Paleomagnetic data bearing on the Mesozoic deformation of the Qiangtang Block: Implications for the evolution of the Paleo- and Meso-Tethys |
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| Institution: | 1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;4. School of Earth Sciences & Key Laboratory of Western China''s Mineral Resources of Gansu Province, Lanzhou University, Lanzhou 730000, China;1. Department of Geosciences, Eberhard Karls University Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany;2. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;3. State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, CAGS, Beijing 100037, China;1. Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China;2. Key Laboratory of Paleomagnetism and Tectonic Reconstruction, The Ministry of Land and Resources, Beijing 100081, China;3. College of Resources, Environment and Tourism, Capital Normal University, Beijing 100048, China;4. Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | Paleomagnetism has played an important role in quantifying the Mesozoic evolution of “Proto-Tibet”. In this paper, we present new paleomagnetic data from five Middle-Upper Jurassic sedimentary sequences (Quemo Co, Buqu, Xiali, Suowa and Xueshan Fms.) of the eastern North Qiangtang Terrane (QT) at Yanshiping (33.6°N, 92.1°E). The new paleomagnetic results form a large dataset (99 sites, 1702 samples) and reveal a paleopole at 79.1°N/306.9°E (dp = 3.9°, dm = 6.3°) for the Quemo Co Fm., at 68.9°N/313.8°E (dp = 2.1°, dm = 3.7°) for the Buqu Fm., at 66.1°N/332.1°E (dp = 2.7°, dm = 4.6°) for the Xiali Fm., at 72.4°N/318.6°E (dp = 3.9°, dm = 6.7°) for the Suowa Fm., and at 76.9°N/301.1°E (dp = 7.9°, dm = 13.2°) for the Xueshan Fm. These results indicate clockwise (CW) rotations of ~ 19.8 ± 9.4° between ~ 171.2 and 161.7 Ma and counterclockwise (CCW) rotations of ~ 15.4 ± 13.4° between ~ 161.7 and < 157.2 Ma for Yanshiping. We attribute the change in rotation sense at approximately ~ 161.7 Ma to the initial collision of the Lhasa and Qiangtang terranes. Using this and other paleomagnetic data from the Lhasa, Qiangtang and Tarim terranes, as well as other geological evidence (e.g., tectonism-related sedimentary sequences, volcanism, and HP metamorphism), we propose a new conceptual evolution model for the Mesozoic QT and Tethyan Oceans. The Longmo Co-Shuanghu oceanic slab was subducted before 248 Ma, followed by continental collision of the North-South Qiangtang subterranes between ~ 245 and 237 Ma. The Qiangtang Terrane experienced post-collisional exhumation between ~ 237 and 230 Ma during subduction of the Jinsha oceanic slab. The collision of the Qiangtang and Songpan-Ganzi terranes occurred between ~ 230 and 225 Ma. The QT experienced post-collisional relaxation from ~ 225 to ~ 200 Ma, followed by subsidence and extension-related exhumation between ~ 200 and 162 Ma in association with subduction of the Bangong-Nujiang oceanic slab. Finally, these events were followed by the scissor-like diachronous collisions of the Lhasa and Qiangtang terranes between ~ 162 Ma and the mid-Cretaceous. |
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