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[SIT25-04] Origin of carbonado, an enigmatic polycrystalline diamond deduced from its microtexture and inclusions
Keywords:Carbonado, Diamond, Inclusion
Here, we found several types of primary mineral inclusions (majoritic garnets, phengite, rutile, apatite, etc.) in nano-sized negative crystals within diamond grains by detailed FE-SEM and TEM observations. Those precipitates usually occur as an assemblage of a few to several mineral phases that are mostly in euhedral forms in the negative crystals. They are most likely quenched products from silicic fluid that were trapped during the crystal growth of diamonds that comprise carbonado. The presence of these mineral phases in negative crystals suggests that the formation of carbonado occurred in fluid-saturated environments to which crustal materials (e.g. basalt) are supplied potentially by the subduction of oceanic plates or extensive collision of continental plates to form a thick mantle keel.