IGPP Seminar Series 2023: Dayanthie Weeraratne

IGPP is pleased to invite you to join its Fall 2023 Seminar Series presentation featuring CSU Northridge's Dayanthie Weeraratne. Dr. Weeraratne's talk, "A Primordial Source for Multiscale Large Low Velocities Provinces (LLSVP) and Ultra-low Velocity Zones (ULVZ) From Differentiation of the Earth’s Core" will occur at 12pm September 26, 2023.

Time: 12:00 pm, Pacific Time
Location: Munk Conference Room and Zoom https://ucsd.zoom.us/j/93654851631?pwd=eHBzVkRxN3ZZZllxNHlmWXdRZjdEUT09 (password: igpp)

Abstract: Isotopic studies of ocean island basalts suggest that ultra low velocity zones (ULVZ) as well as large low shear velocity provinces (LLSVP) may have a primordial signature. Seismic studies indicate these structures coincide in many locations where thin ULVZ’s underlie the base of LLSVP’s, however, the length scales vary by several orders of magnitude from 10’s of km versus 1000’s of km, respectively. Here we present a model that suggests both LLSVP’s and ULVZ’s form as a product of core-mantle differentiation. We conduct laboratory fluid experiments of liquid metal settling and convection using liquid metal gallium and glucose solutions. Settling experiments are found to coat liquid metal drops with a film of viscous, low density fluid. A metal pond consisting of emulsified metal drops is found to descend rapidly as a coherent Rayleigh−Taylor instability entraining low density material within a film layer. We find that agitation of liquid metal and glucose creates finite scale metallic flakes. Experiments show that increasing the agitation rate, agitation time, and ambient fluid viscosities increases the volume of metal flakes produced. Two-layer convection experiments indicate that 95% of a basal metal sediment layer is stable and survives in the presence of vigorous convection, and meets requirements for a strong seismic velocity reduction and at least a 10% density increase in the ULVZ. Our fluid dynamic model suggests that meteorite impacts which melt the surface and impactor may emulsify molten metal into droplets as well as form finite scale iron metal flakes during turbulent mixing. Our experiments indicate that liquid metal-silicate plumes develop and descend, entraining light elements as well as iron sediments to the core creating temporary stratification. Later, at times scaled to many core formation times, light elements are observed to slowly migrate upwards out of the proto-core in waves. We suggest that thermochemical plumes may be a model for a common primordial origin for the ULVZ and LLSVP structures rooted at the CMB where buoyant light elements migrate out of the core for time scales up to 5 By after core formation, enriching, re-oxidizing, and hydrating the mantle interior and leaving a thin stable metal sediment residual layer at the base of the core-mantle boundary.

Sep 26 2023 - 12:00pm