Multiple Sulfur Isotope Geochemistry of the Precambrian Mafic Dykes and Komatiites in the Dharwar Craton, Southern India: Evidence for Crustal Recycling and Enrichment in the Subcontinental Lithospheric Mantle

Abstract

Komatiites, greenstone volcanic rocks, and mafic dyke swarms are constituents of early earth magmatic activity, crucial for understanding the chemical evolution of the Archean mantle. The composition of the subcontinental lithospheric mantle (SCLM) is systematically modified throughout the Earth’s history by the addition of geochemically diverse oceanic and continental crustal materials through subduction and can be sampled through intraplate mafic/ultramafic volcanic activities. Here, we present a first report on the multiple sulfur isotope characteristics of the mafic dyke swarms and komatiites from the Dharwar craton in southern India and discuss the geochemical modifications of SCLM through crustal recycling. δ34SV-CDT values of the samples are all negative ranging from -0.15 to -2.91‰. Δ33S values for all the samples are close to 0 with the lowest value of -0.060‰ and highest of 0.146‰. Δ36S values are mostly negative with very few exceptions, ranging from -1.184 to 1.111‰. Near zero values of Δ33S and negative values for δ34S indicate an early formed mantle reservoir with a possible mixture of sulfur from subducting oceanic sediments. Together with trace element geochemistry, we suggest a depleted MORB source mantle (DMM) modified by oceanic crustal components and a depleted mantle (DM) modified by recycled continental crustal sediments as the two end members of the mantle source that produced mafic dyke swarms in the Late Archean to Proterozoic Dharwar craton.

Sm-Nd isotopic constraints on the metadolerite dykes from Western Dharwar Craton, Southern India: implications on the evolution of Archean subcontinental lithospheric mantle

“…Minor biotite and chlorite were observed in a few thin sections. The opaque minerals are mostly pyrrhotite, pyrite and chalcopyrite (Silpa and Satish-Kumar, 2022). Despite low-temperature metamorphism, remnants of the original mineralogy and original igneous textures (eg., ophitic texture; Figures 3C, D) are well preserved and hence we termed these rocks metadolerites.…”