Inference of Granitic Batholiths by Gravity Studies in South India

Three well-defined gravity 'lows' in Kodaikanal, Gudalur and Erode regions are explained as due to granitic batholiths at depth. The scattered outcrops of granitic bodies exposed in these regions are suggested to be interconnected at depth, and, therefore, are merely the surface expressions of the three concealed batholiths. Although the exposures of the individual granitic bodies in the Kodaikanal-Coimbatore region are elongated in an east-west direction, it is surmised, from structural evidences, that the main batholith is elongated in a roughly NNW-SSE direction.

A striking correspondence between the isoseismals for the Coimbatore earthquake of February 8, 1900 and the gravity contours is noticed. It is suggested that the Coimbatore earthquake (and the reported seismicity near Kottayam and 'Palghat Gap') could be the result of some minor readjustments of the boundaries of the batholith along fault planes.