5–0.3 wt%) which are significantly less than those required (1.0–0.8 wt%) for equilibrium with melt at conditions of 6 kbar and 860 °C. The CO2 contents of cordierite in migmatites range from negligible (〈 0.1 wt%) to high (0.5–1.0 wt%), and bear no simple relationship to preserved cordierite H2O contents and aH2O. In most cases the cordierite volatile contents yield total calculated fluid activities (aH2O + aCO2) that are significantly less than those required for fluid saturation at the P–T conditions of their formation. Whether this reflects fluid absence, dilution of H2O and CO2 by other components, or leakage of H2O from cordierite is an issue that must be evaluated on a case-by-case basis.

Notes: Chemically zoned porphyroblasts in metamorphic rocks indicate that diffusional processes could not maintain equilibrium conditions on a grain scale during porphyroblast growth or establish it afterwards. An effect of this inability to maintain equilibrium is the progressive removal of elements forming garnet cores from any metamorphic reaction that occurs at the porphyroblast boundaries or in the matrix of the rock. To examine this effect on mineral assemblages, the Bence–Albee matrix correction was applied to X-ray intensity maps collected using eclogite samples from northern New Caledonia in order to determine the chemical composition of all parts of the sample. The manipulation of these element maps allows a quantitative analysis of the fractionation of the bulk rock composition between garnet cores and the matrix. A series of calculated equilibrium-volume compositions represents the change in matrix chemistry with progressive elemental fractionation as a consequence of prograde garnet growth under high-P conditions. Pressure–temperature pseudosections are calculated for these compositions, in the CaO–Na2O–FeO–MgO–Al2O3–SiO2–H2O system. Assemblages, modal proportions and mineral textures observed in the New Caledonian eclogites can be closely modelled by progressively ‘removing’ elements forming garnet cores from the bulk rock composition. The pseudosections demonstrate how chemical fractionation effects the peak metamorphic assemblage, prograde textures and the development of retrograde assemblages.

Notes: Quartz–sillimanite segregations, quartz–albite lithologies (Ab95–98), and Kiruna-type low-Ti iron-oxide deposits are associated with late- to post-tectonic (c. 1055 Ma) leucogranites of Lyon Mountain Gneiss (LMG) in the Adirondack Mountains, New York State. Most recent interpretations of these controversial features, which are global in occurrence, favour hydrothermal origins in agreement with results presented here.Field relations document that quartz–sillimanite veins and nodules cut, and therefore post-date, emplacement of host LMG leucogranites. Veins occur in oriented fracture networks, and aligned trains of nodules are interpreted as disrupted early veins. Late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism. Veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall-rock feldspar indicating leaching of Na and K from LMG feldspar by acidic hydrothermal fluids. Subsequent, and repeated, ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric.Geochemical and petrographic studies of quartz–albite rock indicate that it formed through metasomatic replacement (albitization) of LMG microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite. Low-Ti iron-oxide ores are commonly associated with the quartz–albite sub-unit, and it is proposed that hydrothermal fluids related to albitization transported Fe as well. The regional extent of sodic alteration suggests large quantities of surface-derived hydrothermal fluids. Fluid inclusion and oxygen isotope data are consistent with high temperature, regionally extensive fluids consisting primarily of evolved surface-derived brines enriched in Na and Cl. Quartz–sillimanite veins and nodules, which are significantly more localised phenomena and require acidic fluids, were most likely formed from local magmatic fluids in the crystallizing carapaces of LMG plutons.

Notes: Rocks of the Snake Creek Anticline are mainly pelitic schists, psammitic schists and quartzites that were metamorphosed during multiple high-T/low-P events extending from D1 to D5, with the metamorphic peak occurring late to post-D3. Albitites are widespread, but are concentrated in five areas. They are typically fine- to medium-grained, and consist of albite, with or without combinations of quartz, biotite, staurolite, cordierite, garnet, andalusite, sillimanite, kyanite, gedrite and tourmaline. From the presence or absence of albite inclusions in porphyroblasts, the albitites are interpreted as forming early in the D3 event as a result of infiltration of external fluids. Psammitic schists and quartzites were preferentially altered, but pelitic schists were also albitized in localities where the alteration was more extreme, with the replacement of muscovite total and the replacement of quartz and biotite variable. Structural controls on albitization include fracturing and syn-D3 shear zones in fold hinges. Biotite schists with abundant porphyroblasts (combinations of staurolite, garnet, andalusite and cordierite) occur adjacent to albitites, and it is argued that they formed by the addition of Fe and Mg sourced from the albitites. In several albitite-rich areas, cordierite grew early in D3 and was partly or entirely replaced during or after D3 by combinations of biotite, andalusite, tourmaline, staurolite and sillimanite. A postulated P–T–d path involved an increase in pressure (with or without a decrease in temperature) subsequent to early D3 albitization, followed by an increase in temperature up to the metamorphic peak (late D3 to early D4. The metamorphism was contemporary in part with the emplacement of the Williams Batholith (c. 1550–1500 Ma), which probably supplied the Na-rich fluids.

Notes: Andalusite–staurolite–biotite hornfels metamorphosed beneath the mafic layered rocks of the Bushveld Complex, South Africa, preserves a detailed record of the relative timing of porphyroblast growth and metamorphic reactions. The sequence inferred from microstructures shows considerable overlap of the period of growth of porphyroblasts of staurolite, cordierite, biotite and andalusite, and the persistence over a similar interval of the reactant porphyroblastic phase chloritoid. This is inconsistent with calculations of equilibrium phase relations, and implies that disequilibrium processes controlled the prograde reaction sequence, despite the slow heating rates involved (1 °C per 10 000 yr). The early appearance of cordierite by a metastable reaction and its subsequent disappearance indicates that delayed nucleation of porphyroblastic phases, rather than simply sluggish reaction, is required to account for the sequence of growth. The predicted reactions for the first appearance of andalusite and staurolite have low entropy of reaction, and do not occur until they have been overtaken in terms of reaction affinity by high-entropy devolatilisation reactions involving the breakdown of chlorite. Once the porphyroblasts have nucleated, metastable chloritoid-breakdown reactions also contribute to their growth. The implied magnitude of the critical overstepping for andalusite nucleation is around 5 kJ mole−1 (equivalent to 40 °C for the chlorite-breakdown reaction), and that for other phases is expected to decrease in the order andalusite〉staurolite〉cordierite. Coupling between nucleation rate, crystal growth rates and the resulting grain size distribution suggests that the rate constants of natural reactions are at least an order of magnitude lower than those measured in the laboratory. Pseudomorphs after chloritoid and cordierite conserve volume but not Al or other species of low mobility, suggesting a breakdown mechanism controlled by an interface process such as the slow dissolution of the refractory porphyroblast phase, rather than by a transport step.

Notes: Fe-rich metapelitic granulites of the Musgrave Block, central Australia, contain several symplectic and coronal reaction textures that post-date a peak S2 metamorphic assemblage involving garnet, sillimanite, spinel, ilmenite, K-feldspar and quartz. The earliest reaction textures involve spinel- and quartz-bearing symplectites that enclose garnet and to a lesser extent sillimanite. The symplectic spinel and quartz are in places separated by later garnet and/or sillimanite coronas. The metamorphic effects of a later, D3, event are restricted to zones of moderate to high strain where a metamorphic assemblage of garnet, sillimanite, K-feldspar, magnetite, ilmenite, quartz and biotite is preserved. Quantitative mineral equilibria calculations in the system K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (KFMASHTO) using Thermocalc 3.0 and the accompanying internally consistent dataset provide important constraints on the influence of TiO2 and Fe2O3 on biotite-bearing and spinel-bearing equilibria, respectively. Biotite-bearing equilibria are shifted to higher temperatures and spinel-bearing equilibria to higher pressures and lower temperatures in comparison to the equivalent equilibria in K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH). The sequence of reaction textures involving spinel is consistent with a D2 P–T path that involved a small amount of decompression followed predominantly by cooling within a single mineral assemblage stability field. Thus, the reaction textures reflect changes in modal proportions within an equilibrium assemblage rather than the crossing of a univariant reaction. The D3 metamorphic assemblage is consistent with lower temperatures than those inferred for D2.

Notes: In the contact aureole of the Oligocene granodiorite of Cima di Vila, granitic pegmatites of Variscan age were strongly deformed during eo-Alpine regional metamorphism, with local development of ultramylonites. In the ultramylonite matrix, consisting of quartz, plagioclase, muscovite and biotite, microstructures show grain growth of quartz within quartz ribbons, and development of decussate arrangements of mica. These features indicate that dynamic recrystallization related to mylonite development was followed by extensive static growth during contact metamorphism. K-feldspar porphyroclasts up to 1.5 cm are mantled by myrmekite that forms a continuous corona with thickness of about 1 mm. In both XZ and YZ sections, myrmekite tubules are undeformed, and symmetrically distributed in the corona, and oligoclase-andesine hosts have random crystallographic orientation. Myrmekite development has been modelled from the P–T–t evolution of the ultramylonites, assuming that the development of the ultramylonites occurred during eo-Alpine metamorphism at c. 450 °C, 7.5 kbar, followed by contact metamorphism at c. 530 °C, 2.75 kbar. Phase diagram pseudosections calculated from the measured bulk composition of granitic pegmatite protolith indicate that the equilibrium assemblage changes from Qtz–Phe–Ab ± Zo ± Cpx ± Kfs during the ultramylonite stage to Qtz–Pl(An30–40)–Ms–Kfs–Bt(Ann55) during the contact metamorphic stage. The thermodynamic prediction of increasing plagioclase mode and anorthite content, change of white mica composition and growth of biotite, occurring during the end of the heating path, are in agreement with the observed microstructures and analysed phase compositions of ultramylonites. Along with microstructural evidence, this supports the model that K-feldspar replacement by myrmekite took place under static conditions, and was coeval with the static growth accompanying contact metamorphism. Myrmekite associated with muscovite can develop under prograde (up-temperature) conditions in granites involved in polymetamorphism.

