The chronological characteristics of the Gangdese granite in the Ali area and its tectonic significance
Mo Yasi1,2, Wang Shifeng3, Wang Chao1,2
1. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101;
2. University of Chinese Academy of Science, Beijing 100049;
3. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100085
The Gangdese granite belt is a 2 500 km long,100～300 km wide volcanic belt almost E-W striking along the north side of the Yalu-Zangpo suture in South Tibet. The granite around Kailas area experienced periods of tectonic events during the collision of the Indian and Eurasian plates,such as the activity of the Great Counter Thrust fault and the Karakorum fault,which complicated the situation between the granites and the faults. For example,some researchers attributed the 32～25 Ma granite around the North Ayilari range to the syn-tectonic granites of the Karakorum fault,which is in high debate nowadays. In this paper,new zircon U-Pb data around Kalas area demonstrates that the Gangdese granites are consisted of 110 Ma,60 Ma and 50 Ma three ages of granite. Zircon ages are similar whether in ductile shear zone or not showing no deformation of zircons by the fault activity. However,the mica ages in ductile shear zone is round 12 Ma,differs from the 60～50 Ma mica ages of undeformed rocks nearby,proving the fault imposed on the Gangdese granites around 12 Ma. The case that no 32～25 Ma ages in ductile shear zone around Kailas area precludes the hypothesis that the initiation age of the Karakoram fault is around 32～25 Ma in Ali area.