The transition from normal subduction to slab window, unraveling its effect on the subcontinental lithospheric mantle of southern Patagonia

Brown University, Providence RI

Investigators

Abstract

This team plans to evaluate the processes that create, modify and destroy the Earth’s continents. They will also estimate how changes in composition and mechanical properties of the continental roots affect its stability. This proposal focuses on Southern Patagonia, where the continental roots have been sampled by lavas erupted over the last 50 million years. Very recent seismological data also shows clear evidence of continental root removal. This research together with the new seismological observations will provide the necessary information to evaluate the evolution and stability of the Southern Patagonia continental root and how its removal might affect the composition of the nearby Earth’s interior. The results of this work will inform a similar ongoing study of the continental roots of West Antarctica. Combined, these projects have global implications for the stability of Patagonia and West Antarctica, which were once a single continent. The research team will collaborate nationally and internationally, and this project supports five analytical facilities in three US research institutions. The proposal supports an early-career researcher and a graduate and an undergraduate student at Brown University. The goal of the proposed work is to understand how subduction processes have affected the stability of the Southern Patagonia subcontinental lithospheric mantle (SCLM). This proposal aims to collect new geochemical and microstructural data on mantle xenoliths from across Southern Patagonia. The xenoliths have been sampled by erupted lavas over the last 50 million years; this time encompasses the tectonic transition from normal subduction of the Nazca oceanic plate to the formation of a slab window during the Chile Ridge-South America trench collision. The main objectives of this study are to determine the P-T conditions, extent of hydration, refertilization and deformation of the SCLM during this transition. It will allow estimation of the effective viscosity and stability of the lithospheric mantle and evaluation of whether the deformation occurred prior to or was affected by the introduction of water/melt. Furthermore, the proposed new data will be combined with new seismological observations to evaluate how these geologic processes affected the seismic properties (velocities, anisotropy) of the Southern Patagonia SCLM. Because the new seismological data show clear evidence of lithospheric mantle removal, the geochemical characterization of the mantle xenoliths will help test the hypothesis that the removed lithospheric mantle contributed to the composition of the volcanism not only in Southern Patagonia, but also in the Chile Ridge system. Finally, this proposal will be combined with an ongoing study of the lithospheric mantle of West Antarctica, which formed a single continental block with Southern Patagonia before the opening of the Drake passage. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.