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[SCG45-08] Petrological characteristics of two types of episyenites in Hakata Island, Ehime Prefecture: contrasting behavior of elements during metasomatism
Keywords:Hakata Island, Episyenite, metasomatism, Fluid-rock interaction, Granitoids, elemental behaviour
Metasomatism is ascribed to pervasive fluids, leading to mass transfer and ultimately contributing to chemical evolution of continental crust. In this study, we describe field occurrences, petrographic remarks and geochemical characteristics of adjacent two contrasting episyenites associated with Cretaceous granitoid from Hakata Island, Ehime Prefecture. We further discuss behavior of elements during metasomatism.
The episyenites in the study area can be grouped into pearl white-colored (PW) episyenite and oyster white-colored (OW) episyenite. The whole-rock REE compositions of the PW episyenite are lower than those of host granitoid, while those of OW episyenite are higher than the granitoid.
Chemical changes during metasomatism are estimated from the isocon diagram assuming the Al to be immobile element. Compared to the host granitoid, both of episyenites show an increase in alkaline metal elements. On the other hand, most of the elements such as Ti, Fe, Ca (hosted in mafic minerals), and Zr are decreased in PW episyenite and increased in OW episyenite.
The PW episyenite shows similar εSrt (90 Ma) and lower εNdt (90 Ma) compared to the host granitoid.
Based on the geochemical and isotopic data obtained in this study, we interpret that the PW episyenite have been formed through the removal of metal elements (except alkaline metal elements) from the host granitoid, followed by the miner involvement of fluids with lower Nd isotopic composition. On the other hand, the OW episyenite have been formed through the addition of metal elements which have been removed from the host granite.
The episyenites in the study area can be grouped into pearl white-colored (PW) episyenite and oyster white-colored (OW) episyenite. The whole-rock REE compositions of the PW episyenite are lower than those of host granitoid, while those of OW episyenite are higher than the granitoid.
Chemical changes during metasomatism are estimated from the isocon diagram assuming the Al to be immobile element. Compared to the host granitoid, both of episyenites show an increase in alkaline metal elements. On the other hand, most of the elements such as Ti, Fe, Ca (hosted in mafic minerals), and Zr are decreased in PW episyenite and increased in OW episyenite.
The PW episyenite shows similar εSrt (90 Ma) and lower εNdt (90 Ma) compared to the host granitoid.
Based on the geochemical and isotopic data obtained in this study, we interpret that the PW episyenite have been formed through the removal of metal elements (except alkaline metal elements) from the host granitoid, followed by the miner involvement of fluids with lower Nd isotopic composition. On the other hand, the OW episyenite have been formed through the addition of metal elements which have been removed from the host granite.