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New U-Pb zircon ages from volcanic, plutonic, and sedimentary units in the Avalonian Caledonia terrane of southern New Brunswick provide better timing constraints in this geologically complex area. Previous ca. 620 Ma ages from the Broad River Group are now corroborated by additional dates from felsic tuff in the Gordon Falls Formation and rhyolite in the former Fairfield (now East Branch Black River) Formation of 620 [+ or -] 5 Ma and 622 [+ or -] 1.9 Ma, respectively. Combined with ages ranging from ca. 625 Ma to 615 Ma from cross-cutting plutons, the data suggest that the minimum age of the Broad River Group is about 615 Ma. A quartz-feldspar porphyry dyke in mafic volcanic rocks of the previously undated Long Beach Formation yielded an igneous crystallization age of 685 [+ or -] 10 Ma, the oldest unit yet dated in the Caledonia terrane but similar in age to porphyry in the Stirling belt in the Avalonian Mira terrane of Nova Scotia. The age of the Coldbrook Group was constrained previously by U-Pb (zircon) ages of volcanic rocks between 560 and 550 Ma as well as by similar ages from comagmatic plutons. Five additional samples from both volcanic and plutonic units lie in the same range of 560-550 Ma, including errors, demonstrating that the Coldbrook Group and related plutons formed in less than 10 million years. Such a large volume of mainly felsic magma erupted and emplaced in a short time span suggests a 'supereruption/supervolcano' environment such as the late Cenozoic southwestern USA but not yet recognized at ca. 560-550 Ma elsewhere in Avalonia. Two units yielded Paleozoic ages: felsite of the Bloomsbury Mountain Formation with a zircon population at 427 [+ or -] 9 Ma, indicating a Silurian maximum emplacement age, and dacite of the Grassy Lake Formation with several zircon grains at 382.8 [+ or -] 8.3 Ma, indicating a maximum age of middle Devonian, the first rocks of this age to be identified in the Caledonia terrane. De nouveaux ages U - Pb sur zircon provenant d'unites volcaniques, plutoniques et sedimentaires dans le terrane avalonien Caledonie du sud du Nouveau-Brunswick fournissent de meilleures contraintes temporelles dans cette region geologiquement complexe. Les ages d'environ 620 Ma precedemment obtenus du Groupe de Broad River sont maintenant appuyes par des dates supplementaires provenant du tuf felsique dans la Formation de Gordon Falls et de la rhyolite dans l'ancienne Formation de Fairfield (maintenant East Branch Black River) de 620 [+ or -] 5 Ma et 622 [+ or -] 1,9 Ma, respectivement. Combine avec des ages allant de 625 Ma a 615 Ma a partir de plutons encaisses, les donnees suggerent que l'age minimum du Broad River Group est d'environ 615 Ma. Un dyke de porphyre de quartz-feldspath dans des roches volcaniques mafiques de la Formation de Long Beach non datee a donne un age de cristallisation ignee de 685 [+ or -] 10 Ma, la plus ancienne unite encore datee dans le terrane de Caledonie mais similaire en age au porphyre dans la ceinture de Stirling dans le terrane avalonien Mira de la Nouvelle-Ecosse. L'age du Groupe de Coldbrook etait auparavant limite par les ages U - Pb (zircon) des roches volcaniques entre 560 et 550 Ma, ainsi que par les ages similaires des plutons co-magmatiques. Cinq echantillons supplementaires provenant des unites volcaniques et plutoniques se situent dans la meme periode de 560 a 550 Ma, y compris les erreurs, demontrant que le Groupe de Coldbrook et les plutons associes se sont formes en moins de 10 millions d'annees. Un volume aussi important de magma principalement felsique ayant entre en eruption et mis en place dans un court laps de temps suggere un environnement de 'super-eruption / supervolcan' tel que le sud-ouest du Cenozoique superieur aux etats-Unis, mais pas encore reconnu entre 560-550 Ma ailleurs dans la zone d'Avalonia. Deux unites ont donne des ages paleozoiques: la felsite de la Formation de Bloomsbury Mountain avec une population de zircon a 427 [+ or -] 9 Ma, indiquant un age de mise en place maximal du Silurien, et la dacite de la Formation de Grassy Lake avec plusieurs grains de zircon a 382,8 [+ or -] 8,3 Ma, indiquant un age maximal du Devonien moyen, premieres roches de cet age identifiees dans le terrane de Caledonie. [Traduit par la redaction], INTRODUCTION The Caledonia terrane is a large area of mainly Neoproterozoic rocks that forms the Avalonian part of southern New Brunswick, extending from the Saint John area to the northeast [...]

