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Despite the first-order importance of crystallisation-differentiation for arc magma evolution, several other processes contribute to their compositional diversity. Among them is the remelting of partly crystallised magmas, also known as cumulate melting or 'petrological cannibalism'. The impact of this process on the plutonic record is poorly constrained. We investigate a nepheline-normative dyke suite close to the Blumone gabbros, a large amphibole-gabbro unit of the Tertiary Southern Alpine Adamello igneous complex. The compositions of the studied dykes are characterised by low SiO.sub.2 (43-46 wt. %), MgO (5.0-7.2 wt. %), Ni (18-40 [mu]g/g), and high Al.sub.2O.sub.3 (20.2-22.0 wt. %) contents. Phenocrystic plagioclase in these dykes exhibits major, trace, and Sr isotope compositions similar to Blumone cumulate plagioclase, suggesting a genetic link between the nepheline-normative dykes and the amphibole-gabbro cumulates. We tested this hypothesis by performing saturation experiments on a nepheline-normative dyke composition in an externally heated pressure vessel at 200 MPa between 975 and 1100 °C at fO.sub.2 conditions close to the Ni-NiO buffer. Plagioclase and spinel are near-liquidus phases at and above 1050 °C, contrasting with the typical near-liquidus olivine ± spinel assemblage in hydrous calc-alkaline basalts. The alkaline nature of the dykes results from the abundance of amphibole in the protolith, consistent with melting of amphibole-gabbro cumulates. We modelled the heat budget from the repeated injection of basaltic andesite into a partly crystallised amphibole-gabbro cumulate. The results of this model show that no more than 7% of the cumulate pile reaches temperatures high enough to produce nepheline-normative melts. We propose that such nepheline-normative dykes are a hallmark of hydrous cumulate melting in subvolcanic plumbing systems. Therefore, ne-normative dykes in arc batholiths may indicate periods with high magma fluxes., Author(s): Manuel Pimenta Silva [sup.1], Felix Marxer [sup.1] [sup.2], Tobias Keller [sup.1], Andrea Giuliani [sup.1], Peter Ulmer [sup.1], Othmar Müntener [sup.3] Author Affiliations: (1) grid.5801.c, 0000 0001 2156 2780, Institute [...]

The Azufre volcano (21°47'S; 68°14'W) is emplaced above the western boundary of the Altiplano Puna Magma Body. The youngest lava of the Azufre volcano (50-331 ka) was selected for detailed studies because of the relevant petrological information that could emerge to understand its reservoir as a potential heat source of the neighboring Cerro Pabellón geothermal system. The studied lava corresponds to an andesite-dacite (61-63 SiO.sub.2 wt%) with phenocrysts of plagioclase, amphibole (Group 1), biotite, pyroxenes, quartz, and olivine. The lava also contains aphanitic enclaves (58-60 SiO.sub.2 wt%), whose groundmass have the same mineralogy of lava samples groundmass consisting of amphibole microphenocryts (Group 2) and microlites of plagioclase, pyroxenes, and Fe-Ti oxides. Disequilibrium textures are commonly observed in the studied samples such as partially resorbed plagioclase phenocrysts, amphibole breakdown, and reverse zoning in pyroxene and plagioclase phenocrysts. Thermobarometry calculations indicated pressures of ~ 2 kbar for Group 1 amphiboles, temperatures of 905-1097 °C for Mg-rich pyroxene phenocrysts and Ca-rich plagioclase (An [greater than or equal to] 66), and near-solidus temperatures of 712-788 °C for Group 1 amphibole-plagioclase pairs. Group 1 amphiboles also indicate crystallization from an evolved liquid (63-79 wt% of SiO.sub.2). Oxidation conditions of QFM + 0.9-2.5 log units were recorded in amphibole and Fe-Ti oxides. Rhyolite-MELTS models reproduce the composition of the high-temperature phases from a melt composition (andesitic enclave) at similar P-T-fO.sub.2. The arrival of new hot andesite magma into a crystal-rich shallow reservoir, thermally and compositionally zoned, would have triggered the studied eruption. Diffusion models in Fe-Ti oxides microlites indicated cooling temperatures of 742-866 °C during the sub-aerial emplacement of the lava., Author(s): Darío Salvador Hübner [sup.1] [sup.2], Miguel-Ángel Parada [sup.1] [sup.2], Eduardo Morgado [sup.3], Francisca Mallea-Lillo [sup.1] [sup.2] Author Affiliations: (1) grid.443909.3, 0000 0004 0385 4466, Department of Geology, Faculty of [...]

Basanite lavas near Craven Lake, British Columbia, host a spinel lherzolite xenolith containing cross-cutting veins with pargasitic amphibole (plus minor apatite). The occurrence of vein amphibole in spinel lherzolite is singular for the Canadian Cordillera. The vein crosscuts foliated peridotite and is itself cut by the basanite host. The amphibole is pargasite, which is the most common amphibole composition in mantle peridotite. Rare earth element concentrations in the pargasite are similar to those for mafic alkaline rocks across the northern Cordilleran volcanic province (light rare earth elements ~50x chondrite and heavy rare earth elements ~5x chondrite). Two-pyroxene geothermometry suggests that the vein and host peridotite were thermally equilibrated prior to sampling by the basanite magma. Calculated temperature conditions for the sample, assuming equilibration along a model steady-state geotherm, are between 990 and 1050 [degrees]C and correspond to a pressure of 0.15 GPa (~52 [+ or -] 2 km depth). These conditions are consistent with the stability limits of mantle pargasite in the presence of a fluid having XH2O < ~0.1. The pargasite vein and associated apatite provide direct evidence for postaccretion fracture infiltration of [CO.sub.2]-F-[H.sub.2]O-bearing silicate fluids into the Cordilleran mantle lithosphere. Pargasite with low aH2O is in equilibrium with parts per million concentrations of H2O in mantle olivine, potentially lowering the mechanical strength of the lithospheric mantle underlying the Cordillera and making it more susceptible to processes such as lithospheric delamination. Remelting of Cordilleran mantle lithosphere containing amphibole veins may be involved in the formation of sporadic nephelinite found in the Canadian Cordillera. Key words: Canadian Cordillera, pargasitic amphibole, mantle xenolith, basanite, apatite. Des laves de basanite pres du lac Craven (Colombie-Britannique) renferment un xenolite de lherzolite a spinelle recoupe par des veines contenant de l'amphibole pargasitique (en plus d'apatite en quantite mineure). La presence d'amphibole en veines dans de la lherzolite a spinelle est singuliere pour la Cordillere canadienne. La veine recoupe de la peridotite foliee et est elle-meme recoupee par la basanite hote. L'amphibole est de la pargasite, l'amphibole la plus courante dans les peridotites mantelliques. Les concentrations de elements terres rares dans la pargasite sont semblables a celles de roches alcalines mafiques dans toute la province volcanique du nord de la Cordillere (elements terres rares legers ~50x chondrite et elements terres rares lourds ~5x chondrite). La geothermometrie a deux pyroxenes donne a penser que la veine et la peridotite hote ont subi une equilibration thermique avant l'echantillonnage par le magma basanitique. Les conditions de temperature calculees pour l'echantillon, en presumant une equilibration le long d'un geotherme modele stable, sont entre 990 et 1050 [degrees]C et correspondent a une pression de 0,15 GPa (profondeur ~52 [+ or -] 2 km). Ces conditions concordent avec les limites de stabilite de la pargasite mantellique en presence d'un fluide de XH2O < ~0,1. La veine de pargasite et l'apatite associee fournissent des preuves directes de l'infiltration post-accretion le long de fractures de fluides silicates a CO2-F-H2O dans la lithosphere mantellique de la Cordillere. De la pargasite de faible aH2O est en equilibre avec des concentrations de H2O de l'ordre de parties par million dans l'olivine mantellique, reduisant potentiellement la resistance mecanique du manteau lithospherique qui sous-tend la Cordillere et le rendant plus susceptible a des processus comme la delamination lithospherique. La refusion de lithosphere mantellique contenant des veines d'amphibole pourrait intervenir dans la formation des nephelinites sporadiquement presentes dans la Cordillere canadienne. [Traduit par la Redaction] Mots-cles: Cordillere canadienne, amphibole pargasitique, xenolite mantellique, basinite, apatite., Introduction The lithospheric mantle underlying the northwestern Cordillera of North America was formed and modified by a series of complex processes including terrane accretion, subduction, and extension related to postsubduction [...]

