CRYSTALLOGRAPHIC ORIENTATION AND GEOCHEMICAL SPECIFICS OF MINERAL INCLUSIONS IN DIAMONDS
N.V. Sobolev1,2, Yu.V. Seryotkin1,2, A.M. Logvinova1,2, A.D. Pavlushin3, S.S. Ugap’eva3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
3Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: High and ultrahigh pressures, eclogite, peridotite, olivine, garnet, chromite, diamond, coesite, mutual orientation of diamond and inclusions, paragenesis, mineral equilibria, geothermobarometry, morphology of inclusions, high-density fluid inclusions
Abstract
The orientation of 76 mineral inclusions - olivine (25), pyrope (13), and magnesiochromite (38) - was measured in 16 diamond samples from major primary diamond deposits in Yakutia, such as the Mir, Udachnaya, Internatsional’naya, Aikhal, and Yubileinaya kimberlite pipes. The novelty of the performed research is a special approach to a choice of samples containing not only olivine inclusions, plenty of which have been studied in recent years after the publication of the book «Carbon of the Earth» in 2013, but others as well. Our collection comprises 25% of the studied world’s diamond samples, including the most typical diamonds of prevailing peridotite paragenesis, which were found in almost all known kimberlites. Neither our experiments nor similar studies carried out by the world’s researchers in 2014-2019 revealed any inclusions with orientation meeting the epitaxial criterion in the diamonds. Only a few magnesiochromite inclusions in three diamonds have a near-regular orientation. The carbon isotope composition shows a significant correlation with the composition of mineral inclusions in the diamonds of peridotite and eclogite parageneses and no correlation with other properties of the inclusions, which can be considered the geochemical specifics of the latter. At the same time, there are numerous literature and our data on the intricate growth history of diamonds and on the wide variations in the composition of mineral inclusions in different zones of some diamonds. Taking into account this fact and the different morphology of diamonds, we assume the possible coexistence of syngenetic and protogenetic inclusions in the same diamond. This hypothesis is confirmed by finding of peridotite and eclogite xenoliths with garnet- or olivine-enclosed diamonds in kimberlites. All the samples contain heavy hydrocarbons, from pentane (С5H12) to hexadecane (C16H34), prevailing in fluid inclusions in kimberlite and placer diamonds and in pyrope and olivine of diamond-bearing peridotite xenoliths.
DOI: 10.15372/RGG2020144
|
