A layered gabbro-anorthosite suite from Attappadi: Chemical and isotopic signature of Neoarchean subduction tectonics in the Southern Granulite Terrane, India

Archean layered complexes offer important windows into early Earth tectonic styles and continental crust building. The Dharwar Craton (3.3–2.7 Ga) in Southern India is bordered by Archean granulite facies crustal blocks and exposes some of the oldest rock suites that are archives of the Archean crust including the Niligiri Block where the major rock types include metapyroxenite, metagabbro, layered gabbroic anorthosite, garnet-bearing metagabbro, pyroxene granulite, and anorthositic gabbro. Here, we report a dismembered layered gabbro-anorthosite suite from the flanks of this block and present the results from an integrated study on field investigation, petrology, whole-rock geochemistry, and zircon U[sbnd]Pb geochronology with a view to understand the nature and timing of magmatism and to elucidate the tectonic history. The geochemical data suggest a supra-subduction zone affinity for the magmatism, with arc signature, including a high concentration of large ion-lithophile elements combined with low high field-strength elements. The ultramafic-mafic-anorthosite suite was generated through the partial melting of an enriched mantle source within an island arc setting. Zircon U[sbnd]Pb ages from six samples show weighted mean ages of 2526 ± 16 Ma, 2512 ± 13 Ma, 2563 ± 27 Ma, 2505 ± 21 Ma, 2490 ± 13 Ma, and 2425 ± 51 Ma. The Neoarchean ages from these rocks are comparable to those from the adjacent Agali Hill ophiolite complex and correlate with major crust formation in a subduction-related setting. Our study provides further insights into the Archean tectonic history of Peninsular India.