| Co-Investigator(Kenkyū-buntansha) |
NAKASHIMA Kazuo Yamagata Univ., Fac. Sci., Assoc. Prof., 理学部, 助教授 (70159060)
TAKENO Setsuo Hiroshima Univ., Fac. Sci., Prof., 理学部, 教授 (00033829)
HOSHINO Kenichi Hiroshima Univ., Fac. Sci., Res. Ass., 理学部, 助手 (80190198)
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| Research Abstract |
The Hobenzan granitic bodies, forming a complex, are divided into the three rock facies, (1)Bi-Hb granodiorite, (2)Hb-Bi granite and(3)Bi granite. In order to know a behavior of fluids associated with granitic magmatism, we have attempted to clarify a spatial distribution of the primary fluid inclusions within the complex and analyzed the Cl and F contents of apatite and biotite. Fluid inclusions observed mainly in quartz grains are grouped into the three types, (1)Type I(gas-rich), (2)Type II(water-rich)and(3)Type III(chlorides-rich). Fluid inclusion characteristics represented by the vol. % of the inclusion types vary significantly even within a same rock facies. Therefore, there is no regularity in the distribution of the primary fluid inclusions within the complex. It is important to note that the Type I inclusions are commonly coexisting with the Type III ones even within a single quartz grain throughout the complex, indicating boiling during entrapment of the fluid inclusions. Water-unsaturated : granitic magmas become water-saturated in the higher level of the earth crust, resulting in a separation of hydrothermal fluids from the magmas. During this process, Cl is effectively partitioned into the fluids, especially under low pressure condition prevailing during cooling of the complex. Therefore, the resultant fluids bacome saline. On the other hand, boiling as evidenced by the fluid inclusion characteristics can yield much more saline fluids, which is reflecting on the compositions of both apatite and biotite, resulting in an enrichment of Cl and/or F. The presence of highly saline fluids, as well as Cl-rich apatite and biotite, is accordant with the abundant base metal mineralizations in and around the Hobenzan granitic complex.
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