资源环境科技发展态势分析平台

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 (P2(1)/c) at 27 GPa and 1,500 K with a negative Clapeyron slope of -4.3(9) MPa/K. CaCO3-VII is stable between 23 and 38 GPa at 2,300 K and transforms into post-aragonite at 42 GPa and 1,400 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.