Diamond resorption morphology as a fluid proxy in diamond-bearing environments: Constraints from empirical and experimental studies

Abstract

Despite of numerous studies the compositions of C-O-H fluids in the mantle and kimberlites remain uncertain due to limitations of conventional methods. My study shows no correlation between internal properties in diamond outer rims and resorption morphologies, suggesting little effect of internal factors on resorption morphologies. Diamond dissolution experiments were conducted at 1-3 GPa and 1150 – 1400 oC in C-O-H fluids with XCO2 =0 -1, monitored in-situ by synthetic fluid inclusions. The experimental results show that 1) a miscibility gap exists in the CO2-H2O-dominated system at 1250 oC under 1 and 3 GPa, 2) circular pits form on tetrahexahedral faces in pure H2O at 1 GPa buffered by MgO-forsterite, and 3) the bulk composition of C-O-H fluids controls the pressure effects on diamond rounding rates and resorption morphologies. The combined empirical and experimental studies demonstrate diamond resorption morphology robustly semi-quantitatively recording compositions of the latest diamond-etching fluids.