Tracing oceanic plateau relics in the basement of mainland China: A synthesis of aeromagnetic and seismic refraction data

Abstract

Mainland China has the most complex continental tectonics on Earth, making it one of the ideal laboratories for probing the tectonics and evolution of the Earth. However, no consensus has been reached regarding the basement tectonic architectures and evolution of mainland China. This paper focuses on the interpretation of aeromagnetic and seismic refraction data, closely incorporating available surface geological data, borehole data, and seismic data to trace the likely occurrences of oceanic plateau slices in the basement architecture of mainland China. We suggest that the highly positive aeromagnetic anomalies and thick high-velocity lower crustal layer indicate that the Junggar basin is floored by an oceanic plateau. The Tarim basin can be divided into a southeastern oceanic plateau block with strongly positive aeromagnetic anomalies and a northwestern passive continental margin block with weak aeromagnetic anomalies. Both blocks got amalgamated together during the late Paleoproterozoic, and the irregular, promiscuous aeromagnetic anomalies within the northwestern block are spatially consistent with and attributed genetically to the Tarim Large Igneous Province (LIP). The lower crust of the Qaidam basin is characterized by large P-wave velocity, suggesting that the basin is floored by an Early Paleozoic oceanic plateau, and the deep-seated subduction of the oceanic plateau could be responsible for the ultrahigh-pressure (UHP) metamorphism in the northern Qaidam margin during the Early Paleozoic. The western North China craton could be an assembly of multiple oceanic plateau fragments along irregular continental margins during the Paleoproterozoic. An intraplate suture (Miaowan suture) divides the Yangtze craton kernel to the east and the Shennong terrane to the west; both were amalgamated during the Neoproterozoic. The Yangtze craton kernel could be floored by an oceanic plateau basement characterized by large P-wave velocity and strongly positive aeromagnetic anomalies. All these oceanic plateau basements exhibit strong rigidity to resist later tectonic deformation and generally remain intact.