EPSS Colloquium winter-2016

Geophysical and geochemical constraints on mantle temperature and composition beneath the oceans

Plate tectonics is expressed most simply in oceanic plates. Various types of observations, including seafloor bathymetry and heat flow, provide general support for a simple model of the evolution of the ocean basins. In this model passively upwelling mantle melts beneath the mid-ocean ridge, the melt ultimately forms the oceanic crust, and a thermal boundary layer grows thicker with distance from the ridge and therefore with age of the seafloor. In this talk I will present two examples, using seismic data, that this simple model requires some refinement. First, I will describe a global comparison of seismic velocity, basalt chemistry, and axial depth along the mid-ocean ridge system that allows us to quantify mantle temperature variations beneath the ridge. Second, I will describe our seismic study of the upper mantle beneath the Atlantic Ocean. Notably, the dependence of seismic velocity on seafloor age is different from the age dependence in the Pacific upper mantle, which suggests different cooling histories for the two basins.