Magnetotelluric survey across Singhbhum granite batholith |
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| Authors: | K K Roy C K Rao A Chattopadhyay |
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| Institution: | 1. Department of Geology and Geophysics, Indian Institute of Technology, 721 302, Kharagpur, India
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| Abstract: | Magnetotelluric soundings have been carried out across the archaean terrain of Singhbhum granite batholith from Bangriposhi
to Keonjhar for a distance of about 100 km. One-dimensional inversion models reveal that the depth of the moho varied between
23 and 40 km. The depth of the lithosphere asthenosphere boundary varied from 58 to 76 km. A zone of higher electrical conductivity
detected at the base of the lower crust just above the moho is present along the entire profile. Signals within the range
of 0.25 to 600 seconds, which crossed the coherency threshold of 0.8 to 0.9, could be stacked. Resistivity ranges of the crust
mantle silicates below Singhbhum granite batholith vary over a wide range. Resistivity ranges are (i) 30,000–80,000 ohm for
Singhbhum granite phase II, (ii) 2,000 to 9,000 ohm-m for Singhbhum granite phase III, (iii) 250 to 2,200 ohm-m for lower
crust (iv) 3,000 to 47,000 ohm for the upper mantle and (v) 200 to 2300 ohm-m for the asthenosphere. Sharp break in electrical
resistivity at the (i) upper crust-lower crust (ii) lower crust upper mantle and (iii) lithosphere-asthenosphere boundary
is obtained along the entire profile. Signals could see up to 100 km below the granite batholith. Singhbhum granite phase
II and III could be demarcated on the basis of resistivity. Low resistive zones in the lower crust and upper mantle might
have formed due to (i) water (ii) combined effect of water and carbon and (iii) high temperature and partial melt. |
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| Keywords: | Magnetotelluric survey Singhbhum granite batholith inversion model magnetometer array |
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