Geochemistry and Origin of Acidic Rocks of Shimoga, Karnataka, India

Acid igneous rocks of Shimoga which were earlier mapped as single granite unit actually consist of two distinct lithological units: an older tonalite and a younger granodiorite. Tonalite is highly disturbed, migmatised and appears to have been derived by partial melting of a basic crust. Younger granodiorite is coarse grained to often porphyritic with higher concentration of K, Ni, Cr and V. Its field relationship with tonalite suggests a different late stage intrusive mode of origin.