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1.
Maria Luce Frezzotti Gianfranco Di Vincenzo Claudio Ghezzo Ernst A. J. Burke 《Contributions to Mineralogy and Petrology》1994,117(2):111-123
Fine-grained peraluminous synkinematic leuco-monzogranites (SKG), of Cambro-Ordovician age, occur as veins and sills (up to 20–30 m thick) in the Deep Freeze Range, within the medium to high-grade metamorphics of the Wilson Terrane. Secondary fibrolite + graphite intergrowths occur in feldspars and subordinately in quartz. Four main solid and fluid inclusion populations are observed: primary mixed CO2+H2O inclusions + Al2SiO5 ± brines in garnet (type 1); early CO2-rich inclusions (± brines) in quartz (type 2); early CO2+CH4 (up to 4 mol%)±H2O inclusions + graphite + fibrolite in quartz (type 3); late CH4+CO2+N2 inclusions and H2O inclusions in quartz (type 4). Densities of type 1 inclusions are consistent with the crystallization conditions of SKG (750°C and 3 kbar). The other types are post-magmatic: densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature (700–550°C). Type 4 inclusions were trapped below 500°C. The SKG crystallized from a magma that was at some stage vapour-saturated; fluids were CO2-rich, possibly with immiscible brines. CO2-rich fluids (±brines) characterize the transition from magmatic to post-magmatic stages; progressive isobaric cooling (T<670°C) led to a continuous decrease off
O
2 can entering in the graphite stability field; at the same time, the feldspars reacted with CO2-rich fluids to give secondary fibrolite + graphite. Decrease ofT andf
O
2 can explain the progressive variation in the fluid composition from CO2-rich to CH4 and water dominated in a closed system (in situ evolution). The presence of N2 the late stages indicates interaction with external metamorphic fluids.Contribution within the network Hydrothermal/metamorphic water-rock interactions in crystalline rocks: a multidisciplinary approach on paleofluid analysis. CEC program: Human Capital and Mobility 相似文献
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The point of zero charge of forsterite shifts from an estimated 8.9 for the unaltered mineral to 8.4 and 8.0, respectively, after being weathered artificially for 1 h and 4 h. These results corroborate the presence of magnesium-deficient surfaces on the weathered minerals, also indicated by chemical analyses of the solutions. H+ and OH? are shown to be potential-determining ions in this system 相似文献
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Describing the spatial variability of heterogeneous snowpacks at a watershed or mountain‐front scale is important for improvements in large‐scale snowmelt modelling. Snowmelt depletion curves, which relate fractional decreases in snow‐covered area (SCA) against normalized decreases in snow water equivalent (SWE), are a common approach to scale‐up snowmelt models. Unfortunately, the kinds of ground‐based observations that are used to develop depletion curves are expensive to gather and impractical for large areas. We describe an approach incorporating remotely sensed fractional SCA (FSCA) data with coinciding daily snowmelt SWE outputs during ablation to quantify the shape of a depletion curve. We joined melt estimates from the Utah Energy Balance Snow Accumulation and Melt Model (UEB) with FSCA data calculated from a normalized difference snow index snow algorithm using NASA's moderate resolution imaging spectroradiometer (MODIS) visible (0·545–0·565 µm) and shortwave infrared (1·628–1·652 µm) reflectance data. We tested the approach at three 500 m2 study sites, one in central Idaho and the other two on the North Slope in the Alaskan arctic. The UEB‐MODIS‐derived depletion curves were evaluated against depletion curves derived from ground‐based snow surveys. Comparisons showed strong agreement between the independent estimates. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Frezzotti Maria Luce; Ferrando Simona; Dallai Luigi; Compagnoni Roberto 《Journal of Petrology》2007,48(6):1219-1241
Minerals, fluid inclusions and stable isotopes have been studiedin ultrahigh-pressure (UHP) OH-rich topazkyanite quartzitesfrom Hushan (west of Dongai), in southern Sulu (China). Thequartzites underwent a metamorphic evolution characterized bya peak stage (3·5 GPa and 730820°C) with theanhydrous assemblage coesite + kyanite I, followed by an earlynear-isothermal decompression stage (2·9 GPa and 705780°C)with growth of kyanite II, muscovite, and OH-rich topaz, andby decompression-cooling stages, represented by paragonite (1·9GPa and 700780°C) and pyrophyllite (0·3 GPaand 400°C) on kyanite (I and II) and OH-rich topaz, respectively.These rocks may exhibit unusually low 18O and D values acquiredbefore undergoing UHP metamorphism. Five distinct fluid generationsare recognized. Type I: concentrated peak solutions rich inSi, Al, and alkalis, present within multiphase inclusions inkyanite I. Type II: CaCl2-rich brines present during the growthof early retrograde OH-rich topaz. Type III, IV, and V: lateaqueous fluids of variable salinity, and rare CO2 present duringamphibolite- and late greenschist-facies conditions. A numberof conclusions may be drawn from these relationships that havean effect on fluid evolution in deeply subducted continentalrocks. (1) At a pressure of about 3·5 GPa alkalialumino-silicateaqueous solutions, with compositions intermediate between H2Ofluid and melt (H2O > 25 and 50 wt %) evolved from quartzites,probably generated by dehydration reactions. (2) During earlydecompression stages, at the transition from UHP to high-pressure(2·9 GPa) conditions, brines of external origin withhigher water contents (82 wt % H2O) initiated the growth ofOH-rich topaz and muscovite. (3) The subsequent decompression,at P <2 GPa, was defined by a limited circulation of NaClaqueous fluids, and CO2 infiltration. Overall, fluid inclusionsand stable isotopes highlight a metamorphic fluidrockinteraction characterized by internally derived intermediateaqueous solutions at UHP, followed by infiltration of Cl-richbrines with higher water activities. KEY WORDS: ultrahigh-pressure metamorphism; OH-rich topaz; fluid inclusions; stable isotopes; supercritical liquids 相似文献
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Quantification of both normal and right‐lateral late Quaternary activity along the Kongur Shan extensional system,Chinese Pamir 下载免费PDF全文
The Kongur Shan Extensional System (KES) is a ~250 km long normal fault system that bounds the Muji–Tashkorgan basin of the Chinese Pamir. It accommodates E–W extension due to the northward indentation of the Pamir salient, and its late Miocene activity has been the focus of tectonic studies. While the KES has a main normal component, ~WNW–ESE‐striking segments have an additional right‐lateral strike‐slip component. Here, we quantify late Quaternary horizontal and vertical slip rates at three locations along the KES, where active faults cut and offset abandoned geomorphic features. We find rates of >3–4 mm a?1 (horizontal) along the western Muji fault in the north and of ~1.7 mm a?1 (vertical) and ~1 mm a?1 (horizontal) along the Kongur Shan fault in the south during the late Pleistocene. These rates are consistent with GPS and late Miocene rates, and imply that E–W extension in the Muji–Tashkorgan basin is faster in the north than in the south. 相似文献
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