Phase relations and melting in the system CaCO3 und MgCO3 at high pressures and temperatures

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Calcite and magnesite are among the most common carbonates of the Earth. A deeper insight into the phase relations and melting behavior of the anhydrous and hydrous CaCO3 and MgCO3 system is crucial to understand the carbon cycle in the Earth mantle and project 8 of the Research Unit is dealing with this topicThe project is devided in three parts:In part 1 we will determine of the melting curve of magnesite under anhydrous conditions in the pressure range of 4 to 13 GPa by in situ measurements of the electrical conductivity change in a multi anvil press when magnesite melts. In part 2 we will determine the sub and super solidus phase relations of the CaCO3 and MgCO3 system at 9 GPa and high temperature (starting from 900 C) by quenched multi anvil runs under anhydrous conditions and then establish the phase relations in the super solidus P, T space of the hydrous CaCO3 and MgCO3 system. We will use a rotating multi anvil press to overcome quenching problems as observed in previous studies.In part 3 we will examine the pressure dependence of the melting curve of magnesite under hydrous conditions by means of in situ X ray diffraction measurements with the newly installed multi anvil apparatus at the synchrotron storage ring PETRA III in Hamburg. Here melting at high pressures and temperatures will be established by the occurrence of diffuse scattering in the X ray diffraction pattern.This different experimental approach to determine the melting relation in the hydrous system is necessary as the presence of water would falsify the results on the electrical conductivity.