PALEOMAGNETISM AND GEOCHRONOLOGY OF THE GWALIOR SILLS, BUNDELKHAND CRATON, INDIA

Peninsular India is comprised of six distinct cratonic elements that include some of the oldest crust on the planet. The six ancient nuclei are the Bundelkhand and Aravalli-Banded Gneiss Complex (BGC) in the north; the Singhbhum, Bastar, Dharwar, and Southern Granulite Province in the south. The Dharwar and Bastar cratons are separated by the Prahnita-Godavari Rift, the Singhbhum and Bastar cratons by the Mahanadi Rift and the Bastar/Singhbhum and Bundelkhand/Aravalli cratons are separated by the Central Indian Tectonic Zone. We present an updated paleomagnetic pole from the Gwalior Sills in the Bundelkhand craton within the Northern India Block (NIB). Geochronological results from zircon and baddeleyite grains from one of the sills yielded ages between 1715-1740 Ma. The paleomagnetic pole calculated in this study combined with previous studies falls at 14.4° N, 173° E (A95=3.9°, K=97) indicating near equatorial latitudes for northern India. Although the pole lacks field and reversals tests, it does not resemble any younger poles from Peninsular India and receives a reliability grade of R=5. We consider the magnetic signature as primary. Dykes in the Singhbhum craton are slightly older (1765 Ma) and indicate low paleolatitudes for the Southern Indian blocks (SIB). Although these data indicate low latitudes for both the NIB and SIB, the poles are statistically different and a rotation of at least 65° is required to bring the poles into accord. We propose that the NIB and SIB were in proximity between 1715-1765 Ma but were separated by an expanding ocean basin. We propose the name Gotosindhu Ocean for the body of water separating the NIB and SIB which began to close around 1.65 Ga based on deformational events in the CITZ to the south. We also review previous models for the assembly of the Columbia supercontinent during this time and critically examine the position of the NIB/SIB in those reconstructions.