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

Abstract

AbstractBased 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, the 3‐D group velocity structure of S wave in the studied area is investigated by the dispersion effects of Rayleigh wave. The results show that there is a high‐velocity subduction slab of tongue shape with underthrusting depth 160km extending from east to west. A low velocity mantle hotspot with a 500km wide head is found at depth of 70km in the upper mantle beneath the 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 Tanlu fault zone and the inland subduction.