Landward mantle flow associated with the Pacific subduction system opened the South China Sea

Abstract

Abstract Whether Tethyan or Pacific subduction controlled the formation of the South China Sea (SCS) is debated. Here, using high resolution seismic data, we reveal that the continental extension across the northern SCS margin experienced a transition from the Early-Eocene narrow-rift mode to the Late Eocene wide-rift mode. Using 4D geodynamic models, we propose that the evolving rifting mode was dominated by the landward mantle flow associated with Pacific subduction: 1) Toroidal mantle flow through a hole in the retreating flat slab initially thinned the continent to form a narrow rift; 2) Strong landward mantle wind through a broad trench-parallel slab window since ~40 Ma stretched the narrow rift into a wide rift and eventually an oceanic basin. We conclude that the landward mantle flow represents a new mechanism of continental extension, where increasingly strong hot upwelling caused the intermediate SCS rifted margin between the traditional magma-poor and magma-rich end-members.