<p>Carbonates appear to be one group of the main carbon-bearing minerals in the Earth&#8217;s interior. Inclusions of carbonates in diamonds of lower mantle origin support the assumption that they are present even in the Earth&#8217;s lower mantle. Although the carbonates&#8217; phase diagrams have been intensively studied, their stability in presence of mantle silicates at deep mantle conditions (>25 GPa) remains unclear. Furthermore, the carbonate inclusions show a high REE enrichment. This raises questions on the distribution of trace elements between carbonates and silicates and on the possible role of carbonates as trace element carrier in the Earth&#8217;s mantle.</p><p>Numerous studies show that magnesite is likely to be the major solid carbonate carried by subduction into the Earth&#8217;s lower mantle. We investigated the stability of MgCO<sub>3</sub> in presence of mantle silicates and the Fe, Sr and La partitioning in high-pressure and high-temperature experiments. One set of experiments was conducted with multi-anvil presses at BGI, Bayreuth, at conditions ranging from 24 GPa to 30 GPa and 2000 K. The investigated reaction is between natural magnesite and (Mg,Fe)SiO<sub>3</sub>-glasses doped with either Sr or La. Preliminary data from the multi-anvil press at 24 GPa and 2000K show the onset of carbonate melting which is consistent with the previous study of the melting curve in the enstatite-magnesite system [1]. Decomposition of MgCO<sub>3</sub> is not observed, in contrast to experiments using magnesite and SiO<sub>2</sub> as starting materials [2], suggesting that MgCO<sub>3</sub> is stable at these conditions in the presence of silicates phases. The silicate glass react to bridgmanite (Mg,Fe)SiO<sub>3</sub> as well as stishovite SiO<sub>2</sub> and magnesiow&#252;stite (Mg,Fe)O. The Fe-Mg partitioning coefficient between bridgmanite and magnesite calculated in this study is ~2 and in agreement with previous experiments at similar conditions [3].<br>Laser-heated diamond anvil cell (LH-DAC) experiments were performed at University of Potsdam [4] at conditions 30 to 40 GPa and 1800 to 2300 K. The run products were characterized in-situ at high-pressure by XRD and XRF mapping at the P02.2 beamline at PETRA III. Our data show a transformation of the starting silicate glass into bridgmanite. We also observed stishovite and magnesiow&#252;stite in the center of the hotspot where the temperature had reached >2000 K. In this case, the presence of magnesiow&#252;stite might be the result of MgCO<sub>3 </sub>decomposition at higher temperature. Additional TEM analyses on the post-mortem sample will allow us to further characterize the different phases present in the laser-heated hotspot.</p><p>[1] Thompson et al. (2014) Chemistry and mineralogy of the earth&#8217;s mantle. Experimental determination of melting in the systems enstatite-magnesite and magnesite-calcite from 15 to 80 GPa. American Mineralogist 99(8-9), 1544-1554.<br>[2] Drewitt et al. (2019) The fate of carbonate in oceanic crust subducted into Earth&#8217;s lower mantle. EPSL 511, 213-222<br>[3] Martinez, et al. (1998). Experimental investigation of silicate-carbonate system at high pressure and high temperature.&#160;Journal of Geophysical Research: Solid Earth, 103(B3), 5143-5163.<br>[4] Spiekermann et al. (2020). A portable on-axis laser heating system for near-90&#176; X-ray spectroscopy: Application to ferropericlase and iron silicide. Journal of Synchrotron Radiation. (accepted)</p>
From Slater to Mott physics by epitaxially engineering electronic correlations in oxide interfaces