tectonomagmatic setting of lava packages in the mandla lobe of the eastern deccan volcanic province,...

Tectonomagmatic setting of lava packages in the Mandla lobe of the

eastern Deccan volcanic province, India: palaeomagnetism and

magnetostratigraphic evidence

VAMDEV PATHAK1,2, S. K. PATIL1 & J. P. SHRIVASTAVA2*1Dr K.S. Krishnan Geomagnetic Research Laboratory, Jhunsi, Allahabad 221505, India

2Department of Geology, University of Delhi, Delhi 110 007, India

*Corresponding author (e-mail: jpshrivastava.du@gmail.com)

Abstract: Flow-by-flow palaeomagnetic measurements of 37 lava flows in the 900 m-thick, iso-lated lava pile around Mandla in the eastern Deccan Volcanic Province (DVP) reveals multiplemagnetic polarity events: implying C29n–C28r–C28n magnetostratigraphy. Magnetic polarityresults when traced out from section to section, maintaining the order of superposition, show jux-taposition of lava packages with distinct characters near Deori (e.g. flows 1–4 abated against flows5–14) and the Dindori areas. At Dindori and towards its south, the distinct lava packages (e.g. flows15–27 and flows 28–37) are juxtaposed along the course of Narmada river. It is explained by thepresence of four normal post-Deccan faults in the Nagapahar, Kundam–Deori, Dindori and Badar-garh–Amarkantak sectors: thus, signifying structural complexity with vertical shifts or offset of150–300 m. Magnetic chron reversals in conjunction with field and chemical data support thesefindings. Further, these lavas are compositionally akin to Bushe, Poladpur, Ambenali and Maha-bleshwar Formational lavas, and follow the same stratigraphic order as in the Western Ghats. Alter-nating field (AFD) and thermal demagnetizations (THD) isolate the normal mean direction of theMandla lobe: D ¼ 344.58 and I ¼ 2308, where D and I are the mean declination and inclination ofthe each lava flow (a95 ¼ 8.2; K ¼ 72.6; N ¼ 17, where a95 is the half-angle of the cone of 95%confidence about the mean direction, K is the precision parameter and N is the number of flows).The Virtual Geomagnetic Pole (VGP) position determined for these lavas, when compared with theDeccan Super Pole, indicates concordance with the main Deccan volcanic province, thus assigninga shorter period of eruption close to the Cretaceous–Palaeogene boundary (K/PB) for the easternand western Deccan Traps.

The Deccan Volcanic Province (DVP) in India(Fig. 1), covering an area of 0.51 × 106 km2, repre-sents one of the large igneous provinces that recordsvast accumulations of tholeiitic magma over a rela-tively short time span (e.g. Vandamme et al. 1991;Venkatesan et al. 1993; Chenet et al. 2008, 2009)straddling the Cretaceous–Palaeogene boundary(66 Ma: Gradstein et al. 2012). Flows of variablethicknesses (1–100 m) are superimposed to forma lava pile that attains its maximum thickness(3.5 km) in the SW of the DVP. Most of the trapsare horizontal or gently dipping and show no lat-eral or vertical compositional variations for almost100 km of along-strike length (Lightfoot & Haw-kesworth 1988). The thickest accumulation of Dec-can basalt in western India (Fig. 1), referred to asthe Western Deccan Volcanic Province (WDVP),is stratigraphically controlled and geochemicallywell characterized (Shrivastava et al. 2014 andreferences therein). The western Deccan strike-slip faults appear somewhat similar to first-orderstructures that developed during the Late Creta-ceous–Early Palaeogene period (Misra et al.2014). Moreover, post-volcanic deformation and

reactivation of vertical faults in the area are appar-ently a tectonic inheritance of pre-existing anisotro-pies: controlled rifting (Misra & Mukherjee 2015)and reactivation of the faults occurred after highmagmatic heating due to the Reunion plume (Misraet al. 2015). The stratigraphic framework of theWestern Ghats region is known from detailedfield, chemical, isotopic and palaeomagnetic stud-ies, and has been correlated with the other DeccanTraps Formations. Palaeomagnetic investigationsof Deccan Trap lava flows have been carried outby a number of workers (Sahasrabudhe 1963; Bhi-masankaram & Pal 1968; Athavale 1970; Pal et al.1971; Verma & Pullaiah 1971; Wensink & Kloot-wijk 1971; Athavale & Anjaneyulu 1972; Konoet al. 1972; Verma & Mittal 1972, 1974; Vermaet al. 1973; Wensink 1973; Bhalla & Anjaneyulu1974; Bhalla & Rao 1974; Courtillot et al. 1986;Prasad et al. 1996; Patil & Rao 2002; Patil &Arora 2003; Chenet et al. 2008; Jay et al. 2009;Keller et al. 2009a, b; Schobel et al. 2014). Theseinvestigations provided a better understanding ofthe nature of the geomagnetic field (relative to theIndian sub-continent during the interval of Deccan

From: Mukherjee, S., Misra, A. A., Calves, G. & Nemcok, M. (eds) Tectonics of the Deccan Large IgneousProvince. Geological Society, London, Special Publications, 445, http://doi.org/10.1144/SP445.3# 2016 The Author(s). Published by The Geological Society of London. All rights reserved.For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

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Fig. 1. (a) Map in the inset showing the DVP and the Mandla lobe in India. (b) Map (modified after Shrivastava et al. 2014) of the DVP showing the Mandla lobe (area of thepresent study). (c) The SW Deccan formational stratigraphy (after Cox & Hawkesworth 1985; Beane et al. 1986; Subbarao & Hooper 1988; Lightfoot et al. 1990).

