Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 Tectonics of the Deccan Large Igneous Province: an introduction SOUMYAJIT MUKHERJEE1*, ACHYUTA AYAN MISRA2,GE´ ROˆ ME CALVE` S3 & MICHAL NEMCˇ OK4,5 1Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai 400 076, Maharashtra, India 2Exploration, Reliance Industries Ltd, Mumbai 400 701, Maharashtra, India 3Universite´ Toulouse 3, Paul Sabatier, Ge´osciences Environnement Toulouse, 14 avenue Edouard Belin, 31400, Toulouse, France 4EGI at University of Utah, 423 Wakara Way, Suite 300, Salt Lake City, UT 84108, USA 5EGI Laboratory at SAV, Du´bravska´cesta 9, 840 05 Bratislava, Slovakia *Correspondence: [email protected] Gold Open Access: This article is published under the terms of the CC-BY 3.0 license. Many questions have been raised about the tectonic c. 65 + 0.5 Ma (Chenet et al. 2007; review by Val- controls and structural evolution of the large igne- diya 2010). Most of the research on the onshore part ous provinces (LIPs) of the world; these provinces of the DLIP has focused on the lithology, geochem- are of enormous interest to tectonicians (see recent istry, isotopic ages and overall relationship of the review by Ernst 2014) and the Deccan Traps are volcanism with continental rifting. Organized stud- no exception (e.g. Dessai & Bertrand 1995; Peshwa ies on the tectonic structure of the underlying conti- & Kale 1997; Collier et al. 2008; Corfield et al. nental lithosphere, the structural development of the 2010; Hooper et al. 2010; Calve`s et al. 2011; Dixit volcanic province and the post-eruption tectonic et al. 2014; Misra 2015; Misra et al. 2014, 2015, development of the province have been relatively 2016; Misra & Mukherjee 2015). The Deccan undocumented, pending fresh studies (e.g. Misra large igneous province (DLIP) (the Deccan Traps) et al. 2014). The western DLIP is an exposed pas- is the product of the voluminous outpouring of sive continental margin and is a globally signi- mainly basaltic lavas at the Cretaceous–Tertiary ficant example of a volcanic margin, crucial in (K–T) boundary and constitutes one of the lar- our understanding of the dynamics of such margins. gest known LIPs in the world (Bryan et al. 2010). The offshore areas of the passive margin have The Deccan Volcanic Province (DVP) covers been investigated using single-channel and seismic .500 000 km2 (Watts & Cox 1989; Deshpande refraction studies, although none of these studies 1998; Chandrasekharam 2003 and references cited has produced images deep enough to image the therein; see reviews by Vaidhyanadhan & Rama- entire crust. New data from many sources have krishnan 2008; Philpotts & Ague 2009). Pre-erosion now been made available (Misra et al. 2015, estimates for the area covered by the lavas vary 2016). This book presents further research in the widely, but are typically 1–2.6 × 106 km2 (Chan- onshore and offshore passive margin regions. The drasekharam 2003 from references cited therein; northern areas of the DLIP in Kutch (Gujarat, Vaidhyanadhan & Ramakrishnan 2008). The total India) are highly active and the central parts are thickness of the Deccan Traps exceeds 2000 m moderately active in terms of present day deforma- (Kaila et al. 1981; Deshpande 1998; Harinarayana tion manifested by recurring earthquakes, possibly et al. 2007). The Deccan Traps are one of the related to the ongoing Himalayan orogeny (Bilham most important LIPs in studies of the origin and et al. 2001; Bodin & Horton 2004; Mukherjee et al. eruption of large volumes of basaltic magma since 2013, 2015). The Early Tertiary was characterized the Mesozoic. by tensile to strike-slip stresses due to rifting, The Deccan volcanism produced outpourings of which changed to compressive to strike-slip stresses lavas over an extended period of time from c. 68 to from the Miocene Himalayan collision onwards 60 Ma (reviews by Pande 2002; Chenet et al. 2007 (Bilham et al. 2001; Misra et al. 2014, 2015, 2016). and references cited therein; Hooper et al. 2010; Comprehending the tectonics of the Deccan Valdiya 2010, 2011; Baksi 2014), possibly in pulses Traps, which outcrop mainly in the Indian states (Chenet et al. 2007). Peak volcanism occurred at of Maharashtra, Gujarat, Madhya Pradesh, Andhra From:Mukherjee, S., Misra, A. A., Calve`s,G.&Nemcˇok, M. (eds) 2017. Tectonics of the Deccan Large Igneous Province. Geological Society, London, Special Publications, 445,1–9. First published online December 8, 2016, https://doi.org/10.1144/SP445.14 # 2017 The Author(s). