Mantle upwelling after Gondwana subduction death explains anomalous topography and subsidence histories of eastern New Zealand and West Antarctica

Abstract

West Antarctica and adjacent seafloor have topographic elevations 0.5–1.2 km greater than expected from models of lithospheric age and crustal structure. Ocean crust near New Zealand has no equivalent depth anomaly, but tectonic subsidence histories from Campbell Plateau petroleum wells show anomalously high subsidence rates during the Paleogene, and total subsidence 0.5–0.9 km greater than expected from rift basin models. Geophysical and geochemical anomalies suggest that upward mantle flow supports the anomalous topography beneath Antarctica, and the Campbell Plateau subsidence history indicates that topographic support mechanisms were long lived (>80 Ma) and recoverable over a period of ~30 m.y. as plate motions moved New Zealand from Antarctica. We construct models of Late Cretaceous and Cenozoic mantle flow with a slab graveyard and upwelling above that is initially rooted at 1000–1500 km depth. Our models match topography and subsidence history anomalies, and are consistent with mantle seismic wave speed anomalies and the geoid. We suggest that when thermally driven slab downwelling ceased ca. 100 Ma, low-density material that was fertilized within a broad zone in the lower mantle during the previous ~400 m.y. of Gondwana subduction was released and able to rise. Mantle upwelling from depths of 700–1500 km, lasting for periods of ~100–200 m.y., with enriched chemistry related to the prior subduction history may be a general process that follows subduction death, and has not previously been recognized.