Rb-Sr Geochronology of the Rocks of the Himalayas, Eastern Nepal : Part II. The Age and the Origin of the Granite on the Higher Himalayas

Abstract

Rb-Sr isotopic measurements are made on the Makalu granite, which is one of leucocratic granite occurring sporadically in the high range of the Himalayas. The granite is intruded between the Himalayan gneiss and the Tethyan sediments. In this study, Rb-Sr analyses have been made on both whole rock and small sliced rock. The Rb-Sr isotopic analytical results on whole rock of the Makalu granite define the age of 92.7±9.4 m.y. The analytical results on small slabs suggest that Sr isotopic redistribution occurred after the intrusion of the granite. The initial 87Sr/86Sr ratio of the Makalu granite is 0.7433±0.0019 and is remarkably high. Such high ratio indicates that the granite originated from the remelting or partial remelting of old crustal materials such as Himalayan gneiss.