In Late Proterozoic mafic granulites of the Sandmata Complex in Rajasthan, northwestern India, multilayer corona textures were formed along the interface between orthopyroxene and plagioclase. We examined the metamorphic conditions and processes of formation of these coronae, which provide an insight into the interplay between steady state and sequential diffusion-controlled mineral growth mechanisms. The individual corona-symplectite layers consist of clinopyroxene + quartz|garnet + clinopyroxene|garnet + quartz|K-feldspar, from the inner to the outer margins of the coronae. The single-value decomposition models suggest that the multilayered coronae were formed in a locally closed system, via sequential diffusion of Mg, Fe and Ca into the reaction zone, which has acted as the main driving force for the growth of corona textures. The relict orthopyroxene with exsolved clinopyroxene yields primary crystallization conditions of 8.4 ± 1.5 kbar and ~ 1100-1000 °C. Clinopyroxene in the innermost corona layer grew at ~ 9 kbar and 850-800 °C, whereas clinopyroxene + garnet grew outward at ~ 8 kbar and 700-600 °C. Subsequent hydrous retrogression (~ 6 kbar and 600-550 °C) resulted in the development of rimward zoning in garnet and the growth of amphibole. On combining textural relations and the above conventional P-T estimates, a near-isobaric cooling P-T path was reconstructed using phase equilibria modeling. Further, the near-isobaric cooling path is consistent with the magmatic underplating hypothesis in the Sandmata Complex, where the intrusion of magmatic bodies (i.e., Gyangarh-Asind igneous complex and Anjana granite) favored the development of granulite facies assemblage in norite and gabbronorite protoliths., Author(s): Suranjan Ghosh [sup.1], N. Prabhakar [sup.1], Joseph D'Souza [sup.1] [sup.2] Author Affiliations: (1) grid.417971.d, 0000 0001 2198 7527, Department of Earth Sciences, Indian Institute of Technology Bombay, , 400076, [...]

Quenched juvenile mafic inclusions (enclaves) are an occasional but informative component in the deposits of large felsic eruptions. Typically, the groundmasses of these inclusions rapidly crystallize as the mafic magma is chilled against a more voluminous, cooler felsic host, providing a physical and chemical record of the nature and timing of mafic-felsic interactions. We examine mafic inclusions of two compositional lineages (tholeiitic and calc-alkaline) from deposits of the 25.4 ka Oruanui eruption (Taupo, New Zealand). 2-D quantitative textural data from analysis of back-scattered electron images reveal a marked diversity in the groundmass textures of the inclusions, including median crystal sizes (amphibole: 14-45 [micro]m; plagioclase: 21-75 [micro]m) and aspect ratios (amphibole: 1.7-4.2; plagioclase: 2.1-4.0), area number densities (amphibole: 122-2660 mm.sup.-2; plagioclase: 117-2990 mm.sup.-2), area fractions ([phi]) of minerals ([phi].sub.plag = 23-45%, [phi].sub.amph = 0-28%, [phi].sub.cpx = 0-6%, [phi].sub.oxides = 0.6-5.5%), and the relative abundance of plagioclase and amphibole ([phi].sub.plag/[phi].sub.amph = 1.0-4.6). Textural parameters vary more significantly within, rather than between, the two compositional lineages, and in some cases show marked variations across individual clasts, implying that each inclusion's cooling history, rather than bulk composition, was the dominant control on textural development. Groundmass mineral compositions are also diverse both within and between inclusions (e.g. plagioclase from An.sub.34-92, with typical intra-clast variability of ~ 20 mol%), and do not correlate with bulk chemistry. Diverse groundmass textures and mineral and glass chemistries are inferred to reflect complex interplay of a range of factors including the degree and rate of undercooling, bulk composition, water content and, possibly, intensive variables. Our data are inconsistent with breakup of a crystallizing ponded mafic layer at the base of the Oruanui melt-dominant body, instead implying that each inclusion partially crystallized as a discrete body with a unique cooling history. Extensive ingestion of mush-derived macro-crystals suggests that mechanical breakup of mafic feeder dikes occurred within a transition zone between the mush and melt-dominant magma body. In this zone, the mush lacked yield strength, as has been inferred from field studies of narrow (meters to few tens of meters) mush-melt transition zones preserved in composite intrusions. Evidence for plastic deformation of inclusions during eruption and the abundance of fresh residual glass in inclusions from all eruptive phases suggest that the inclusions formed syn-eruptively, and must have been formed recurrently at multiple stages throughout the eruption., Author(s): Shane M. Rooyakkers [sup.1] [sup.2], Colin J. N. Wilson [sup.1], C. Ian Schipper [sup.1], Simon J. Barker [sup.1] [sup.3], Aidan S. R. Allan [sup.1] [sup.4] Author Affiliations: (1) 0000 [...]

The water-saturated phase relations have been determined for a primitive magnesian andesite (57 wt% Si[O.sub.2], 9 wt% MgO) from the Mt. Shasta, CA region over the pressure range 200-800 MPa, temperature range of 915-1,070°C, and oxygen fugacities varying from the nickel-nickel oxide (NNO) buffer to three log units above NNO (NNO+3). The phase diagram of a primitive basaltic andesite (52 wt% Si[O.sub.2], 10.5 wt% MgO) also from the Mt. Shasta region (Grove et al. in Contrib Miner Petrol 145:515-533; 2003) has been supplemented with additional experimental data at 500 MPa. Hydrous phase relations for these compositions allow a comparison of the dramatic effects of dissolved [H.sub.2]O on the crystallization sequence. Liquidus mineral phase stability and appearance temperatures vary sensitively in response to variation in pressure and [H.sub.2]O content, and this information is used to calibrate magmatic barometers-hygrometers for primitive arc magmas. [H.sub.2]O-saturated experiments on both compositions reveal the strong dependence of amphibole stability on the partial pressure of [H.sub.2]O. A narrow stability field is identified where olivine and amphibole are coexisting phases in the primitive andesite composition above 500 MPa and at least until 800 MPa, between 975-1,025 °C. With increasing [H.sub.2]O pressure ([MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]), the temperature difference between the liquidus and amphibole appearance decreases, causing a change in chemical composition of the first amphibole to crystallize. An empirical calibration is proposed for an amphibole first appearance barometer-hygrometer that uses Mg# of the amphibole and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]: [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] This barometer gives a minimum [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] recorded by the first appearance of amphibole in primitive arc basaltic andesite and andesite. We apply this barometer to amphibole antecrysts erupted in mixed andesite and dacite lavas from the Mt. Shasta, CA stratocone. Both high [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] pressures (500-900 MPa) and high pre-eruptive magmatic [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] contents (10-14 wt% [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]) are indicated for the primitive end members of magma mixing that are preserved in the Shasta lavas. We also use these new experimental data to explore and evaluate the empirical hornblende barometer of Larocque and Canil (2010). Keywords Amphibole * Experimental petrology * Shasta * Water in magma * Subduction zone volcanism, Introduction This study examines the [H.sub.2]O-saturated phase relations of two primitive arc magmas; a basaltic andesite and primitive magnesian andesite from the Mt. Shasta region, CA. Each of these compositions [...]

Byline: C. D. Deering (1,4), D. M. Gravley (1), T. A. Vogel (2), J. W. Cole (1), G. S. Leonard (3) Keywords: Taupo Volcanic Zone; Subduction zone; Fluid; Magma distribution; Oxidation state Abstract: Slab-derived aqueous fluid components (Ba, Cl) correlate well with oxygen fugacity, and other well-defined characteristics of silicic magmas in the Taupo Volcanic Zone (TVZ) between a cold-wet-oxidizing magma type [R1: amphibole +- biotite high Sr, low Zr and FeO*/MgO, depleted middle rare-earth elements (MREE)] and a hot-dry-reducing magma type (R2: orthopyroxene +- clinopyroxene low Sr, high Zr, and FeO*/MgO, less depleted MREE). Oxygen fugacity was obtained from analysis of Fe--Ti oxides and ranges between -0.04 and +2.1 log units (IQFM, where QFM = quartz + fayalite + magnetite buffer) and is positively correlated with the bulk-rock Ba/La ratio, indicating that slab-derived fluid is the oxidizing agent in the rhyolites. Chlorine contents in hornblende also correlate with the bulk-rock Ba/La ratio. Hence, high-fluid flux typically correlates with the R1 and low-fluid flux with R2 rhyolite magma types. A geochemical evolution and distribution can be tracked in time and space throughout the central region of the TVZ from 550 ka to present and has revealed two distinct magmatic cycles that vary in length. The first cycle included widespread R1 type magmatism across the central TVZ beginning ca. 550 ka and was directly associated with previously unreported dome-building and ignimbrite-forming volcanism, and led to a voluminous (>3,000 km.sup.3) ignimbrite 'flare-up' between ca. 340 and 240 ka. The second cycle began roughly 180 ka, erupting ca. 800 km.sup.3 of magma, and continues to the present. The duration, rate, and composition of magma production within these cycles appears to be governed by the flux of fluid released from the subducting slab, while the distribution of magmas may be governed more by extension along the central rift axis. Shorter cycles have also been identified and are unrelated to subduction processes, but occur following large, caldera-forming events. Author Affiliation: (1) Department of Geological Sciences, University of Canterbury, PO Box 4800, Christchurch, 8020, New Zealand (4) Department of Earth and Space Sciences, University of Washington, Mailstop, Seattle, 98195-1310, USA (2) Department of Geological Sciences, Michigan State University, 206 Natural Sciences Bldg., East Lansing, MI, 48824-1115, USA (3) Institute of Geological and Nuclear Sciences, PO Box 30368, Lower Hutt, 6315, New Zealand Article History: Registration Date: 28/01/2010 Received Date: 24/08/2009 Accepted Date: 28/01/2010 Online Date: 25/02/2010 Article note: Communicated by J. Hoefs. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-010-0496-0) contains supplementary material, which is available to authorized users.

