Abstract
Abstract Major and trace element data for ultramafic and mafic metavolcanic rocks from the volcano-sedimentary belts at Holenarsipur and Shigegudda are presented. Although the Holenarsipur belt has been regarded as representing two stratigraphic groups separated widely in time — the Sargur (pre-3,4 Ga) and Dharwar (post-3,4 Ga) Groups — and Shigegudda is clearly younger than the 3.4 Ga gneisses, representative samples from all three suites are part of the same geochemical population. This comprises komatiitic to tholeiitic lavas which are genetically related by progressive fractional crystallization of olivine + pyroxene ± Cr-spinel. Some of the variability in the high-MgO rocks may reflect differential, partial melting of the mantle. There are two sub-populations, separable into light rare-earth-enriched and light rare-earth-depleted, which may reflect different depths of melting of compositionally homogeneous mantle. Many of the geochemical characteristics of the population bear a strong resemblance to modern basic volcanics formed in destructive plate margin environments.
Published Version
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