Temperature-induced amorphization in CaCO3 at high pressure and implications for recycled CaCO3 in subduction zones

摘要

Calcium carbonate (CaCOsub3/sub) significantly affects the properties of upper mantle and plays a key role in deep carbon recycling. However, its phase relations above 3?GPa and 1000?K are controversial. Here we report a reversible temperature-induced aragonite-amorphization transition in CaCOsub3/sub at 3.9-7.5?GPa and temperature above 1000?K. Amorphous CaCOsub3/sub shares a similar structure as liquid CaCOsub3/sub but with much larger C-O and Ca-Ca bond lengths, indicating a lower density and a mechanism of lattice collapse for the temperature-induced amorphous phase. The less dense amorphous phase compared with the liquid provides an explanation for the observed CaCOsub3/sub melting curve overturn at about 6?GPa. Amorphous CaCOsub3/sub is stable at subduction zone conditions and could aid the recycling of carbon to the surface.