FEATURES OF DIAMOND FORMATION PROCESSES IN SUBDUCTION ZONES
V.S. Shatsky1,2,3, A.L. Ragozin1, V.N. Reutsky1, V.V. Kalinina1
1 V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Science, Novosibirsk, Russia
2 Novosibirsk State University, Novosibirsk, Russia
3 A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: inclusions in diamonds, diamond formation, mantle, subduction zone
Abstract
Evidence of the involvement of Fe-C-O melts in diamond formation from placers in the northeastern Siberian Craton, along with our previously obtained data on iron carbide inclusions and literature sources, has provided a new perspective on processes diamond formation in subduction zones. Iron carbide and oxide inclusions in diamonds, along with the presence of moissanite and carbonates in polyphase inclusions, indicate a heterogeneous diamond environment. Extreme variations in oxygen fugacity during diamond formation processes can be caused by the generation of hydrogen and hydrocarbons during the interaction of carbonated rocks of the subducting oceanic lithospheric plate with aqueous fluids. Separated hydrocarbon fluids can create local areas of ultra-reduced mantle, where silicon carbide can be formed under conditions of the absence of equilibrium with the surrounding rocks.. A characteristic feature of the diamonds studied is that they were subjected to brittle deformation, followed by crack healing, accompanied by the formation of polyphase inclusions of iron carbides and oxides, which we interpret as melt inclusions. Brittle deformations of diamonds, in the conditions of the lower lithosphere, are explained by high deformation rates, which can be realized in the hypocenters of deep-focus earthquakes of the subducting lithospheric plate, during dehydration processes or the formation of carbonatite melts.
|
