Journal - Occurrence of augen gneisses in the Nepal Himalayas

Occurrence of augen gneisses in the Nepal Himalayas

Takashi Kano

Department of Mineralogical Science and Geology, Yamaguchi University

Yamaguchi 753, Japan

Jour. Nep. Geol. Soc., Vol. 4, Special Issue, 1984, 121-139


Abstract

The Nepal Himalaya is divided into three regions based on the extent and style of the nappe structure and of the associated augen gneisses and granitoids. The central Nepal Himalayas are geologically distinguished by simple homoclinal structure, narrow Himalayan gneiss zone and less amount of the augen gneiss and granitoid. The west Nepal Himalaya are recognized by the extreme displacement of the Himalayan gneiss producing a large klippe, wide distribution of the augen gneiss and vast intrusive body of tourmaline granite in the root zaone. The east Nepal Himalayas are characterized by the development of nappe structure, widespread augen gneiss and well exposed migmatitic gneiss and tourmaline granite in the root zone. The nappe structure seems to be developed in the region where the augen gneiss and tourmaline granite or migmatitic gneiss are widely activated.

 

It is concluded that the augen gneiss including potash-feldspar megacrysts are regarded as the sheared equivalents of the younger tourmaline granites emplaced along the thrusting zone, because of the gradational series of rock facies (blastomylonitic, phyllitic, migmatitic augen gneiss ® gneissose porphyritic granite ®  massive granite) observed within single intrusive body of the tourmaline granite.

 

The displacement of the nappe on the MCT is associated with the injection of the tourmaline granites some of which are emplaced into the MCT zone producing the augen gneisses.

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