What is it about?

The study of the Sr, Nd, and Pb isotopic composition of plume-related basaltic melts makes it possible to establish the geochemical parameters of main mantle source and to recognize the contribution of enriched (EM-I, EM-II, HIMU) or depleted (DM) model components. In this paper, we are focused on the analysis of isotopic composition of plume magmas of East Antarctica and comparison with that of simultaneous magmatic rocks of South Africa, as well as on the determination of their distinctive characteristics and deciphering their geodynamic setting. Special attention is given to the osmium isotopic systematics (187Os/188Os).

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Why is it important?

Mantle plumes significantly affected the Earth’s evolution and largely determined both geodynamic evolution of tectonic provinces and style of magmatism (White and McKenzie, 1989; Dalziel et al., 2000; Burke et al., 2008; Hassan et al., 2015). The Jurassic Karoo--Maud plume that was emplaced ~ 180 Ma in the lithosphere beneath central Gondwana occupies a special place among plumes responsible for the formation of large igneous provinces. It is possible that exactly impact of this plume caused the destruction of paleocontinent and further significantly affected the evolution of the Indian and Atlantic oceans up to the present (Leitchenkov et al., 2003; Torsvik et al., 2016).

Perspectives

The study of Sr, Pb, Nd, and Os isotopic composition in the Mesozoic magmatic rocks of East Antarctica, which are related to the thermal impact of the Karoo Plume 180 Ma and formed the Karoo (South Africa), DML, and Ferrar (East Antarctica) igneous provinces as well as with impact of the Kerguelen plume on the Antarctic margin in the Lamber Glacier area 120 Ma, showed that in all cases the magma source was ancient mantle of the Gondwana paleocontinent. The Nd–Pb–Sr isotopic compositions of melts indicate that the mantle heterogeneity was caused by the early evolution of Gondwana. However, these processes did not cause significant heterogeneity of Re–Os isotopic system. The lithospheric mantle sources of all melt types, the high- and low-Ti magmas, high-Mg ferroan magmas related to pyroxenite melting in East Antarctica and South Africa, have similar 187Os/188Os. This is likely because magmas that are related to the initial impact of the Karoo-Maud plume and were derived from pyroxenite mantle, represented melts of deep-seated portions of the Gondwana lithosphere. The Nd, Pb, and Sr isotopic composition of a source of the basalts of the Ferrar igneous province differs from that of the Karoo and DML provinces. Magmas of the latter provinces are characterized by significant variations of 187Os/188Os ratio (from 0.1 to 0.31) and lowered Os contents at limited variations of Nd–Pb–Sr isotopic characteristics, thus indicating an admixture of EM-II mantle component. Such characteristics of magma source are consistent with inferred subduction reworking of the mantle beneath the western margin of East Antarctica, but this assumption requires further confirmation.

Boris V Belyatsky
Karpinsky Geological Institute (VSEGEI)

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This page is a summary of: Sr, Nd, Pb, and Os Isotope Systematics and Derivation of Mesozoic Plume-Related Basalts of Antarctica: Karoo-Maud and Kerguelen Plume Realm, Geochemistry International, January 2023, Pleiades Publishing Ltd,
DOI: 10.1134/s001670292301007x.
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