Byline: Heather Katherine Handley (1,2), Colin G. Macpherson (1), Jon P. Davidson (1) Keywords: Crustal contamination; Fractional crystallisation; Geochemistry; Magma mixing; Sunda arc Abstract: The Gede Volcanic Complex (GVC) of the Sunda island arc (West Java, Indonesia) consists of multiple volcanic centres and eruptive groups with complex magmatic histories. We present new petrological, mineralogical, whole-rock major and trace element and Sr--O isotopic data to provide constraints on the relative importance of fractional crystallisation and magma mixing in petrogenesis, as well as on the role and nature of the arc crust. Banded juvenile scoria from Young and Old Gede provide unequivocal evidence for the (late-stage) interaction of distinct magmas at Gede volcano. However, the relatively small-degree compositional zoning observed in plagioclase phenocrysts of all eruptive groups (up to ~20 mol% An) may be attributed to physical changes in magma properties (e.g. P, T, and P[H.sub.2]O) rather than changes in melt composition. Major element and trace element variations within each eruptive series are inconsistent with magmatic evolution through simple mixing processes. Instead, mixing of variably fractionated magma batches is suggested to account for the significant scatter in some element variation diagrams. No correlation is observed between textural complexity and/or mineral disequilibrium and whole-rock geochemistry. REE data and geochemical modelling indicate that fractional crystallisation involving amphibole in the mid- to lower crust, and fractionation of plagioclase, clinopyroxene, Fe--Ti oxide +- olivine +- orthopyroxene provide strong control on the geochemical evolution of GVC rocks. Two-pyroxene geothermobarometry provides pre-eruption crystallisation temperatures of 891--1,046degC and pressures of 3.4--6.5 kbar, equivalent to ~13--24 km depth beneath the volcanoes (mid- to lower crust). Low, mantle-like clinopyroxene [delt[a].sup.18]O values of GVC lavas and poor correlation of Sr isotope ratios with indices of differentiation precludes significant assimilation of isotopically distinct crust during magmatic differentiation. Therefore, we suggest that the geochemical character of the moderately thick West Javan arc crust is relatively immature compared to typical continental crust. Trace element ratios and strontium isotopes show that the magmatic source composition of the older geographical units, Gegerbentang and Older Quaternary, is distinct from the other GVC groups. Author Affiliation: (1) Department of Earth Sciences, Durham University, Durham, DH1 3LE, UK (2) GEMOC Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW, 2109, Australia Article History: Registration Date: 22/10/2009 Received Date: 17/02/2009 Accepted Date: 22/10/2009 Online Date: 21/11/2009 Article note: Communicated by T.L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0460-z) contains supplementary material, which is available to authorized users.

Byline: Sebastien Pilet (1), Peter Ulmer (2), Samuel Villiger (2) Keywords: Experimental petrology; Basanite; Metasomatism; High-pressure crystallization; Alkaline lavas Abstract: The metasomatism observed in the oceanic and continental lithosphere is generally interpreted to represent a continuous differentiation process forming anhydrous and hydrous veins plus a cryptic enrichment in the surrounding peridotite. In order to constrain the mechanisms of vein formation and potentially clarify the nature and origin of the initial metasomatic agent, we performed a series of high-pressure experiments simulating the liquid line of descent of a basanitic magma differentiating within continental or mature oceanic lithosphere. This series of experiments has been conducted in an end-loaded piston cylinder apparatus starting from an initial hydrous ne-normative basanite at 1.5 GPa and temperature varying between 1,250 and 980degC. Near-pure fractional crystallization process was achieved in a stepwise manner in 30degC temperature steps and starting compositions corresponding to the liquid composition of the previous, higher-temperature glass composition. Liquids evolve progressively from basanite to peralkaline, aluminum-rich compositions without significant SiO.sub.2 variation. The resulting cumulates are characterized by an anhydrous clinopyroxene + olivine assemblage at high temperature (1,250--1,160degC), while at lower temperature (1,130--980degC), hydrous cumulates with dominantly amphibole + minor clinopyroxene, spinel, ilmenite, titanomagnetite and apatite (1,130--980degC) are formed. This new data set supports the interpretation that anhydrous and hydrous metasomatic veins could be produced during continuous differentiation processes of primary, hydrous alkaline magmas at high pressure. However, the comparison between the cumulates generated by the fractional crystallization from an initial ne-normative liquid or from hy-normative initial compositions (hawaiite or picrobasalt) indicates that for all hydrous liquids, the different phases formed upon differentiation are mostly similar even though the proportions of hydrous versus anhydrous minerals could vary significantly. This suggests that the formation of amphibole-bearing metasomatic veins observed in the lithospheric mantle could be linked to the differentiation of initial liquids ranging from ne-normative to hy-normative in composition. The present study does not resolve the question whether the metasomatism observed in lithospheric mantle is a precursor or a consequence of alkaline magmatism however, it confirms that the percolation and differentiation of a liquid produced by a low degree of partial melting of a source similar or slightly more enriched than depleted MORB mantle could generate hydrous metasomatic veins interpreted as a potential source for alkaline magmatism by various authors. Author Affiliation: (1) Institute of Mineralogy and Geochemistry, University of Lausanne, Anthropole, 1015, Lausanne, Switzerland (2) Department of Earth Sciences, ETH-Zurich, Clausiusstrasse 25, 8092, Zurich, Switzerland Article History: Registration Date: 01/09/2009 Received Date: 23/01/2009 Accepted Date: 31/08/2009 Online Date: 21/09/2009 Article note: Communicated by J. Blundy.

Byline: Franziska Nehring (1), Stephen F. Foley (1), Pentti Holtta (2) Keywords: Partition coefficients; Crustal melting; Granulite; LA-ICP-MS; Trace element distribution Abstract: Analyses of trace elements in the mineral phases of granulites provide important information about the trace element distribution in the lower crust. Since granulites are often considered residues of partial melting processes, trace element characteristics of their mineral phases may record mineral/melt equilibria thus giving an opportunity to understand the nature and composition of melts in the lower continental crust. This study provides an extensive set of mineral trace element data obtained by LA-ICP-MS analyses of mafic and intermediate granulites from Central Finland. Mass balance calculations using the analytical data indicate a pronounced contribution of the accessory minerals apatite for the REE and ilmenite for the HFSE. Coherent mineral/mineral ratios between samples point to a close approach to equilibrium except for minerals intergrown with garnet porphyroblasts. Mineral trace element data were used for the formulation of a set of D .sup.mineral/melt partition coefficients that is applicable for trace element modelling under lower crustal conditions. D .sup.mineral/melt were derived by the application of predictive models and using observed constant mineral/mineral ratios. The comparison of the calculated D .sup.mineral/melt with experimental data as well as the relationship between mineral trace element contents and a leucosome with a composition close to an equilibrium melt provides additional constraints on mineral/melt partitioning. The D values derived in this study are broadly similar to magmatic partition coefficients for intermediate melt compositions. They provide a first coherent set of D values for Sc, V, Cr and Ni between clinopyroxene, amphibole, garnet, orthopyroxene, ilmenite and melt. In addition, they emphasize the strong impact that ilmenite exerts on the distribution of Nb and Ta. Author Affiliation: (1) Earth System Science Research Centre and Institute of Geosciences, Johannes Gutenberg University, Becher-Weg 21, 55099, Mainz, Germany (2) Geological Survey of Finland, Betonimiehenkuja 4, 02151, Espoo, Finland Article History: Registration Date: 05/08/2009 Received Date: 09/07/2008 Accepted Date: 05/08/2009 Online Date: 28/08/2009 Article note: Communicated by J. Blundy.

Byline: Fleurice Parat (1), Francois Holtz (2), Milos Rene (3), Renat Almeev (2) Keywords: Experimental study; Ultrapotassic magma; Durbachite; TAebic; Bohemian Massif Abstract: The equilibrium phase relations of a mafic durbachite (53 wt.% SiO.sub.2) from the TAebic pluton, representative of the Variscan ultrapotassic magmatism of the Bohemian Massif (338--335 Ma), have been determined as a function of temperature (900--1,100degC), pressure (100--200 MPa), and [H.sub.2]O activity (1.1--6.1 wt.% [H.sub.2]O in the melt). Two oxygen fugacity ranges were investigated: close to the Ni--NiO (NNO) buffer and 2.6 log unit above NNO buffer (aNNO + 2.6). At 1,100degC, olivine is the liquidus phase and co-crystallized with phlogopite and augite at 1,000degC for the whole range of investigated pressure and water content in the melt. At 900degC, the mineral assemblage consists of augite and phlogopite, whereas olivine is not stable. The stability field of both alkali feldspar and plagioclase is restricted to low pressure (100 MPa) at nearly water-saturated conditions ( Author Affiliation: (1) Institut fur Geowissenschaften, Mineralogie-Geochemie, Universitat Freiburg, Albertstrasse 23b, 79104, Freiburg, Germany (2) Institut fur Mineralogie, Leibniz Universitat Hannover, Callinstrasse 3, 30167, Hannover, Germany (3) Institute of Rock Structure and Mechanics, ASCR V, Holesovickach 41, 182 09, Prague, Czech Republic Article History: Registration Date: 13/07/2009 Received Date: 20/11/2008 Accepted Date: 13/07/2009 Online Date: 04/08/2009 Article note: Communicated by J. Hoefs.

