Deep crustal structure in central India using magnetotelluric studies

Abstract

Magnetotelluric studies over the Damoh–Jabalpur–Mandla–Anjaneya profile in central India have delineated Vindhyan sediments which are about 5 km thick in the Damoh–Katangi region. The crust below the Vindhyan sediments shows the characteristics of lower crust, as observed from the relatively lower resistivity of about 200 &OHgr; m and high seismic velocities (P-wave velocities of 6.5 km s−1 compared with 5.8–6.2 km s−1 in the surrounding region). It is conjectured that the upper crust may have been completely eroded in the uplift and erosion process and thus the Vindhyan sedimentation has occurred directly over the lower crust. An anomalous conductivity is observed at depths of 10–12 km in the Vindhyan crust. The conductance of more than 1200 S observed here may be due to either the serpentinization of the mafic and ultramafic rocks or the presence of grain boundary graphites. The thickness of the Deccan traps is about 100 m near Jabalpur and decreases near Mandla. On the south of Mandla, the Archaean crust is exposed. Two crustal conductors are delineated below the Deccan volcanics with a resistivity of about 30 &OHgr; m. The first on the immediate south of Jabalpur seems to mark the southern boundary of the Jabalpur horst block. The second conductor was delineated about 40 km southeast of Jabalpur, coincident with a positive gravity anomaly of about 30 mGal. Deep seismic sounding studies do not show any significant density contrast associated with this conductive feature. It is proposed that the gravity high may be due to the upwarp of the Moho. The high electrical conductivity is attributed to the fluids in the upper crust.