The ultramafic-mafic volcanic rocks of Archean greenstone belts are important archives for lithospheric and asthenospheric processes of the early Earth. Despite decades of research on this context, many issues still remain unsolved. For example, the process of komatiite magma genesis and the genetic relationship among komatiites, komatiitic basalts and tholeiitic basalts in Archean greenstone belts are not clearly understood. The metavolcanic rocks of the Badampahar greenstone belt (BGB), Singhbhum Craton are studied by major-trace element geochemistry to address the said problems and better understand the evolution of melts in Archean lithosphere. Our research suggests that the protoliths of the metavolcanic rocks were komatiites (both Al -depleted and -undepleted), komatiitic basalts and tholeiitic basalts. The Al-heavy rare earth element (HREE) depleted komatiites were formed by moderate degree mantle melting at a higher depth and the Al-HREE undepleted komatiites are products of moderate to high degree mantle melting at a shallower depth. The melting-assimilationfractional crystallization modelling result shows that komatiitic basalts were generated from Al-undepleted komatiites, and tholeiitic basalts were generated from evolved komatiitic basalts by assimilation and fractional crystallization processes. The older age limit of the BGB is determined to be 3.25 Ga. and the basement of sedimentation and volcanism was composed of plutonic felsic rocks.

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The present study is an integrated approach consisting of field observations, petrography, rock magnetism and Anisotropy of Magnetic Susceptibility (AMS) measurements which are used to determine the magneto-mineralogical characteristics and the nature of the magnetic fabrics of the high grade rocks from the Chilka Lake Area, Eastern Ghats Belts, India. Petrographic study reveals the textural relationship of the magnetic minerals with that of the silicates. The study of the thin-polished sections under reflected light microscope depicted the presence of magnetite, titano-magnetite and ilmenite as the dominant magnetic minerals. More than one generation of these minerals was found in these sections corresponding to different conditions of temperature that prevailed during their oxidation. The different generations of the magnetic minerals have significant tectonic results and points towards crustal upliftment. IRM and hysteresis curves were obtained which show the presence of both the ferromagnetic and paramagnetic minerals. Further, the determination of the Curie temperature confirmed the presence of magnetite and haematite. However, haematite was not observed in the petrographic/ore-petrographic studies. AMS studies unravelled the overall nature of the magnetic fabrics in the region. The susceptibility ellipsoids were dominantly oblate in the region as evident from the F-L and the P j -T j plots. The magnetic foliation plane has a highly variable strike varying from NE-SW to NW-SE with a moderate amount of dip. The magnetic lineation, i.e. the maximum susceptibility axes (K 1 ) showed clusters in the NE, SW and the NW quadrants having close accordance with that of the F 3 and F 4 fold axes pointing towards the structural controls of the magnetic fabrics.

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