Provenance and Tectonic Setting of Late Archaean Greywackes from Dharwar Craton: Karnataka, India

Geochemical characteristics of greywacke and intercalated phyllites from Haveri and Dharwad block (long N 75° 10' to 75° 25' E and lat 15° 30' to 45° 00'S and (long 75° 05'E and lat S 15° 15' to 15° 35') of Shimoga basin have been studied to unravel the provenance and the tectonic setting of the greywackes. The greywackes are medium grained feldspatholithic and show presence of perthitic feldspars, and phyllites are fine grained and show feeble schistocity. Both, greywacke and phyllites are intermediate in composition having high SiO2/MgO ratio 10.21 to 19.89 and 9.20 to 26. 36 and Al2O3/TiO2 ratio is 21.70 to 80.50 to 23.28 to 84.09, respectively. Greywacke of both the blocks show insignificant enrichment of Si, Fe, Mg, Sc and Co with respect to AUCC. But phyllites show depletion in Cr/Ni (0.52 to 1.9) and in Cu/Zn ratio (0.41 to 1.41). But both greywacke and phyllites have similar REE pattern. The geochemical characters such as negative Eu anomaly and high LREE/HREE (La/Rb)n, suggest granodioritic source for them, whereas, mafic source is indicated by enrichment of Ni, Sc, Sr, & co. The Cu/Zn ratio ranging between 0.48 to 1.20 and 0.41 to 1.41 for greywacke and phyllites respectively. It indicate Komatitic source where as Rb/ Sr content together with presence of perthitic feldspar suggest granitic type source. Based on present studies a mixed provenance dominated by intermediate composition with lesser proportion basic to ultra basic and granitic source is suggested for these greywackes and phyllites. As the source from the lithologic association along with tectonic discriminatory plots, it is concluded that juxtaposition of two tectonic regimes have given rise to the present configuration of outcrop pattern.