Notes: Crustal thermal regimes are sensitive to both the amount and distribution of heat producing elements (HPEs). Since a significant proportion of the crustal complement of HPEs is contained within granites, granite generation and emplacement should lead to significant long-term changes in the thermal structure of the crust. Using HPE concentrations appropriate to representative Australian Proterozoic granites we show that granite segregation leads to changes in the temperature field of the crust of up to c. 50 °C, producing long-term cooling in the source regions and heating at emplacement levels, relative to the pre-granite conductive thermal regime. Because of the intimate connection between thermal regime and lithospheric strength, granite-assisted redistribution of HPEs is likely to be fundamental to cratonisation.

Notes: Coupled thermal-mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr−1, and a slope-dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m−3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m−3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro-side of the system, and is driven by a depth-dependent pressure gradient that is facilitated by the development of a temperature-dependent low viscosity horizon in the mid-crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post-convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust-related exhumation on the flanks. Velocities in the pro-side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro-side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal-sense offset at its upper boundary, reverse-sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen.

Notes: Mid-crustal Archean pelitic granulites in the Vredefort Dome experienced a static, low-P granulite facies overprint associated with the formation of the dome by meteorite impact at 2.02 Ga. Heating and exhumation were virtually instantaneous, with the main source of heat being provided by energy released from nonadiabatic decay of the impact shock wave. Maximum temperatures within a radius of a few kilometres of the centre of the structure exceeded 900 °C and locally even exceeded 1350 °C. This led to comprehensive melting of the precursor Archean granulite assemblages (Grt + Bt + Qtz + Pl + Ksp ± Crd ± Opx ± Sil) followed by peritectic crystallization of aluminous alkali feldspar+Crd + Spl ± Crn ± Sil parageneses and the segregation of small, evolved, biotite leucogranite bodies. However, at a distance of c. 6 km from the centre pre-impact rock features are largely preserved, although partial replacement of garnet by symplectitic coronas of Crd + Opx ± Spl ± Pl and biotite by orthopyroxene indicate that peak temperatures approached 775 ± 50 °C. Thin interstitial moats of K-feldspar are closely associated with the orthopyroxene coronas; they are interpreted as the remnants of low-proportion partial melts generated by biotite breakdown. Both the textures and mineral compositional data support reduced equilibration volumes in these rocks, which reflect rapid isobaric cooling following shock heating and exhumation. The high temperatures and strong lateral thermal gradient are consistent with the modelled impact-induced isotherm pattern for a 200–300 km diameter impact crater.

Notes: The transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite/smectite mixed-layering sequence, or an equilibrated discontinuous sequence involving smectite–corrensite–chlorite. Here, analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving (i) a continuous mixed-layer chlorite/smectite series; (ii) a discontinuous smectite–corrensite–chlorite series and (iii) a direct smectite to chlorite transition. Such contrasting pathways are not in accord with an equilibrium mineral reaction series, suggesting that these pathways record kinetically controlled reaction progress. In the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization, and not to differences in thermal gradients or clay grain size. This suggests a kinetic effect linked to variation in fluid/rock ratios and/or a contrast between advective or diffusive fluid transport. The mode of fluid transport provides a means by which the rates of dissolution/nucleation/growth can control the reaction style and the reaction progress of the smectite to chlorite transition. Slow rates of growth are linked to the first reaction pathway involving mixed-layering, while increasing rates of growth, relative to nucleation, promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition, representative of the third pathway.

Notes: The Cooma Complex of the Lachlan Fold Belt, south-eastern Australia, is characterised by a large (c. 10 km wide) low-P, high-T metamorphic aureole surrounding a small (3 × 6 km) granite pluton. The aureole extends northward to envelop the eastern lobe of the Murrumbidgee Batholith and progressively narrows to a kilometre wide hornfelsic aureole some 50 km north of Cooma. At its northern extremity, the batholith has intruded its own volcanic cover. These regional relations suggest that the Murrumbidgee Batholith is gently tilted to the north, with the Cooma Complex representing the aureole beneath the batholith.Two main deformation events, D3 and D5, affected the aureole. The inner, high-grade migmatitic domain contains upright F5 folds defined by a composite, transposed S3/S0 fabric and S3/S0 concordant leucosomes. The folded stromatic migmatites define the western limb of a F5 synform, with its axis located in the batholith. Lenses and sheets of the Murrumbidgee Batholith intruded along S3 but also preserve S3 as a strong, solid-state foliation. S3 and the granite sheets but are also folded by F5, outlining a fanning positive flower structure. These relations indicate that most of the batholith was emplaced before and during D3, but intrusion persisted until early syn-D5.Formation of the Cooma Granodiorite occurred post-D3 to early syn-D5, after formation of the wide metamorphic aureole during early syn-D3 to early syn-D5. The Murrumbidgee Batholith was emplaced between pre-D3 to early syn-D5, synchronous with the formation of the Cooma Complex. The structural and metamorphic relations indicate that the Murrumbidgee Batholith was the ultimate heat source responsible for the Cooma Metamorphic Complex.D3 structures and metamorphic isograds are subparallel to the batholith margin for over 50 km. This concordance probably extends vertically, suggesting that the isograds also fan outward from the batholith margin. This implies an inverted metamorphic sequence focused on the Murrumbidgee Batholith, although the base has been almost completely removed by erosion in the Cooma Complex. The field evidence at Cooma, combined with previous thermal modelling results, suggest that extensive LPHT metamorphic terranes may represent regional metamorphic aureoles developed beneath high-level granitic batholiths.

Notes: This Special Issue is in celebration of the career contribution of Ron Vernon. It arises from the ‘Ron Vernon Symposium’, which was held as part of the 15th Australian Geological Convention in Sydney in 2000. To date Ron has published more than one hundred scientific papers, several books and contributed widely to international conferences. He is the doyen in the multidisciplinary field of microstructures, which spans petrology and structural geology. However, Ron's range is phenomenal, and he has contributed to many aspects of metamorphism, magmatism and rock deformation. He has drawn on data from his work in these areas to contribute widely to understanding thermal regimes, crustal evolution and tectonics, as exemplified by his ideas about HTLP metamorphism and emplacement of granites. Ron has followed the scientific method in his work; it has led him to many innovative interpretations, some of which undermined established dogma. By example, Ron has been a positive role model for the younger generation. However, for the older generation, he has been something of a bête noire! The papers in this Special Issue cover the range from low- to high-grade metamorphism, from metasomatism to melting, from microstructures to tectonics, and from fieldwork to experiments. It is our hope that in reading them you will take time to think about what has been achieved in the past 40 years, and use this as motivation for what remains to be done.

Notes: Many migmatites and granulites preserve evidence of a clockwise P–T evolution involving decompression (decrease in P) while close to the thermal peak. The extent of post-thermal peak reaction is influenced by several factors, including: (1) the P–T path in relation to invariants in the system and the Clapeyron slopes of the equilibria; (2) the rate of cooling; and (3) the availability of fluid (H2O-rich volatile phase or melt) for fluid-consuming reactions. Reaction may occur between products of a prograde (increasing T) fluid-generating reaction as the same equilibrium is re-crossed in the retrograde (decreasing T) sense. In general, reaction reversal or ‘back reaction’ requires the P–T path to approximate isobaric heating and cooling, without significant decompression, and evolved fluid to remain within the equilibration volume. The larger the decompression segment in the P–T evolution, the more chance there is of crossing different reactions along the retrograde segment from those crossed along the prograde segment. For common pelite compositions, we may generalize by considering three pressure regimes separated by the [Spl, Ms, H2O] invariant in KFMASH (approximately 9 kbar) and the intersection of muscovite breakdown with the H2O-rich volatile phase-saturated solidus (approximately 4 kbar). Reaction reversal cannot occur along P–T paths that traverse around one of these points, but may occur along P–T paths confined to one of the three regimes in between. Additionally, above the solidus, melt segregation and loss potentially change the composition of the equilibration volume; and, the size of the equilibration volume shrinks with decreasing T. Since the proportion of melt to residue in the equilibration volume may change with decreasing size, the composition of the equilibration volume may change throughout the supra-solidus part of the retrograde segment of the P–T evolution. If melt has been lost from the equilibration volume, reaction reversal may not be possible or may be only partial; indeed, the common preservation of close-to-peak mineral assemblages in migmatite and granulite demonstrates that extensive reaction with melt is uncommon, which implies melt isolation or loss prior to crossing potential melt-consuming reactions. Water dissolved in melt is transported through the crust to be exsolved on crystallization at the solidus appropriate to the intrinsic a(H2O). This recycled water causes retrogression at subsolidus conditions. Consideration of the evidence for supra-solidus decompression-dehydration reactions, and review of microstructures that have proven controversial, such as corona and related microstructures, selvage microstructures and ‘late’ muscovite, leads to the conclusion that there is more than one way for these microstructures to form and reminds us that we should always consider multiple working hypotheses!

Notes: The reaction muscovite+cordierite→biotite+Al2SiO5 +quartz+H2O is of considerable importance in the low pressure metamorphism of pelitic rocks: (1) its operation is implied in the widespread assemblage Ms + Crd +And± Sil + Bt + Qtz, a common mineral assemblage in contact aureoles and low pressure regional terranes; (2) it is potentially an important equilibrium for pressure estimation in low pressure assemblages lacking garnet; and (3) it has been used to distinguish between clockwise and anticlockwise P–T paths in low pressure metamorphic settings. Experiments and thermodynamic databases provide conflicting constraints on the slope and position of the reaction, with most thermodynamic databases predicting a positive slope for the reaction. Evidence from mineral assemblages and microtextures from a large number of natural prograde sequences, in particular contact aureoles, is most consistent with a negative slope (andalusite and/or sillimanite occurs upgrade of, and may show evidence for replacement of, cordierite). Mineral compositional trends as a function of grade are variable but taken as a whole are more consistent with a negative slope than a positive slope. Thermodynamic modelling of reaction 1 and associated equilibria results in a low pressure metapelitic petrogenetic grid in the system K2O–FeO–MgO–Al2O3–SiO2–H2O (KFMASH) which satisfies most of the natural and experimental constraints. Contouring of the Fe–Mg divariant interval represented by reaction 1 allows for pressure estimation in garnet-absent andalusite+cordierite-bearing schists and hornfelses. The revised topology of reaction 1 allows for improved analysis of P–T paths from mineral assemblage sequences and microtextures in the same rocks.

