Effects of subduction termination processes on continental lithosphere

Subduction is the main driver of tectonic activity on Earth. Termination of subduction is followed by diverse and unexpected tectonic activity, such as anomalous magmatism, exhumation, subsidence and subsequent rapid uplift. What fundamentally drives these processes remain enigmatic. A prime example of subduction termination can be found in northern Borneo (Malaysia), where subduction ceased in the late Miocene and was followed by puzzling tectonic activity, as reconstructed from geological and petrological evidence. Our current understanding of the subduction cycle cannot be reconciled with evidence of post-subduction tectonics in both the near-surface geology and mantle of northern Borneo.

We use new passive-seismic data to image at unprecedent detail a sub-vertical lithospheric drip that developed as a Rayleigh-Taylor gravitational instability from the root of a volcanic arc, which formed above a subducting plate. We use thermo-mechanical simulations to reconcile these images with time-dependent dynamical processes within the crust and underlying mantle, following subduction termination. Our model predictions illustrate how significant extension from a downwelling lithospheric drip can thin the crust in an adjacent orogenic belt, causing lower crustal melting and possible exhumation of subcontinental material, which can explain core-complex formations seen in other areas of recent subduction termination.