Mid-oceanic-ridge volcanics of the Northwest Indian Ocean exhibit significant chemical and isotopic heterogeneities that indicate the presence of distinct mantle components beneath the ridge. In this study, we conducted a comprehensive petrological and geochemical investigation of two groups of Carlsberg Ridge basalts to determine the nature of their mantle source. Based on the geochemical data, the samples can be divided into two different groups. The first group, comprising whole-rock samples and corresponding volcanic glasses, is located at 2.8°N, and displays “arc-type” trace element patterns, including enrichment in fluid-mobile elements and depletion in Nb (e.g., high Pb/Ce, La/Nb, and Zr/Nb). Despite showing some signatures of seawater alteration, the second group, comprising whole-rock samples and located at 0°, displays similar rare earth element (REE) and high field strength element patterns and εNd as the first group, which suggests that they likely share a similar mantle source. Both groups are depleted in trace elements but isotopically enriched, with (La/Sm)N <0.8 and εNd <9. We propose that these lavas are products of the multistage melting of a mantle source that had been metasomatized by slab-derived fluids. Our study, combined with previously published Carlsberg Ridge data, lead us to suggest a widespread subduction influence in this region. Based on existing plate reconstruction, seismic tomography data, and geochemical evidence, we further propose that the current Carlsberg Ridge formed above the former site of the intraoceanic subduction of the Neo-Tethys Ocean. The arc mantle was integrated into the upwelling mantle and ultimately contributed to present-day Carlsberg Ridge mid-oceanic-ridge basalt (MORB).

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