TECTONIC EVOLUTION OF THE PRECAMBRIAN BUNDELKHAND CRATON, CENTRAL INDIA: INSIGHTS FROM THE PALEOMAGNETIC AND GEOCHRONOLOGIC STUDIES ON THE MAFIC DYKE SWARMS

The Bundelkhand craton (BC) is a semicircular to triangular outcrop that forms the northern most part of the Indian peninsula. It is delimited to the north by the Indo-Gangetic plains and to the south by Narmada-Son Lineament and covers an area of 26,000 sq.km between 24º30’N and 26º00’N and 77º30’E and 81º00’ E (Sharma, 1998). It may be broadly divided into three litho-tectonic units, (a) the highly deformed older granite-greenstone basement, (b) multiphase granitoid plutons and associated quartz reefs (BKGC) and (c) mafic dyke swarms (Sharma and Rahman, 2000). Within this last dyke emplacement episode at least three generations of dykes may be distinguished using cross-cutting field relationships. The oldest, NW-SE trending suite is coarse-grained and cut across by NE-SW trending medium-grained dykes, which include small bodies and lenticles of a very fine grained aphanitic dolerite (Basu, 1986). However, the radiometric ages for these mafic dykes are unreliable and have been bracketed between ca. 2150 Ma and ca. 1500 Ma based on the in-situ ⁴⁰Ar/³⁹Ar and whole rock K-Ar isotopic analysis (Rao, 2004; Sarkar et al., 1997). We undertook a paleomagnetic and geochronologic study of these dolerite dykes and collected ~380 core samples and representative hand specimens from 27 sites to provide preliminary clues on the tectonic evolution and paleogeography of the Bundelkhand craton during Precambrian. Both thermal and alternating field demagnetizations were conducted on these core samples and in most cases the characteristic component was isolated by thermal demagnetization beyond 450ºC. The paleomagnetic analysis on these dykes yielded three groups of directions. The NW-SE trending dyke suite yielded a south-east declination and shallow negative inclination with a mean value of declination=156º, Inclination=-16.3º (a95=8.4; k=45). The NE-SW Great Mahoba Dyke and related suite yielded a northward declination and a negative inclination with a mean of D=~17º, I=~-37º (a95=6.7; k=340). The third one shows a vertical downward inclination. In our presentation, we will discuss various tectonic implications of the generated paleomagnetic and geochronologic data to understand the paleogeography and evolution of the Bundelkhand craton and its correlation with other Indian Precambrian cratonic blocks.