Zircon U-Pb geochronology and Hf isotopic composition of the Cretaceous volcanic rocks and constraint of the collision age of Bangong-Nujiang suture zone in Dongco area, Gaize, Tibet
Fu Jiajun1,2, Ding Lin1, Xu Qiang1, Cai Fulong1, Yue Yahui1, Guo Yu3
1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101;
2. University of Chinese Academy of Sciences, Beijing 100049;
3. Bohai Steel Group International Trading., Ltd., Tianjin 300050
Bangong-Nujiang is an important suture zone of Tibet Plateau. However, its subduction polarity and closure time are still remaining controversial, which undoubtedly limits our understanding of the evolution of the Tibet Plateau. To constrain some information regarding this aspect, this research was carried out on Zhonggang andesitic basalt and a newly discovered andesite. The obtained zircon U-Pb ages of these two units are 123.75±0.92 Ma and 74.23±0.76 Ma respectively. The obtained zircon εHf(t) values of Zhonggang basalt ranging between -7.3 and +4.4, which is identical with the island arc basalts, indicate that Bangong-Nujiang oceanic basin continues its northward subduction in research area. The εHf(t) values of the Late Cretaceous andesite are +3.1～+11.1, indicative of depleted mantle melting continental crust. The Late Cretaceous andesite is unconformably overlying the ophiolite. Therefore, the Bangong-Nujiang ocean basin has already closed at that moment. Combined with regional data, this study concludes that the closure time of Bangong-Nujiang ocean basin was between 100 Ma and 75 Ma in the Gaize area.
. Zircon U-Pb geochronology and Hf isotopic composition of the Cretaceous volcanic rocks and constraint of the collision age of Bangong-Nujiang suture zone in Dongco area, Gaize, Tibet[J]. Chinese Journal of Geology, 2015, 50(1): 182-202.