Trace element behavior in Miocene I-type and S-type granitic rocks in the Ohmine District, central Kii Peninsula

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Authors:Murata, Mamoru; Yoshida, Takeyoshi
Volume Title:Ganseki Kobutsu Kosho Gakkai-Shi Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
Source:Ganseki Kobutsu Kosho Gakkai-Shi = Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 80(6), p.227-245. Publisher: Nippon Ganseki Kobutsu Kosho Gakkai, c/o: Tohoku Daigaku Rigakubu, Sendai, Japan. ISSN: 0021-4825
Publication Date:1985
Note:In Japanese with English summary. 92 refs.; illus. incl. 6 tables, geol. sketch map
Summary:The Ohmine granitic rocks of Miocene age are divided into S-type and I-type. Abundance of trace elements of these rocks is given as well as petrography and major element abundance. The S-type granitic rocks are higher in SiO2, F and Rb/Sr, and lower in Sr than the I-type rocks. The Shirakura rocks (I-type) formed at an early stage are higher in differentiation index, Ce, Rb and Nb and lower in MgO/(MgO + FeO), Co, Cr, Ni and Sr than the Drogara rocks (S-type). On the basis of these data, the authors discuss the genesis of the granitic rocks. The S-type magma was formed by partial melting of biotite- and orthoclase-bearing sedimentary and/or metasedimentary rocks at approx 700°C and 5 kbar. The I- type granitic rocks would be generated by partial melting of Ca- amphibole and plagioclase-bearing intermediate igneous and/or meta-igneous rocks. Fractional crystallization of plagioclase, Ca-amphibole, and biotite occurred in the I-type magma. Judging from the trace element behaviour, it is unlikely that the granitic rocks are the products of large-scale magma-crust interaction and of mixing between basaltic and granitic magma. The authors also propose a revised classification of calc-alkaline granitic rocks; C-type (sub- to meta-aluminous, SrIo >0.708) and W-type (peraluminous, SrIo <0.708) beside I- and S-type; C-type is not yet found. I- and W-type occur in mature continental regions. S-type occurs in the regions consisting of immature crust without basaltic layer and in the region of crust exceeding 50 km in thickness such as continental margin and continent-continent collision zones. [K.O.]
Subjects:Cenozoic; Chemical composition; Classification; Differentiation; Distribution; Fractional crystallization; Geochemistry; Granites; Igneous rocks; Magmas; Miocene; Neogene; Partial melting; Plutonic rocks; Protoliths; Rb/Sr; Revision; Tertiary; Trace elements; Asia; Far East; Honshu; Japan; Kii Peninsula; C-type; Calk-alkalic composition; Fractionation; I-type; Ohmine; Outer Zone; S-type; W-type
Abstract Numbers:87M/6278
Record ID:1986002136
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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