Northern Limit of the Concealed Bundelkhand Craton: A Synthesis of New Magnetotelluric Results from the Ganga Basin

Abstract

Abstract The Bundelkhand craton is a relatively small craton of the Indian shield in terms of its exposed surface area. It continues beneath the sediments of the Ganga Basin in NE-to-NNE direction as the Faizabad Ridge. However, its northern extent into the Ganga Basin is not known and the northern margin of the exposed craton is generally taken as the northern limit of the craton. Here, we present a synthesis of new magnetotelluric (MT) results from the Ganga Basin to demarcate the northern limit of the Bundelkhand craton. Broadband MT data were acquired at 148 sites along the four profiles and the MT impedance tensors of 132 sites were used for two-dimensional inversion along these profiles. The top 15 km sections of the geoelectric models along these profiles were used to prepare a conductance map to extract the northern limit of the electrically resistive craton. The results reveal that the northern boundary of the craton lies much to the north of the presently known northern limit. It also follows the basement depth contours of 2 km and 3 km obtained from the aeromagnetic data. Thus, a significant part of the craton is also buried in the Ganga Basin north of its present limit. The areal extent of this new buried block is about 0.82 times the area of the exposed Bundelkhand craton. Together with the Faizabad Ridge, the Bundelkhand craton covers an area of about 1,03,000 sq.km, 72% of which is concealed under the sediments of the Ganga Basin. The results also indicate westward subsurface continuation of at least a part of the craton towards the Great Boundary Fault.