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Russian Geology and Geophysics

2015 year, number 1-2

EVIDENCE FOR PHASE TRANSITIONS IN MINERAL INCLUSIONS IN SUPERDEEP DIAMONDS OF THE SAO LUIZ DEPOSIT (Brazil)

D.A. Zedgenizov1,2, V.S. Shatsky1,3,2, A.V. Panin4, O.V. Evtushenko4, A.L. Ragozin1, H. Kagi5
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 2, Novosibirsk, 630090, Russia
3A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk, 664033, Russia
4Institute of Strength Physics and Materials Science, Siberian Branch of the Russian Academy of Sciences, pr. Akademicheskii 2/4, Tomsk, 634021, Russia
5University of Tokyo, Tokyo 113-0032, Japan
Keywords: Diamond, inclusions, deformation, superdeep minerals, upper mantle, transition zone, lower mantle

Abstract

Evidence for phase transitions in mineral inclusions in superdeep diamonds of alluvial placers in the São Luiz River deposits (Brazil) is obtained by the electron backscatter diffraction technique. It has been shown that the crystal structure of superdeep diamonds is significantly deformed around inclusions of MgSi-, CaSi-, and CaTiSi-perovskites, SiO2 (stishovite?), and Mg2SiO4 (ringwoodite?). On the contrary, significant deformations around inclusions of olivine, ferropericlase, and majoritic garnet are not detected. The absence of deformation near these minerals reveals the lack of phase transitions with dramatic volume changes. The present study suggests that the formation of superdeep diamonds proceeds at different levels of the sublithospheric mantle, transition zone, and lower mantle.

DOI: http://dx.doi.org/10.1016/j.rgg.2015.01.021