Byline: David J. Kratzmann (1), Steven Carey (1), Roberto A. Scasso (2), Jose-Antonio Naranjo (3) Keywords: Hudson volcano; Southern Volcanic Zone; Amphibole crystallization; Magma differentiation; Andean margin Abstract: Hudson volcano (Chile) is the southern most stratovolcano of the Andean Southern Volcanic Zone and has produced some of the largest Holocene eruptions in South America. There have been at least 12 recorded Holocene explosive events at Hudson, with the 6700 years BP, 3600 years BP, and 1991 eruptions the largest of these. Hudson volcano has consistently discharged magmas of similar trachyandesitic and trachydacitic composition, with comparable anhydrous phenocryst assemblages, and pre-eruptive temperatures and oxygen fugacities. Pre-eruptive storage conditions for the three largest Holocene events have been estimated using mineral geothermometry, melt inclusion volatile contents, and comparisons to analogous high pressure experiments. Throughout the Holocene, storage of the trachyandesitic magmas occurred at depths between 0.2 and 2.7 km at approximately ~972degC (+-25) and log fO.sub.2 -10.33--10.24 (+-0.2) (one log unit above the NNO buffer), with between 1 and 3 wt% [H.sub.2]O in the melt. Pre-eruptive storage of the trachydacitic magma occurred between 1.1 and 2.0 km, at ~942degC (+-26) and log fO.sub.2 -10.68 (+-0.2), with ~2.5 wt% [H.sub.2]O in the melt. The evolved trachyandesitic and trachydacitic magmas can be derived from a basaltic parent primarily via fractional crystallization. Entrapment pressures estimated from plagioclase-hosted melt inclusions suggest relatively shallow levels of crystallization. However, trace element data (e.g., Dy/Yb ratio trends) suggests amphibole played an important role in the differentiation of the Hudson magmas, and this fractionation is likely to have occurred at depths >6 km. The absence of a garnet signal in the Hudson trace element data, the potential staging point for differentiation of parental mafic magmas [i.e., ~20 km (e.g., Annen et al. in J Petrol 47(3):505--539, 2006)], and the inferred amphibolite facies [~24 km (e.g., Rudnick and Fountain in Rev Geophys 33:267--309, 1995)] combine to place some constraint on the lower limit of depth of differentiation (i.e., ~20--24 km). These constraints suggest that differentiation of mantle-derived magmas occurred at upper-mid to lower crustal levels and involved a hydrous mineral assemblage that included amphibole, and generated a basaltic to basaltic andesitic composition similar to the magma discharged during the first phase of the 1991 eruption. Continued fractionation at this depth resulted in the formation of the trachyandesitic and trachydacitic compositions. These more evolved magmas ascended and stalled in the shallow crust, as suggested by the pressures of entrapment obtained from the melt inclusions. The decrease in pressure that accompanied ascent, combined with the potential heating of the magma body through decompression-induced crystallization would cause the magma to cross out of the amphibole stability field. Further shallow crystallization involved an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the Hudson suite. Author Affiliation: (1) Graduate School of Oceanography, URI, S. Ferry Rd., Narragansett, RI, 02882, USA (2) Dpto. de Cs. Geologicas, FCEN, Univ. de Buenos Aires Cuidad Univ., Pab 2, 1 Piso, 1428, Buenos Aires, Argentina (3) Serv. Nacional Geol. y Mineria, Casilla, Santiago, 10465, Chile Article History: Registration Date: 09/07/2009 Received Date: 25/02/2009 Accepted Date: 09/07/2009 Online Date: 31/07/2009 Article note: Communicated by T.L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0426-1) contains supplementary material, which is available to authorized users.

Byline: P. Fumagalli (1), S. Zanchetta (2), S. Poli (1) Keywords: Metasomatism; Phlogopite; Ca-amphibole; 10 A phase; Subduction zones; K-doped lherzolites Abstract: Subsolidus phase relations for a K-doped lherzolite are investigated in the model system [K.sub.2][O--Na.sub.2][O--CaO--FeO--MgO--Al.sub.2]O.sub.3--SiO.sub.2--[H.sub.2]O at 1.5--6.0 GPa and 680--1,000degC. Phlogopite is ubiquitous and coexists with Ca-amphibole up to 3.2 GPa and 900degC. High-pressure phlogopites show a peculiar mineral chemistry dependent on pressure: e.g., at 5.5 GPa and 680degC, excess of Si (up to 3.4 apfu) coupled with deficiency in Al (as low as 0.58 apfu) and K + Na (as low as 0.97 apfu), suggest a significant amount of a talc/10 A phase component ([v].sup.XII][Si.sub.1][K.sub.-1]Al .sub.-1 .sup.IV , where [v].sup.XII is interlayer vacancy). Mixed layering or solid solution relations between high-pressure phlogopites and the 10 A phase, [Mg.sub.3][Si.sub.4]O.sub.10(OH).sub.2 n[H.sub.2]O, are envisaged. Phlogopite modal abundance, derived by weighted least squares, is maximum at high-pressure and relative low-temperature conditions and therefore along the slab--mantle interface (10.3 +- 0.7 wt.%, at 4.8 GPa, 680degC). In phlogopite-bearing systems, Ca-amphibole breaks down between 2.5 and 3.0 GPa, and 1,000degC, through the water conservative reaction 5(pa + 0.2 KNa.sub.-1) + 17en + 15phl = (10di + 4jd) + 5py + 12fo + 20(phl + 0.2 talc), governed by bulk composition and pressure-dependent variations of K/OH in K-bearing phases and as a result, it does not necessarily imply a release of fluid. Author Affiliation: (1) Dipartimento di Scienze della Terra, Universita degli Studi di Milano, Via Botticelli 23, 20133, Milan, Italy (2) Dipartimento di Scienze Geologiche e Geotecnologie, Universita degli Studi di Milano Bicocca, Piazza della Scienza 4, 20126, Milan, Italy Article History: Registration Date: 20/04/2009 Received Date: 02/12/2008 Accepted Date: 20/04/2009 Online Date: 08/05/2009 Article note: Communicated by J. Hoefs. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0407-4) contains supplementary material, which is available to authorized users.

Byline: Oliver E. Jagoutz (1,2), J.-P. Burg (1), S. Hussain (3), H. Dawood (3), T. Pettke (4), T. Iizuka (5), S. Maruyama (6) Abstract: We present major and trace element analyses and U--Pb zircon intrusion ages from I-type granitoids sampled along a crustal transect in the vicinity of the Chilas gabbronorite of the Kohistan paleo-arc. The aim is to investigate the roles of fractional crystallization of mantle-derived melts and partial melting of lower crustal amphibolites to produce the magmatic upper crust of an island arc. The analyzed samples span a wide calc-alkaline compositional range (diorite--tonalite--granodiorite--granite) and have typical subduction-related trace element signatures. Their intrusion ages (75.1 +- 4.5--42.1 +- 4.4 Ma) are younger than the Chilas Complex (~85 Ma). The new results indicate, in conjunction with literature data, that granitoid formation in the Kohistan arc was a continuous rather than punctuated process. Field observations and the presence of inherited zircons indicate the importance of assimilation processes. Field relations, petrographic observations and major and trace element compositions of the granitoid indicate the importance of amphibole fractionation for their origin. It is concluded that granitoids in the Kohistan arc are derivative products of mantle derived melts that evolved through amphibole-dominated fractionation and intra crustal assimilation. Author Affiliation: (1) Department of Earth Sciences, ETH and University Zurich, Sonneggstrasse 5/NO, 8092, Zurich, Switzerland (2) Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, USA (3) Pakistan Museum of Natural History, Garden Avenue, Shakarparian, Islamabad, 44 000, Pakistan (4) Department of Earth Sciences, University of Bern, Baltzerstrasse 1+3, 3012, Bern, Switzerland (5) Research School of Earth Sciences, The Australian National University, Mills Rd., Canberra, ACT, 0200, Australia (6) Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, 152, Japan Article History: Registration Date: 21/04/2009 Received Date: 10/06/2008 Accepted Date: 21/04/2009 Online Date: 31/05/2009 Article note: Communicated by T. L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0408-3) contains supplementary material, which is available to authorized users.

