Collision tectonics of the Central Indian Suture zone as inferred from a deep seismic sounding study D.M. Mall a , P.R. Reddy a , W.D. Mooney b, ⁎ a National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India b U.S. Geological Survey, 345, Middlefield Road, MS 977, Menlo Park, California 94025, USA abstract article info Article history: Received 25 July 2007 Received in revised form 3 July 2008 Accepted 14 July 2008 Available online 20 July 2008 Keywords: Crustal structure Convergence Central Indian Suture Seismic reflection India The Central Indian Suture (CIS) is a mega-shear zone extending for hundreds of kilometers across central India. Reprocessing of deep seismic reflection data acquired across the CIS was carried out using workstation- based commercial software. The data distinctly indicate different reflectivity characteristics northwest and southeast of the CIS. Reflections northwest of the CIS predominantly dip southward, while the reflection horizons southeast of the CIS dip northward. We interpret these two adjacent seismic fabric domains, dipping towards each other, to represent a suture between two crustal blocks. The CIS itself is not imaged as a sharp boundary, probably due to the disturbed character of the crust in a 20 to 30-km-wide zone. The time sections also show the presence of strong bands of reflectors covering the entire crustal column in the first 65 km of the northwestern portion of the profile. These reflections predominantly dip northward creating a domal structure with the apex around 30 km northwest of the CIS. There are a very few reflections in the upper 2–2.5 s two-way time (TWT), but the reflectivity is good below 2.5 s TWT. The reflection Moho, taken as the depth to the deepest set of reflections, varies in depth from 41 to 46 km and is imaged sporadically across the profile with the largest amplitude occurring in the northwest. We interpret these data as recording the presence of a mid-Proterozoic collision between two micro-continents, with the Satpura Mobile Belt being thrust over the Bastar craton. © 2008 Published by Elsevier B.V. 1. Introduction The Central Indian Suture (CIS) (Fig. 1) has been the focus of several studies since its discovery by Radhakrishna and Naqvi (1986) and further description by Yedekar et al. (1990). The suture trends roughly ENE–WSW across the central Indian craton, and separates two regions with distinctly different geology: a high-grade metamorphic terrain to the north and a lower-grade volcanic and volcaniclastic terrain to the south (Radhakrishna and Naqvi, 1986). In the present study, we have reprocessed and interpreted deep seismic reflection data acquired in 1994–95 by the National Geophysical Research Institute, India (Reddy et al., 1995a,b). The seismic profile trends almost perpendicular to the CIS (Fig. 2) and offers an opportunity to investigate the crustal signature of the suture as expressed in deep seismic reflection data. In addition, we correlate our results with a coincident seismic refraction/ wide-angle reflection survey (Reddy et al., 1996). The primary objective of this study is to obtain evidence regarding the geologic evolution of the crust in this area, especially as it relates to the hypothetical collision of the cratonic blocks (the Satpura Mobile Belt and the Bastar craton) that comprise the Indian subcontinent. In many cases, such a crustal suture produces a very complicated reflectivity pattern that often includes evidence of low- angle thrust faulting. In order to enhance the imaging of the crust, it was necessary to reprocess available seismic reflection data collected across the CIS. Using better processing facilities than were available previously (Reddy et al., 1995a, b), we have obtained an improved time section. 2. Regional geology and tectonics The Indian subcontinent consists of a mosaic of six Precambrian terrains, the Dharwar, Bastar, and Singhbhum cratons, the Southern Granulite Terrain, the Eastern Ghat Mobile Belt (EGMB), and the Aravalli– Delhi Mobile Belt (ADMB) including the Bundelkhand Complex (Fig. 1). These cratons are separated by linear structures, most prominently by suture zones, mobile belts, and rifts. The most prominent among them is the ENE–WSW trending central Indian tectonic zone (CITZ) comprising several low to medium grade supracrustal belts, composite gneisses, granite, and granulite crust which are demarcated by a number of ductile shear zone complexes (Fig. 2). The Narmada–Son Lineament (NSL), which cuts across central India, forms the northern limit of the Satpura mobile belt (Fig. 1). Table 1 shows a general tectonostratigraphy in the region (after Divakara Rao et al., 1998). Tectonophysics 460 (2008) 116–123 ⁎ Corresponding author. E-mail addresses: malldm@yahoo.com (D.M. Mall), paravata@yahoo.com (P.R. Reddy), mooney@usgs.gov (W.D. Mooney). 0040-1951/$ – see front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.tecto.2008.07.010 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto