Experimental Studies of the Mechanism of Diamond Crystallization From COH Supercritical Fluid in SiO2-Rich Media

University Of California-Riverside, Riverside CA

Investigators

Abstract

Dobrzhinetskaya EAR-0229666 The recognition of microdiamonds within ultra-high pressure metamorphic rocks a decade ago initiated a revolution in the understanding of continental collision terranes. Two concepts are known to explain the origin of such diamonds: (1) crystallization from a supercritical COH fluid; (2) crystallization from fluid-bearing alkaline-carbonate melt. Traditionally, experimental attempts to replicate natural diamond formation have been based on synthesis in metal-carbon systems in a highly reduced environment. Only recently has experimental modeling of natural diamonds at high P and T conditions been extended to the alkaline-carbonate-carbon system in the presence of H2O. We have established experimentally that H2O is an active catalyst promoting diamond crystallization from graphite at high pressure and high temperature and that incubation time is dependent on metal ions in solution. In particular, we find that Mg facilitates nucleation and Si does not. This work will extend our work in diamond synthesis with a focus on diamond nucleation in the COH-SiO2 system at varying parameters such as pressure, temperature, time and oxygen fugacity to constrain the mechanism of diamond growth in quartzofeldspathic gneisses and quartzites from ultra-high pressure metamorphic terranes. Experimental investigations related to diamond synthesis from supercritical COH fluid in the diamond stability field is a new but fast-growing research field of great importance for understanding of the mechanism of diamond crystallization within subducted rocks of continental affinity and may bring interesting application for industrial diamond synthesis.