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Introduction: Metadolerite dykes in the Western Dharwar Craton represent the oldest generation of mafic dyke swarms in the craton. The emplacement of these dykes after a period of crust building activity and komatiite volcanism, helps to understand the evolution of Subcontinental Lithospheric Mantle (SCLM) and Archean dynamics.Methods: We report whole rock major, trace element geochemistry and Sr-Nd isotope characteristics for this weakly metamorphosed suite of dykes. Remnant igneous textures and mineralogy are well preserved.Results: The trace and rare earth element concentrations and an overall flat pattern suggests depleted mantle source for these dykes. Three groups are primarily identified: Group one with initial 87Sr/86Sr ratios varying between 0.70041 and 0.70102, Group two dykes and Group three dykes with initial ratios 0.70045–0.70154, and 0.70041–0.70153 respectively. Group one dykes show a good Rb-Sr isochron relationship and an errorchron age of ca. 3,003 ± 102 Ma is obtained. The initial 143Nd/144Nd ratios varies from 0.508,245 to 0.509,172. The epsilon Nd values are mostly negative, ranging between −12 and +5. Group one and two show an epsilon Nd value ranging between −1 and +5 and 0.1 to +5 respectively and group three varies between −0.5 and −12.Discussion: The geochemical characteristics suggest that the group one dykes are derived from a homogenous depleted SCLM source, group two formed by a lower degree of partial melting of a source mantle with enriched components. Group three may have formed from a progressively enriched group one source. All these dykes can be considered as exposed remnants of feeders for the greenstone volcanism in the Western Dharwar Craton.

The major and trace element characteristics of the clinopyroxene from two generations of dykes, dolerite and olivine dolerite dykes of Western Dharwar Craton were investigated by using electron microprobe and LA-ICPMS. The clinopyroxene in dolerite dykes show a compositional zoning with Mg# decreasing from the core to the rim (85 to 51) and Cr 2 O 3 contents decrease towards the rim. The trace and rare earth element (REE) pattern of the core shows lower concentrations of REEs compared to the rim. The clinopyroxene in the olivine dolerites are devoid of zoning and compositionally more primitive than the dolerites as visible in the trace element and REE concentrations. The dolerite and olivine dolerite are formed from different source magmas and the fractional crystallization of clinopyroxene is dominant in dolerites. The present estimated melt composition in equilibrium with clinopyroxene is consistent with the bulk rock composition for dolerite and olivine dolerite.

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.