Continental Reworking in the Eastern South China Block and Its Adjacent Areas Revealed by F-J Multimodal Ambient Noise Tomography

Abstract

The eastern South China Block (SCB) has experienced complex and drastic reworking processes since the early Neoproterozoic, the mechanisms of which remain unclear. To better understand the continental reworking mechanisms in the eastern SCB, we imaged the shear-wave velocity structure of the crust and upper mantle in the eastern SCB and its adjacent areas with the F-J multimodal ambient noise tomography method. The seismic ambient noise data were acquired by 652 seismic stations in this area. The shear-wave velocity model presents widespread mid-crustal low-velocity zones (MCLVZs) and upper mantle low-velocity zones (UMLVZs), the distribution of which shows a good correlation with regional tectonics. The MCLVZs formed due to compositional and structural layering during the late Neoproterozoic to the early Phanerozoic. The disrupted MCLVZs near the Qinling-Dabie orogen can be linked to metamorphism caused by a continental collision between the SCB and the North China Craton during the Triassic Indosinian event. The thin crustal and lithospheric thicknesses east of the North-South Gravity Lineament may be the result of asthenospheric upwelling due to the subduction of the Pacific plate since the late Mesozoic. In the areas near the Shaoxing-Jiangshan-Pingxiang fault zone and the Tanlu fault zone, upheaval UMLVZs indicate that these ancient fault zones were reactivated by the subduction of the Pacific plate, providing channels for asthenospheric upwelling. Well-preserved MCLVZs north of the Qinling-Dabie orogen can be used to assess compressions and extensions induced by the subduction of the Pacific plate.