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Abstract:
The Moho in a continental lithosphere is marked by significant change in the composition, from felsic/mafic in the crust to ultramafic in the upper mantle. While this change is prominently seen in terms of a distinct increase in seismic velocity, the electrical resistivity contrast across this boundary is not always so prominent. In some cratonic regions, the Moho is associated with electrical resistivity contrast and is known as the e-Moho. Here, we report the presence of the e-Moho in the Bundelkhand craton (BKC) through broadband MT investigations along a profile covering a part of the exposed BKC and its northward subsurface continuation beneath the central Ganga Basin. We obtained the e-Moho at 40–42 km depth within the buried segment and an almost flat contact between the highly resistive crust and moderately resistive mantle lithosphere in the exposed part of the BKC. Together with the information of low heat flow in the BKC, the Moho depth estimate at a few seismological stations, and relatively flat topography in the region we infer metasomatism of the mantle lithosphere as a plausible cause for moderate resistivity of the lithospheric mantle. We hypothesize that infiltration of melt fractions originated either in the deep mantle or at the subducted oceanic slab have altered the mantle rheology and metasomatized the lithosphere. The results also yield the presence of vertical shear zones, one coinciding with the exposed Bundelkhand Tectonic Zone (BTZ) and other concealed beneath about half-a-km thick alluvial sediments of the Ganga Basin further north.
