Sub-surface structure of a craton–mobile belt interface: Evidence from geological and gravity studies across the Rengali Province–Eastern Ghats Belt boundary, eastern India Animesh Mandal 1 , Saibal Gupta ⁎, William K. Mohanty, Surajit Misra Dept. of Geology & Geophysics, Indian Institute of Technology, Kharagpur 721 302, India abstract article info Article history: Received 18 August 2014 Received in revised form 8 December 2014 Accepted 10 January 2015 Available online xxxx Keywords: Eastern Ghats Belt Rengali Province Talchir basin Craton–mobile belt Bouguer anomaly 2-D and 3-D gravity modeling Bouguer gravity anomalies characteristically vary from negative to positive values across craton–mobile belt boundaries in Precambrian shields. This transition is also documented in eastern India, where Proterozoic granulites of the Eastern Ghats Belt (EGB) form part of a mobile belt to the south of the late Archaean, amphibolite facies Rengali Province. The northern margin of the EGB with the Rengali Province is a sub-vertical Cambro- Ordovician strike-slip shear zone, on which the Talchir Gondwana sedimentary basin was deposited during late Palaeozoic extension. This extension also led to partial uplift of the lower crust below the terrane boundary. Closely coordinated geological and gravity studies were conducted through the basin, across the craton–mobile belt contact. Modeling of the Bouguer anomaly using 2-D and 3-D compact inversion schemes, along with 2-D forward modeling, indicates significant differences in the density configurations of the uppermost crusts of the EGB and the Rengali Province, as indicated by the surface geology. However, both inverse and forward models consistently predict that below ~7 km, density configurations across the contact are similar and have low upper crustal values, suggesting that typically cratonic crust lies below both terranes. Since it is highly unlikely that lower crust can remain unaffected during granulite facies metamorphism, it is inferred that the present sub-surface EGB crust could not have experienced the high grade event. Rather, the EGB rocks were probably overthrust onto the craton significantly after granulite metamorphism. The top of the thrust sheet may have been eroded prior to or post-dating the overthrusting, leaving the present EGB granulites stranded on low density cratonic crust below. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Contacts between cratons and bounding high grade, granulite facies mobile belts in many Precambrian shield areas have been interpreted as ancient suture zones (e.g. Adetunji et al., 2014; Bierlein and Betts, 2004; Black et al., 1979; Mosley, 1993; Pharaoh, 1999; Ramesh et al., 2010; Roering et al., 1992; Stockwell, 1970). Geophysical studies across these suspected ancient sutures have revealed that they are commonly associated with a characteristic Bouguer gravity anomaly signature, with high positive values over the mobile belt dropping steeply to negative values across the contact into the adjoining craton (e.g. Black et al., 1979; Fountain and Salisbury, 1981; Gibb and Thomas, 1976; Gibb et al., 1983; Mathur, 1974; Mishra and Ravi Kumar, 2014; Nyblade and Pollack, 1992; Subrahmanyam and Verma, 1986; Tesha et al., 1997; Thomas and Tanner, 1975; Veeraswamy and Raval, 2004; Vijaya Rao et al., 2006). The negative part of this paired anomaly is commonly attributed to depression of the Moho in the craton adjacent to the suture, either because of crustal thickening at the collisional front (e.g. Gibb et al., 1983), or due to flexure of the downgoing cratonic lithosphere due to subsurface loading as a consequence of the subduction process (e.g. Pilkington, 1990). On the other hand, the positive part of the Bouguer anomaly is assumed to result either from the intrinsically denser and thicker granulitic crust of the mobile belt (Gibb and Thomas, 1976; Gibb et al., 1983), or alternatively, from uplift of a denser lower crust of the mobile belt to shallower levels following collision and erosion (Kearey, 1976; Kearey et al., 1975, 2009). Discriminating between the above models requires knowledge of the subsurface lithological configuration of the craton and the mobile belt across the suspected suture. However, wavelengths of subsurface density anomalies become broader and lower in amplitude with depth, making the correlation of their gravity anomalies with lithology increasingly ambiguous. In this study, therefore, we have conducted integrated geological and gravity studies across a craton–mobile belt contact in the eastern Indian shield, where the lower and middle crust across the earlier contact has been uplifted to shallower levels by Tectonophysics xxx (2015) xxx–xxx ⁎ Corresponding author. Tel.: +91 3222 283370; fax: +91 03222 255303. E-mail addresses: animeshphys@gmail.com (A. Mandal), saibl2008@gmail.com (S. Gupta), wkmohanty@gg.iitkgp.ernet.in (W.K. Mohanty), misrasurajit@gmail.com (S. Misra). 1 Currently at CSIR-National Geophysical Research institute, Uppal Road, Hyderabad 500007, India. TECTO-126531; No of Pages 13 http://dx.doi.org/10.1016/j.tecto.2015.01.016 0040-1951/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Please cite this article as: Mandal, A., et al., Sub-surface structure of a craton–mobile belt interface: Evidence from geological and gravity studies across the Rengali Province..., Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.01.016