SUBDUCTION, OBDUCTION, AND SLAB GRAVEYARDS IN THE NEW GUINEA REGION

The New Guinea region evolved within the obliquely and rapidly converging Australian (AUS) and Pacific plate boundary zone and is arguably one of the most tectonically complex regions of the world. Its geodynamic evolution involves collisional orogenesis, ophiolite obduction, microplate formation and rotation, lithospheric rupture to form ocean basins, arc-continent collision, subduction polarity reversal, and exhumation of (U)HP rocks. As the AUS plate moved northwards ~30° during the Cenozoic, its leading northern edge, a former rifted margin, was subducted resulting in high P/T metamorphism of sediments and basalts beneath the forearc(s) of oceanic island arc(s). Ophiolites and subduction complexes presently mark the suture zone between deformed AUS continental margin sediments to the south (fold and thrust belts), and accreted volcanic arc(s) and microplates to the north. Ophiolite obduction is thought to have occurred in the Late Cretaceous-Paleocene, well before the onset of Late Oligocene-Recent arc collision. Within Eocene–Pliocene exhumed subduction complexes metamorphic grade generally increases from south to north. In the Woodlark rift (easternmost New Guinea), prehnite–pumpellyite–greenschist and amphibolite facies metamorphic rocks of the southern rifted margin, and blueschist–amphibolite–eclogite facies metamorphic rocks in the lower plates of core complexes provide evidence for diachronous Miocene to Pliocene regional metamorphism. The variably metamorphosed rocks were exhumed from beneath dismembered ophiolites sequentially from east to west, in the same direction as Woodlark rift propagation. The world's youngest (2–8 Ma) (U)HP metamorphic rocks were exhumed from > 90 km at cm/my rates in this transient plate boundary zone, where convergence has switched to extension. A pronounced geoid high in the New Guinea region likely results from high-density slabs in the upper mantle. However, little is known about what the slab graveyard looks like beneath New Guinea and how it evolved during the Cenozoic. Given the abundance of obducted ophiolites, and the occurrence of the world’s youngest exhumed (U)HP rocks, tremendous potential exists for discovering additional (U)HP materials exhumed from this slab graveyard, and for linking deep earth processes to (U)HP exhumation.