Flyover Crustal Structures Beneath the Qinling Orogenic Belt and Its Tectonic Implications

Abstract

AbstractDetermining high‐resolution three‐dimensional (3‐D) crustal structures of the Qinling Orogenic Belt (QOB) can reveal significant evidences to enhance our understanding of its tectonic evolution. By jointly inverting group and phase velocity dispersion curves, we obtain a high‐resolution 3‐D shear wave velocity model for the QOB. According to the obviously layered features, which include an E‐W trending high‐velocity structure in the upper crust (0–10 km), a transitional zone in the middle crust (10–30 km), and an approximately N‐S trending low‐velocity zone in the middle‐lower crust (20–40 km), we elucidate the crustal structure as a flyover model to explain how the crust beneath the QOB was deformed under the perpendicular force systems from the NE‐SW and E‐W directions during the Meso‐Cenozoic. First, the apparent NE‐SW trending low‐velocity zone in the middle‐lower crust indicates that the low‐viscosity crustal materials beneath the northeastern Tibetan Plateau did not flow eastward into the eastern Qinling terrane during the Cenozoic. Second, the extension in the northern Qinling Mountains and Weihe Basin was not largely affected by the lateral crustal growth of the NE Tibetan Plateau, which might be the result of deep mantle upwelling and/or residual effects from the subduction of the western Pacific plate. Third, during the Mesozoic, the high‐velocity structures beneath the Hannan‐Micang and Shennongjia‐Huangling domes served as anchors resisting the northward subduction, rotation, and continuous collision of the Yangtze Block. The eastward extruding Hannan‐Micang dome served as an indenter that eventually shaped the present‐day asymmetric style of the Dabashan Orocline during the Cenozoic.