The chemical composition of fluid inclusions in quartz crystals from Alpine fissure veins was determined by combination of microthermometry, Raman spectroscopy, and LA-ICPMS analysis. The veins are hosted in carbonate-bearing, organic-rich, low-grade metamorphic metapelites of the Bundnerschiefer of the eastern Central Alps (Switzerland). This strongly deformed tectonic unit is interpreted as a partly subducted accretionary wedge, on the basis of widespread carpholite assemblages that were later overprinted by lower greenschist facies metamorphism. Veins and their host rocks from two locations were studied to compare several indicators for the conditions during metamorphism, including illite crystallinity, graphite thermometry, stability of mineral assemblages, chlorite thermometry, fluid inclusion solute thermometry, and fluid inclusion isochores. Fluid inclusions are aqueous two-phase with 3.7-4.0 wt% equivalent NaCl at Thusis and 1.6-1.7 wt% at Schiers. Reproducible concentrations of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, B, Al, Mn, Cu, Zn, Pb, As, Sb, Cl, Br, and S could be determined for 97 fluid inclusion assemblages. Fluid and mineral geothermometry consistently indicate temperatures of 320 ± 20°C for the host rocks at Thusis and of 250 ± 30°C at Schiers. Combining fluid inclusion isochores with independent geothermometers results in pressure estimates of 2.8-3.8 kbar for Thusis, and of 3.3-3.4 kbar for Schiers. Pressure-temperature estimates are confirmed by pseudosection modeling. Fluid compositions and petrological modeling consistently demonstrate that chemical fluid-rock equilibrium was attained during vein formation, indicating that the fluids originated locally by metamorphic dehydration during near-isothermal decompression in a rock-buffered system. Keywords Fluid inclusions * LA-ICPMS * Low-grade metamorphism * Accretionary wedge * Veins * Fluid-rock equilibrium * Graphitic metasediments, Introduction The chemical composition of metamorphic fluids is of fundamental importance for predicting mineral stability, evaluating the pressure-temperature history of rocks, and assessing rates and scales of mass transfer during [...]

We have reconstructed the compositional evolution of the silicate and carbonate melt, and various crystalline phases in the subvolcanic reservoir of Kerimasi Volcano in the East African Rift. Trace element concentrations of silicate and carbonate melt inclusions trapped in nepheline, apatite and magnetite from plutonic afrikandite (clinopyroxene-nepheline-perovskite-magnetite-melilite rock) and calciocarbonatite (calcite-apatite-magnetite-perovskite-monticellite-phlogopite rock) show that liquid immiscibility occurred during the generation of carbonatite magmas from a C[O.sub.2]-rich melilite-nephelinite magma formed at relatively high temperatures (1,100 °C). This carbonatite magma is notably more calcic and less alkaline than that occurring at Oldoinyo Lengai. The CaO-rich (32-41 wt%) nature and alkali-'poor' (at least 7-10 wt% [Na.sub.2]O + [K.sub.2]O) nature of these high-temperature (>1,000 °C) carbonate melts result from strong partitioning of Ca (relative to Mg, Fe and Mn) in the immiscible carbonate and the CaO-rich nature (12-17 wt%) of its silicate parent (e.g., melilite-nephelinite). Evolution of the Kerimasi carbonate magma can result in the formation of natrocarbonatite melts with similar composition to those of Oldoinyo Lengai, but with pronounced depletion in REE and HFSE elements. We suggest that this compositional difference results from the different initial parental magmas, e.g., melilite-nephelinite at Kerimasi and a nephelinite at Oldoinyo Lengai. The difference in parental magma composition led to a significant difference in the fractionating mineral phase assemblage and the element partitioning systematics upon silicate-carbonate melt immiscibility. LA-ICP-MS analysis of coeval silicate and carbonate melt inclusions provides an opportunity to infer carbonate melt/silicate melt partition coefficients for a wide range of elements. These data show that Li, Na, Pb, Ca, Sr, Ba, B, all REE (except Sc), U, V, Nb, Ta, P, Mo, W and S are partitioned into the carbonate melt, whereas Mg, Mn, Fe, Co, Cu, Zn, Al, Sc, Ti, Hf and Zr are partitioned into the silicate melt. Potassium and Rb show no preferential partitioning. Kerimasi melt inclusions show that the immiscible calcic carbonate melt is strongly enriched in Sr, Ba, Pb, LREE, P, W, Mo and S relative to other trace elements. Comparison of our data with experimental results indicates that preferential partitioning of oxidized sulfur (as S[O.sub.4.sup.2-]), Ca and P (as P[O.sub.4.sup.3-]) into the carbonate melt may promote the partitioning of Nb, Ta, Pb and all REE, excluding Sc, into this phase. Therefore, it is suggested that P and S enrichment in calcic carbonate magmas promotes the genesis of REE-rich carbonatites by liquid immiscibility. Our study shows that changes in the partition coefficients of elements between minerals and the coexisting melts along the liquid line of descent are rather significant at Kerimasi. This is why, in addition to the REE, Nb, Ta and Zr are also enriched in Kerimasi calciocarbonatites. We consider significant amounts of apatite and perovskite precipitated from melilite-nephelinite-derived carbonate melt as igneous minerals can have high LREE, Nb and Zr contents relative to other carbonatite minerals. Keywords Liquid immiscibility * Melt inclusions * Element partitioning * Kerimasi * LA-ICP-MS, Introduction The study of primary melt inclusions is a powerful tool to reconstruct the compositional evolution of various melt phases in magmas, but has rarely been utilized in carbonate-rich systems [...]