The granitic gneisses from the Namjagbarwa Group Complex within the eastern Himalayan syntaxis,Xizang

The old granites from the Higher Himalayan crystallines within the eastern Himalayan syntaxis,Xizang are mostly emplaced into the Zhibai Formation Complex in the Namjagbarwa Group Complex and constitute the granitic gneissic suites resulted from the granulite-facies metamorphism.Nine granitic intrusives may be delineated in the Luxia region,and the rock types include granodioritic gneiss,biotite granitic gneiss and dioritic gneiss.The features of the "S" type granites indicate by chemical compositions suggests the possibility of the addition of deep-seated mantle-derived matter.These granites may be localized at the depth of 1-5 km and 552-525 Ma in age latest Neoproterozoic,representing the products generated during the Pan-African intracontinental orogenesis.The presence of the Pan-African granitic gneisses and associated amphibolite has disclosed that the amphibolite-facies metamorphism accompanied with ganitic intrusion once occurred during the latest Neoproterozoic 575.20±5.24 Ma-525 Ma.This tectonic-thermal event marked the formation of the Higher Himalayan crystalline basement,and a new cycle of tectonism in the surveyed area.