Geology and Petrograpby of the Yamato Sanmyaku, East Antarctica

概要

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The Yamato Sanmyaku is a mountain range located at about 200km south of the Prins Harald Kyst, East Antarctica. The range forms an arcuate chain, extending 50km north-south, comprising seven massifs temporarily named A, B, C, D, E, F and G. The rocks of the area are divided into a charnockitic group (pyroxene gneisses and pyroxene syenites) and a granitic group (migmatitic gneisses, granitic gneiss, and microcline granites). In addition, metabasite interlayers and metadikes are found everywhere, associated with microcline pegmatites. The charnockitic group is involved in the older complex which crystallized under the conditions of a granulite facies. It has been partly modified by later granitization related to the granitic group which itself shows various stages of granitization. The grade of metamorphism increases towards the north, parallel to the gneissosity. The intercalated metabasite layers correspond to the host rocks in mineral paragenesis. Basic dikes are intruded obliquely into both the granitic gneisses and the pyroxene syenites, and are metamorphosed into various metabasites under the conditions of an amphibolite facies. This metamorphism is probably related to the subsequent intrusion of microcline granites and associated microcline pegmatite. A thrust movement from east to west represents the last stage of the structural evolution.
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