Role of Depleted-MORB Mantle in the Genesis of Basalts from the Neoarchean Eastern Felsic Volcanic Terrane of the Sandur Greenstone belt, Dharwar Craton, India

Abstract

The mafic volcanic rocks from the eastern felsic volcanic terrane (EFVT) of the Neoarchean Sandur greenstone belt of Western Dharwar Craton (WDC) are studied to evaluate their geochemical characteristics and tectonic implications. Characterised as sub-alkaline, tholeiitic basalts, they display moderate SiO2 (49.82-53.74 wt.%), Al2O3 (9.08-15.91 wt.%), TiO2 (0.25-0.66 wt.%) and total alkalies (Na2O+K2O= 0.60-3.97 wt.%) with Mg# ranging from 37-55 at low Cr (7-33 ppm), Ni (8-24 ppm) and V (252-612 ppm). Their rare earth and trace element patterns are coherent exhibiting moderate fractionation (La/Yb=0.16-1.09), slight negative Eu anomalies indicating limited plagioclase fractionation (Eu/Eu*= 0.69-0.96), negative Nb, Ta, Ti and Zr-Hf anomalies revealing their arc signatures. The Nb-Th and Zr-Y relationships of these basalts suggest their derivation from the partial melting of depleted mantle in an intra-oceanic arc setting. Trace element modelling of these basalts indicates their genesis by ~15% partial melting of depleted MORB-mantle and depletion of the source is attributed to previous melting events. These basalts are geochemically similar with the depleted arc and forearc basalts of the Phanerozoic Tonga and Izu-Bonin-Mariana arcs emphasising the operation of analogous tectonic processes during the Archean era.