Abstract
A magnesian low-Ti shoshonite dike intruding Archean Norwegian Terrane includes numerous grains of black, blue and gray moissanite (SiC). Moissanite contains inclusions of native Si, Fe and Al, Fe-Cr carbides, Fe-Cr-Mn alloys and diamond. The range of observed δ13C values (-24.8 to -29.6‰) is similar to ophiolite-hosted SiC, lower mantle diamonds and slab-derived biogenic carbon. Norwegian moissanites may have been formed during interaction of Earth’s mantle with carbonaceous slab fluids under extremely reducing conditions as suggested by native metal and carbide inclusions. 13C-depleted moissanite can be used as a new exploration tool for sub-lithospheric diamonds in Archean to Phanerozoic accreted terranes and mobile belts.
Highlights
Moissanite (SiC) occurs in kimberlites, alkaline basalts, podiform chromitites in ophiolites and inclusions in diamonds [1,2,3]
(-24.8 to -29.6‰) in Norwegian moissanites is similar to that reported for several suites of kimberlitic diamonds and carbides as well as to the 13Cdepleted signature of biogenic carbon [2,3,9]
Severe 13C depletion in the lower mantle has been linked to the so-called CLIPPIR (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed) diamond reservoir believed to be the source for large diamonds of exceptional quality and value as well as very rare blue (“boron-spiked”) diamonds [15]
Summary
Moissanite (SiC) occurs in kimberlites, alkaline basalts, podiform chromitites in ophiolites and inclusions in diamonds [1,2,3]. This, together with common association with diamond, abundance of native metal and metal carbide inclusions and 13C-depleted isotope composition, led several authors to propose lower mantle or transitional zone origin for natural moissanite [3,5].
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