Lateral evolution of the rift-to-drift transition in the South China Sea: Evidence from multi-channel seismic data and IODP Expeditions 367&368 drilling results

Abstract

The South China Sea margins represent a critical natural laboratory to study the processes and parameters controlling the rift-to-drift transition. High quality seismic data previously suggested the occurrence of a relatively sharp transition between the continental and oceanic domains, a hypothesis recently validated by the results of the IODP Expedition 367&368 drilled in the northern South China Sea distal margin. Drilling results in this transition cored Mid-Ocean Ridge type basaltic basement (Site U1502), while its lateral equivalent showed continental affinities (Site U1499). Seismic data document the lateral evolution of this narrow transition zone (∼15 to 25 km wide) and tectono-magmatic context related to breakup. A short-period magmatic event occurred during the latest stage of continental rifting and intruded the edge of the thinned continental crust, triggering crustal breakup and onset of steady-state seafloor spreading. The architecture of the transitional domain documented in this work is in marked contrast with those interpreted as either magma-starved or magma-rich at breakup time, suggesting that the continental margin of the SCS is intermediate between the classical end-member magmatic archetypes. We propose that the magmatic event triggering continental breakup is related to decompression melting linked to the ascending asthenosphere. It is assumed that this event was rapid at geological time scale (<10 Ma) and was favored by a high mantle temperature.