Poroelastic response to rapid decarbonatisation as a mechanism of the diamonds formation in the mantle wedge of Kamchatka

Abstract

Various geodynamic mechanisms can lead to the penetration of siliceous carbonates into the mantle wedge. Their thermal decomposition in the "mantle olivine autoclave" can be a mechanism for the formation of diamond erupted in subduction zone of Kamchatka. Using the theory of poroelasticity, we showed that rapid heating of a mixture of sideritic dolomite and silica on 150-200 ∘ C in the closed system conditions can temporarily lead to an increase in the fluid pressure by 2-3 GPa. With the initial parameters = 2 GPa and = 830 ∘ C, the carbonic fluid produced during the reaction would get into the PT stability field of the diamond. The growth of diamond at the fluid decomposition in the PT field of metastable graphite can be enhanced by microparticles of native Ni and Mn formed by the thermal decomposition of gaseous metals carbonyls. The corresponding abundant micro-inclusions of Ni and Mn were found in Kamchatka diamonds.

A New Insight into the Genesis of Graphite Deposits in Madagascar Using U–Pb Zircon Dating and Electron Microprobe Analysis

“…However, large concentrations of highly crystalline graphite can also precipitate from moderatetemperature fluids [35]. In veined graphite deposits associated with magmatism, during the main stage of graphite formation, graphitization can be achieved via the following reactions: CO 2 → C + O 2 [61] [62]; and 2CO → C + CO 2 [63]. Each of these reactions happens under specific conditions, and the focus is on the state and solubility of CO 2 in magma.…”