ARCHEAN DIAMONDIFEROUS ROCKS OF THE OLONDO GREENSTONE BELT( western Aldan-Stanovoy shield )
A.P. Smelova, V.S. Shatskyb, A.L. Ragozinb, V.N. Reutskiib, and A.E. Molotkova
aDiamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, ul. Lenina 39, Yakutsk, 677980, Russia
bV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Diamond, Archean, komatiites, greenstone belt, Aldan-Stanovoy shield
Pages: 1012-1022
Subsection: PETROLOGY, GEOCHEMISTRY, AND MINERALOGY
Abstract
Diamond from metaultramafic rocks of the Mesoarchean (2.96-3.0 Ga) Olondo greenstone belt, located in the western Aldan-Stanovoy shield, has been studied. Diamonds occur in lenses of olivine-serpentine-talc rocks within metaultramafic rocks of intrusive habit, whose composition corresponds to peridotite komatiites. All diamonds from the metaultramafic rocks are crystal fragments 0.3 to 0.5 mm in size. Morphological examination has revealed laminar octahedra, their transitional forms to dodecahedroids, crystals with polycentric faces, and spinel twins. The crystals vary in photoluminescence color: dark blue, green, yellow, red, or albescent. Characteristic absorption bands in crystals point to nitrogen impurities in the form of A and B1 defects and tabular B2 defects. The crystals studied belong to the IaA/B type, common among natural diamonds. The overall nitrogen content varies from <<100 to 3800 ppm. The relative content of nitrogen in B1 centers varies from 0 to 94 %, pointing to long stay in the mantle. The carbon isotope ratio in the diamonds, δ13 C = -26 ‰, is indicative of involvement of subducted crust matter in diamond formation in the Archean.
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