Modelling Mantle Mineralogy 1 Modelling Mantle Mineralogy: A Novel Experimental Approach Main supervisor & contact: Dr. Oliver T. Lord (Bristol) — email: [email protected], tel: 01173314762 Co-supervisors: Prof. Michael J. Walter (Bristol) Earth's lowermost mantle contains enigmatic seismically-detected structures including two vast, dense regions termed large low shear-wave velocity provinces (LLSVPs), one below the Pacific and one below Africa, as well as smaller, even denser patches of material at the core mantle boundary (CMB) called ultra-low velocity zones (ULVZs) 1 . One of the most prevalent hypotheses for the origin of this set of complex structures is that they represent the vestiges of the crystallization of one or more impact induced global magma ocean(s) present during the Hadean Eon 2 . Alternatively, these structures may represent the remnants of dense, subducted oceanic crust that has accumulated at the CMB as a result of mantle convection with residence times anywhere from ~3 Ga 3 to only ~100s of Ma 4 . The aim of this project is to develop mineralogical models of the lowermost mantle by comparing its seismic response with the thermoelastic properties of the relevant mineral phases, namely their densities and sound velocities. The studentship will be based in the School of Earth Sciences at the University of Bristol, home to the best-equipped high-pressure petrology laboratory in the country. The student will continue development work on a new internal restive heating method designed to recreate the extreme pressures and temperatures of the deep mantle with unprecedented accuracy. This method will then be used to study the major mantle phases MgSiO 3 bridgmanite / post- bridgmanite, (Mg,Fe)O ferropericlase, CaSiO 3 perovskite, SiO 2 post-stishovite (p-st) / seifertite and Ca-ferrite structured NaAl-rich phase (NAL). The measurements of the thermoelastic properties of these phases will be performed using several complementary, cutting edge techniques. First, densities will be determined as a function of pressure and temperature by X-ray Diffraction on the extreme conditions beamline (I15) at Diamond, the UK's X-ray synchrotron Some of the techniques and facilities that will be employed in this project: (top left) Internal resistive heating in the diamond anvil cell to re-create the pressures of the deep mantle in the laboratory at Bristol. (top right) The state-of-the- art laser heating system at Bristol used to re-create mantle temperatures in the diamond anvil cell. (bottom) The European Synchrotron Radiation Facility at Grenoble, France, where some of the experiments will be performed.