HR: 0800h
AN: GP11A-0818    [Abstracts]
TI: Electrical image of the crust below Deccan Volcanic Province of Indian peninsular shield: Is the lower crust anisotropic?
AU: * Patro, P K
EM: patrobpk@rediffmail.com
AF: National Geophysical Research Institute, Uppal Road, , Hyderabad, AP 500 007 India
AB: The Deccan Volcanic Province (DVP) of the Indian shield has witnessed major stable continental region (SCR) earthquakes in the last few decades. The deeper crust below the Deccan traps, where thick basaltic layers cover large areas of the Indian shield, remains little known until today. A magnetotelluric study covering a broad period range (T = 0.001 - 1000 s) was conducted to achieve more insights into the nature of the crustal electrical structure below the flood basalts. The results from isotropic 2D inversion suggests that the basalts are characterized by low electrical resistivities, while the crust is in general highly resistive. Enhanced conductivity zones were delineated in the middle to lower crust, which are explained as imaging hidden, partly reactivated faults/fractures of the Precambrian basement. The basement in the DVP is highly resistive (5000 - 10,000 Ohm-m) representing the top of the upper crust. It is also seen that the upper crustal resistivities though generally high, vary along the traverse. For example along the 300 km long Sangole (in the south)-Partur (in the north) traverse they tend to become relatively low (less than 5000 Ohm-m) in its central portion as compared to those on either side (greater than 10,000 Ohm-m) of this segment. The results indicate that the high resistive layer representing the upper crust though shows some variations in its thickness along the traverse, extends in general down to about 20 km; and the subsurface region further down, corresponding to lower crust is characterized by resistivities ranging from about 1000-3000 Ohm-m. This shows that the lower crustal region in the Deccan Volcanic Province is characterized by relatively higher resistivity values compared to some of the other continental lower crusts. Relatively higher resistivities for the lower crust indicate that the deeper horizons of the crust in this part of the Deccan Volcanic Province are dry and compact. Similarity of sounding curves and an almost constant phase split over large parts of the measuring area indicate an anisotropic (macro?) lower crust or mantle. Synthetic anisotropic model study was carried out to generate the phase split in the case of 1-D and 2-D environments. The influence of different model parameters like, anisotropic strike, geometry of the layer/block and anisortopic ratio was analysed. Preliminary results of these model studies will be presented here.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 0600 ELECTROMAGNETICS
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting