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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 [...]

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 [...]

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 [...]