Notes: Numerical 3D simulations of the development of spiral inclusion trails in porphyroblasts were conducted in order to test the proposals that (a) 3D spiral geometry differs between the rotation and nonrotation end-member models of spiral formation proposed in the literature, and (b) 3D spiral geometry can be used as a criterion to distinguish between the two end-member models in rocks. Four principal differences are identified between the two sets of simulations: smoothness of spiral curvature; spacing of foliation planes; alignment of individual foliation planes either side of the sphere representing the porphyroblast; and spiral asymmetry with respect to matrix shear sense. Of these differences, only spiral asymmetry and possibly the alignment of individual foliation planes are diagnostic criteria for distinguishing between the end-member models. In the absence of a readily applied test to distinguish the end-member models, interpretation of spiral inclusion trails is problematic. It is necessary to determine complementary evidence to distinguish porphyroblast rotation or nonrotation during spiral formation.

Notes: Metasedimentary rocks generally contain carbonaceous material (CM) deriving from the evolution of organic matter originally present in the host sedimentary rock. During metamorphic processes, this organic matter is progressively transformed into graphite s.s. and the degree of organisation of CM is known as a reliable indicator of metamorphic grade. In this study, the degree of organisation of CM was systematically characterised by Raman microspectroscopy across several Mesozoic and Cenozoic reference metamorphic belts. This degree of organisation, including within-sample heterogeneity, was quantified by the relative area of the defect band (R2 ratio). The results from the Schistes Lustrés (Western Alps) and Sanbagawa (Japan) cross-sections show that (1) even through simple visual inspection, changes in the CM Raman spectrum appear sensitive to variations of metamorphic grade, (2) there is an excellent agreement between the R2 values calculated for the two sections when considering samples with an equivalent metamorphic grade, and (3) the evolution of the R2 ratio with metamorphic grade is controlled by temperature (T). Along the Tinos cross-section (Greece), which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks, the R2 ratio is nearly constant. Consequently, the degree of organisation of CM is not affected by the retrogression and records peak metamorphic conditions. More generally, analysis of 54 samples representative of high-temperature, low-pressure to high-pressure, low-temperature metamorphic gradients shows that there is a linear correlation between the R2 ratio and the peak temperature [T(°C) = −445 R2 + 641], whatever the metamorphic gradient and, probably, the organic precursor. The Raman spectrum of CM can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism. Temperature can be estimated to ± 50 °C in the range 330–650 °C. A few technical indications are given for optimal application.

Notes: Eclogite facies metatroctolites from a variety of Western Alps localities (Voltri, Monviso, Lanzo, Allalin, Zermat–Saas, etc.) that preserve textural evidence of their original form as bimineralic olivine-plagioclase rocks are considered in terms of calculated mineral equilibria in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH). Pseudosections, based on a new petrogenetic grid for NCFMASH presented here, are used to unravel the metamorphic history of the metatroctolites, considering the rocks to consist of different composition microdomains corresponding to the original olivine and plagioclase grains. On the basis that the preservation of the mineral assemblage in each microdomain will tend to be from where on a rock's P–T path the metamorphic fluid phase is used up via rehydration reactions, P–T pseudosections contoured for water content, and P–T path-MH2O (amount of water) pseudosections, are used to examine fluid behaviour in each microdomain. We show that the different microdomains are likely to preserve their mineral assemblages from different places on the P–T path. For the olivine microdomain, the diagnostic mineral assemblage is chloritoid + talc (+ garnet + omphacite). The preservation of this assemblage, in the light of the closed system P–T path-MH2O relationships, implies that the microdomain loses its metamorphic fluid as it starts to decompress, and, in the absence of subsequent hydration, the high pressure mineral assemblage is then preserved. In the plagioclase microdomain, the diagnostic assemblage is epidote (or zoisite) + kyanite + quartz suggesting a lower pressure (of about 2 GPa) than for the olivine microdomain. In the light of P–T path-MH2O relationships, development of this assemblage implies breakdown of lawsonite across the lawsonite breakdown reaction, regardless of the maximum pressure reached. It is likely that the plagioclase microdomain was mainly fluid-absent prior to lawsonite breakdown, only becoming fluid-present across the reaction, then immediately becoming fluid-absent again.

Notes: Dense, CO2-rich fluid inclusions hosted by plagioclases, An45 to An54, of the O.-v.-Gruber- Anorthosite body, central Dronning Maud Land, East Antarctica, contain varying amounts of small calcite, paragonite and pyrophyllite crystals detected by Raman microspectroscopy. These crystals are reaction products that have formed during cooling of the host and the original CO2-rich H2O-bearing enclosed fluid. Variable amounts of these reaction products illustrates that the reaction did not take place uniformly in all fluid inclusions, possibly due to differences in kinetics as caused by differences in shape and size, or due to compositional variation in the originally trapped fluid. The reaction albite + 2anorthite + 2H2O + 2CO2 = pyrophyllite + paragonite + 2calcite was thermodynamically modelled with consideration of different original fluid compositions. Although free H2O is not detectable in most fluid inclusions, the occurrence of OH-bearing sheet silicates indicates that the original fluid was not pure CO2, but contained significant amounts of H2O. Compared to an actual fluid inclusion it is obvious, that volume estimations of solid phases can be used as a starting point to reverse the retrograde reaction and recalculate the compositional and volumetrical properties of the original fluid. Isochores for an unmodified inclusion can thus be reconstructed, leading to a more realistic estimation of P–T conditions during earlier metamorphic stages or fluid capturing.

Notes: High-pressure basic granulites are widely distributed as enclaves and sheet-like blocks in the Huaian TTG gneiss terrane in the Sanggan area of the Central Zone of the North China craton. Four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion, exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles. The P–T conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers. The low-Ca core of growth-zoned garnet, along with inclusion minerals, defines a prograde assemblage (M1) of garnet + clinopyroxene + plagioclase + quartz, yielding 700 °C and 10 kbar. The peak of metamorphism at about 750–870 °C and 11–14.5 kbar (M2) is defined by high-Ca domains in garnet interiors and inclusion minerals of clinopyroxene, plagioclase and quartz. Kelyphites or coronas of orthopyroxene + plagioclase ± magnetite around garnet porphyroblasts indicate garnet breakdown reactions (M3) at conditions around 770–830 °C and 8.5–10.5 kbar. Garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole + plagioclase around garnet formed during the cooling process at about 500–650 °C and 5.5–8 kbar (M4). These results help define a sequential P–T path containing prograde, near-isothermal decompression (ITD) and near-isobaric cooling (IBC) stages.The clockwise hybrid ITD and IBC P–T paths of the HP granulites in the Sanggan area imply a model of thickening followed by extension in a collisional environment. Furthermore, the relatively high-pressures (6–14.5 kbar) of the four metamorphic stages and the geometry of the P–T paths suggest that the HP granulites, together with their host Huaian TTG gneisses, represent the lower plate in a crust thickened during collision. The corresponding upper-plate might be the tectonically overlying Khondalite series, which was subjected to medium- to low-pressure (MP/LP: 7–4 kbar) granulite facies metamorphism with a clockwise P–T path including an ITD segment. Both the HP and the MP/LP granulite facies events occurred contemporaneously at c. 1.90–1.85 Ga in a collisional environment created by the assembly process of the North China craton.

Notes: An eclogite sample from the Grossgockner region of the Hohe Tauern, Austria contains garnet with a pronounced compositional discontinuity between a Mn-rich core and an Fe-rich rim. This jump in composition was caused by a garnet-consuming reaction followed by growth of the garnet rim + omphacite and marks the prograde transition from epidote–amphibolite to eclogite facies metamorphism. Garnet growth ended at peak metamorphic conditions of 570 °C, 17 kbar, but intracrystalline diffusion continued until about 450 °C, 4 kbar on the retrograde path. This garnet overgrowth texture represents a natural diffusion couple and a time span of 1 Myr was calculated from the diffusion profile developing out of the original sharp compositional step. For typical crustal densities, this time corresponds to a minimum average velocity in the range 4.6–7.4 cm yr−1 (for vertical movement), which is one of the fastest exhumation rates reported. The diffusion of all divalent cations of four profiles was modelled, both analytically and numerically. Both approaches gave comparable results, but the times computed for each element were always discrepant up to a factor of 2. Variations of diffusion coefficients within 2 in analytical calculations remedied this and gave consistent upper time limits. Numerical modelling does not require the simplifications introduced in the analytical approach. On the other hand, error propagation was computationally unfeasible with this method.

Notes: Low-T, intermediate to high-P assemblages indicative of the prehnite–pumpellyite, greenschist and blueschist facies are preserved in mélange zones and slivers of oceanic crust within two major fault zones of the turbidite-dominated Lachlan Orogen. In one of these fault zones (Governor Fault Zone), blueschists occur as Franciscan-like blocks in a serpentinite/talc matrix that is interleaved with phyllites and slates, and structurally overlain by a fault slice or duplex of predominantly pillow basalt, chert, and turbidite. The blueschist metavolcanics are interpreted to have formed at 〈 450 °C and at a depth of approximately 21–27 km. The presence of blue amphibole in the blocks, rinds and matrix indicate that the metavolcanics were emplaced in the matrix prior to blueschist metamorphism. Blocks and matrix were partially exhumed, interleaved with tectonic slices of phyllite and slate, and subsequently folded at about 10–12 km depth, inferred from bo values of the dominant mica fabric in the phyllites and slates. Metamorphic P–T is highest in the structurally lowest slice (mélange zone) and lowest in the overlying ophiolitic fault slice, suggestive of an accretionary burial metamorphic pattern formed by underplating of the mélange. In the other fault zone (Heathcote Fault Zone), blueschists transitional to greenschist facies are interpreted to have formed at 〈 450 °C and at a depth of approximately 15–21 km. They occur as blocks in serpentinite/talc-matrix mélange and are also associated with fault slices of oceanic crust. Textural and mineralogical evidence suggests that the protoliths for the blueschists in both fault zones were boninitic pillow lavas. The metamorphic facies and patterns, and the structural and lithological associations, can be interpreted in terms of disruption of oceanic crust and overlying sediments during subduction, and formation of serpentinite-matrix mélange overprinted by blueschist metamorphism either prior to or during underplating of the mélange and duplex formation. The presence of blueschist metavolcanics indicate that these processes occurred at considerable depth. These interpretations have implications for the evolution of large-scale fault zones in noncollisional, convergent oceanic settings.

