Petrology and geochemistry of the troctolite and ultramafic from the Paleoproterozoic Kandra Ophiolite Complex, Eastern Dharwar Craton, SE India

Field and petrological studies indicate the presence of two spatially associated high Mg lithounits; troctolite and ultramafic within the southern gabbros of the Paleoproterozoic Kandra Ophiolite Complex (KOC), Eastern Dharwar Craton, SE India. Petrographic studies indicated that troctolite is essentially composed of olivine and plagioclase with sub-ordinate augite, while magnetite and ilmenite are noticed as accessory oxides. Mineral chemistry studies by EPMA reveal that olivine in troctolite is forsterite (Fo63.14) plagioclase is labrodorite (An 69.96) and the Fe-Ti oxide ilmenite in troctolite analysed TiO2-53.08 %, FeOT-44.22%). Major oxides of troctolite indicated SiO2 - 43.10%, TiO2 - 0.29%, Al2O3 - 15.81%, FeO -10.44%, Fe2O3 5.56%, CaO-7.92% and MgO - 13.08%. Petrographically, ultramafic is essentially composed of magnesio hornblende with subordinate chlorite, while ilmenite is the accessory oxide phase. Mineral chemistry studies by EPMA of the ultramafic indicate that the magnesio hornblende analysed SiO2 - 43.71%, Al2O3 - 14.61%, FeO - 15.35% and MgO - 9.94%, while chlorite analysed SiO2 - 27.02%, Al(2)O3 - 22.6%, FeO - 19.75% and MgO - 19.7%. Ilmenite in the ultramafic analysed FeO - 45.14%, TiO2 - 53.44%. Major oxides of ultramafic indicated SiO2 - 28.6%, TiO2 - 0.65 %, Al2O3 - 17.22 %, FeO - 6.84 %, Fe2O3 - 6.88%, CaO - 0.41% and MgO-26.84%. HFSE depletion is noticed in both these high Mg lithounits; (Zr-42.17 ppm, Nb-2.65ppm and Y-5.35ppm) in troctolite and (Zr-40.13ppm, Nb-2.47ppm and Y-3.16 ppm) in ultramafic. Rare Earth Element (REE) geochemical studies indicate that these spatially co-existing troctolite and ultramafic show an overall depleted but contrasting REE patterns. Troctolite exhibits a low magnitude positive Eu anomaly while the ultramafic exhibit a negative Eu anomaly indicating co-magmatic origin of the mafic-ultramafic lithounits in the southern gabbros of KOC.