Asthenospheric Pacific-Atlantic flow barriers and the West Scotia Ridge extinction

Abstract

The Drake Passage is considered a gateway for oceanic and asthenospheric flows since its opening, entailing widespread consequences for climate and plate tectonics, respectively. Both the surface and the 50 km upward continued Bouguer anomaly maps of the Scotia Sea and surrounding areas, based on Gravity Recovery and Climate Experiment gravity satellite data, improve our knowledge of deep lithospheric structures and the asthenosphere. We show that the West Scotia Sea is likely to be underlain by an anomalously low-density upper mantle. Gravity data are compatible with variable lithospheric thicknesses related to asthenospheric currents. The new data suggest that the development of the Shackleton Fracture Zone since the middle Miocene was probably a main factor that determined the evolution of the eastward Pacific mantle flows and the extinction of the West Scotia Sea oceanic spreading around 6 Ma ago. Deep lithospheric roots are likely to divert asthenospheric currents around them, flowing eastward through Drake Passage. Key Points Pacific mantle outflow is still present through the Drake Passage The Shackleton Fracture Zone modified asthenospheric flow patterns A redistribution of mantle flow may have caused West Scotia Ridge extinction ©2013. American Geophysical Union. All Rights Reserved.