Notes: Regional variation in the P–T path of the Sambagawa metamorphic rocks, central Shikoku, Japan has been inferred from compositional zoning of metamorphic amphibole. Rocks constituting the northern part (Saruta River area) exhibit a hairpin type P–T path, where winchite/actinolite grew at the prograde stage, the peak metamorphism was recorded by the growth of barroisite to hornblende and sodic amphibole to winchite/actinolite grew at the retrograde stage. In the southern part (Asemi River area), rocks exhibit a clockwise type P–T path, where barroisite to hornblende core is rimmed by winchite to actinolite. The difference in P–T path could suggest a faster exhumation rate (i.e. more rapid decompression) in the southern than in the northern part. On the other hand, physical conditions of deformation during the exhumation stage have been independently inferred from microstructures in deformed quartz. Recrystallized quartz grains in rocks from the low-grade (chlorite and garnet) zones are much more stretched in the southern part (aspect ratio ≥ 4.0) than in the northern part (aspect ratio〈 4.0), indicating a higher strain rate in the former than in the latter. These facts may indicate that the exhumation and strain rates are correlated (i.e. the exhumation rate increases with increasing the strain rate). The difference in the exhumation rate inferred from amphibole zoning between the northern and southern parts could be explained by an extensional model involving normal faulting, where the lower plate can be exhumed faster than the upper plate due to the displacement along the fault. Furthermore, the model may explain the positive correlation between the exhumation and strain rates, because the lower plate tended to support more stress than the upper plate.

Notes: The loss of a metamorphic fluid via the partitioning of H2O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H2O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H2O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely.

Notes: Mixing properties for muscovite–celadonite–ferroceladonite solid solutions are derived from combining available experimental phase equilibrium data with tabulated thermodynamic data for mineral end-members. When a partially ordered solution model is assumed, the enthalpy of mixing among the end-members muscovite–celadonite–ferroceladonite is nearly ideal, although the Gibbs energies of muscovite–celadonite and muscovite–ferroceladonite solutions are asymmetric due to an asymmetry in the entropy of mixing. Thermodynamic consistency is achieved for data on phengite compositions inassemblages with (a) pyrope+kyanite+quartz/coesite (b) almandine+kyanite+quartz/coesite (c)talc+kyanite+quartz/coesite and (d) garnet–phengite pairs equilibrated both experimentally at high temperatures and natural pairs from low-grade schists. The muscovite–paragonite solvus has been reanalysed using the asymmetric van Laar model, and the effects of the phengite substitution into muscovite have been quantitatively addressed in order to complete the simple thermodynamic mixing model for the solid solution among the mica end-members. Results are applied to a natural pyrope–coesite–phengite–talc rock from the Western Alps, and to investigate the conditions under which biotite-bearing mica schists transform to whiteschist-like biotite-absent assemblages for average pelite bulk compositions.

Notes: Three texturally distinct symplectites occur in mafic granofels of the Arthur River Complex at MtDaniel, Fiordland, New Zealand. These include symplectic intergrowths of clinopyroxene and kyanite, described here for the first time. Pods of mafic granofels occur within the contact aureole of the Early Cretaceous Western Fiordland Orthogneiss batholith. The pods have cores formed entirely of garnet and clinopyroxene, and rims of pseudomorphous coarse-grained symplectic intergrowths of hornblende and clinozoisite that reflect hydration at moderate to high-P. These hornfelsic rocks are enveloped by a hornblende–clinozoisite gneissic foliation (S1). Narrow garnet reaction zones, in which hornblende and clinozoisite are replaced by garnet–clinopyroxene assemblages, developed adjacent to fractures and veins that cut S1. Fine-grained symplectic intergrowths of (1) clinopyroxene and kyanite and (2) clinozoisite, quartz, kyanite and plagioclase form part of the garnet reaction zones and partially replace coarse-grained S1 hornblende and clinozoisite. The development of the garnet reaction zones and symplectites was promoted by dehydration most probably following cooling of the contact aureole. Maps of oxide weight percent and cation proportions, calculated by performing matrix corrections on maps of X-ray intensities, are used to study the microstructure of the symplectites.

Notes: Eclogite facies carbonate rocks have been discovered associated with the granulite–eclogite transitional rocks within Bergen Arc system, Caledonian Orogen of western Norway. The local occurrences of marbles and calc-silicates are found subparallel to the mafic eclogite facies shear zones on Holsnøy Island. Marbles contain the assemblage calcite (Ca0.99Sr0.01CO3), calcian strontianite (Ca0.18−0.44Sr0.53−0.84CO3), clinopyroxene (Jd7−32), epidote/allanite (Ps0−33), titanite, garnet (Alm52−56Grs28−33Pyp11−16), barite (Ba0.90−0.99Sr0.01−0.10SO4), celestine (Sr0.67−0.98Ba0.01−0.23Ca0.01−0.11SO4), and one apparently homogeneous grain of intermediate composition (Ba0.49Ca0.01Sr0.50SO4). Adjacent eclogites have clinopyroxene with similar jadeite contents (Jd14−34) and similar garnet (Alm51−60Grs26−36Pyp8−14) compositions. The marbles have high contents of Sr (9500–11000 p.p.m) and Y (115–130 p.p.m). However, low concentrations of some key trace elements (110–160 p.p.m. Ba and 〈5 p.p.m. Nb) appear to indicate that the marble is not a metamorphosed carbonatite. The 87Sr/86Sr ratios range from 0.7051 to 0.7059. Field and petrological relationships suggest that metasomatic reactions and fluids played a significant role in producing and/or modifying the marbles. The breakdown of scapolite in the granulite into carbonates and sulphates during eclogite facies metamorphism may have contributed to the metasomatic formation of the marbles along shear zones.Fluids involved during subduction are an important catalyst for metamorphism and are recognized to have played a critical role in the localized transformation from granulite to eclogite in the Holsnøy Island area. Thermobarometry indicates 640–690 °C and 18–20 kbar for adjacent eclogites and temperatures of 580–650 °C for the calc-silicates. The marble assemblages are consistent with fluid that is dominantly comprised of H2O (XCO2 〈 0.03) under high-pressure conditions. Phase equilibria of the marbles constrain the fO2 of the fluids and imply oxidizing conditions of the deep crustal fluids. At present the source of the fluids remains unresolved. The results provide additional insights into the variable and evolving nature of fluids related to subduction and high-pressure metamorphism.

Notes: We formulate an algorithm for the calculation of stable phase relations of a system with constrained bulk composition as a function of its environmental variables. The basis of this algorithm is the approximate representation of the free energy composition surfaces of solution phases by inscribed polyhedra. This representation leads to discretization of high variance phase fields into a continuous mesh of smaller polygonal fields within which the composition and physical properties of the phases are uniquely determined. The resulting phase diagram sections are useful for understanding the phase relations of complex metamorphic systems and for applications in which it is necessary to establish the variations in rock properties such as density, seismic velocities and volatile-content through a metamorphic cycle. The algorithm has been implemented within a computer program that is general with respect to both the choice of variables and the number of components and phases possible in a system, and is independent of the structure of the equations of state used to describe the phases of the system.

Notes: Migmatitic cordierite gneisses within the Achankovil Zone (AZ) of southern Pan-African India record melt-producing and subsequent melt-consuming mineral reactions. Early mineral assemblages Bt-Sil-Qtz and Bt-Sil-Spl, deduced from inclusion textures in garnet prophyroblasts, break down via successive dehydration melting reactions to high-T phase assemblages (e.g. Grt-Crd-Liq, Opx-Liq, Spl-Crd-Liq). Later back reactions between the restite and the in situ crystallizing melt resulted in thin cordierite coronas separating garnet from the leucosome, and partial resorption of garnet to Opx-Crd or Crd-Bt-Qtz symplectites. Leucosomes generally display a moderate (low-strain gneisses) to strong (high-strain gneisses) depletion of alkali feldspar attributed to mineral-melt back reactions partly controlled by the degree of melt segregation.Using a KFMASH partial petrogenetic grid that includes a melt phase, and qualitative pseudosections for microdomains of high and low Al/Si ratios, the successive phase assemblages and reaction textures are interpreted in terms of a clockwise P–T path culminating at about 6–7 kbar and 900–950 °C. This P–T path is consistent with, but more detailed than published results, which suggests that taking a melt phase into account is not only a valid, but also a useful approach. Comparing P–T data and lithological and isotopic data for the AZ with adjacent East Gondwana fragments, suggests the presence of a coherent metasedimentary unit exposed from southern Madagascar via South India (AZ) and Sri Lanka (Wanni Complex) to the Lützow–Holm Bay in Eastern Antarctica.

Notes: Fine grained rodingite-like rocks containing epidote, clinozoisite, garnet, chlorite, phengite and titanite occur within antigorite serpentinite boudins from the high-pressure metamorphic Maksyutovo Complex in the Southern Urals. Pseudomorphs after lawsonite, resorption of garnet by chlorite and phengite and stoichiometry suggest the reaction lawsonite + garnet + K-bearing fluid → clinozoisite + chlorite + phengite, and define a relic assemblage of lawsonite + garnet + chlorite + titanite ± epidote as well as a later post-lawsonite assemblage of clinozoisite + phengite + chlorite + titanite. The reaction lawsonite + titanite → clinozoisite + rutile + pyrophyllite + H2O delimits the maximum stability of former lawsonite + titanite to pressures 〉13 kbar. P–T conditions of 18–21 kbar/520–540 °C result, if the average chlorite, Mg-rich garnet rim and average epidote compositions are used as equilibrium compositions of the former lawsonite assemblage. These estimates indicate a similar depth of formation but lower temperatures to those recorded in nearby eclogites. The metamorphic conditions of the lawsonite assemblage are considerably higher than previously suggested and, together with published structural data, support a model in which a normal fault within the Maksyutovo complex acted as the major transport plane of eclogite exhumation.The maximum Si content of phengite and minimum Fe content in clinozoisite constrain the metamorphic conditions of the later pseudomorph assemblage to be 〉4.5 kbar and 〈440 °C. Rb–Sr isotopic dating of the pseudomorph assemblage results in a formation age of 339 ± 6 and 338 ± 5 Ma, respectively. These results support the recent exhumation models for this complex.

