Global study of the mantle transition zone structure from geoid anomalies and SS wave propagation

Abstract

Understanding the mantle transition zone structure can provide important constraints on the convection style that prevails in the mantle, a fundamental open problem in geodynamics. The transition zone is characterized by phase changes in olivine, the most abundant mineral in the mantle, and plays a key role in determining the mantle convection style, either layered convection or whole-mantle convection. This proposal focuses on determining the topography of the 410 and 660 km discontinuities and on estimating their density structure in a global scale using traveltimes of SS precursors analysis and from the inversion of geoid anomalies. We will make a critical evaluation of currents methods used to derive such topographies, trying to understand how theoretical simplifications on the ray theory could affect the estimative of the transition zone thickness. Using the finite frequency theory, we intent to derive more accurate maps of the undulations at the 410 and 660 km discontinuities. These maps will be used as a priori information in the inversion of geoid anomalies, after removing the lithospheric effects, to determine a density distribution model. A joint interpretation of the thickness variation of the transition zone, which is frequently used as a "thermometer" of the mantle, the signal of the density contrast and the laboratorial experiments provided by mineral physics will give us more reliable results about the actual mantle thermal state beneath subduction zones or hot spots. We will also correlate the results obtained for the mantle underneath the Paraná Magmatic Province (PMP) with other Large Igneous Provinces (LIP) around the Earth in order to find common signatures so that we can reach a better knowledge of the mantle underneath the PMP. This analysis will be integrated with results from FAPESP Thematic Project Process 09/50493-8 entitled "Crustal and lithospheric mantle models under the Paraná and Chaco-Paraná basins by merging satellite gravity gradiometry, terrestrial gravity and geomagnetic and electromagnetic soundings." coordinated by Professor Icaro Vitorello (INPE-MCT) and Professor Naomi Ussami from IAG-USP as principal investigator. (AU)