[S21-P] Poster

[S21-P-18] Crustal structure across the central Ganga foreland basin by magnetotellurics

^○A Manglik, L Adilakshmi, S Thiagarajan, M Suresh (CSIR-National Geophysical Research Institute, Hyderabad, India)

The Ganga basin, a foreland basin of the Himalayan collision belt, formed due the flexure of the Indian plate, consists of a thick pile of sedimentary sequence especially in its northern part. Hydrocarbon exploration activities provided the details of the basin architecture and lithologies. However, the structure of the underlying Indian plate is largely unknown despite its important role in influencing the Himalayan tectonics. We acquired MT data along a 285 km long profile at average station spacing of 6 - 8 km across the central Ganga basin to delineate the crustal structure. The profile passes over the sedimentary cover of the basin but at the southern end it covers a part of the exposed Bundhelkhand massif. MT impedance tensors were estimated in 0.001 – 1000 Hz frequency band and decomposed into TE and TM modes by distortion and decomposition analyses. These datasets were jointly inverted along with the Hz data to obtain a geoelectric model of the crustal structure. The results reveal significant variations in the subsurface structure. In the southern segment, the model yields three highly resistive blocks, the southernmost of which correlates with the Bundelkhand craton and extends down to about 150 km while the remaining two blocks are of smaller dimension and buried under the sediments. Based on these results, we infer that the lithosphere of the Bundhelkhand craton is at least about 150 km thick, which is contrary to some previous results suggesting thin lithosphere for the Indian shield. Further, the Bundelkhand craton extends far north of its earlier demarcated position but buried under 0.5 to 1 km thick sediment cover. At the northern end of the profile, an electrically conductive crustal structure has been delineated. In this region, we have earlier reported the presence of thick sedimentary sequence. Thus, our results suggest a highly heterogeneous crustal architecture of the Indian plate in the central Ganga foreland basin.