Notes: Exotic blocks of eclogite from distant localities along the Northern Serpentinite Melange of Cuba have comparable P–T histories that include high-pressure prograde sections (450–600 °C, 〉15 kbar) associated with subduction of oceanic lithosphere, and retrograde sections within the albite–epidote amphibolite facies (〈500 °C, 〈10 kbar) related to melange uplift. 40Ar/39Ar and Rb/Sr cooling ages (118–103 Ma) of one of the blocks indicate pre-Aptian subduction and Aptian–Albian uplift. Detailed X-ray imaging and profiling further reveals that minerals in these eclogite blocks (notably garnet and amphibole) display subtle but well defined oscillatory zoning that developed along the prograde trajectory of the rocks, previous to attainment of peak eclogitic conditions. The chemistry (e.g. coupled changes of Mg# and Mn in garnet, and of Si, Ti, Al and Na in amphibole) and geometry (euhedral to anhedral shapes) of the oscillations can be interpreted in terms of subtle fluctuations in P–T during the general prograde subduction-related metamorphic path. A (near-) equilibrium model is presented for the formation of oscillations at near peak conditions by means of recurrent dissolution-growth reaction processes. This model for near-peak conditions, and the chemical signatures of earlier oscillations (notably in amphibole), suggest that episodes of retrogression (upward movement?) affected parts of the subducting slab. It is proposed that these retrograde episodes record the tectonic rupture of the subducting slab and, probably, of the upper plate mantle, either due to the intrinsic dynamic behaviour of subduction systems or to the effects of the plate-tectonic rearrangement of the Caribbean region during the Early Cretaceous.

Notes: The relative timing of two discrete pulses of metamorphic fluid flow is constrained based on chemical zoning in several garnet crystals from Kvaløya, Troms, northern Norway. The garnet crystals measured 1–2 cm in diameter and were contained within c. 1.6 Ga, staurolite grade metasediments. Major element zoning indicates that garnet grew under normal prograde conditions in the garnet and/or staurolite zones.Timing constraints are based on comparisons between major and trace element chemical zoning, oxygen isotope (δ18O) zoning and deformational (inclusion trail) zoning in one of the garnet. We interpret at least two pulses of metamorphic fluid flow. The first pulse occurred during the syn-tectonic growth interval. The δ18O zoning was reversed relative to ‘normal’ prograde zoning and the δ18O maximum was located within the syn-tectonic growth zone, displaced 3–4 mm from the garnet core. The fluid might have been sourced in neighbouring calcareous pelites and may also have caused formation of an Y ring. The second (and subsequent) pulse(s) occurred during/after the post-tectonic growth interval. δ18O was locally increased at the garnet rim, particularly where the rim was sheared. The incomplete rim was also enriched in calcium. Transport of oxygen and calcium by metamorphic fluids is well documented. Transport of Y is both problematic and poorly understood, but might have been facilitated by complexing with F and/or CO2.

Notes: Creation of pathways for melt to migrate from its source is the necessary first step for transport of magma to the upper crust. To test the role of different dehydration-melting reactions in the development of permeability during partial melting and deformation in the crust, we experimentally deformed two common crustal rock types. A muscovite-biotite metapelite and a biotite gneiss were deformed at conditions below, at and above their fluid-absent solidus. For the metapelite, temperatures ranged between 650 and 800 °C at Pc=700 MPa to investigate the muscovite-dehydration melting reaction. For the biotite gneiss, temperatures ranged between 850 and 950 °C at Pc=1000 MPa to explore biotite dehydration-melting under lower crustal conditions. Deformation for both sets of experiments was performed at the same strain rate (ε.) 1.37×10−5 s−1. In the presence of deformation, the positive ΔV and associated high dilational strain of the muscovite dehydration-melting reaction produces an increase in melt pore pressure with partial melting of the metapelite. In contrast, the biotite dehydration-melting reaction is not associated with a large dilational strain and during deformation and partial melting of the biotite gneiss melt pore pressure builds more gradually. Due to the different rates in pore pressure increase, melt-enhanced deformation microstructures reflect the different dehydration melting reactions themselves. Permeability development in the two rocks differs because grain boundaries control melt distribution to a greater extent in the gneiss. Muscovite-dehydration melting may develop melt pathways at low melt fractions due to a larger volume of melt, in comparison with biotite-dehydration melting, generated at the solidus. This may be a viable physical mechanism in which rapid melt segregation from a metapelitic source rock can occur. Alternatively, the results from the gneiss experiments suggest continual draining of biotite-derived magma from the lower crust with melt migration paths controlled by structural anisotropies in the protolith.

Notes: Observations of oriented SiO2 precipitates in omphacite from eclogite with tholeiitic basalt protolith bordering the Alpe Arami garnet peridotite massif, Ticino, Switzerland, and petrological studies of the eclogitic mineral assemblages, suggest that this rock was subjected to higher-pressure metamorphism than previously realized. We employed various calibrations of the Fe2+ − Mg exchange thermometer and calculations of equilibria with thermodynamic data, considering the calcium–Tschermak's component (CaAl2SiO6), of garnet-pyroxene pairs. From these calculations, it is concluded that the eclogitic lenses have recorded at least four stages of mineral growth corresponding to the following: Stage I (prograde) c. 2.4 GPa; 700 °C; Stage IIa (maximum recorded grade) c. 7.0 GPa; 1100 °C; Stage IIb (retrograde) c. 3.7 GPa; 900 °C; Stage III (retrograde) c. 2.1 GPa; 750 °C. Because of the preservation of Stage I, a relatively rapid subduction and exhumation of Alpe Arami eclogite is suggested. The exhumation path of the eclogitic rock is in good agreement with most exhumation paths inferred for the Alpe Arami garnet lherzolite proposed previously by several authors based upon a variety of different observations, although the eclogite and peridotite exhumation paths may diverge at depths greater than 120 km.

Notes: The Tenda crystalline massif (northern Corsica) is a fragment of the western Corsica basement involved in the Alpine orogeny. Rhyolite dykes crosscutting the gabbroic complex of Bocca di Tenda (southern sector of the Tenda crystalline massif) show an unusual metamorphic mineral assemblage, defined by jadeite-bearing (up to 46 mol percentage) aegirine, riebeckite, celadonite-rich phengite (Si=3.50–3.65 apfu), quartz, albite and K-feldspar. Jadeite-bearing aegirine and riebeckite mostly occur as coronas around jadeite-free aegirine and arfvedsonite, respectively, which both are relics of igneous origin. This metamorphic assemblage reflects the peralkaline compositions, which are characterised by anomalously high contents of SiO2 and Na2O, and negligible CaO and MgO. The evolved rocks of the gabbroic sequence (quartz-diorites to tonalites) and the surrounding granitoids are characterised by the development of riebeckite/ferroglaucophane, epidote, celadonite-rich phengite and albite, thus pointing to a metamorphic crystallization in the epidote-blueschist facies. In all the studied rocks, metamorphic reactions were controlled by fluid-assisted mass-transfer through grain boundaries and microfractures. The different mineral assemblages allow the peak P–T metamorphic conditions to be constrained to between 0.8 GPa/300 °C and 1.1 GPa/500 °C. These estimates attest to a geothermal gradient (dT/dP) of 10–13 °C km−1 and indicate that the Tenda crystalline massif was buried to a minimum depth of 27 km during the Alpine orogeny. The blueschist facies recrystallization in the Tenda crystalline massif has been related to the cessation of an eastward-dipping subduction event.

Notes: Growth rates of wollastonite reaction rims between quartz and calcite were experimentally determined at 0.1 and 1 GPa and temperatures from 850 to 1200 °C. Rim growth follows a parabolic rate law indicating that this reaction is diffusion-controlled. From the rate constants, the D′δ-values of the rate-limiting species were derived, i.e. the product of grain boundary diffusion coefficient D′ and the effective grain boundary width, δ. In dry runs at 0.1 GPa, wollastonite grew exclusively on quartz surfaces. From volume considerations it is inferred that (D′CaOδ)/(D′SiO2δ)≥1.33, and that SiO2 diffusion controls rim growth. D′SiO2δ increases from about 10−25 to 10−23 m3 s−1 as temperature increases from 850 to 1000 °C, yielding an apparent activation energy of 330±36 kJ mol−1. In runs at 1 GPa, performed in a piston-cylinder apparatus, there were always small amounts of water present. Here, wollastonite rims always overgrew calcite. Rims around calcite grains in quartz matrix are porous and their growth rates are controlled by a complex diffusion-advection mechanism. Rim growth on matrix calcite around quartz grains is controlled by grain boundary diffusion, but it is not clear whether CaO or SiO2 diffusion is rate-limiting. D′δ increases from about 10−21 to 10−20 m3 s−1 as temperature increases from 1100 to 1200 °C. D′SiO2δ or D′CaOδ in rims on calcite is c. 10 times larger than D′SiO2δ in dry rims at the same temperature. Growth structures of the experimentally produced rims are very similar to contact-metamorphic wollastonite rims between metachert bands and limestone in the Bufa del Diente aureole, Mexico, whereby noninfiltrated metacherts correspond to dry and brine-infiltrated metacherts to water-bearing experiments. However, the observed diffusivities were 4 to 5 orders of magnitude larger during contact-metamorphism as compared to our experimental results.

Notes: Fiordland, New Zealand exposes the lower crustal root of an Early Cretaceous magmatic arc that now forms one of Earth's most extensive high-P granulite facies belts. The Arthur River Complex, a dioritic to gabbroic suite in northern Fiordland, is part of the root of the arc, and records an Early Cretaceous history of emplacement, tectonic burial, and high-P granulite facies metamorphism that accompanied partial melting of the crust. Late random intergrowths of kyanite, quartz and plagioclase partially pseudomorph minerals in the earlier high-T assemblages of the Arthur River Complex, indicating high-P cooling of an over thickened crustal root by c. 200 °C. The kyanite intergrowths are themselves partially pseudomorphed by paragonite, commonly in the presence of phengitic white mica. Biotite–plagioclase intergrowths that partially pseudomorph phengitic white mica and diopside–plagioclase intergrowths that partially pseudomorph jadeitic diopside, combined with published thermochronology results, are consistent with later rapid decompression. A short duration anticlockwise P–T path may be explained by the high-P juxtaposition of comparatively cool upper crustal rocks following their tectonic burial and under thrusting during the waning stages of Early Cretaceous orogenesis. This was then followed by the decompression giving the rapid exhumation within 20 Myr of peak metamorphism, as suggested by the isotopic data.

