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EIL-04 The continental lithosphere from geophysical and geochemical data
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Structure of Earth's crust and upper mantle, inland subduction and its coupling effects on the Dabie orogenic belt and the Tancheng-Lujiang fault zone
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Jiwen Teng, Institute of Geology and Geophysics, CAS (China)
Yafen Yan, Institute of Geology and Geophysics, CAS (China)
Guangjie Wang, Institute of Geology and Geophysics, CAS (China)
Xiong Xiong, Institute of Geodesy and Geophysics, CAS (China)
Yongqian Zhang, Institute of Geology and Geophysics, CAS (China)
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The Dabie Mountains was a nearly EW trending collision orogenic belt under the roughly NS directed compressive force during the Indo-China and early Yanshan movement periods. It separates the North China and Yangtze continental blocks, between which exposed broad cores of metamorphic rocks. Since it lies at the west side of the place where the mountains and Tancheng-Lujiang fault zone intersect and converge, the orogenic belt must be constrained by strong translational offset of the Tancheng-Lujiang fault zone during the late period (late Jurassic-early Cretaceous). This fault zone is an inland giant system of translational fractures on the eastern margin of the Chinese mainland, which appeared after the formation of the Dabie orogenic belt.
Based on the rock chronology, the metamorphic pressure difference in the peak period and the discovered coesite in Alpine metamorphic sedimentary rock, the coesite and eclogite from the Dabie orogenic belt is inferred to be the consequence resulted from their reentry from mantle around the depth of 120km to the shallow crust. To provide the quantitative evidence of the deep structure and dynamic process beneath the Dabie orogenic belt, we attempt to explore the 3-D wave beneath this region by using the inversion method with 4°4° network based on the dispersion effect of Rayleigh wave. Our purpose is to reveal the formation mechanism of the UHPM zone in the Dabie Mountains, exchange of deep and shallow materials and energy, as well as deep dynamic processes of inland tectonics in terms of block-like features of structure in crust and upper mantle. Then we would propose new insights and evidence for the strong translational dislocation of the Dabie and Tancheng-Lujiang fault zone, and the coupling effects of inland subduction. The results show that, there is a high-velocity subduction slab of tongue shape with underthrusting depth of 160km extending from east to west. A low velocity mantle hotspot with a 500km wide head is found at depth of 70km in Qinling-Dabie orogenic belt. The outcrop of coesite and eclogites in the Dabie orogenic belt is the synthetic consequence of the movement and dynamic effects of deep (upper mantle) material resulted from the deep substance and energy exchange, strong strike-slip motion along the Tancheng-Lujiang fault zone and the inland subduction.
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