3D Magnetic Inversion with Mixed Lp Norm Regularization for Unveiling the Spatial Distribution of Mesozoic Volcanic Arcs in the Northern South China Sea

The high magnetic anomaly belt trending in the NE direction in the northern slope of the South China Sea (SCS) has long been associated with an ancient volcanic arc zone. However, the exact spatial distribution of the ancient volcanic arc zone remain unclear, limiting the understanding of its formation and controls on the evolution of the SCS. In this paper, we assemble the high-resolution reduced-to-pole (RTP) aeromagnetic anomaly data around the northern SCS, and then conduct the 3-D magnetic inversion based on mixed Lp norm regularization upon the RTP aeromagnetic data to obtain the 3-D susceptibility model of the crust in the study area. Previous borehole and deep seismic reflection profiling data are involved in the inversion for constraints. Our result confirms that the high magnetic anomaly belt in the study area is caused by deep-seated magnetic bodies, which, supported by drilling and magnetization data, are identified as the Mesozoic volcanic arc zone induced by the ancient subduction. Our model demonstrates that the Mesozoic volcanic arc zone trends northeastward and extends at least from the Dongsha Rise to Taiwan Island, primarily distributed at depths of 20-28 km in the lower crust. Our model provides significant evidence for understanding the tectonic evolution of the northern SCS prior to its extensional phase.