Sr, Nd, Pb, and Os Isotope Systematics and Derivation of Mesozoic Plume-Related Basalts of Antarctica: Karoo-Maud and Kerguelen Plume Realm

Abstract

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.