Paleomagnetism and Geochronology of Proterozoic Basic Dike swarms of Indian subcontinent.

Out of more than 2000 core samples that we collected during 2005-2006 field season, a paleomagnetic investigation was carried out from the doleritic to alkaline dikes intruding the Dharwar and Bastar cratons in Central and Southern India. Dike swarms were sampled for both paleomagnetic and geochronologic investigation with the goal of establishing a more robust Proterozoic apparent polar wander path for the Indian subcontinent. Previous work which has been conducted for these intrusives lack in density as well as age constraints. Dike swarms that were sampled and then analysed for generating high resolution paleomagnetic data include the Bastar, Nalgonda, Mahbubnagar, Keskal, Harohalli, Anantapur and Tiptur dikes. Special attention has been paid to Harohalli section as it represents the only paleomagnetic pole from India with an imprecise age of 814 ± 34 Ma (Radhakrisna and Mathew, 1996). Resultant paleogeographic reconstructions from these studies will document India's place in Proterozoic supercontinental assemblies such as Rodinia and Columbia. Preliminary data from the Anantapur dikes (Andhra Pradesh) yield three distinct vectors. The first has a mean Declination of 50.5 and Inclination of -4.4° (k=24.2, α95=13.9). The second group has a mean Declination of 65.3 and Inclination of -78.7° (k=65, α95=8.4). The third grouping has a mean Declination of 319 and Inclination of -15.5° (k=38.6, α95=10.9). Dikes 1 and 2 have similar NE- SW strikes whereas dike 3 shows a more SE-NW strike. These directions are consistent with a previous study of five Anantapur dikes conducted by Kumar and Bhalla (1983) who used only thermal demagnetization and no vector component analysis. The preliminary NRM data from the Dhone dikes (Andhra Pradesh) shows a mean Declination of ~338 and Inclination of -7° (k=26.4, α95=9.0). Nalgonda dikes show two distinct directions where one group of dikes has a mean Declination of ~13 and shallow Inclination of -2° to -10° (k=51.7, α95=4.9) while the other group shows a Declination of ~268 with a steep Inclination of -72° (k=5.0, α95=15.5). Dikes swarms from Mahbubnagar also show only one prominent direction with Declination of ~358 and Inclination of -40° (k=19.1, α95=11.3). Keskal suite of dikes represents two distinct directions with Declination ~267 and ~112 and Inclination -34° (k=54.0, α95=4.9) and -24° (k=20.8, α95=6.5) respectively. NRM data from Tiptur dikes (Karnataka) shows a Declination of ~283 and a shallow Inclination ranging from -7° to -25°(k=22.2, α95=8.6).