Asymmetric oceanic crustal accretion and mantle serpentinization in the southwestern propagator tip of the South China Sea basin

Abstract

A multi-channel seismic profile crossing the conjugate continental margins at the southwestern propagator tip of the South China Sea unveils asymmetric crustal structures. The southern margin exhibits rapid necking of the continental crust, while the northern margin features hyper-thinned crust controlled by detachment faults. The northern margin has thicker syn-rift deposits, while in the most distal parts of the southern margin, these deposits become thin or vanish entirely. Notably, the oceanic crustal structure is also asymmetric with respect to the spreading center. North of the spreading center, the oceanic crust is only 2–3 km thick, whereas to the south it is ∼5 km thick. Two sub-horizontal intra-basement reflections are identified in the northern oceanic domain, one representing the interface between basaltic oceanic crust and serpentinized mantle, and the second from gabbroic intrusions. Joint inversion of gravity, magnetic, and seismic data supports the presence of a highly serpentinized mantle beneath the thin oceanic crust. The reduced melting at the ridge-segment end may explain the observed asymmetrical rifting and seafloor spreading.