High-resolution seismic models of the upper mantle beneath the Indian Ocean

Brown University, Providence RI

Investigators

Abstract

This study addresses the relationship between the physical structure of tectonic plates and the chemistry and partial melting processes of the underlying mantle, from which magma that forms new plates is generated. Past studies have focused on the fast-spreading Pacific but plates formed at slower spreading rate and lower magma supply may have different structure and different types of chemical variability. Analysis of data covering the slow-spreading Indian Ocean basin will provide the first seismic and geochemical results at a resolution similar to that available for the Pacific. Comparison will distinguish characteristics that are global features of plate aging versus regional features reflecting a particular basin's magmatic development. Regional models of upper mantle seismic velocity, attenuation, and radial anisotropy beneath the Indian Ocean will be developed. Both the average age-dependent seismic structure and deviations from the average will be determined. Only earthquakes and seismic stations located within or on the margins of the Indian Ocean will be used, to avoid paths with significant length through continental upper mantle. Frequency-dependent phase and amplitude of fundamental-mode and higher-mode surface waves will be measured and jointly inverted for elastic and anelastic seismic models. This approach takes advantage of the amplitude sensitivity to short wavelength structure to allow estimation of attenuation and shear velocity in a self-consistent manner. Mantle temperature, partial-melt content, and composition of the upper mantle will be estimated by interpreting the seismic models together with existing mineral physics, mid-ocean-ridge basalt composition, and bathymetry data. The research will be the basis of a PhD thesis and undergraduates will also be involved in aspects of the research.