The Transition from Back Arc to Slab Window to Continental Rifting, Evidence from the Subcontinental Lithospheric Mantle of West Antarctica

Brown University, Providence RI

Investigators

Abstract

The subcontinental mantle lithosphere is created and modified at plate boundaries through a complex and variable mix of tectonic and magmatic processes that ultimately affect the evolution of the Earth's continents and mantle. The project goal is to evaluate the processes that create, modify, and destroy the subcontinental mantle lithosphere beneath Western Antarctica through the interpretation of a well-integrated set of geochemical and microstructural data from rock samples. The new data will be integrated with already existing seismological observations and geochemistry of erupted basalts. The project will estimate how the composition, structure, mechanical properties, temperature, and foundering potential of the subcontinental mantle lithosphere change along a transect through the Antarctic Peninsula, Jones Mountain, Marie Byrd Land and Ross Island; areas that represent different tectonic and magmatic conditions. This project assesses the geochemistry and microstructure on mantle xenoliths collected in West Antarctica to establish: 1) the xenolith pressure-temperature conditions of the tectono-magmatic events, 2) the variations in the degree of mantle hydration in time and space and its effect on the associated microstructure, 3) the time and source of the subcontinental mantle lithosphere metasomatic agents, 4) the link between mantle xenolith data and the already existing seismological observations and geochemistry of erupted basalts, 5) the effective viscosity of the subcontinental mantle lithosphere and whether the deformation occurred prior to or was affected by the introduction of water and melt, and 6) the contribution of the subcontinental mantle lithosphere into the composition of the erupted basalts across West Antarctica. A key question the project will address is how normal subduction, slab window and continental rifting have produced differences in the inferred density and viscosity structures; and how such difference affected the stability of the subcontinental mantle lithosphere and its potential for ablation by mantle wedge flow, aided by reductions in viscosity due to volatiles and melt, and/or foundering beneath West Antarctica. 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.