New Paleomagnetic and Geochronologic Data from the Bundelkhand Craton, India

Abstract:

The Bundelkhand craton, located in the north-central part of Peninsular India, represents the oldest region in the Northern Indian Block. It is separated from the southern Indian blocks (SIB) by the WSW-ENE trending Central Indian Tectonic Zone (CITZ). Several previous paleomagnetic studies have identified at least 5 generations of mafic intrusive activity in this craton. In addition, the Paleoproterozoic Gwalior Traps volcanics and associated sills are exposed in a basin to the NNW of the Bundelkhand granite-gneiss belt. Only two of these suites have reliable age constraints. A suite of NW-SE trending dykes yielded an age of ~1.98 Ga and the Great Dyke of Mahoba yielded an age of 1.1 Ga. Two attempts at dating the Gwalior traps/sills yielded conflicting ages of ~1.8 Ga (K-Ar) and 2.1 Ga (Sm-Nd). The 1.98 Ga dykes yield a mean pole at 58 N, 309 E (A95=5, R/Q=6). The Mahoba dykes yield a mean VGP at 38 N, 230 E (A95=15, R/Q=4). In this study, we add new paleomagnetic and geochronology data from dykes in the Bundelkhand craton and the Gwalior sills. Our new paleomagnetic pole for the Gwalior traps/sills falls at 16.1 N, 173.6 E (dp=3.9, dm=7.8). In addition, we have isolated new directional data from a suite of mostly NE-SW trending dykes. Preliminary work shows a dual polarity magnetization that is either NW-intermediate down (+45-60 inclination) or SE-intermediate up (-45-60 inclination). The latter study includes a positive baked contact test. Zircons/baddeleyite have been isolated from both the Gwalior sills and the NE-SW trending dykes and results will be presented this fall. These data can be compared to the SIB (Dharwar, Bastar, Singhbhum) in order to ascertain the timing of assembly for Peninsular India. Current models posit a close approach of the NIB/SIB at 1.6 Ga with final assembly at 1.1-1.0 Ga.