Tectonic settings of Paleozoic turbidites in the Beishan orogen and its implications for regional accretionary tectonics
Guo Qianqian1,2, Xiao Wenjiao2,3, Hou Quanlin1, Han Chunming2, Qu Junfeng4, Tian Zhonghua1,2, Song Dongfang1,2
1. Key Laboratory of Computational Geodynamics, Graduate University of Chinese Academy of Sciences, Beijing 100049;
2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
3. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Vrümqi, Xinjiang 830011;
4. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037
The Beishan orogen is one of the key parts to study the accretionary orogenesis of the Altaids, and turbidites are an important composition of the accretionary orogenic belt.The Paleozoic turbidites in the Beishan are mainly distributed in the Yingmaotuo, Liuyuan and Heishankou areas.The turbidites in the Yingmaotuo area is Early Ordovician in age and were derived from felsic sources by medium-high weathering degree, indicating a passive continental margin tectonic setting.The turbidites in the Liuyuan area is Early Permian in age, and were derived from intermediate-basic sources by low-medium weathering degree, indicating an oceanic arc tectonic setting.The Heishankou turbidites are a little younger than the Liuyuan turbidites, and were derived from felsic sources by medium weathering degree, indicating a continental arc tectonic setting.Together with other data, we conclude that a complex oceanic subduction process took place in the Beishan orogen in the Paleozoic.There was a northward subduction zone in Huaniushan-Huoshishan area, and to the south of this subduction zone the Yingmaotuo turbidites formed in a passive margin in the Early Paleozoic.In the Late Paleozoic, the subduction zone was retreated southward, forming the Dundunshan arc and the Liuyuan and Heishankou turbidites were formed by two way subductions.Our work supports the Late Paleozoic active margin model and indicates that complicated accretionary orogenesis might have happened until the end Permian or even to the Middle Triassic in the Beishan.Therefore the termination of the CAOB was at least to the end-Permian.