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The study of Re–Os isotopic systematics of the Mesozoic magmas in East Antarctica and its comparison with Sr–Nd–Pb–Os published data allowed us to reveal the main features of Antarctic magmatism associated with the activity of the Karoo–Maud (Dronning Maud Land (DML), Karoo and Ferrar provinces) and the Kerguelen (Lambert rift area) plumes. It is shown that a melt source of the 180-Ma Karoo–Maud plume could be enriched lithospheric mantle. Variations of the 187Os/188Os ratio in the range of 0.1242–0.1426 characterize almost all types of melts in the Karoo and DML provinces, including both high- and low-Ti magmas as well as high-Mg ferropicrites produced by melting of mantle pyroxenite. This observation is consistent with previous assumption that magmas derived from pyroxenite mantle at the initial stage of plume impact represented melts of deep lithospheric fragments of ancient Gondwana paleocontinent that were entrapped by plume. Thereby, mantle heterogeneity recorded in the Nd–Pb–Sr isotopic compositions of the basalts is not expressed in the systematic variations of Re–Os isotope system. The magmatic source of the basalts of the Ferrar province differs from the source of Mesozoic magmatism in the Karoo and DML provinces by great variations in the 187Os/188Os ratio: from 0.1 to 0.31, and by the lower osmium contents, with limited variations of other isotopic systems, indicating an admixture of enriched EM-II source. This is consistent with inferred subduction reworking of the mantle of the western Antarctic margin (Sushchevskaya et al., 2022). Ultramafic picritic magmas from the Lambert Glacier area are characterized by a radiogenic osmium isotopic composition: 187Os/188Os 0.1582–0.2388. Source of these magmas could be ancient depleted mantle, which later experienced mantle metasomatism due to the multiple interactions with fluid-saturated melts. Picritic melts of the paleorift zone of the Lambert Glacier are close to a magma source of the Karoo and DML provinces in terms of Sr-Nd isotopic composition, but differ in more radiogenic lead. [ABSTRACT FROM AUTHOR]

The first results of the study of the Re–Os isotope system of native gold from the orogenic Malo-Tarynskoe, Khangalas, and Bazovskoe deposits located in the central part of the Yana–Kolyma metallogenic belt are reported. The concentration of Re in the studied gold samples varies from 0.168 to 6.997 ppb, while the concentration of Os ranges from 0.068 to 1.443 ppb. The obtained data allowed us to calculate the isochrone age, which is consistent with the 40Ar–39Ar and K–Ar ages of sericite from these deposits within the error. The results indicate that the studied gold deposits were formed in the range of 147.8–137.1 Ma, synchronously with the Late Jurassic–Early Cretaceous orogenic processes in the Yana–Kolyma metallogenic belt and on the eastern margin of the Siberian Continent. The initial Os isotope ratios in the studied samples and fractions of gold from the Malo-Tarynskoe, Khangalas, and Bazovskoe deposits, (187Os/188Os)i = 0.1844–0.2475, suggest a significant role of a nonradiogenic component normally associated with mantle sources. [ABSTRACT FROM AUTHOR]

The mantle xenoliths of lherzolite composition from Mesozoic alkaline–ultrabasic diatremes of Jetty Oasis were studied. The treated xenoliths represent the mantle section of the East Antarctic Craton down to depths of 60–80 km. The osmium isotope composition of these nodules testifies to the beginning of the formation of the lithospheric mantle in the considered region of the craton 2400 Ma ago. The absence of any signs of Early Archeozoic lithosphere points either to partial destruction of the lithosphere at the convergent boundary of the plates in the Late Archean or to thermal erosion of the Archean lithosphere under the effect of a deep-seated plume in the Mesozoic during rift formation. [ABSTRACT FROM AUTHOR]