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A family of geophysical lineaments have been identified in ∼15,000 km 2 in central Kerala between 9°30′N to 10°45′N and 76°00′E to 77°30′E, integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ∼90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of younger geophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust. They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from (1) the back-thrust from the Himalayan Collision; (2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and (3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.

Whole-rock gamma-ray spectrometric data for U, Th and K contents of 133 samples belonging to the granulite belts of North Arcot-Pallavaram (NAP), Eastern Ghats (EG) and Kondapalli and the greenstone gneiss belts of Sargur, Holenarsipur and Kclar are presented. The data reveal that the grarulite and greenstone belt rocks have distinctive radioelement abundances and characrerisric enrichment patterns for U and Th in relation to K. The main rocks aralysed from. the granulite belts include pyroxene granulites, charrockites, associated anorthcsites and migmatite gneisses. They are divided into two broad groups on the basis of their silica content; (a) intermediate and basic rooks with SiO 2 , content less than 65%, and (b) more acidic rocks with SiO 2 content greater than 65%. Compared with normal magmatic rocks the more basic granulites and charnockites are depleted in U and Th in relation to K. The more acidic rocks, however, have higher concentrations of all three elements and high Th/U ratios, indicating enrichment of Th over U. Later quartzo-feldspathic rocks intrusive into the charnookite-pyroxene granalite group shew higher concentrations of all three radioelements and a higher Th/U ratio. These show depletion in U but enrichment in Th in relation to K. The main rocks from the Dharwar schist belts include amphibolites and associated gneisses, granites and the “Champion gmeiss”, These show a relavive enriohment of U and Th in relation to K, in marked contrast to the patterns of the radioelemental ratios in the granulite belt. The significance is discussed of the contrasting trends of the radioelement distribution in the granulite and greenstone belts.