Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

C. V. R. K. Prasad ¹, V. Damodara Reddy ¹

Affiliations
1 Department of Geology, Sri Venkateswara University, Tirupati, IN

Abstract

The magnetic studies on the ferruginous sandstone samples from the Kaverisamudram area and the metamorphosed shales from Beduduru area of Cuddapah basin are presented here along with the results from the dykes near Tirupati. From a comparison of these results with those obtained from other Precambrian formations of India, it is found that the Bijawars are equivalent to Cuddapahs. The results from the metamorphosed shales have indicated that the igneous activity in Cuddapah basin was contemporaneous with sedimentation. This igneous activity is also found to be contemporaneous with one of the intrusive phases of the Tirupati area.

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V. Damodara Reddy ¹, C. V. R. K. Prasad ¹

Affiliations
1 Department of Geology, S. V. University, Tirupati-517502, IN

Abstract

Results of the palaeomagnetic studies on five dykes intruding the Archaean schists from the Nundydroog mine (lat. 12°57', long. 78°15") of the Kolar Gold Fields are reported. Three dykes have given consistent and stable directions after cleaning in an alternating field of 150-200 oe. The virtual geomagnetic poles (VGP's) of these dykes are 47°N, 163°W; 50°N 36°W; and 45°N, 30°W. A Precambrian polar wandering curve for India is drawn taking into consideration radiometric ages and the palaeomagnetic data, available from the formations other than the dykes. Based on this polar wandering curve the ages of the dykes are interpreted. It is suggested that these dykes occupy the fractures which were probably formed during Precambrian times, due to an East-West compressive stress. Continental drift in Precambrian era is indicated.

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M. R. Goutham ¹, K. Raghubabu ², C. V. R. K. Prasad ³, K. V. Subbarao ⁴, V. Damodara Reddy ²

Affiliations
1 Department of Geophysics, Osmania University, Hyderabad - 500 007, IN
2 Department of Geology, Sri Venkateswara University, Tirupati - 517 502, IN
3 "Amararama" Venkataratnam Street, Suryaraopet, Vijayawada - 520 002, IN
4 Centre for Earth and Space Sciences, University of Hyderabad, Hyderabad - 500 046, IN

Abstract

The Proterozoic Cuddapah Supergroup is predominantly of normal magnetization but has a reversely magnetized level coinciding with the Srisailam Quartzite at the top of the succession. The Kurnool Group overlies the Cuddapah Supergroup with an unconformity and we present palaeomagnetic results from the Kurnool Group members comprising the Banganapalli Quartzite and the Narji Limestone. The Neoproterozoic Banganapalli Quartzite carries stable normal and reverse magnetizations suggesting a geomagnetic field reversal at the time of its formation. The Narji Limestone is normally magnetized. A similar magnetization to that in the Banganapalli Quartzite is reported -1000km away in the Baghain Sandstone of the Vindhyan Supergroup. A possible correlation is made between Cuddapah Supergroup and Kurnool Group with the Vindhyan Supergroup. Based on palaeomagnetic poles, palaeolatitudes, palaeoclimatic and structural evidence it is suggested that India and Australia collided possibly during Neo-Proterozoic times in an attempt to form larger Gondwana.

Keywords

Palaeomagnetism, Reversal of Poles, Magnetostratigraphy, Gondwana Evolution, Cuddapah Supergroup, Kurnool Group, Andhra Pradesh.

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