What is it about?

oceanic crust formation within the slow-spreading Southwest Indian Ridge (SWIR), as evidenced by the petrology (liquidus olivine and spinel compositions) and geochemistry (lithophile elements and Sr–Nd–Pb isotopes) of basalts from the transform fault zone at the western extremity of the ridge

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Why is it important?

The petrological-geochemical study of basalts of the Andrew Bain Fault Zone and adjacent rift valley revealed significant differences in basalt compositions. The rift valley comprises tholeiites enriched in Na and depleted in Fe (Na-TOR genetic type), whereas the western wall of the Andrew Bain Fault zone contains basalts of deep-seated TOR-1 type. The eruption of magmas of these types reflects a change in the geodynamic setting during their melting, namely: a change in conditions from the deeper and higher temperature conditions (within pressure range of 20– 10 kbar, at average Т 1300°С, F >15%) to shallower ones (Р 15–4 kbar, Т 1250°С, F ≈ 10%).

Perspectives

The enriched characteristics of tholeiites from the Andrew Bain Fault are close to those of enriched magmas of the Indian Ocean rises (Crozet, Marion, Bouvet), but differ from those of the Conrad and Afanasy Nikitin rises. Their source is confined to the model HIMU source (with high initial U/Pb ratios) likely with admixture of EM-II type matter (mantle with elevated Rb/Sr ratio). This component represents either oceanic lithosphere recycled through deep mantle (Hoffmann, 2003), or fragments of previously formed oceanic crust that then was involved in melting at jump of the spreading axes (Sushchevskaya et al., 2003; Migdisova et al., 2017). Similar process is typical of BTJ area, where olivine shows significant trace element heterogeneity.

Boris V Belyatsky
Karpinsky Geological Institute (VSEGEI)

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This page is a summary of: Oceanic Crust Formation within the Andrew Bain Fault Zone, Southwest Indian Ridge: Petrological and Geochemical Evidence, Geochemistry International, January 2024, Pleiades Publishing Ltd,
DOI: 10.1134/s0016702924010026.
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