Structure, petrography, and geochemistry of gneisses and charnockites of Chamarajanagar, Southern Karnataka [India]

Field, petrog., and geochem. data is presented for the foliated charnockite and gneisses from Chamarajanagar area of southern Karnataka, India. The area lies well within the amphibolite- to granulite-​facies transition zone. The major lithol. includes older supracrustals, ultramafic rocks, amphibolite, gneisses, charnockites, granite and dolerites of different ages. Field observations show a complex deformational history and complex pattern of parallel shears, fractures and faults. The area under study exhibits innumerable parallel minor shear zones. The shear zones :noticed in the study area are the replicas of the regional shear zone (Moyar-​Bhavani shear) along which uplift of the terrain had taken place and various intrusive bodies have been emplaced. Major and trace element data of gneisses and charnockite despite their trondhjemitic compn. indicate low K2O​/SiO2 ratio. Foliated charnockite-​exhibits slightly higher Fe2O3, high Na2O relative to K2O and CaO. Gneisses and charnockites together show depletion of LIL elements, which is considered to be diagnostic of Chamarajanagar area and this, can be attributed to the formation of gneisses from foliated charnockites due to retrogression.