Byline: Giovanna T. Sapienza (1,3), Marco Scambelluri (2), Roberto Braga (1) Keywords: Dolomite-bearing peridotites; Mantle wedge; C--O--H fluid; Subduction fluids; Ulten Zone Abstract: We document the presence of dolomite +- apatite in orogenic peridotites from the Ulten Zone (UZ, Italian Alps), the remnants of a Variscan mantle wedge tectonically coupled with eclogitized continental crust. These dolomite peridotites are associated with dominant carbonate-free amphibole peridotites, which formed in response to infiltration of aqueous subduction fluids lost by the associated crustal rocks during high-pressure (HP) metamorphism and retrogression. Dolomite-free and dolomite-bearing peridotites share the same metamorphic evolution, from garnet- (HP) to spinel-facies (low-pressure, LP) conditions. Dolomite and the texturally coexisting phases display equilibrium redistribution of rare earth elements and of incompatible trace elements during HP and LP metamorphism clinopyroxene and amphiboles from carbonate-free and carbonate-bearing peridotites have quite similar compositions. These features indicate that the UZ mantle rocks equilibrated with the same metasomatic agents: aqueous CO.sub.2-bearing fluids enriched in incompatible elements released by the crust. The P--T crystallization conditions of the dolomite peridotites (outside the field of carbonatite melt + amphibole peridotite coexistence), a lack of textures indicating quench of carbonic melts, a lack of increase in modal clinopyroxene by reaction with such melts and the observed amphibole increase at the expense of clinopyroxene, all suggest that dolomite formation was assisted by aqueous CO.sub.2-bearing fluids. A comparison of the trace element compositions of carbonates and amphiboles from the UZ peridotites and from peridotites metasomatized by carbonatite and/or carbon-bearing silicate melts does not help to unambiguously discriminate between the different agents (fluids or melts). The few observed differences (lower trace element contents in the fluid-related dolomite) may ultimately depend on the solute content of the metasomatic agent (CO.sub.2-bearing fluid versus carbonatite melt). This study provides strong evidence that C--O--H subduction fluids can produce 'carbonatite-like' assemblages in mantle rocks, thus being effective C carriers from the slab to the mantle wedge at relatively low P--T. If transported beyond the carbonate and amphibole solidus by further subduction, dolomite-bearing garnet + amphibole peridotites like the ones from Ulten can become sources of carbonatite and/or C-bearing silicate melts in the mantle wedge. Author Affiliation: (1) Dipartimento di Scienze della Terra e Geologico-Ambientali, Universita di Bologna, Bologna, Italy (2) Dipartimento per lo Studio del Territorio e delle sue Risorse, Universita di Genova, Genova, Italy (3) D&M Schlumberger Italiana S.p.A., Via Bondi 32, 48100, Ravenna, Italy Article History: Registration Date: 29/01/2009 Received Date: 07/07/2008 Accepted Date: 29/01/2009 Online Date: 03/03/2009 Article note: In memory of Lauro Morten 1941--2006. Communicated by J. Hoefs. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0389-2) contains supplementary material, which is available to authorized users.

Byline: Jose F. Molina (1), Jane H. Scarrow (1), Pilar G. Montero (1), Fernando Bea (1) Abstract: Central Iberian Variscan granite batholiths and anatectic complexes are punctuated by coeval stocks of hydrous, high-K calc-alkaline, ultrabasic to intermediate rock series. Despite their overall calc-alkaline affinity, the mafic--ultramafic members contain high-Ti amphibole oikocrysts rimmed by lower-Ti amphibole +- cummingtonite and high-Ti amphibole replacing early phlogopite. To understand the factors controlling the saturation of high-Ti amphibole in the parental magmas, clinopyroxene-melt, phlogopite-melt and amphibole-melt relationships are reviewed. This analysis reveals that for melts with intermediate compositions, the affinity of TiO.sub.2 for amphibole rises in alkalic magmas. Accordingly, mildly alkalic trachytoid to subalkaline medium- to high-K andesite and dacite compositions are estimated for interstitial high-Ti amphibole-saturated melts. Amphibole Ce/Pb ratios reveal a mantle--crust hybrid nature for interstitial melts with subalkaline trachytoid compositions. The hydrous character of the Variscan basic magmas favoured an overall magmatic evolutionary trend with a low rate of variation of [Na.sub.2]O with respect to silica during amphibole crystallization. Author Affiliation: (1) Department of Mineralogy and Petrology, Campus Fuentenueva, University of Granada, 18002, Granada, Spain Article History: Registration Date: 29/12/2008 Received Date: 12/03/2008 Accepted Date: 29/12/2008 Online Date: 08/02/2009 Article note: Communicated by M. W. Schmidt. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-008-0371-4) contains supplementary material, which is available to authorized users.

Byline: Steven Michael Reddy (1), Nicholas E. Timms (1), Patrick Joseph Hamilton (1,3), Helen R. Smyth (2) Keywords: Arc magmatism; Cumulate; Electron backscatter diffraction (EBSD); Cathodoluminescence; Crystal plasticity; Dislocation creep Abstract: An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 +- 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30deg in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of {100} and {010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction ( Author Affiliation: (1) Department of Applied Geology, The Institute for Geoscience Research, Curtin University of Technology, GPO Box U1987, Perth, WA, 6845, Australia (2) Department of Earth Sciences, CASP, University of Cambridge, Cambridge, CB3 0DH, UK (3) Intellection Pty. Ltd, 27 Mayneview Street, Milton, QL, 4064, Australia Article History: Registration Date: 18/07/2008 Received Date: 15/10/2007 Accepted Date: 18/07/2008 Online Date: 05/08/2008 Article note: Communicated by B. Collins.

Byline: Kwan-Nang Pang (1), Chusi Li (2), Mei-Fu Zhou (1), Edward M. Ripley (2) Keywords: Fe--Ti oxides; Inclusion; Layered intrusion; Panzhihua; Hongge; SW China Abstract: Abundant Fe--Ti oxide inclusions in cumulus olivine (Fo.sub.77--81) from the Panzhihua and Hongge intrusions, Emeishan large igneous province, SW China, document the first evidence for early crystallization of Fe--Ti oxides in ferrobasaltic systems in nature. The intrusions also contain significant stratiform Fe--Ti--V oxide ores. The oxide inclusions are sub-rounded or irregular, range from [proportional to]5 to 50 um in diameter, and are dominated by either titanomagnetite or ilmenite. The fact that the inclusions are either titanomagnetite- or ilmenite-dominant suggests that they are trapped crystals, instead of immiscible oxide melt, formed during growth of the host olivine. The absence of other silicate phases in the inclusion-bearing olivine is difficult to reconcile with a possible xenocrystic origin of the oxide inclusions. These oxide inclusions are thus interpreted to be cumulus minerals crystallized together and trapped in olivine from the same parental magma. In addition to Fe--Ti oxides, some inclusions contain amphibole + biotite +- fluorapatite that might have formed by reaction of trapped hydrous liquid with the host olivine. Numerical modeling of high-Ti Emeishan basalts using the MELTS program successfully simulates early crystallization of olivine ([proportional to]Fo.sub.81) and Fe--Ti spinel in the presence of a moderate amount of [H.sub.2]O ([proportional to]1.5 wt%) under pressure and fO.sub.2 conditions generally pertinent to the Panzhihua and Hongge intrusions. The modal mineralogy of the oxide inclusions is in good agreement with the bulk compositions of the ore, as inferred from whole-rock data, in a given intrusion. This is consistent with the interpretation that the stratiform oxide ores in the intrusions formed by accumulation of Fe--Ti oxide crystals that appeared on the liquidus with olivine and clinopyroxene. Author Affiliation: (1) Department of Earth Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (2) Department of Geological Sciences, Indiana University, Bloomington, IN, 47405, USA Article History: Registration Date: 11/02/2008 Received Date: 24/10/2007 Accepted Date: 11/02/2008 Online Date: 27/02/2008 Article note: Communicated by T. L. Grove.

This work reports the crystal-chemical characterization of Mn-rich amphiboles from the Grenville Marble of the Arnold mine, Fowler, St. Lawrence Co., New York (U.S.A.), which were previously described by Benimoff et al. (1991) as 'manganoan silicic edenite.' According to the new nomenclature scheme for monoclinic amphiboles (Leake et al. 2004) the ideal composition of reference, [sup.A]Na [sup.B](CaMn) [sup.C][[Mg.sub.5][sup.T]([Si.sub.7]Al)[O.sub.22][(OH).sub.2] with Ca > 1 apfu, is an end-member of the newly defined Group 5, and is named parvo-mangano-edenite. Re-examination of the original rock specimen showed significant inter- and intra-crystalline compositional variations, which can be expressed by the [sup.A][Na.sub.-1][sup.T][Al.sub.-1][sup.A][[??].sub.1][sup.T] [Si.sup.1] and [sup.B][Mn.sub.2][sup.B][Ca.sub.-2] exchange vectors. The first vector leads to parvo-manganotremolite, ideally [sup.A][??][sup.B] (CaMn)[sup.C][Mg.sub.5][sup.T][Si.sub.8][O.sub.22][(OH).sup.2] with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., [sup.A] ([Na.sub.0.74][K.sub.0.02])[sup.B]([Ca.sub.1.27][Mn.sub.0.73])[sup.C] ([Mg.sub.4.51][Mn.sup.2+.sub.0.28][Fe.sup.2+.sub.0.05][Fe.sup.3+.sub.0.03] [Al.sub.0.12][Ti.sub.0.01])[sup.T]([Si.sub.7.07][Al.sub.0.93] [O.sub.22][(OH).sub.2], has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) [Angstrom], [beta] = 104.55(1)[degrees], V = 907.1 [Angstrom] (Z = 2); the calculated density is 3.11 g/[cm.sup.3]. The parvo-mangano tremolite crystal, with composition [sup.A]([Na.sub.0.44][K.sub.0.01])[sup.B]([Ca.sub.1.13] [Mn.sub.0.83][Na.sub.0.04][sup.C]([Mg.sub.4.69][Mn.sup.2+.sub.0.21] [Fe.sup.2+.sub.0.03][Fe.sup.3+.sub.0.01][Al.sub.0.06])[sup.T] ([Si.sub.7.52][Al.sub.0.48])[O.sub.22][(OH).sup.2], has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4)[Angstrom], [beta] = [104.19(1)sup.o] V = 906.1 [[Angstrom].sup.3] 3 (Z = 2); the calculated density is 3.08 g/[cm.sup.3.]The different compositions are virtually indistinguishable under the optical microscope, but can be identified by a measure of their unit-cell parameters. The single-crystal FTIR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 [cm.sup.-1], plus shoulders at 3695, 3660, and 3641 [cm.sup.-1], respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles. Keywords: Analysis, chemical (mineral), amphiboles, crystal structure, parvo-mangano-edenite, parvo-manganotremolite, IR spectroscopy, new minerals

