DIFFERENT VARIETIES OF MIOCENE LEUCOGRANITE IN THE ARUN VALLEY—EVEREST—MAKALU AREA:FIELD RELATIONS, PETROLOGY AND ISOTOPE GEOCHEMISTRY

Large plutons and dyke networks of Miocene leucogranite, magnificently exposed in Makalu, Nuptse and Cho Oyu, occur in the Cho—Oyu—Everest—Makalu Range at the top of the Higher Himalayan Crystalline (HHC) nappe and along the South Tibetan Detachment (STD). In the Kharta\|Dzakar Chu area, in the western limb of the Arun transverse anticline, discordant leucogranite dykes were found in the Precambrian—Cambrian (?) sediments of the Tibetan Series just above the STD (North Col Formation), throughout the HHC nappe, in the thrust sheets of the MCT zone (Main Central Thrust II sensu Arita, 1983) and in the underlying granite gneisses of the Lesser Himalayan Crystallines (LHC) which crop out in the Ama Drime —Nyonno Ri Range. While Miocene leucogranites in the HHC and in the Tibetan Series are known from end to end of the Himalaya, Miocene leucogranites in the MCT zone and in the Lesser Himalaya have not been frequently described.