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Origin of Ru-Os Sulfides from the Verkh-Neivinsk Ophiolite Massif (Middle Urals, Russia): Compositional and S-Os Isotope Evidence
oleh: Kreshimir N. Malitch, Inna Yu. Badanina, Elena A. Belousova, Valery V. Murzin, Tatiana A. Velivetskaya
Format: | Article |
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Diterbitkan: | MDPI AG 2021-03-01 |
Deskripsi
This study presents new compositional and S-Os isotope data for primary Ru-Os sulfides within a platinum-group mineral (PGM) assemblage from placer deposits associated with the Verkh-Neivinsk massif, which is part of the mantle ophiolite association of Middle Urals (Russia). The primary nature of Ru-Os sulfides represented by laurite (RuS<sub>2</sub>)–erlichmanite (OsS<sub>2</sub>) series is supported by occurrence of euhedral inclusions of high-Mg olivine (Fo<sub>92–94</sub>) that fall within the compositional range of mantle (primitive) olivine (Fo <sub>88–93</sub>). The sulfur isotope signatures of Ru-Os sulfides reveal a range of δ<sup>34</sup>S values from 0.3 to 3.3‰, with a mean of 2.05‰ and a standard deviation of 0.86‰ (<i>n</i> = 18), implying that the sulfur derived from a subchondritic source. A range of sub-chondritic initial <sup>187</sup>Os/<sup>188</sup>Os values defined for Ru-Os sulfides (0.1173–0.1278) are clearly indicative of derivation from a sub-chondritic source. Re-depletion (T<sub>RD</sub>) ages of the Verkh-Neivinsk Ru-Os sulfides are consistent with prolonged melt-extraction processes and likely multi-stage evolution of highly siderophile elements (HSE) within the upper mantle. A single radiogenic <sup>187</sup>Os/<sup>188</sup>Os value of 0.13459 ± 0.00002 determined in the erlichmanite is indicative of a supra-chondritic source of HSE. This feature can be interpreted as evidence of a radiogenic crustal component associated with a subduction event or as an indication of an enriched mantle source. The mineralogical and Os-isotope data point to a high-temperature origin of the studied PGM and two contrasting sources for HSE in Ru-Os sulfides of the Verkh-Neivinsk massif.