Gravity field and subsurface geometry of the Kalpatta granite, South Indiaand the tectonic significance

The Kalpatta granite, of Pan-African age occurs in the southern granulite t errain of Peninsular India. Bouguer anomaly map of the Kalpatta and adjoini ng areas reveals a gravity low of 8-10 mGal centered over the Kalpatta gran ite and a minor low of 4-6 mGal over the adjacent Ambalavayal granite pluto n. The residual anomaly map prepared For the Kalpatta granite has been util ized to obtain depth extent and 3-D geometry of the pluton. The analysis su ggests that the Kalpatta granite is an elliptical and somewhat pear shaped body with horizontal dimensions of 6-11 km and extending to a depth of 6.5k m, has steeply inward dipping contacts and the shape seen on the surface co ntinues throughout its depth. The smooth oval shape could indicate low duct ility contrast, deeper level of emplacement and permissive nature of the pl uton. The 3-D depth model indicates an oblique section with much deeper lev els exposed in the south, in other words, the crustal block encompassing th e pluton has suffered a NNW tilt during uplift after the emplacement. It is further inferred that there was no post intrusive shape modification, the NW tilting of the region and denudation gave rise to the present outcrop pa ttern of the body.