Original paper

Petrogenesis of mineral micro-inclusions in an uncommon carbonado

Sautter, Violaine; Lorand, Jean -Pierre; Cordier, Patrick; Rondeau, Benjamin; Leroux, Hugues; Ferraris, Cristiano; Pont, Sylvain


A unique Brazilian sample of a carbonado, displaying unusually large amount of diamond clasts merged within a finegrained diamond matrix, has been studied by Secondary Ion Mass Spectrometry (SIMS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) on Focused Ion Beam (FIB)-extracted foils. We found for the first time in the diamond clasts (stage-1) micrometer to nanometer-sized inclusions of augite, ilmenite and phlogopite (all Fe-rich). Inclusions of metallic phases (Fe, Ti, Cr, Al and alloys of Fe-Cr, Al-Cr, Al-Fe Cr) described in worldwide carbonado occur in the studied sample exclusively within the fine-grained matrix (stage-2). The carbon isotopic composition of the diamond clasts and the fine-grained matrix falls within the range 27 % to 32 % , like worldwide carbonado. The iron-rich silicate-oxide assemblage isolated inside clasts points to an initial growth of that diamond from mafic-rock minerals under oxidizing conditions (f O2


carbonadomicro-inclusionsdiamond texturecarbon isotopefib-temredox conditionsmetamorphic diamondplastic deformation