Origin of water in granitic magma.

点击翻译按钮获取中文摘要

There are several approaches to study the origin of granitic magma. Our Japanese Group, the leader is Prof. Y.Kuroda, has established the method to explore the origin of water incorporated granitic magma, judging from the relationship between the chemical compositions (X_<Fe>) and hydrogen isotopic ratios (deltaD) of co-existing biotite and hornblende in granitic rocks. We have already investigated many granitic masses from Japan and also from Scandinavian shield and Italian Alps. But some problems have not settled yet.So, we collected many samples from the Miyazu granite in the San'in belt, the Hiroshima granite in the Sanyo belt, and the Tokuwa granite mass in Fossa Magna and analyzed chemically and isotopically. The results are as follows,(1) The Miyazu granite suggest that belongs the equilibrium type in regard to deltaD-X_<Fe> pattern, but the range of X_<Fe> values is widely scattered from 0.3 to 0.8, and deltaD values also ranged from -80 to -130*. This pattern is nearly the sam … More e to the Shirakawa granite in the Hida Mountains. The primary equilibrium relationships between co-existing biotite nad hornblende are seemed to be broken down after the emplacement of the mass by hydrothermal event.(2) the Hiroshima granite shows a very complicated pattern on the deltaD-X_<Fe> diagram, the range of X_<Fe> values of biotite and hornblende are some wide, 0.6-0.85, and many tie-line between coexisting biotite and hornblende on the diagram show the disequilibrium relationship. This characteristics are explained as the isotopic exchange had took place during the hydrothermal events observed in the granite-mass.(3) The Tokuwa mass is composed of magnetite-and ilmenite-series granites. but the slopes of tie-line between co-existing biotite and hornblende from both series are essentially parallel to that derived from Suzuoki-Epstein's experimental work, that is, they show typical equilibrium relationship. The fact is explained that the isotopic equilibration has been held during the crystallization of biotite and hornblende from the magma containning sufficient water, and there is no difference of D/H ratio and temperature in the magma between the magnetite-series and ilmenite-series granites. Less