Tectonoph.vsics, 84 (I 982) 225-245 Elsevier Scientific Publishing Company, Amsterdam-Printed in The Netherlands 225 zyxwvutsrqp GRAVITY INTERPRETATION OF THE DHARWAR GREENSTONIhGNEISS-GRANITE TIZRRAIN IN THE SOUTHERN INDIAN SHIELD AND ITS GEOLOGICAL IMPLICATIONS C. SUBRAHMANYAM and R.K. VERMA Nutionol Geophysical Reseurch Institute, Hyderubud-500 007 (Indiu) Indian School of Mines, Dhunhad 826 004 (Indiu) (Received January 1, 198I; revised version accepted October 28, 1981) ABSTRACT Subrahmanyam, C. and Verma, R.K., 1982. Gravity interpretation of the Dharwar greenstone-gneiss- granite terrain in the southern Indian shield and its geological implications. Te~~onop~ysi~s, 84: 225-245. The Dhanvar craton in the southern Indian shield has a wide distribution of volcano-sedimentary sequences surrounded by a vast gneissic complex, both of which have been intruded by younger granites. A gravity anomaly map of this craton, compiled from all the available data, is analysed here to study the structures and depths of the greenstone belts, the mode of granite emplacements and the greenstone- gneiss-granite associations in general. The anomaly map is a mosaic of well-defined gravity highs and lows characterizing the dense volcano-sedimentary sequences and exposed and/or concealed granites respectively. Gravity modelling indicates that the Shimoga belt has a limited depth range of only 3-4 km while the Chitradurga and Sandur belts have greater depths of over 10 km. The structures inferred for the Dhanvar formations are alternating bands of synclines, filled with dense scbistose rocks, separated by anticlinal ridges of gneisses and granites. INTRODUCTION Dharwar craton in the southern Indian shield, well known for its greenstone- granite-gneiss association, is classified as a typical Archaean low-grade terrain (Swami Nath et al, 1976; Naqvi et al, 1978). It has a wide distribution of Archaean volcano-sedimentary schist belts and intruding granites, surrounded by a vast gneiss-migmatite complex, commonly known as the Peninsular Gneiss Complex. Some workers believe that the Dharwars constitute a nucleus around which con- tinental growth in the southern peninsula of India has taken place (Pich~uthu, 1970) and that the Archaean schist relics from this region hold the key to our understanding of the nature of the primitive Archaean crust and Precambrian continental crustal evolution in the southern Indian shield (Naqvi et al., 1974, 1978). OO40- 195l/82/~-~/$02.75 0 1982 Elsevier Scientific Publishing Company