Magmatic records of Neoarchean Suprasubduction Zone fore arc mantle: Constraints from geochemical signatures of ultramafic rocks from Goa, western India

Neoarchean-Paleoproterozoic accretionary and collisional orogens archive vestiges of paleo-subduction zones， ancient ocean basins and polyrecycled continental crust deciphering the thermo-tectonic evolution of the earth. This study presents mineral and bulk chemical along with Re-Os isotopic data for 2.6-2.5 Ga ultramafic cumulates from Bondla-Usgao region of Goa， western India， to address their source characteristics， implications on mantle heterogeneity and tectonothermal evolution of paleo-oceanic crust during the Neoarchean subduction-accretion-collision processes. The ultramafic cumulate rocks predominantly comprises peridotite-dunite assemblage showing primary melt signatures. The ultramafic rocks are characterized by large ion lithophile elements （LILE） -light rare earth elements （LREE） enrichment and high field strength elements （HFSE） depletion relative to primitive mantle evolved through a multistage petrogenetic process of a refertilized mantle wedge. Mineral chemistry and whole rock geochemical attributes suggest that the studied lithologies represent lower oceanic crust formed by fractional crystallization of hydrous arc melt composition during incipient intraoceanic subduction in an extensional fore arc setting associated with the supra subduction zone （SSZ） environment. This conjecture is substantiated by suprachondritic Os [¹⁸⁷Os/¹⁸⁸Os_{（present）}: 0.1341 to 0.1713] isotope compositions and Re addition to mantle source thereby attesting to a chemically heterogeneous SSZ mantle wedge metasomatized by slab-derived fluids and silicate melts. Re-Os isotope signatures reveal imprints of cratonic lithospheric mantle （CLM） on the studied oceanic crustal ultramafics thereby postulating （i） probable entrapment and incorporation of ancient subcontinental lithospheric mantle （SCLM） fragments into arc mantle by upwelling asthenosphere during fore-arc extension in response to subduction initiation （ii） refertilization of fore-arc mantle wedge by infiltration of subduction-derived fluids and melts （iii） Os mobilization facilitated by slab to wedge melt migration， infiltrative melt percolation and melt-rock interaction.