Field and geochemical characteristics of the amphibolites from the Gadag greenstone belt, southern India: Implications for petrogenesis

The preliminary field, petrographic and whole-rock geochemical data of the amphibolites from the southwestern part of the Gadag greenstone belt is presented in this study. The studied amphibolites in the southwestern part of the Gadag greenstone belt occur as isolated bands and occasionally exhibit distinct banding. The NE trending amphibolites are composed chiefly of hornblende+quartz+plagioclase. The analysed samples show tholeiitic basalt affinity, characterised by flat REE patterns and display no Nb-Ta or Zr-Hf anomalies on the multi-element spidergrams. The elemental ratios indicate that the studied rock samples are relatively immobile and devoid of crustal contamination. Petrogenetic studies indicate that their source of studied amphibolites was derived from the partial melting of the amphibole+spinel bearing peridotite within the spinel stability field. Trace elemental modelling suggests that the chemical composition can be reproduced by similar to 10-11% partial melting of the source with 38% olivine, 35% clinopyroxene, 25% amphibole, 1% plagioclase, and 1% spinel. The studied amphibolites show a strong affinity towards the MORB-type plate tectonic setting.