Feedback between rifting and diapirism can exhume ultrahigh-pressure rocks

Abstract

The processes by which crustal rocks are buried to tremendous depths and subsequently exhumed to Earth's surface remain controversial. Rapid exhumation of Earth's youngest (ultra-) high-pressure (UHP) rocks in the Woodlark Basin, Papua New Guinea, is occurring within an active rift, in contrast to more common scenarios of UHP exhumation during plate convergence. We use 2D and 3D thermo-mechanical models to demonstrate that UHP exhumation can result from feedback between rifting and the diapiric rise of a previously subducted continental fragment through the lithosphere. We infer that this feedback is responsible for the exhumation of the UHP rocks in gneiss domes in the Woodlark Basin. Our models successfully reproduce UHP exhumation paths and rates, and geological structures within the gneiss domes. We show that UHP exhumation by diapirism is mechanically consistent in post-collisional rifts. Our models highlight the complex feedback between diapiric ascent and extension.