固体地球物理专业研究生学术论坛——李新阳

Surface carbon can be transported to the Earth's deep interior through sinking subduction slabs. Carbonates, including CaCO3, MgCO3 and MgCa(CO3)2, are important carbon carriers for the deep carbon cycle. Experimental studies on the phase stability of carbonates with coexisting mantle minerals at relevant pressure and temperature conditions are thus important in understanding the deep carbon cycle. In this study, we have investigated the stability of CaCO3 at high pressures and temperatures using synchrotron X-ray diffraction in laser heated diamond anvil cells. Our experimental results have shown that CaCO3 in the aragonite structure transforms into CaCO3-VII (P21/c) at 27 GPa and 1500 K with a negative Clapeyron slope of -4.3(9) MPa/K. CaCO3-VII, is stable between 23 and 38 GPa at 2300 K and transforms into post-aragonite at 42 GPa and 1400 K. Furthermore, it reacts with stishovite, an abundant form of SiO2 in subducted oceanic crust, forming CaSiO3-perovskite. The occurrence of CaSiO3-perovskite via the reaction of CaCO3-VII and stishovite provides an explanation for the observation of the high concentrations of CaSiO3-perovskite and some amount of CaCO3 in deep-mantle inclusions. CaCO3-VII is thus an important carbon-bearing phase at the topmost lower mantle and may provide necessary carbon to produce deep mantle diamonds.