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Oxygen Isotope Exchange Kinetics Between Coexisting Minerals and Water in the Aral Granite Pliiton of the Altay Mountains, Northern Xinjiang
Author(s) -
Wei Liu,
Baichu He,
Zhensheng Chen
Publication year - 1996
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.1996.mp9004004.x
Subject(s) - pluton , geology , geochemistry , quartz , feldspar , hydrothermal circulation , plagioclase , biotite , magmatic water , isotopes of oxygen , mineralogy , magma , fluid inclusions , volcano , tectonics , paleontology , seismology
Coexisting quartz, feldspar and biotite vary widely in their δ 18 O values and display a remarkable 18 O / 16 O disequilibrium relation; especially, a quartz–feldspar reversal (Δ 18 O Quartz−feldspar <0) exsists in the Aral granite pluton of the Altay Mountains, northern Xinjiang. The 18 O / 16 O exchange reaction definitely occurred between granite and water. Initial δ 18 O 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 δ 18 O values of either whole rock or separate minerals is misleading and unreliable. Experiments carried out by the authors show that the 18 O / 16 O 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.