Dr. Zhixue Du [Geophysical Laboratory, CIW, USA]

Title: Origin of Earth’s ancient magnetic field: driven by MgO exsolution?

Time: 10:00 - 11:00 AM, Friday, September 1, 2017

Place: Conference room 410, HPSTAR (Shanghai)

Host: Ho-Kwang Mao

Abstract

The origin of Earth’s ancient magnetic field is an outstanding problem. Exsolution of MgO or SiO2 from the core during cooling has been proposed as a viable mechanism to drive an early geodynamo. We conducted new experiments on Mg partitioning between an iron-rich liquid and silicate/oxide melt. Our results indicate that MgO exsolution is limited and insufficient to drive an early geodynamo alone. In order to understand the effect of the possible exsolution-driven dynamo, we constructed a thermal model by including the process of exsolution. Our thermal model predicts inner core nucleation (ICN) at ~850 Ma and a nearly constant paleointensity using our experimentally determined data. Interestingly, strong exsolution in the form of either MgO or SiO2  would lead to a distinct trend in paleointensity after ICN. This potentially provides an observational test for the exsolution model and ICN.

Biography of the Speaker:





Dr. Zhixue Du joins the Geophysical Laboratory as a Carnegie Fellow from Yale University, where he just received his Ph.D. in Geophysics. He is working with Yingwei Fei and the rest of the staff on various projects and is very interested in mineral physics.

EDUCATION

Yale University, Department of Geology & Geophysics, PhD, Geophysics, December 2015

   • Dissertation: Melting and rheology of (Mg,Fe)O ferropericlase at high pressures  

Peking University, Bachelor of Science, Geochemistry, July 2007

RESEARCH EXPERIENCE

September 2015 – Present

Geophysical Laboratory, Carnegie Institution of Washington

Carnegie Postdoctoral Fellow, Advisors: Yingwei Fei, Peter Driscoll

   • Reaction between silicate melt and liquid iron, in particular, MgO solubility in Earth’s core and its implication for early geodynamo

   • Elemental partitioning during Earth’s core formation.

September 2008 – June 2015

Yale University, Department of Geology & Geophysics

Research Assistant, Advisor: Kanani K.M. Lee

   • Melting of (Mg,Fe)O using Laser heated Diamond Anvil Cell

Developed a program controlled Laser Heating System, achieved steady, controllable high temperature conditions and successfully measured the melting curve of MgO under Earth’s lower mantle conditions. This study potentially resolves long-standing controversy between previous experimental and theoretical studies

   • Determining melting using 2D temperature maps

Established a new method to determine melting temperatures by coupling multi-wavelength imaging with secondary electron microscope (SEM) measurements of the sample after flash heating. This method has been successfully applied to measure the melting temperatures of rhenium, molybdenum, tungsten, iron, platinum, ferropericlase, etc.

   • External Resistive heating and heater design

Invented a graphite heater design for steady, efficient, uniform heating at high pressures and determined the melting curve of water under pressures

   • Equation of state of Earth’s mantle minerals using synchrotron x-ray diffraction