Structural Stability and Mobility of Carbonate Minerals and Melts in the Earth’s Mantle

Abstract:

Knowledge of potential carbon carriers such as the mantle carbonate minerals and melts is critical for our understanding of the deep-carbon cycle and related geological processes within the planet. Although rhombohedral carbonates (e.g., calcite, magnesite, and siderite) have been proposed as a major carbon carrier in the Earth’s crust and upper mantle, several distinct scenarios have been proposed for these carbonates at deep-mantle conditions including chemical dissociation and various structural transitions. Recently, carbonate melts have been reported to be highly mobile at high pressure and temperature (P-T) conditions, which may have significant impact on magmatic processes in Earth’s upper mantle. However, the high P-T behaviors of carbonate minerals and melts are still not well understood, in terms of their structural stability and mobility in the Earth’s lower mantle. Combining in-situ synchrotron X-ray diffraction (XRD), transmission X-ray microscopy (TXM), and Raman spectroscopy experiments in a laser-heated diamond anvil cell with complementary theoretical calculations, we investigate the phase stability of carbonates, the equation of state (EoS) of carbonatic glasses, as well as the distribution of carbonate melts in a silicate matrix up to lower-mantle conditions.