Notes: Abstract. This paper compares nitrate leaching losses from organic farms, which depended on legumes for their nitrogen inputs (66 site years) with those from conventional farms using fertilizers under similar cropping and climatic conditions (188 site years). The conventional farms were within Nitrate Sensitive Areas in England, but sites following special practices associated with that scheme were excluded. Nitrate losses during the organic ley phase (including the winter of ploughing out) were similar (45 kg N ha–1) to those from conventional long-term grass receiving fertilizer N inputs of less than 200 kg N ha–1 (44 kg N ha–1) and from the grass phase of conventional ley-arable rotations (50 kg N ha–1). Losses from conventional grass receiving higher N inputs were greater than from organic or less intensive grass. Nitrate losses following arable crops averaged 47 and 58 kg N ha–1 for the organic and conventional systems respectively, with part of the difference being due to the greater proportion of non-cereal break crops in the latter. Thus under similar cropping, losses from organic systems are similar to or slightly smaller than those from conventional farms following best practice.

Notes: Abstract. In the Sahel, promising technologies for agricultural intensification include millet stover mulching and ridging. A four year on-farm experiment was set-up in order to assess the effect of various combinations of these two technologies on crop development and yield in a millet (Pennisetum glaucum (L.) R. Br.) - cowpea (Vigna unguiculata (L.) Walp.) intercropping system. Treatments included bare surface, ridging, a surface applied banded millet stover mulch (2 t ha–1) and a banded millet stover mulch (2 t ha–1) buried in ridges. The latter three treatments were implemented exclusively in the cowpea rows, with an annual rotation between the millet and cowpea rows. On bare and ridged plots, millet yields fell below 100 kg grain ha–1 after the first year. This was ascribed mainly to soil acidification and loss of soil organic matter rather than to soil physical constraints or water availability despite extensive surface crusting and high soil penetration resistance and bulk density. Compared to the bare plots, ridging increased cowpea hay production by 330% over the four years which was attributed to lower soil penetration resistance and bulk density but also to a reduction of 0.15 cmol+ kg–1 exchangeable acidity in the ridges. Except during the severe drought year of 1997, millet grain yield in the banded mulch treatment remained fairly stable over time at 526 ± 9 kg ha–1. However, a detailed analysis revealed yield compensation mechanisms between various yield components depending on the timing of occurrence of the abiotic stresses. Cowpea productivity was always higher in buried banded mulch plots than in surface applied banded mulch plots but the former treatment appeared unable to sustain millet yields. This decline was attributed to a greater nutrient uptake by cowpea and more rapid acidification in the buried mulch treatment compared to the banded mulch treatment.

Notes: Abstract. Nutrient balance calculations have been advocated as indicators of the risk of nitrate loss from agricultural land. To explore this concept, a spatially distributed UK agricultural nitrogen balance was derived using annually updated statistics. The mean UK N surplus for 1995 was 115 kg N ha–1, made up of 51 kg ha–1for arable land, 140 kg ha–1 for agricultural grassland (excluding rough grazing) and an additional 14 kg N ha–1for agricultural land from pig and poultry units. Nitrogen surpluses were greater in lowland grassland (mainly in western, wetter areas) than in arable areas. However nitrate concentrations in rivers were generally greater in arable areas. The relationship between N balance and nitrate leaching was very different for grassland and arable systems, and was also sensitive to climate, level of inputs and management practices. Nitrogen surplus was therefore weakly or even negatively correlated with river nitrate concentrations or loads. A positive correlation was found only where the comparison was restricted to grassland-dominated catchments. Nitrogen surplus calculations identified areas of very high livestock densities, which would be associated with increased risk of pollution. However their use in isolation as indicators of N leaching, or of progress towards mitigation, could be misleading especially if comparing areas differing in land use, climate or soil type.

Notes: Abstract. Dynamic simulation models are increasingly used in environmental and agricultural science. Here we present a method that allows models to be used to determine optimum timing of sampling for field trials. The model is used to decide when to concentrate sampling effort before the field trial begins. The model chosen to design sampling strategy should include an appropriately sensitive description of all processes that influence measurements significantly. The simulation is run, using predicted weather data, to generate the full time series before the trial begins. Every point in the simulation is considered initially to be a potential sampling point. The potential error due to not including a measurement at each point is calculated using the ‘dot-to-dot’ method of b10Smith et al. (2002) by omitting simulated values consecutively. The calculated potential error provides a measure of the priority that should be given to sampling at each point. Where the error introduced by omitting the simulated value exceeds an acceptable error, the value at the last discernible time step should be measured so that all statistically significant changes in the system can be observed. The output from the calculation is a plan of sampling times needed to capture all statistically significant events that are likely to occur over the course of the trial.

Notes: Abstract. In grazed dairy pasture systems, a major source of NO3– leached and N2O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3– leaching and N2O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free-draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO3–-N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO3–-N leaching loss in a grazed paddock from 118 to 46 kg N ha–1 yr–1. The NO3–-N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L–1, with the latter being below the drinking water guideline of 11.3 mg N L–1. Total N2O emissions following two urine applications were reduced from 46 kg N2O-N ha–1 without DCD to 8.5 kg N2O-N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha–1 yr–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO3– leaching and N2O emissions.

Notes: Abstract. This paper describes a study of 37 farms in the Batinah region of Oman where fodder crops and date palms are grown using saline irrigation water. Soil water salinities (εs) range from 2 to 50 dS m–1. Soil water salinity depends on irrigation water quality and management factors such as the amount and frequency of irrigation and the area of the irrigation basin relative to the vegetation canopy. An irrigation management model for soil salinity control IMAGE has been developed, based on the salt balance of the profile assuming that the εs is in equilibrium with the irrigation water. The input parameters required to run the model include the annual water application, irrigation interval, soil textural class, potential evaporation, the ratio of crop canopy to irrigation basin area and the salinity of irrigation water. Verification of the model using rather uncertain data from a survey of the farms showed that this simple approach predicted εs to within 2.5 dS m–1 in 82% of cases. The model showed that εs was highly sensitive to the size of irrigation basin and the amount and scheduling of irrigation, and so provides a tool for optimizing salinity management.

Notes: Abstract. There is increasing evidence that phosphorus (P) can be transferred to surface waters by leaching as well as by erosion and surface runoff. Recently it has been suggested that P soluble in 0.01 m CaCl2 may be a good indicator of the specific Olsen-P concentration (usually termed the ‘Change Point’) at which the rate of P leaching from soil suddenly increases and poses a greater threat of eutrophication to standing waters. We know that these ‘Change Points’ vary from soil to soil but, so far, we do not fully understand the mechanism(s) involved. Here, we combine methods for assessing isotopically exchangeable P and P sequential fractionation to gain an insight into the processes which cause this sudden increase in P solubilization. We suggest that Change-Points simply define the asymtote of rapid desorption isotherms relating to that P which is most readily isotopically exchangeable (i.e at 24 h –33P24) with the soil solution. This involves ligand exchange at hydroxyl sites associated with Fe and Al cations, which is kinetically governed by the concentration of surface complexes on soil minerals. Individual Change-Points reflect the mineralogy and surface chemistry of different soil types. Laboratory and field measurements of the Olsen-P Change-Point reflect these surface phenomena and are similar. Olsen-P extracts the portion of the exchangeable pool that most readily controls solution P, and the Olsen-P/33P24 ratio is linearly related to Olsen-P Change-Points. This may provide a method for estimating P Change-Points where gradients of soil P are not available.

Notes: Abstract. Soil removed on sugarbeet (Beta vulgaris L.) at harvest may be an important factor in soil degradation causing significant decline in soil productivity. This study evaluated soil losses on sugarbeet and estimated the cost of plant nutrients lost by this process. The losses were calculated using data from the agricultural reports published by the General Directorate of the Turkish Sugar Industry. Organic matter and plant available nutrient contents of soils removed from sugarbeet fields were determined. It was estimated that approximately 30 000 t of soil is lost annually in Erzurum, and 1.2 million t in the whole of Turkey. The cost of N, P and K losses is approximately 60 000 US$ annually for the study area.

Notes: Abstract. Inputs and outputs of sulphur (S) were quantified over a three year period using field lysimeters containing undisturbed 60 cm deep soil monoliths of a sandy loam. There were four treatments, including a control (no S) and three forms of sulphur fertilizers: ammonium sulphate (AS); micronized elemental sulphur (MS0); and bentonite clay and elemental sulphur mixture (BS0). Sulphur was applied at the beginning of the experiment in autumn at 50 kg ha–1. Atmospheric deposition varied between 6.7 and 7.8 kg S ha–1 yr–1. Leaching losses of S ranged from 35 kg ha–1 in the control to 83 kg ha–1 in the AS treatment over three years, with dissolved organic S accounting for 6–10% of the S leached. In the first year, 7, 26 and 72% of the applied S was lost to drainage water in the BS0, MS0 and AS treatments, respectively, and the percentages increased to 33, 75 and 96% by the end of year 3. No significant differences in sulphur uptake by herbage were found in any of the harvests except a significant increase in the BS0 treatment in the second cut of the second year. Over three years, total S outputs exceeded total S inputs in all treatments, with the control and the AS treatments showing a larger S deficit (34–35 kg ha–1) than the MS0 (23 kg ha–1) and BS0 (7 kg ha–1) treatments. The deficits indicate a depletion of soil S, probably through net mineralization of organic S. The results confirm that sulphate was highly mobile and prone to leaching under the experimental conditions, whereas the slow release characteristics of elemental S, particularly BS0, led to smaller leaching losses and larger residual values.

Notes: Nitrate and Man: Toxic, harmless or beneficial? By J. L ‘Hirondel and J-L L ‘Hirondel.

Notes: Abstract. In general, agricultural management has focused on differences between fields or on the gross differences within them. Recent developments in agricultural technology, yield mapping, Global Positioning Systems and variable rate applications, have made it possible to consider managing the considerable variation in soil and other properties within fields. This system is known as precision agriculture. More precise management of fields depends on a better understanding of the factors that affect crop input decisions. This paper examines the spatial variation in crop yield, soil nutrient status and soil pH within two agricultural fields using geostatistics. The observed properties vary considerably within each field. The relation between yield and the measured soil properties appears to be weak in general. However, the range of spatial correlation for yield, shown by the variogram, is similar to that of the soil chemical properties. In addition the latter changed little over two years. This suggests that information on the scale of variation of soil chemical properties can be derived from yield maps, which can also be used as a guide to a suitable sampling interval for soil properties.

