S-type and I-type granitic rocks of the Ohmine district, central Kii peninsula
S-type and I-type granitic rocks of the Ohmine district, central Kii peninsula
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纪伊半岛中部大峰地区的 S 型和 I 型花岗岩
DOI：
10.2465/ganko1941.77.267
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发表时间：
1982
期刊：
影响因子：
--
通讯作者：
M. Murata
中科院分区：
文献类型：
--
作者：
M. Murata
日本西南部喜井半岛中部中新世（14 Ma）的大明花岗岩侵入了Chichibu、Shimanto和kummano群的沉积岩中。这些花岗质岩石以北向南的小型高层岩体形式出现，即自北向南的多罗川、白仓、高濑、朝日、天谷山、白谷和片谷-木黑岩体。花岗岩的岩石学和化学特征显示北为i型（多罗川和白仓岩体），南为s型（高色、朝日、天谷山、白谷和片ago- mukuro岩体）；前者以角闪石为主，Al2O3/(CaO+Na2O+K2O)比低，后者含白云母，比值大于1.1。多洛川岩体为i型，由细粒斑状花岗闪长岩和花岗岩组成，在石英与正长石显微共生体和斜长石组成的岩体中嵌有自面状至亚面状斜长石、角闪石和黑云母等斑晶。白仓岩体为i型，由细粒斑状角闪花岗岩组成。Dorogawa块体与Shirakura块体的区别在于缺少正长石斑晶和高MgO/(MgO+FeOt)比值。与西南外带型花岗质岩石相比，i型岩石的CaO/FeO和Na2O/K2O比值较高，尤以多洛川花岗岩为突出。白仓i型花岗岩被高斯s型花岗岩侵入。s型、高濑、朝日、天谷山和白谷岩块体由斑岩质花岗岩组成，而片ago- mukuro块体由花岗斑岩和少量石英斑岩组成。这些s型岩石通常含有正长石斑晶和白云母，很少含有石英-正长石显微共生。研究区东南方著名的“熊野酸性岩”被认为是s型花岗岩的蚀变物。s型、Tenguyama和Shiratani块体的特征包括硅线石（包括纤维岩）、红柱石、石榴石、堇青石、正辉石、黑云母、刚玉和绿尖晶石。然而，这些矿物在乡村岩石和捕虏体中是不存在的。含有这些矿物的高品位变质岩在Kii半岛中部的地表暴露中也不存在。
The Ohmine granitic rocks of Miocene age (14 Ma) intrude into sedimentary rocks of the Chichibu, Shimanto and Kumano Groups in the central Kii peninsula, southwestern Japan. These granitic rocks occur as small high-level plutons in a N-S direction, namely from north to south, Dorogawa, Shirakura, Kose, Asahi, Tenguyama, Shiratani and Katago-Mukuro masses. Petrography and chemistry of these granitic rocks reveal I-type with north (Dorogawa and Shirakura masses) and S-type with south (Kose, Asahi, Tenguyama, Shiratani and Katago-Mukuro masses); the former characterized by the presence of hornblende and by low mole Al2O3/(CaO+Na2O+K2O) ratio, whereas the latter containing muscovite and the ratio higher than 1.1. The I-type, Dorogawa mass consists of fine-grained porphyritic granodiorite and granite, with phenocrysts of euhedral to subhedral plagioclase, hornblende and biotite set in groundmass composed of quartz and orthoclase micrographic intergrowth and plagioclase. The I-type, Shirakura mass is made up of fine-grained porphyritic hornblende granite. The Dorogawa mass is distinguished from the Shirakura mass by the absence of orthoclase phenocryst and high MgO/(MgO+FeOt) ratio. The I-types, especially the Dorogawa rocks, have higher CaO/FeO and Na2O/K2O ratios than the Southwest Outer Zone-type granitic rocks. The I-type, Shirakura granite is intruded by the S-type, Kose granite. The S-type, Kose, Asahi, Tenguyama and Shiratani masses consist of porphyritic granite, while Katago-Mukuro masses are composed of granite porphyry accompanying a small amount of quartz porphyry. These S-type rocks commonly contain orthoclse phenocryst and muscovite, and rarely contain quartz-orthoclase micrographic intergrowth. The well known “Kumano acidic rocks” occurring to the southeast of the studied area are considered deroofing equivalent of the S-type granitoids. The S-type, Tenguyama and Shiratani masses characteristically include clots of sillimanite (including fibrolite), andalusite, garnet, cordierite, orthopyroxene, biotite, corundum and green spinel. However, these minerals are absent in the country rocks and xenoliths. High-grade metamorphic rocks containing these minerals are also absent in the surface exposure of the central Kii peninsula.