GEOBAROMETRIC CONSTRAINTS ON THE DEPTH OF EMPLACEMENT OF GRANITE FROM THE LADAKH BATHOLITH, NORTHWEST HIMALAYA, INDIA

The Ladakh batholith is exposed along the 600km long and 20 to 80km wide NW—SE trending Ladakh range north of the Indus|Tsangpo Suture Zone. It was emplaced into an unmetamorphosed thick pile of mafic and felsic volcanics, ultramafics and sediments of Upper Cretaceous|Eocene age (Dras Volcanics, Khardung Volcanics). The granites from the Ladakh batholith within the Leh|Khardung La and Sakti—Chang La sections (samples collected between altitude of 3600m and 5440m above mean sea level, Fig.1) have been estimated for pressure and temperature of crystallization employing the hornblende geobarometer of Schmidt (1992) and hornblende|plagioclase geothermometer of Blundy and Holland (1990), with the results of pressure of (250±60)MPa and temperature of (695±22)℃. Therefore, these granites were solidified at a depth of (8 6±2)km suggesting an unroofing of this thickness in this region. The importance of this geobarometric data in conjunction with age data on the cooling and unroofing history of the Trans|Himalayan Ladakh batholith and geodynamic implications of the India—Asia collision are discussed.