Notes: Abstract. This study employed both natural and social sciences to examine the relationship between resources and economic development in the Red Soil Zone along the coast of South China. Based on the data collected by field investigation and laboratory analysis as well as from literature sources, the authors discuss the environmental problems and the main factors influencing them by using the case of Guangdong province. The results indicate that there are three important problems of Red Soil utilization: soil degradation and pollution, soil erosion and geological hazards. The main reasons for these problems involve the physical and chemical characteristics and mineral composition of the soil, climate and meteorological changes and human activities. The latter is currently the dominant factor influencing the change and deterioration of the Red Soils.

Notes: Abstract. The dual porosity soil water and contaminant transport model MACRO was tested for its suitability to represent water flows and leaching of phosphorus (P) through field drains following spreading of slurry. These flows are characterized by very high loadings of P, including a high proportion in colloidally attached form, for about one week following winter spreading of slurry, followed by quite a rapid decline to the low background level. Use was made of the option in MACRO for representing colloid facilitated contaminant transport. The model simulates transport through macropores and soil matrix pores (micropores) of contaminant carrying colloids, as well as trapping of colloids by straining and filtration using an adaptation of standard filtration equations. Calibration involved selecting soil hydraulic parameters, colloid filtration coefficients and P sorption characteristics for two soils from measured and literature values. Both P in solution and P attached to colloids were represented in simulated outputs. Reasonable agreement was found between simulated and measured water and leached P flows. Work with the model suggests that macropore flow through the soil to field drains of colloidally transported P is an important component of water pollution associated with slurry spreading

Notes: Abstract. Rising atmospheric CO2 concentrations and their association with global climate change have led to several major international initiatives to reduce net CO2 emissions, including the promotion of bioenergy crops such as short rotation coppice (SRC) willow. Although the above-ground harvested bio-fuel is likely to be the major contributor to the CO2 mitigation potential of bioenergy crops, additional carbon may be sequestered through crop inputs into plantation soils.  Here, we describe a process-based model specifically designed to evaluate the potential for soil carbon sequestration in SRC willow plantations in the UK. According to the model predictions, we conclude that the potential for soil carbon sequestration in these plantations is comparable to, or even greater than, that of naturally regenerating woodland. Our preliminary, site-specific model output suggests that soil carbon sequestration may constitute about 5% of the overall carbon mitigation benefit arising from SRC plantations. Sensitivity analyses identified the following factors as the principal controls on rates and amounts of soil carbon sequestration under SRC: carbon inputs (net primary production), decomposition rates of the major soil carbon pools, initial soil carbon content (an inverse relationship with rates of soil carbon sequestration), crop/plantation management, and depth of soil being influenced by the bioenergy crop. Our results suggest that carbon sequestration potential is greatest in soils whose carbon content has been depleted to relatively low levels due to agricultural land use practices such as annual deep ploughing of agricultural soils.

Notes: Abstract. Leaching of phosphorus (P) from agricultural land is the major cause of eutrophication of surface waters in Northern Ireland. However, soil testing using the Olsen method has shown that while soil P in some catchment areas of the Province is low, surface waters within these catchments are, nonetheless, every bit as eutrophic as other local catchments where soil P is high. Soil P measurements on over 6000 samples from Northern Ireland soils (A horizon only) have indicated that Olsen-P values of improved grassland on most parent materials are linearly related to animal intensification. Exceptions are soils derived from peat, marl and basalt. For each of the latter soils, the measured Olsen-P was shown to be around 10 mg L–1 lower than expected for farms with similar intensification on other parent materials. In particular, the mean Olsen-P values of samples from basaltic soils under grass with total Fe above 62 g kg–1 and total Mg above 16 g kg–1 were significantly lower than those from basaltic soils with low total Fe (〈37 g kg–1) and total Mg (〈8 g kg–1). As a result of the depressed Olsen-P value, excessive quantities of P may be applied to these soils to maintain a recommended soil P index thereby enhancing the potential for nutrient enrichment of adjacent surface waters. In such cases, coworkers have shown that acid ammonium oxalate may be a better extractant than bicarbonate as an indicator of plant-available P.

Notes: Abstract. This paper reviews current understanding of soil structure, the role of soil organic matter (SOM) in soil structure and evidence for or against better soil physical condition under organic farming. It also includes new data from farm case studies in the UK. Young SOM is especially important for soil structural development, improving ephemeral stability through fungal hyphae, extracellular polysaccharides, etc. Thus, to achieve aggregate stability and the advantages that this conveys, frequent input of fresh organic matter is required. Practices that add organic material are routinely a feature of organically farmed soils and the literature generally shows that, comparing like with like, organic farms had at least as good and sometimes better soil structure than conventionally managed farms. Our case studies confirmed this. In the reviewed papers, SOM was generally larger on the biodynamic/organic farms because of the organic additions and/or leys in the rotation. We can therefore hypothesize that, because it is especially the light fraction of SOM that is involved in soil structural development, soil structure will improve in a soil to which fresh organic residues are added regularly. Thus, we argue it is not the farming system per se that is important in promoting better physical condition, but the amount and quality of organic matter returned to a soil.

Notes: Abstract. Soil fertility is defined as the ability of a soil to provide the conditions required for plant growth. It is a result of the physical, chemical and biological processes that act together to provide nutrients, water, aeration and stability to the plant, as well as freedom from any substances that may inhibit growth. Within this definition, it is useful to distinguish between those components of fertility which change relatively slowly, perhaps over the course of a rotation, or in some cases, decades, and the more immediate contribution from materials such as fertilizers and manures. The term ‘inherent fertility’ is used to describe these more stable characteristics, while recognising that they are, to a large extent, products of soil management. We conclude that, although nutrient management in organically managed soils is fundamentally different to soils managed conventionally, the underlying processes supporting soil fertility are not. The same nutrient cycling processes operate in organically farmed soils as those that are farmed conventionally although their relative importance and rates may differ. Nutrient pools in organically farmed soils are also essentially the same as in conventionally managed soils but, in the absence of regular fertilizer inputs, nutrient reserves in less-available pools will be of greater significance.

Notes: Abstract. In an exploratory study land use in 27 catchments covering most of England and Wales was assessed (using the land use classification devised by the then Institute of Terrestrial Ecology, now a part of the Centre for Ecology and Hydrology) and related to loads and concentrations of total nitrogen, phosphorus (mainly as orthophosphate (Op)) and some pesticides in river flows reaching the surrounding seas in the years 1990–1993. There are good correlations between seven land use types and the concentrations of total nitrogen (r=0.83) and Op (r=0.73) entering the seas. The correlations for individual land use types are best for arable land: total nitrogen, r=0.77; Op, r=0.65; and are positive. However, except for the mixed arable and grassland, the relationships between the other five land use types (improved grassland, upland grassland, upland moorland, upland mixed, and afforested and upland) and contaminant concentrations are negative. If data from the Mersey catchment are discarded, on the grounds that contaminant concentrations in the river seem unduly high, correlations between land use and contaminant concentrations reaching the seas are improved for all land uses: total nitrogen, r=0.89; Op, r=0.83; and atrazine, r=0.78. Loads and concentrations of pollutants in rivers entering the sea could be used to validate models of losses from catchments. Models may need to take greater account of runoff and transport of soil particles than they do presently.

Notes: Abstract. Uptake in grass crops of ammonium acetate lactate extractable K (KAL) and reserve K (interlayer K + structural K) in soil was studied in 16 field experiments at different locations on a range of mineral soil types in Norway. The K uptake from soil, both from KAL and reserve K, was considerable, often even at the highest level of K fertilizer. During three years, only on the sandy soils with a low level of acid soluble K (KHNO3 minus KAL) was there a yield response to K fertilization. The KAL values declined rapidly and flattened off at a ‘minimum level’ which differed with soil type. This minimum level for KAL is a useful parameter in fertilizer planning, because the grass usually took up the K in excess of the minimum level over two years. The minimum value of KAL was significantly correlated with the content of clay + silt in soil. The decrease in KAL during the growing season was closely correlated to the KAL value in spring minus the minimum value and, therefore, the amount of K supplied to the grass from the KAL fraction can be calculated. Furthermore, the KAL value for the following spring may be estimated. The release from reserve K was partially related to acid soluble K.

Notes: Abstract. Soil organic carbon and total nitrogen stocks are presented for Central and Eastern Europe. The study uses the soil geographic and attribute data held in a 1:2 500 000 scale Soil and Terrain (SOTER) database, covering Belarus, Bulgaria, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Moldova, Poland, Romania, the Russian Federation (west of the Urals), Slovakia, and Ukraine. Means and coefficients of variation for soil organic carbon and total nitrogen are presented for each major FAO soil grouping. The mean content of organic carbon, to a depth of 1 m, ranges from 3.9 kg C m–2 for coarse textured Arenosols to 72.9 kg C m–2 for poorly drained Histosols. Mean carbon content for the mineral soils, excluding Arenosols, is 15.8 kg C m–2. The top 1 m of soil holds 110 Pg C (Pg=1015 g), which corresponds to about 7% of the global stock of soil organic carbon. About 44% of this carbon pool is held in the top 0.3 m of the soil, the layer that is most prone to be changed by changes in soil use and management. About 166 million ha in Central and Eastern Europe have been degraded by compaction, erosion of topsoil, fertility decline and crusting. The achievable level of carbon sequestration for these soils, upon adoption of ‘best’ management practices or restorative measures, is estimated.

Notes: Abstract. There is a lack of information about the influence of tillage and time of sowing on N2O and NO emission in cereal production. Both factors influence crop growth and soil conditions and thereby can affect trace gas emissions from soils. We measured fluxes of NO and N2O in a tillage experiment where grassland on clay loam soil was converted to arable by either direct drilling or ploughing to 30 cm depth. We made measurements in spring for 20 days after fertilizer application to spring-sown and to winter-sown barley. Both were the second barley crop after grass. Direct drilling enhanced N2O emission primarily as a result of restricted gas diffusivity causing poor aeration after rainfall. Deep ploughing enhanced NO emission, because of the large air-filled porosity in the topsoil. NO and N2O emissions were smaller from winter sown crops than from spring sown crops.  The three rates of N fertilizer application (40, 80 or 120 kg N ha–1) did not produce the expected linear response in either soil available N concentrations or in NO and N2O fluxes. We attributed this to the lack of rainfall in the ten-day period after fertilizer application and therefore very slow incorporation and movement of fertilizer into and through the soil.