Experiments on a MORB (Mid Ocean Ridge Basalt)--derived amphibolite have been conducted in order to determine fluid-absent solidus and supersolidus phase relationships. The solidus has been determined in the range 4-14 kbar by using the incremental heating technique, tested against classical procedures. Peritectic clinopyroxene was produced below 10 kbar and epidote was the stable peritectic phase at pressures greater than 10 kbar for temperatures near the solidus. Garnet was the peritectic phase for temperatures above 800 [degrees] C and pressures of 10 to 14 kbar. The shape of the solidus was similar to previous estimations but the temperature interval between the high- and low-pressure regions was strongly reduced. With these new estimations, the possibilities for melting of the oceanic crust at P below 10 kbar are increased and, consequently, the number of tectonic scenarios needed for magma generation from amphibolite sources is enlarged. In the absence of free water, the solidus in the pressure region above 10 kbar is at higher T than previous estimations.

Mafic eclogites sampled from a restricted area in the Lanterman Range (Antarctica) retrogressed variably under amphibolite facies metamorphism. Assemblages range from well-preserved eclogite, with minor growth of Na-Ca amphibole, to strongly retrogressed ones with extensive development of Ca amphibole. [sup.40]Ar-[sup.39]Ar furnace step-heating experiments on the different amphiboles yield results varying from plateau ages of ~498 Ma to a near-plateau age of ~490 Ma, and the greater the amphibolite retrogression, the younger the age. [sup.40]Ar-[sup.39]Ar infrared laser-probe analyses on rock chips from a well-preserved eclogite and a slightly retrogressed one reveal the presence of an excess argon component. Whereas excess argon is invariably present in garnet and clinopyroxene developed under high-pressure metamorphism, it is heterogeneously distributed in amphibole on a millimetre scale. Results indicate that excess argon was incorporated during high-pressure metamorphism; this component was then lost during retrogression, while a change in composition of ambient argon to atmospheric argon occurred. New [sup.40]Ar-[sup.39]Ar data and previously published Sm-Nd garnet and U-Pb rutile ages obtained from the same well-preserved eclogite sample suggest that the oldest Na-Ca amphibole age is reliable and not an artefact due to the incorporation of excess argon. The variably retrogressed eclogites are thought to derive from different parts of the enclosing metasedimentary rocks that were variably invaded by fluids during amphibolite facies metamorphism. Thus the circulation of fluids promoting (re)crystallisation, and not temperature, was the main process controlling the rate of argon transport in the studied eclogites. The different [sup.40]Ar-[sup.39]Ar ages are interpreted to record diachronous amphibole growth at different crustal levels during exhumation. Data indicate that there was about a 10-Ma interval between the eclogite facies stage (at [greater than or equal to] 1.5 GPa) and the Ca amphibole-hydration forming reaction (at 0.3-0.5 GPa); this translates into an average exhumation rate of 3-4 km/ Ma.

The crystal structures and M-site populations of a series of unheated and heat-treated, near-binary members of the actinolite series were determined from single-crystal X-ray diffraction data. Small, systematic differences in crystal structure (mean and individual bond lengths, octahedral distortions, and Mg-Fe site preferences) between the actinolite and cummingtonite series are documented and rationalized in terms of the bond-valence model. Mg-[Fe.sup.-2+] site preferences among the M1, M2, and M3 sites in the actinolite series are small. Between M1 and M3, site preference ([Fe.sup.2+] slightly in favor of M1) is independent of temperature. Mg is favored in M2 over M1 in unheated samples (less strongly than in cummingtonite-grunerite), but [Fe.sup.2+] and Mg are virtually disordered in samples re-equilibrated at 700 [degrees] C. Site preference between M2 and M3 and possibly also between M1 and M2 appears to undergo a reversal as a result of heat treatment, but consideration of all sources of error renders this conclusion a tentative one, although the observation could be explained in terms of a bond valence deficiency. The ratio of [Fe.sup.2+]/Mg atoms on M4 cannot be accurately determined, but refinements indicate that, like cummingtonite-grunerite, it is larger than on all other M sites. Expansion of the cell dimensions with an increase in Fe/Mg ratio follows a pattern similar to that of thermal expansion, and a and [Beta] are influenced by cummingtonite-grunerite solid solution. The data are consistent with a cell volume of 942.8 [[Angstrom].sup.3] (or molar volume of 2.8388 J/bar) for end-member ferro-actinolite, a first approximation that assumes a reciprocal, quadrilateral [Delta]V of zero.

The structural changes associated with the C2/m-[P2.sub.1]/m phase transition in cummingtonite with (Fe + Mn)/(Fe + Mn + Mg) [similar to] 0.50 have been studied with single-crystal X-ray diffraction at various pressures up to 7.90 GPa and infrared spectroscopy up to 8.63 GPa. With increasing pressure, the crystal transforms from C2/m to [P2.sub.1]/m symmetry at [similar] 1.21 GPa, as determined by the appearance of reflections violating the C2/m space group. Infrared spectra provide additional evidence for the phase transition: A distinct splitting of OH stretching bands results from an increase from one to two nonequivalent OH positions. The C2/m-[P2.sub.1]/m transition is of weakly displacive first-order or tricritical character with apparent slope changes in the plots of the axial ratios a/b and a/c as a function of pressure. The unit-cell compression is considerably anisotropic with the a dimension in both C2/m and [P2.sub.1]/m phases being the most compressible. Major structural changes for the C2/m-[P2.sub.1]/m transition include: (1) One crystallographically distinct silicate chain becomes two discontinuously, coupled by the splitting of the M4-O5 bond, as well as M4O6, into two nonequivalent bonds, and (2) the M4-cation coordination increases from sixfold to sevenfold. More importantly, we observed a change in the sense of rotation for the A chain while the crystal structure maintains [P2.sub.1]/m symmetry: It is O rotated, as the B chain, at 1.32 GPa, but S-rotated at 2.97 GPa and higher pressures. As pressure increases from 1.32 to 7.90 GPa, there is a switching of the nearest bridging O atoms coordinated with the M4 cation: The M4-O5B distance contracts from 2.944 to 2.551 [Angstrom], whereas the M4-O6B distance increases from 2.754 to 2.903 [Angstrom]. Compression mechanisms for the low-and high-pressure polymorphs appear to be slightly different. In the C2/m phase, the behavior of the A and M4 sites controls the compression of the structure, whereas the response of the M1, M2, and M3 octahedra to pressure also plays a role in determining the compression of the [P2.sub.1]/m structure. The phase transition is regarded as primarily driven by the differential compression between the M4 and T sites, and the symmetry breaking provides a necessary tighter coordination for the M4 site. based on our data, the obvious changes in the hyperfine parameters of 57Fe in grunerite between 1.0 and 3.4 GPa, observed by Zhang and Hafner (1992), are likely to result from the C2/m-[P2.sub.1]/m structural transformation.

Accessory monazite crystals in granites are commonly unstable during amphibolite facies regional metamorphism and typically become mantled by newly formed apatite-allanite-epidote coronas. This distinct textural feature of altered monazite and its growth mechanism were studied in detail using backs-cattered electron imaging in a sample of metagranite from the Tauern Window in the eastern Alps. It appears that the outer rims of the former monazites were replaced directly by an aparite ring with tiny thorite intergrowths in connection with Ca supply through metamorphic fluid. Around the apatite zone, a proximal allanite ring and a distal epidote ring developed. This concentric corona structure, with the monazite core regularly preserved in the center, shows that the reaction kinetics were diffusion controlled and relatively slow. Quantitative electron microprobe analyses suggest that the elements released from monazite breakdown (P, REE, Y, Th, U), were diluted and redistributed in the newly formed apatite, allanite, and epidote overgrowth rings and were unable to leave the corona. This supports the common hypothesis that these trace elements are highly immobile during metamorphism. Furthermore, microprobe data suggest that the preserved monazite cores lost little, possibly none of their radiogenic lead during metamorphism. Thus, metastable monazite grains from orthogneisses appear to be very useful for constraining U-Th-Pb protolith ages. On the basis of these findings and a review of literature data, it seems that monazite stability in amphibolite facies metamorphic rocks depends strongly on lithologic composition. While breaking down in granitoids, monazite may grow during prograde metamorphism in other rocks such as metapelites.

