During the final stage of accretion, terrestrial planets experienced violent and highly energetic giant impacts. As a consequence of impact heating, the early Earth was partially or wholly molten, forming a magma ocean in the outer layer of Earth. Subsequent cooling of the magma ocean has led to fractional crystallization of the primitive mantle. Many unknowns remain about accretion of the early Earth, such as extension depth and life time of the magma ocean(s), role of mantle recrystallization on the chemical segregation between the different Earth reservoirs, and so on. The knowledge of melting properties of the deep mantle is also important to investigate the possibility of partial melting at the present time. The aim of this study was to tackle a few major questions concerning the Earth lower mantle : What is the melting sequence between the main lower mantle phases ? Can we explain the ultra-low-velocity zones (ULVZ) by partial melting of pyrolitic (or chondritic) mantle ? How does iron partition between liquid and solid silicate phases in the deep mantle ? Can we provide new information on the properties of the deep magma ocean based on the melting curve of the primitive mantle ? Melting curves and melting relations have been investigated using the laser-heated diamond anvil cell (LH-DAC) for pressure between 25 and 135 GPa and temperature up more than 4000 K, i.e. at P-T conditions corresponding to the entire Earth’s lower mantle. Compositions investigated were the join between MgO and MgSiO3 and a model chondritic-composition for the Earth mantle. Two different in situ synchrotron radiation techniques have been used to infer melting properties at high pressures ; X-ray diffraction and X-ray fluorescence spectroscopy. The new results obtained in this study include : (...)
Experimental investigation of the deep mantle melting properties