Hf-Nd-Sr Isotopic Constraints on the Sources of Pelagic Clays and Silicate Residues of Ferromanganese Crusts in the Central Indian Basin

Abstract

The sources of pelagic clays and the silicate residues of ferromanganese (Fe-Mn) crusts from the Central Indian Basin remain unclear. Here, we present combined Hf-Nd-Sr isotopic compositions for a suite of clays and silicate residues of Fe-Mn crusts from the Afanasiy-Nikitin Seamount (ANS) to constrain their sources and the process influencing their variability. Our results show large and systematic variations with a range of 0.70788–0.73051 for ⁸⁷Sr/⁸⁶Sr, from −15.68 to −7.55 for εNd, and from −3.9 to 6.72 for εHf. Detrital clays are characterized by radiogenic ⁸⁷Sr/⁸⁶Sr, unradiogenic εNd, and εHf. Siliceous clays have less radiogenic ⁸⁷Sr/⁸⁶Sr, radiogenic εNd, and εHf. The silicate residues of ANS Fe-Mn crusts have unradiogenic ⁸⁷Sr/⁸⁶Sr, radiogenic εNd, and highly radiogenic εHf. Despite variable lithologies and depositional environments, all data display highly correlating trends in Nd-Sr and Nd-Hf space suggesting mixing of two common enriched and depleted end-members. Mixing relationships in Nd-Sr space define the sources as the Himalayas and the Indonesian Volcanic Arc (IVA). In the Nd-Hf space, the highly radiogenic Hf isotopic compositions of our sedimentary archives resolve the IVA source, but not the Himalayas that are plagued by zircon effects. Calculated ∆εHf clay ranges from 2.3 to 8.53 suggesting an unlikely presence of zircons in these sedimentary archives. Our results demonstrate that the clays and the silicate residues of ANS Fe-Mn crusts primarily originate from the Himalayas and the IVA, with the Himalayas supplying 47%–98% of the detrital clays and the IVA contributing 46%–62% to the siliceous clays and silicate residues of crusts.