Competition among atomic or molecular species for occupancy of crystallographic sites exaggerates correlations among chemical elements in suites of mineral chemical data, a phenomenon known as closure. Such exaggerated correlations can lead to incorrect conclusions about ionic substitution mechanisms and the petrological forces that drive them. Expressing mineral compositions in terms of a single additive component and molar concentrations of exchange components, eliminates the effects of closure. Statistical analysis of data so transformed can, in some instances, lead to conclusions distinct from analysis of the same data expressed in terms of ionic abundances. The chemical variability of fictive and naturally occurring amphiboles serves to illustrate the potential difficulties brought about by closure and the benefits of its elimination.

Amphiboles were synthesized at 750 [degrees] C, 1 kbar ([H.sub.2]O) for compositions at 20% intervals along the join potassium-richterite-tremolite. Structural variations, site occupancies, and modal analyses of the experimental products (amphibole + minor diopside, quartz, and enstatite) were characterized by Rietveld structure refinement, with final [R.sub.Bragg] indices in the range 4-6%, and by infrared spectroscopy in the principal OH-stretching region. Amphibole compositions were determined by (1) site-scattering refinement for the A and M4 sites that are occupied by (K, [square]) ([square] = vacancy) and (Na,Ca), respectively; and (2) mass-balance calculations involving the modal analysis and the nominal experimental product composition. These measurements agree within 1% absolute and show close agreement with electron-microprobe compositions for the two samples that we could analyze. Deviations from nominal amphibole composition are up to 19% absolute. The resulting relations between cell dimension and composition are linear. The major change in cell dimensions is a decrease of 0.25 [Angstrom] in a with increasing tremolite component. The infrared spectra show two principal peaks at 3735 and 3675 [cm.sup.-1], corresponding to the local arrangements MgMgMg-OH-AK (the Kr band) and MgMgMg-OH-A[square] (the Tr band), respectively. The relative variation in peak intensity as a function of amphibole composition shows that the molar absorptivities of the two bands are significantly different. The ratio of the molar absorptivities for the two bands is 2.2.

The replacement of anhydrous by hydrous minerals is commonly used to infer infiltration of a rock by [H.sub.2]O. However, our work indicates that the formation of pseudomorphic amphibole after clinopyroxene (uralitization) in low-grade metavolcanic rocks is a net dehydration process. In the ophiolitic Slate Creek complex, northern California, clinopyroxene exhibits four textural stages of alteration: (1) clinopyroxene, (2) clinopyroxene + chlorite [+ or -] amphibole, (3) amphibole + chlorite, and (4) amphibole. This transformation occurs in subgreenschist to greenschist facies rocks with a common matrix assemblage: quartz, albite, chlorite, epidote, titanite, [+ or -] amphibole, [+ or -] white mica, [+ or -] rare pumpellyite. A simple reaction space model based on these observations indicates that consumption of chlorite in the rock matrix releases more water than required to produce amphibole pseudomorphs of clinopyroxene. Thus, the net flux of [H.sub.2]O during uralitization of greenschist facies metavolcanic rocks is outward. These results imply that uralitization in metavolcanic rocks results from heating rather than whole-rock hydration, and that natural mass fluxes may be counter to fluxes inferred from textural evidence alone.

Amphibole from alkali granites in the Ramnes cauldron in the Oslo rift was altered hydrothermally by corrosion and growth through multiple events of fluid circulation. The alteration developed successive zones of amphibole at the crystal margins, resulting in a (1) brownish ferro-edenitic hornblende core (FE), (2) deep bluish-green hastingsitic hornblende zone (HH), and (3) light-greenish Ferich actinolite rim (FA). The edenitic core preserves the original igneous amphibole composition. The Cl content of amphibole strongly increases from the FE (0.78-0.82 wt%) to the HH zone (2.07-2.96 wt%) and abruptly decreases in the FA rim (0.01-0.36 wt%). In the Cl-rich HH amphibole zone, amphibole has characteristically high Cl content [2.96 wt%, 0.82 atoms per formula unit (apfu)] and high concentrations in both [4]Al (1.73 apfu) and A-site occupancy (0.86 apfu) with a large K/(Na + K) value of 0.47. Both [4]Al and A-site occupancy increase systematically with positive correlation with Cl content throughout the three amphibole zones. On the other hand, [Fe.sup.2+] content is not so simply correlated to the Cl content. Based on crystal structure considerations on Cl-rich amphiboles, the cation substitutions are illustrated by structural (geometrical) constraints for [4]Al and by a chemical constraint for [Fe.sup.2+]. These contributions for Cl incorporation are expressed empirically by ln[(Cl/OH).sub.amp] = ln[(Cl/OH).sub.fluid] + A[center dot][4]Al[center dot][Fe.sup.2+]/RT + B/RT, where A and B are constant. [4]Al[center dot][Fe.sup.2+] vs. ln(Cl/OH) plots of the three distinct amphibole zones suggest different fluid conditions in chemistry and temperature for the three zones. The zoning was developed through two stages of hydrothermal alteration. In the early hydrothermal event, a saline and high-temperature fluid altered the original hornblende (FE) to the Cl-rich HH zone. Late stage alteration by a high Fe/Cl and relatively low-temperature fluid partially over-printed the FA zone at the crystal margin.

Amphiboles were synthesized at 750 [degrees] C, 1 kbar ([H.sub.2]O) on the binary joins (nickel, magnesium)-richterite and (magnesium, cobalt)-richterite. Structural variations and site occupancies were characterized by Rietveld structure refinement, with final [R.sub.Bragg] indices in the range 4-9%, and by powder infrared spectroscopy in the principal OH-stretching region. Site-occupancy refinement of Ni-Mg and Mg-Co distributions give the partition coefficients over M1,3 and M2 where [K.sup.M2+] = [([M.sup.2+]/Mg).sub.M1,3]/[([M.sup.2+]/Mg).sub.M2], and [M.sup.2+] = [Ni.sup.2+] or [Co.sup.2+], [Mathematical Expression Omitted] and [Mathematical Expression Omitted]. Both [K.sub.d] values are greater than 1.0, whereas [6]r([Ni.sup.2+]) < [6]r(Mg) < [6]r([Co.sup.2+]); this indicates that cation size is not the primary factor affecting the ordering of Ni-Mg and Mg-Co over the octahedral sites. The infrared spectra of intermediate binary compositions show fine structure caused by ordering of Ni-Mg or Mg-Co over the M1,3 sites and by ordering of Na and [square] (vacancy) at the A site; thus intermediate compositions show an eight-band spectrum in the principal OH-stretching region. Precise band intensities were derived by nonlinear least-squares fitting of Gaussian band shapes to the observed spectra. The relative observed intensities of the combinations of bands [Mathematical Expression Omitted] and [Mathematical Expression Omitted] are in accord with the equations of Burns and Strens (1966), indicating that there is no significant variation in molar absorptivity with frequency (energy) for individual bands within a single sample (spectrum). Combined with the results of Skogby and Rossman (1991) on polarized single-crystal infrared spectra of amphiboles, this result suggests that different local configurations of M1,3 cations in amphiboles couple such that the transition probabilities of the associated OH groups are equal.

The amphibolite sole of the Josephine ophiolite (Madstone Cabin thrust) originated from the footwall of the Madstone Cabin thrust, which contains rocks from the Chetco complex. The underthrusting of a cold Josephine ophiolite by an active magmatic arc produced the emplacement of the ophiolite. The metamorphic soles of the Bay of Islands and Oman Ophiolites are different from those of the basal Josephine sole. The geochemically diverse amphibolites contain both metavolcanically and metaplutonically derived rocks.

Amphibole-bearing alkaline magma pockets in mantle xenoliths from Oahu are very primitive hydrous alkaline melts. The source of water for this hydrous melting is probably the plume. In plumes, the core is responsible for shield magmatism whereas the rim provides the water for post erosional volcanism. The melt pockets, such as amphibole-bearing (AMP) and spinel-bearing (SMP) glasses, are distinct in color and composition and are generally characterized by LREE-enriched patterns.

The variation of Fe oxy-component content in a titanian pargasite megacryst amphibole was determined at temperatures from 500 to 1200 degrees celsius, pressures from 1 atmosphere to 10 kbar, and fH2 from that of the IQF buffer to air. It showed a linear variation of log fH2 as a function of log (Fe3+ /Fe2+) at fixed T and P of the form log fH2 = a + b log(Fe3+ /Fe2+). The values of a and b are presented in a tabular form. The results indicate that the relatively high Fe3+/Fe(sub tot) of many natural kaersutitic amphibole occurs due to P-T-fH2 conditions of the upper mantle.

Amphiboles have been useful in petrogenetic models as indicators of temperature and pressure in igneous and metamorphic rock genesis. A calibrated thermodynamic solution model of Fe-MG amphiboles was developed. Molecular electronic probes were incorporated in the experiments. The model developed was subsequently used to create formulation that describe the systems of orthoamphibole and hornblende dynamics. The model showed consistency in comparison with previous results.

