Climate changes control offshore crustal structure at South China Sea continental margin

- Surface processes control continental crustal structure in rifted margins.
- Mid crustal flow is triggered by coupled continental erosion and offshore loading.
- Mid crustal flow explains rapid tectonic subsidence after end of extension.
- Climate change onshore deforms the crystalline crust within the margin offshore.

Rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension. Deep basins on the northern margin of the South China Sea, notably the Baiyun Sag, show basement subsidence accelerating after ∼21 Ma, postdating extension by several million years. We combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following Early Miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension. This illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate-tectonic coupling.