Crustal evolution and tectonics of the Archean Bundelkhand craton, Central India

Magnetotelluric studies over the Bundelkhand craton indicates a high resistivity sub-structure, typically observed in the Archean-Proterozoic regions. The geoelectric section shows a single high resistivity layer in the northern part of the craton, extending from surface to a depth of about 60 km and a three layered resistivity structure overlying a conductive bottom in its southern part. The geological studies reported earlier have delineated an EW trending zone of ultramafic rocks, called the Bundelkhand tectonic zone (BTZ), which marks the divide between the two electrical resistivity patterns. The geoelectric structure is broadly indicative of a northward dipping tectonic fabric in this region which conforms to the Himalayan subduction, to the immediate north of this craton. However this observation cannot explain the findings from geochemical, isotope analysis and geological studies, suggesting possible vertical block movements in the region, which are also indicated in the Bouguer gravity studies. The geoelectric structure beneath the Vindhyan group to the south shows low resistivities even up to 60 km, suggesting that the Bundelkhand craton which is characterized by high resistivity rocks, does not extend to the south beneath the Vindhyans, as was believed by the earlier researchers. A low resistivity body with an extremely high conductance of about 100,000 Siemens is delineated at the mid crustal depths beneath the exposed Bijawars south of Bundelkhand craton. The causative factors behind this low resistivity are not immediately apparent, but some possibilities are discussed here.