The concentration and isotopic composition of argon trapped in fluid inclusions within a mylonitic amphibolite were determined by combining electron microprobe, 40Ar/39Ar laser microprobe, and fluid inclusion analyses on the same samples. Such information provides constraints on the origin of metamorphic fluids. In our study, fluid in inclusions formed during ductile deformation was probably derived locally from the Paleozoic, Caledonian sequences, whereas brines, emplaced in cross-cutting fractures, were derived from Proterozoic footwall rocks several kilometers from the mylonite. By utilizing 38[Ar.sub.Cl] to correct for 'excess 40Ar,' we estimate a 370 Ma closure age for the amphibole, which is distinctly younger than the 440-480 Ma plateau ages indicated by step-heating spectra. The 'excess 40Ar' responsible for the anomalous plateaus probably resulted from diffusive re-equilibration of the amphibole with the fluids present during ductile deformation of the mylonite. The significantly younger cooling age determined by our method is concordant with ages determined from more recent geochronological studies in the region. These ages indicate that the western gneiss terrain, in our study area, records deformation and cooling associated with Siluro-Devonian tectonothermal metamorphism rather than an earlier Caledonian tectonism as proposed in previous 40Ar/39Ar investigations.

Data from (40)Ar-(39)Ar degassing spectra of amphiboles and pre-Alpine low-Si relic, Alpine low-Si and Alpine phengitic white micas from the central Tauern Window in the eastern Alps confirm a correlation between dated white micas and complex PT-evolution in the Window. The high 292 Ma age of higher Alpine is due to a blueschist facies event while the lower Alpine age demonstrates a late nappe pile cooling. Eclogite facies phengites that crystallize at a closure temperature for argon diffusion correlate to the footwall and hanging wall unit cooling ages.

The variation in Al content and Ts component in amphiboles is determined as a function of pressure and temperature using a new equation. The equation is used with suitable thermochemical data for the amphibole. The study of the variation indicates that the mineral assemblages have a strong influence on the pressure-temperature slopes of the Al isopleths.

The Rietveld structure refinement of amphiboles which are prepared along with the K(NaCa)Mg5(SiTi)O22(OH,F)2 from the (OH)2 to F2 atoms per formula unit (ap fu) indicates that the positively ionized Ti is fully ordered at the T2 site. The single-phase amphibole with 0.6 ap fu of titanium is determined for the OH end-member beginning composition. The complex amphibole-priderite-titanite-rutile, produced along the OH-F, joins with a reduction in the end-member fluor-richterite to 0.16 ap fu. A primary band for the titanium-rich OH-end member located at 3728 lines per centimeter is found in the infrared spectra of the principal OH-stretching region.

Dome-stage or backfold-deformation resulted in the formation of several structural features of the small-scale Acadian. Two stages of shearing existed in the Bronson Hill anticlinorium and the eastern side of the Monson Gneiss. Peak metamorphism preceded late-stage deformation during Acadian orogeny. There was a shift into orogen-parallel extension during this deformation. There may be a variation in the orientation of the direction of maximum extension at the backfold-stage uplift, from near vertical to near parallel and horizontal to the orogen at the stage of dome-formation.

Context.--Numerous articles in the scientific literature indicate that pathogenic fibers with respect to asbestos-related diseases are those that exceed 5 [micro]m in length. Nonetheless, some authors have expressed concerns regarding pathogenicity of shorter fibers. Objective.--To review the scientific evidence regarding pathogenicity (or lack thereof) of fibers less than or equal to 5 [micro]m in length, with particular attention to publications indicating that such fibers might be hazardous. Data Sources.--The scientific literature was reviewed for experimental animal studies and human studies that address the role of fiber size in causation of disease. Sources included original studies, as well as review articles related to the topic. Conclusions.--Experimental animal studies involving inhalation of fibers have demonstrated that fibers greater than 5 [micro]m in length are associated with both pulmonary fibrosis (ie, asbestosis) and malignancies (carcinoma of the lung and mesothelioma). There is no convincing evidence for a pathogenic effect for fibers that are 5 [micro]m or less in length. Fiber analyses of human lung tissue samples provide further support for pathogenicity of long fibers, particularly the more biopersistent amphibole fibers. Similar observations have been reported for nonasbestos mineral fibers. Concerns expressed by some authors (eg, the greater abundance of short fibers) do not alter these conclusions. Similarly, in vitro studies demonstrating biological activity of short fibers do not override inhalational studies of whole animals or the epidemiological findings in humans. (Arch Pathol Lab Med. 2015; 139:1052-1057; doi: 10.5858/arpa.2014-0466-RA), Early on during studies of experimental animals exposed by inhalation to asbestos fibers, it was recognized that fiber length was a determining factor in pathogenicity. Vorwald et al (1) concluded [...]

The mechanism behind pargasite stability relations is investigated. Results show that the addition of orthopyroxene effectively reduces the stability field of pargasite by approximately 200 degrees Celsius at one kb. Further calculations on the various behavioral aspects of pargasite are carried out, and the results indicate that pargasitic amphibole can form from a hydrous silicate melt at depths as shallow as eight to ten km.

Trace element abundances and zoning were measured in minerals from a metasomatized garnet-amphibolite block from the Catalina Schist, using both ion and proton microprobes. Zoisite strongly concentrates light rare earth elements (REEs), Sr, Y, and Pb; amphibole concentrates Ni and Zn; garnet concentrates Y and heavy REEs; and titanite concentrates Nb. Major and trace elements in the garnets are zoned. Garnets in the core of the block display an overgrowth enriched in Mn, Y, and heavy REE, on a Y-and heavy-REE-poor core. Zirconium values remain relatively constant. The element enrichments in the garnet overgrowth suggest mobility of REEs at either a hand-sample or regional scale at subduction-zone pressure-temperature conditions. Metamorphic fluids may selectively transport heavy REEs relative to some high field strength elements in some convergent-margin settings. The distribution of Sr and Pb within subduction zones may reflect the dehydration and melting behavior of epidote-group minerals.

Field observations in the Meatiq Dome, Eastern Desert, Egypt, show that amphibolite weathers to form massive outcrops and dense desert pavements that are extensively varnished. Laboratory-based reflectance spectra of representative samples (covering 5 [cm.sup.2]) and spectra extracted from Landsat thematic mapper data (covering 2.25 x [10.sup.4] [m.sup.2]) confirm that varnish dominates the reflectance properties of amphibolite outcrops. Field, laboratory, and Landsat data indicate that granite gneiss weathers to expose mainly bare rock, whereas granitic outcrops evolve to a mix of rock and locally generated sediment. Penetrative foliation in quartz phyllonite leads to production of slab-shaped clasts that cover the surface. The data show that mass wasting of the slabs results in a mix of rock, varnish, and sediment exposures. Outcrop reflectance properties for arid regions are thus dependent on both rock mineralogy and texture, because both parameters modulate bedrock weathering and erosion.

Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz-monzonites to late-stage felsic (63-75 wt% Si[O.sub.2]) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (± phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the 'liquid-like' intrusives of the biotite series (quartz-monzonites and felsic dikes) and follows the water-undersaturated albite-orthoclase cotectic (at 0.2-0.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt has the appropriate major-element composition for early biotite and amphibole crystallization, as is true of the high-Mg basalts from the Dariv Igneous Complex, the relative proximity of these two phases to the liquidus depends on the [H.sub.2]O concentration in the melt. Third, we compare the modeled high-K LLD and whole-rock geochemistry of the Dariv Igneous Complex to the more common calc-alkaline trend. Biotite and K-feldspar fractionation in the alkaline arc series results in the moderation of [K.sub.2]O/[Na.sub.2]O values and LILE concentrations with increasing Si[O.sub.2] as compared to the more common calc-alkaline series characterized by amphibole and plagioclase crystallization and strong increases in [K.sub.2]O/[Na.sub.2]O values. Lastly, we suggest that common calc-alkaline parental melts involve addition of a moderate pressure, sodic, fluid-dominated slab component while more alkaline primitive melts characterized by early biotite saturation involve the addition of a high-pressure potassic sediment melt. Keywords Alkaline * Biotite * Cumulate * Subduction zone * Mongolia, Introduction Based on the trace-element similarities, it is well established that subduction-related magmatism is essential for the production of continental crust (CC). Understanding how primitive arc basalts evolve and form [...]

Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45-66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877-895, 2012) have presented calibrations for calculating temperature, pressure, f[O.sub.2], melt [H.sub.2]O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic-andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated f[O.sub.2] and melt Si[O.sub.2] content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt [H.sub.2]O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi's pyroclasts yields calculated conditions of ~200-800 MPa, ~900-1,050°C, ~ NNO + 0.3-NNO + 1.1, ~ 3.7-7.2 wt% melt [H.sub.2]O, and ~58-71 wt% melt Si[O.sub.2]. We interpret the variations in calculated temperature, f[O.sub.2], and melt Si[O.sub.2] content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas, respectively, and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth. Keywords Amphibole * Chemometer * Barometer * Thermometer * Magma mixing * Merapi, Introduction Amphibole is a characteristic phase of mafic to felsic hydrous magmas (Arculus and Wills 1980; Cawthorn et al. 1973; Davidson et al. 2007). Its textures and composition have been [...]

Results from geologic mapping in south-central Virginia reveal that the stratigraphy and structure of the Carolina slate belt extend northward across a steep thermal gradient into upper amphibolite-facies correlative gneiss and schist.