Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pluton of the Altay Mountains, Northern Xinjiang

Coexisting quartz, feldspar and biotite vary widely in their δ18O values and display a remarkable 18O/16O disequilibrium relation; especially, a quartz-feldspar reversal (△ 18OQUartz_feldspar< 0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The 18O / 16O exchange reaction definitely occurred between granite and water. Initial δ18O values of the granite and exotic fluid are evaluated by the mass balance consideration. The conventional method of discrimination between various magma derivations simply with δ18O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the 18O / 16O exchange reaction is not accompanied by what geologists describe as petrological and mineralogical alteration effect. This decoupling relation implies that exchange reaction occurs at a relatively high temperature during subsolidus-postmagmatic cooling of magmas. The exchange mechanism is mainly diffusion-controlled. It is     

美国天然气水合物研究计划介绍

以美国近年来提出的天然气水合物研究计划和项目申请书为基础,介绍美国科学家在天然气水合物研究领域中所关心的关键科学与技术问题和研究焦点,供我国天然气水合物研究者在项目设计和开展研究工作时参考。美国天然气水合物研究关注的重点科学问题主要集中在 4个方面：天然气水合物的物理与化学特性研究;天然气水合物开采技术研究;天然气水合物灾害-安全性与海底稳定性研究;天然气水合物在全球碳循环中的作用研究。在研究方法上主要采取天然气水合物区的现场地质地球化学观测、实验室合成和测定及计算模拟,特别关注与水合物和油气冷泉相关的生命过程及与水合物的相互作用研究。     

Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pliiton of the Altay Mountains,Northern Xinjiang

Abstract Coexisting quartz, feldspar and biotite vary widely in their δ¹⁸O values and display a remarkable ¹⁸O / ¹⁶O disequilibrium relation; especially, a quartz–feldspar reversal (Δ ¹⁸O_{Quartz?feldspar}<0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The ¹⁸O / ¹⁶O exchange reaction definitely occurred between granite and water. Initial δ¹⁸O values of the granite and exotic fluid are evaluated by the mass balance consideration. The conventional method of discrimination between various magma derivations simply with δ¹⁸O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the ¹⁸O / ¹⁶O exchange reaction is not accompanied by what geologists describe as petrological and mineralogical alteration effect. This decoupling relation implies that exchange reaction occurs at a relatively high temperature during subsolidus–postmagmatic cooling of magmas. The exchange mechanism is mainly diffusion–controlled. It is demonstrated through quantitative modelling that the hydrothermal system associated with the Aral pluton is long–lived (0.8—6 Ma), with a relatively high fluid flow rate (3 x 10^?14 mol. s^?1) and high W/ R ratio (0.79-6.14). This means that an intense flow and convection may exist at the midcrustal level of orogenic magmatic arcs.