SUBDUCTION OF INDIA BENEATH TIBET:MAGMATISM EVIDENCE
The northward subduction of India plate beneath Tibet followed the onset of India collided with Asia is one of the most fundamental questions to the evolution of Tibetan plateau. But it is still in debate. Recently, increasing geophysical studies favor the model that India has subducted beneath Asia to the depth of 200 km beneath the plateau to the Banggong-Nujiang suture. Age, petrology and geochemistry of the wide-spreading postcollisional magmatism in Tibetan plateau allow us to reveal the composition and processes of the plateau's lithosphere after India collided with Asia around 55 Ma ago. Our results suggest that the Gangdese belt is geochemically a part of the north Tibet (Qiangtang, Kunlun, Hoh Kil). North Tibet has an undisturbed, ancient enriched upper mantle source region. Isotopic geochemistry evidence show that India has subducted beneath Gangdese to the north of Yarlung Zangpo suture 13～25 Ma ago. Taking the northward ongoing motion of India into account, we conclude that India plate should have subducted beneath Tibet to Bangong-Nujiang suture at present-day. This model agree very well with the results of helium geochemistry of spring water from southern Tibet and some geophysical survey got recently.