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 2 S. MUKHERJEE ET AL. Pradesh and Karnataka, is also crucial in decipher- 2007; Chandrasekhar et al. 2011; Kumar et al. ing how the Seychelles microcontinent rifted from 2011). The Cambay rift is bound by NNW-trending India, with implications for offshore basin and con- faults affecting the Deccan Traps (Dixit et al. 2014). tinental margin evolution around the northern The east–west-trending Tapti Fault defines the Indian Ocean. north boundary of the main outcrop of the DLIP This Special Publication contains 13 research (Azeez et al. 2011). The west coast passive margin papers on the tectonic aspects of the DLIP, com- is defined by the NNW-trending West Coast Fault monly referred to as the Deccan Traps. The broad (Fig. 1; Chandrasekharam 1985; Biswas 1987). The perspectives of these papers include field-based location of this fault is debatable because compel- structural geology, geochemistry, analytical mod- ling field evidence is difficult to obtain. The Western els, the relationship of geomorphology to structure Ghat escarpment (Figs 2 & 3; Kale 2010) is defined and tectonics, and geophysics (palaeomagnetism, by a sharp change in topography, with the eastern gravity and magnetic anomalies, and seismic imag- side uplifted by 800–1200 m. This escarpment is ing), with respect to both palaeo- and neotectonics. considered to be a rift-bounding fault of the west These papers develop the relatively neglected tec- coast passive margin (Gunnell & Fleitout 1998). The tonic investigations of the Deccan LIP and de- NNW-trending Koyna Fault parallels this escarp- monstrate that it is important to understand the ment. The Kurduwardi Lineament is another impor- structure and deformation of the province as well tant structural element (Peshwa & Kale 1997). The as the petrology, which has been well studied over northernmost region of the Kurduwardi Lineament many years. is manifested by a NW-trending .20 km long series of fractures/faults in Thane district (Maharashtra State, India) (Peshwa & Kale 1997). Slickensides Overview of the tectonics and structural have developed over the fault planes. These faults geology of the DLIP have a c. 10–30 m throw and indicate both dextral and sinistral shear. Flexure, indicated by gently dip- Madagascar, Seychelles and India constituted a ping flow layers (Fig. 3) related to the West Coast single large continental block until Cenomanian– Fault, opened fractures that were subsequently filled Turonian times. Madagascar rifted from India at with igneous material to form dykes (Peshwa & about 90 Ma. In a subsequent rifting event at about Kale 1997). Dessai & Bertrand (1995) and Hooper 63.4 Ma, the Seychelles microcontinent and the et al. (2010) reported north–south shear zones from Laxmi Ridge, a microcontinental block now located the Deccan coastal areas, extending for c. 40 km between India and Seychelles, rifted from India. from Murud to Mumbai (Fig. 4). Dessai & Bertrand This rifting event of the Laxmi and Seychelles (1995) reported steep fault planes with subvertical microcontinents was almost coeval with Deccan displacement and occasional slickensides. Hooper flood volcanism (reviewed in Bhattacharya & et al. (2010) established that the earliest (66– Yatheesh 2015). Geophysical studies have been 65 Ma) dykes have been sheared and that the later already conducted to ascertain the thicknesses of dykes were oriented either along the shear planes the trap/crust/lithosphere, the basement configura- or intruded into them. tion and mantle anisotropies (reviewed in Misra 2015). The elastic thickness (Te) of the plate beneath the Deccan Traps is c. 8–10 km (Tiwari & Misra Why study structures in the DLIP? 1999). The anomalous gravity high in the Mumbai coastal area indicates either a shallow secondary The structural and tectonic features of the Deccan plume that supplied lava for the Deccan volcanics region have significant economic and societal im- (Negi et al. 1992) or a bolide impact at around the portance and the region includes the important city K–T boundary that might have triggered Deccan of Mumbai and its hinterland. Basin development lava eruption (Negi et al. 1993). By contrast, Sethna and the locations of fractures and faults in the (2003) considered acid volcanic rocks, and Bhatta- DLIP have far-reaching implications in hydrocar- charji et al. (2004) mafic bodies, to give rise to the bon exploration (Pandey & Agarwal 2000). There anomalous gravity high. Flows in the Deccan are four petroliferous basins in India within the Traps are mostly sub-horizontal (Watts & Cox DLIP: the Barmer, Kutch, Cambay and Mumbai 1989), although Devey & Lightfoot (1986) deci- shelf basins. The Deccan synclise and Saurashtra phered a regional ‘very open’ antiform around Pan- basins have also been studied for the occurrence of vel (Maharashtra, India), along which the Deccan hydrocarbons. The area is important for groundwa- lava layers steepen to constitute the Panvel Flexure. ter resources and the Deccan structures are impor- Regional faults have been identified in the north tant for groundwater exploration (Rai et al. 2011). and west Deccan Traps from geophysical and The seismicity of the area is a concern and the remote sensing studies (Fig. 1; Harinarayana et al. region around Koyna in the Deccan Traps suffered Downloaded from http://sp.lyellcollection.org/ by guest on September 30, 2021 TECTONICS OF THE DECCAN TRAPS: AN INTRODUCTION 3 Fig.