Oxygen isotope trends and anomalies in granitoids of the Tibetan plateau

Extreme Transhimalayan (oceanic, mantle, I-type) and High Himalayan (anatectic, collision, S-type) granitoids in the Himalaya, Kashmir, and Tibet range in their original oxygen isotope composition from 6 to 7.5 and from 10 to 12.5parts per thousand delta(18)O(SMOW), respectively. In the sutured Paleozoic and Mesozoic orogen of the eastern Tibetan plateau, purely oceanic batholiths seem absent (Shalouli Shan 8 - 10parts per thousand), but High Himalayan values are matched in Dongda Shan and at Luxi. Towards the east, oceanic values are found again only on the margin of the Yangtse platform. The regional pattern of normal oxygen isotope data provides a background for anomalous feldspars (to - 1parts per thousand) in Lhasa Granite and in the active geothermal system at Yangbachen, recharged by similar to 6000 in a.s.l. meteoric water. For Lhasa Granite, oxygen isotope exchange paths and preliminary K-Ar dating of feldspars suggest exchange with meteoric water from over 3000 in altitude before 20 Ma ago. (C) 2002 Elsevier Science Ltd. All rights reserved.