Collision-Induced Subduction Polarity Reversal Explains the Crustal Structure of Northern Borneo: New Results From Virtual Deep Seismic Sounding (VDSS)

Subduction polarity reversal (SPR) is a key subduction initiation mechanism often associated with arc-continent collision zones. Northern Borneo has long been recognized as a location where sequential but opposing subduction zones were present in the Miocene, but has not been examined in the context of SPR. Here, we exploit teleseismic data from northern Borneo to investigate crustal thickness variations using Virtual Deep Seismic Sounding (VDSS). Our results reveal a thick crustal root beneath the Crocker Range and an area of relatively thin crust in the southeast, which appears to extend northeast into the Sulu Sea, where back-arc rifting behind the younger subduction zone developed. Overall, our findings are consistent with predictions from numerical models of SPR involving arc-continent collision, but with several important differences—including a substantial mountain range and more limited back-arc rifting that can be attributed to northern Borneo being an example of SPR involving continent-continent collision.