Notes: Abstract. Preferential flow may enhance phosphorus transport through the soil profile and thereby increase the risks for eutrophication of watercourses. Destruction of continuous macropores in topsoil by tillage provides the possibility for better contact between soil particles and P fertilizer. This is facilitated by incorporation rather than surface application of fertilizer, which should reduce the risk of rapid P transport from the soil surface through the unsaturated zone. To test this hypothesis, undisturbed soil monoliths (0.295 m in diameter and 1.2 m in length) were collected at a field site with a clay soil in which preferential flow is the dominant solute transport mechanism. After three years of observation, average total P loads reached 1.86, 1.59 and 1.25 kg ha–1for no-tillage, conventional tillage, and conventional tillage where the P fertilizer was incorporated, respectively. More than 80% of total losses were in the form of dissolved P. The tillage treatment had no significant effect on P leaching loads compared to no-tillage, but the improved contact between soil particles and P fertilizer resulting from fertilizer incorporation significantly reduced P loads during the first year after application of 100 kg P ha–1. However, after further application of 100 kg P ha–1 two years later, there were no significant differences between the treatments.

Notes: Abstract. The effect of land use on the water retention capacity of Umbric Andosols in south Ecuador was studied. The objective was to acquire a better insight into the hydrological processes of the ecosystem and the role of the soil, in order to assess the impact of changing soil properties due to land use change on the hydrology of the high Andes region. Field data on the water retention capacity at wilting point of Umbric Andosols were collected for both cultivated field conditions and original bush vegetation. The pH in water and in NaF, texture, organic matter content and dry bulk density were measured to show which physicochemical soil characteristics are responsible for the water retention of the Umbric Andosols and for the irreversible loss in water retention due to air drying. Organic matter content appears to be very important and certainly more important than allophane clay content. Water retention of the organic litter layer was calculated to be 16 mm, this would be lost when vegetation was cleared and the land cultivated.

Notes: Abstract. The effects of time and temperature on the changes in Olsen P after phosphate application were studied in 13 calcareous soils from Pakistan, an Oxisol from Colombia and an Inceptisol from England. The phosphate sorption reactions were monitored in two stages. The short-term reaction (30 min shaking with added phosphate in the presence of the Olsen bicarbonate solution) showed that over this time the nature of the sorbing material and number of available sites for P adsorption were important but temperature was not. The extent of the short-term sorption was not related to the amount of calcium carbonate. In the long-term reaction (incubating the soils with phosphate at 10, 25 and 45 °C for one year) the amount of Olsen P decreased with time following a power relationship. Increased temperature increased the rate of reaction, following the Arrhenius principle i.e. Q10⊃ 3 (activation energy 83 kJ mol–1). The effects of time and temperature were well described by a modified power equation Y=a (1 +fTt)-b, where Y is the amount of Olsen P extracted after time t, a is the Olsen P value after the short-term reaction (the initial value), fT is the ratio of the rate constants at any two temperatures and b is a coefficient which represents the loss in extractability with time. On the basis of the initial Olsen P values and subsequent Olsen P values at different times and temperatures a unified decay curve Y/a= (1 +t)–0.20 was developed where the initial Olsen P values are normalized to 1. The parameters of this equation allow, with limitations, the prediction of changes in Olsen P in these soils if the initial Olsen P value of the soil is known.

Notes: Abstract. This study investigated the effect of the same volume of leaching water applied consecutively in either equal amounts or increasing amounts or decreasing amounts on the hydraulic conductivity of a saline sodic soil in 30 cm plastic columns in the laboratory. Gypsum was mixed with the surface 2–3 cm of soil. After leaching, the hydraulic conductivity was measured in each 10 cm depth of soil. Hydraulic conductivity decreased strongly (P〈0.05) with depth and the most effective method of applying the water was in gradually increasing amounts.

Notes: Abstract. The field experiment tested the effects of three management systems on nitrate leaching losses from a five crop rotation on the Lincolnshire Limestone in Eastern England. The Standard system was similar to farming practice in the area. The Protective system integrated individual practices which were expected to decrease nitrate losses (e.g. cover crops, cultivation delay in autumn and reduced intensity, manipulation of drilling dates and, during the first few years of the first rotation, straw incorporation). The Intermediate system was a compromise between the two extremes. All crops were grown at full and half recommended nitrogen rates. This paper reports data from the second full rotation (years 6–10), thus enabling the medium-term effects of continued management practices to be investigated. Average annual nitrogen leaching losses at 49, 35 and 25 kg N ha–1 for Standard, Intermediate and Protective systems, respectively, were significantly different. The respective flow-weighted average NO3 concentrations were 167, 131 and 96 mg l–1. Thus, adopting nitrate retentive practices through the rotation was able to substantially decrease losses. The Protective system was as effective as in the first full rotation, demonstrating that 10 years of such practices had not failed in the medium-term. However, continued minimal cultivation caused serious problems of weed build-up. The cost of weed control and yield loss caused by grass weeds made cereal production uneconomic in some years. Thus, rules for nitrate leaching control need to be tempered with practical and agronomic considerations. Also, few (if any) management techniques tested guaranteed that nitrate losses would be small in all years, as the interaction with winter weather, particularly rainfall, was of vital importance.

Notes: Abstract. A field plot experiment was conducted to investigate P mobilization from fertilized rice fields during rainfall-flooding events. The experiment tested the effects of inorganic fertilizer P, at two rates, and P fertilizer plus manure, at one rate, on the amounts of P lost in drainage water when the plots were subjected to four artificially simulated storm-flooding/drainage events over an eight day period. During the first drainage event, two days after P application, the concentrations and loads of soluble reactive P (SRP) and particulate P (PP) in the drainage water were some three to five times lower than they had been just 24 hours earlier due to rapid sorption and sedimentation. At subsequent events, the concentrations and loads of SRP in drainage water were almost two orders of magnitude lower than at the first event, i.e. the equilibrium between P release from fertilizer and manure and P sorption/fixation by the soil mineral fraction had shifted strongly in favour of the latter processes. During the first drainage event, the concentrations and loads of SRP in drainage water from the low P fertilizer treatment were similar to those on the low P fertilizer plus manure treatment, whereas, 24 hours earlier they had been significantly greater. At subsequent events, though, the highest concentrations and loads of SRP occurred in drainage water from plots treated with equal amounts of P fertilizer and manure. It is suggested that extending the time period between P application and flooding events by applying fertilizer and manure outside the main rainy season should significantly reduce the risk of P loss from paddy rice fields.

Notes: Abstract. Natural secondary succession, forest planting and agricultural practices after deforestation affect soil properties in many ways. During the last 50 years, land uses have greatly changed in the mountainous areas in southwestern China as the result of deforestation and cultivation. A study was initiated in Wolong Nature Reserve, Sichuan province to elucidate the complex relationships in a humid mountainous region. Soil properties under six typical land use types (natural forest, grassland, shrub, secondary forest, cultivated land and reforested land) were compared. Significant differences between land uses were found for soil bulk density (BD), total nitrogen (TN), soil organic carbon (SOC), available phosphorus (AP) and available potassium (AK). Cultivated land had the lowest levels for most soil properties compared to other land uses and shrubland had a higher SOC, TN and available nitrogen (AN) than other land uses. Soils under grassland and shrub contained the greatest carbon mass (TC). Further studies on reforested land indicated that soil properties could be changed by length of reforestation. The SOC and TN in particular showed a linear relationship with years since reforestation. The results suggested that in an area of China where the climate favours secondary succession, ‘leave nature as it is’ is a better choice than the policy ‘change farmland to forest land ‘, especially for the mountainous regions where there is lack of labour and financial support.

Notes: Abstract. Soil erosion and sediment delivery cause many environmental problems posing a substantial financial burden upon society. Policy makers therefore look for a strategy to minimize their impact. The spatial nature of soil erosion and sediment delivery, as well as the variety of possible soil conservation and sediment control measures, requires an integrated approach to catchment management. To evaluate such management, a spatially distributed soil erosion and sediment delivery model is necessary. Such a model (WaTEM/SEDEM) was applied to three agricultural catchments in Flanders (Belgium). The model was first used to identify where the measures to control soil loss should be taken. Secondly, a scenario analysis was used to select the most effective set of techniques. The findings showed that soil conservation measures taken in fields are not only effective in reducing on-site soil loss, but also in drastically reducing sediment yield. Off-site sediment control measures appear to be much less effective in reducing sediment yield than previously thought. The results also suggest that data from field experiments cannot be extrapolated to a catchment scale.

Notes: Abstract. When over exploited and coupled with climatic conditions, tropical soils are subject to increased erosion and a loss of soil organic matter. Countermeasures include the incorporation of organic materials such as crop and animal residues. We studied the effect of adding crop residues and manure to soil, at five sites in Ethiopia, on carbohydrate properties, aggregate stability and the C and N distribution within water-stable aggregates. The effects of organic amendments varied between sites. The largest content of carbohydrates was obtained in the control treatment at Holeta, Ginchi (90 kg ha–1 mustard meal), Jimma (5 t ha–1 cow dung + 9 t ha–1 coffee husk), Awassa (forested soil), and Sirinka (soil alley-cropped with Leuceanae). The aggregate stability of these soils was highly correlated with the OM content but not with carbohydrates. The smaller aggregates (〈1.00 mm) accumulated more carbohydrates than the larger (〉1.00 mm), thereby suggesting a protecting effect within the finer soil fractions. A protecting role played by humified OM components was also indicated by the C and N distribution as well as the C:N ratios which showed preferential accumulation in small rather than in large aggregates. The isotopic 13C-OC values of carbohydrate extracts were generally low, suggesting that OM was from plants with C3 photosynthetic pathways. Soil treatments with maize alone or combined with coffee husks at Jimma decreased the δ13C‰ values slightly, revealing that maize contributed a share of the labile OM. Despite the improvement in the soil OM content, neither the carbohydrate content nor the aggregate stability were increased to the level of the forested sites, suggesting that the additions of crop residues and manure were not alone sufficient to restore the soil physical quality.