Resistivity Structure of the Central Indian Tectonic Zone (CITZ) from Multiple Magnetotelluric (MT) Profiles and Tectoni
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Pure and Applied Geophysics
Resistivity Structure of the Central Indian Tectonic Zone (CITZ) from Multiple Magnetotelluric (MT) Profiles and Tectonic Implications K. K. ABDUL AZEEZ,1 MARTYN J. UNSWORTH,2 PRASANTA K. PATRO,1 T. HARINARAYANA,1,3 and R. S. SASTRY1,4 Abstract—The Central Indian Tectonic Zone (CITZ) is a major tectonic feature extending across the Indian subcontinent. It was formed in the Paleoproterozoic when the Bastar Craton and the Bundelkhand Craton were sutured together. This region is recognized in the geological record as a persistent zone of weakness with many tectonothermal events occurring over geologic time. The weakness of this region may have caused the late Cretaceous/early Tertiary Deccan volcanism to have been localized in the CITZ. The zone is still tectonically active, as evidenced by sustained levels of seismic activity. This paper presents the first systematic investigation of the resistivity structure of the CITZ using multiple magnetotelluric (MT) transects. Two-dimensional (2D) resistivity models were generated for five north–south profiles that cross the CITZ and encompass an area of *60,000 km2. The models were based on the joint inversion of transverse electric (TE), transverse magnetic (TM) and tipper (Hz) data. All the profiles showed a low resistive (10–80 Xm) middle to lower crust beneath the CITZ with a crustal conductance of 300–800 S. The presence of an interconnected fluid phase and/or hydrous/metallic minerals appears to be the most likely explanation for the elevated conductivity that is observed beneath the CITZ. The presence of fluids is significant because it may indicate the cause of persistent weakness at crustal depths. A northward dip of both the crustal conductive layer and coincident seismic reflections favor a northward polarity of the subduction process associated with the formation of the CITZ. Key words: Central Indian Tectonic Zone, resistivity, magnetotellurics, fluids, subduction polarity.
1. Introduction The peninsular shield region of the Indian subcontinent is composed of a number of Precambrian
1
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500007, India. E-mail: [email protected] 2 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada. 3 Present Address: Gujarat Energy Research and Management Institute (GERMI), Gandhinagar, India. 4 Present Address: 5/128, Apparao street, Madanapalle 517325, India.
provinces separated by mobile belts (Fig. 1a) and has a geological history that extends back to the Archaean. The east–west trending Central Indian Tectonic Zone (CITZ) is one of the most important tectonic boundaries in this region and separates the Indian subcontinent into the Southern Peninsular block and Northern foreland block (JAIN et al., 1991; YEDEKAR et al., 1990; ACHARYYA, 2003). It was formed during the Paleoproterozoic collision between the northern block (Bundelkhand and Aravalli cratons) and the southern block (Bastar, Singhbum and Dharwar cratons) and this suturing event formed t
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