Edge-driven convection’s role in producing post-rift magmatism at continental margins of the South China Sea

Observation in the past decade revealed unexpectedly large volumes of post-rift magmatic activity at the continental margins of the South China Sea. However, the underlying driving mechanism remains unclear. Edge-driven convection (EDC) has been widely employed to interpret magmatic activity at various continental margins, but not in the South China Sea yet. This study aims to test and evaluate the role EDC may play in generating post-rift magmatism at the continental margins of the South China Sea. The results indicate that, even after the cessation of seafloor spreading, significant volumes of melt can persist along oceanic-continental margins for tens of millions of years. The formation rate and scale of these melts can be influenced by factors such as the width of the ocean basin, the slope of the continent-ocean transition (COT) zone, the lithosphere step thickness at the COT, and the water content in the mantle. Specifically, melts tend to form on the side of the transition zone closer to the oceanic floor and subsequently migrate towards the continental side driven by the EDC. This is consistent with observations of reduced magmatic activity at the northern margin of the South China Sea transitioning from the ocean towards the continent. It may also explain the transition in magma output state, shifting from extrusion on the ocean side to intrusion as it moves towards the continent. This study represents the first investigation of the impact of EDC on post-rift magmatic activity at the continental margins of the South China Sea. The results are expected to provide new theoretical models and constraints for understanding the development of post-rift magmatism in the research region. Further optimization involves updating model settings based on observational constraints. Additionally, the interpretation of results requires integration with observations of near-surface magmatic activity and deep mantle flow patterns to further validate the role of EDC in post-rift magmatic activity in the South China Sea.