Geophysics and Tectonics Seminar fall-2020

Jewel Abbate: Models of thermal vs. compositional convection in Earth’s core Buoyancy-driven convection in Earth’s liquid outer core is sourced from both thermal and compositional variations induced by the crystallization of the inner core. The turbulent fluid motion resulting from these variations is the primary power source of Earth’s dynamo, and thus the primary focus in both numerical and laboratory studies for generating dynamo models. Most often, these models are built upon a framework accounting for only thermal buoyancy as a source of convective turbulence, but recent measurements of the thermal and electrical conductivity of high-pressure and high-temperature iron suggest compositional anomalies are the primary driver of modern core convection. It remains unexplored exactly how thermally vs. compositionally driven core flow may differ in terms of dynamo physics and therefore change currently acknowledged models. Here we compare results from numerical and laboratory experiments of rotating thermal convection in liquid gallium (a low viscosity metal with thermal properties comparable to that of Earth’s core) to experiments in high viscosity silicone oil (a fluid with thermal properties comparable to compositional properties of Earth’s core). Using silicone oil thermal convection as a proxy for core compositional convection allows for a direct comparison of models of core flow, with which we can further shed light on exactly how Earth’s dynamo is maintained. /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// Boontigan Kuhasubpasin: The effect of lithospheric structure on the lithospheric stress field The state of stress in the lithosphere controls many geological processes from the local scale to plate tectonics. The sources of lithospheric stress range from mantle flow to lithospheric heterogeneity. In this study, I focus on understanding the sensitivity of the stress field to lithospheric heterogeneity by examining different models for lithospheric structure and assumptions regarding compensation and lithospheric mantle density. I use the crustal and mantle structure from Crust 1.0 and a thermodynamically determined lithosphere to calculate the gravitational potential energy (GPE) and mean outward tractions. The gradient of deviatoric stresses that balance it is solved using the finite element package ABAQUS. I compare our results for azimuth of the most compressive stress and inferred regimes to the observations from the World Stress Map 2016, and previous work using CRUST 2.0. Our study confirms how important the uncertainty in lithospheric structure weighs on our understanding of the state of stress of the lithospheric plates.