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首页> 外文期刊>Contributions to Mineralogy and Petrology >Major and trace-element composition and pressure-temperature evolution of rock-buffered fluids in low-grade accretionary-wedge metasediments, Central Alps
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Major and trace-element composition and pressure-temperature evolution of rock-buffered fluids in low-grade accretionary-wedge metasediments, Central Alps

机译：中阿尔卑斯山低品位增高楔变沉积物中岩石缓冲液的主要和微量元素组成及压力-温度演化

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摘要

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 thermom-etry, 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 al 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.
机译：通过微温度计，拉曼光谱和LA-ICPMS分析的组合，确定了来自高山裂缝脉的石英晶体中流体包裹体的化学成分。脉位于中部阿尔卑斯山东部（瑞士）的Bundnerschiefer含碳酸盐，有机质丰富，低品位的变质变质岩中。这种强烈变形的构造单元被解释为部分俯冲的增生楔，其基础是广泛的陨石组合，后来被较低的绿片岩相变质所覆盖。研究了来自两个位置的静脉和它们的宿主岩石，以比较变质过程中条件的几个指标，包括伊利石结晶度，石墨测温，矿物组合的稳定性，绿泥石测温法，流体包裹体溶质测温法和流体包裹体等时线。流体夹杂物是水两相，其中在Teisis的当量NaCl为3.7-4.0％，在Schiers的当量为1.6-1.7wt％。对于97种流体夹杂物，可以确定Li，Na，K，Rb，Cs，Mg，Ca，Sr，Ba，B，Al，Mn，Cu，Zn，Pb，As，Sb，Cl，Br和S的可再现浓度的集合。流体和矿物地热法一致地表明，图西斯的母岩温度为320±20°C，席尔斯为250±30°C。将流体包裹体等渗线与独立的地热仪相结合，对于图西斯而言，压力估计值为2.8-3.8 kbar，对于席尔斯而言，压力估计值为3.3-3.4 kbar。压力-温度估计值通过伪截面模型确定。流体成分和岩石学模型一致地表明，在静脉形成过程中达到了化学流体-岩石平衡，表明在岩石缓冲系统中，近等温减压过程中，流体是通过变质脱水而局部产生的。

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