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basaltic eruptions) and magnetostratigraphy of theflow sequences. However, very few studies pertain-ing to palaeomagnetism have been carried out onthe northern part of the Deccan Traps (Athavale1970; Pal & Bhimasankaram 1971; Pal et al.1971; Verma & Pullaiah 1971; Bhalla & Anjaneyulu1974; Vandamme et al. 1991; Vandamme & Cour-tillot 1992; Schobel et al. 2014). The first palaeo-magnetic study in the eastern part of the Deccanprovince yielded reverse polarities in four flowsnear Linga (e.g. Sahasrabudhe 1963). Subsequently,Athavale (1970) reported a polarity transition in thelava flows of the Mandla section at an altitude of600–625 m above sea level. Verma & Pullaiah(1971) and Verma et al. (1973) confirmed the exis-tence of a polarity reversal in a section near Kun-dam, and recognized that much of the Deccanvolcanism had probably occurred in two relativelylong periods of reversed and normal polarity.Assuming that the lava flows are flat-lying and tak-ing into account their shorter duration comparedwith that of the main eruptive events, then, basedon the altitude of the reversals, a sequence of sixpolarity intervals were recognized. Verma & Pull-aiah (1971) found a normal sequence at an altitudeof between 605 and 685 m to the north of Dindori,whereas Athavale (1970) observed a reversed polar-ity at an altitude of between 701 and 953 m along theroad section from Dindori to Amarkantak. Van-damme & Courtillot (1992) undertook palaeomag-netism measurements of flows near Jabalpur,Kundam and Lakhnadon, and, from the data accu-mulated, they suggested either the existence of twomajor faults with vertical offsets of about 100 m orthe presence of a synform structure of smooth cylin-drical symmetry that reconciles the entire datasetwith the proposed C30n–C29r–C29n reversalsequence (Vandamme et al. 1991) of the well-established magnetostratigraphy of SW Deccan.However, limited palaeomagnetic studies havebeen carried out in the northern part of the DeccanTraps. Schobel et al. (2014) attempted to establish amagnetostratigraphy of the Malwa Plateau. Basedon palaeomagnetic and 40Ar/39Ar geochronologyof the Malwa area, they suggested that the Malwaflows erupted during C30n and C29r, while theMandla lava flows fall in a similar age bracket.These observations were also based on close geo-chemical similarity (Peng et al. 1998; Shrivastavaet al. 2014) and the presence of the C30n–C29rtransition (e.g. Rao & Bhalla 1981). However, Sch-obel et al. (2014) concluded that the northernDeccan Province segments are spatially indepen-dent and are not correlatable with the youngerFormations, but with geochemically similar Forma-tions of the Western Ghats (e.g. the Bushe, Polad-pur or Ambenali Formations). Crookshank (1936)opined that the emplacement of the intrusive

complex, with contemporaneous domal warping,uplift and rifting, may have resulted in the fault-ing of lava flows along the Satpura Range, andCox (1988) attributed the reason for post-Deccanfaulting to post-eruptive isostatic adjustments. Themagnetic polarity bias might be the result of the con-jugate effects of erosion, altitude and undetectedfaults, which demand detailed work. Thus, themagnetostratigraphy of the Eastern Deccan Volca-nic Province (EDVP) is important for a better under-standing of the DVP in terms of precise age,eruptive span, flow pattern mechanisms, chemostra-tigraphic differences and the Deccan magmatismremagnetization effects. Although covering a largegeographical terrain, the Mandla lava flows in theEDVP remained neglected (Schobel et al. 2014).Previous studies have been restricted to some spe-cific localities, and magnetostratigraphy was notattempted. The main objective of this present workis to carry out detailed palaeomagnetic and magne-tostratigraphic studies on the Mandla lobe (Fig. 2)in combination with previous petrological andgeochemical results (Pattanayak & Shrivastava1999; Shrivastava et al. 2014) to constrain age andtectonomagmatic settings, and to find a possible cor-relation within the western Deccan stratigraphicframework.

Geological setting

The Mandla lobe forms an isolated outlier on the NEpart of the DVP. It covers an area of 29 400 km2,comprising thick pile of lava flows, preserved asremnant of erosion on the eastern extremity of theTraps (Fig. 2). Combined field, petrographical andmajor-elemental studies (Pattanayak & Shrivastava1999; Shrivastava & Pattanayak 2002; Shrivast-ava & Ahmad 2005; Shrivastava et al. 2014) haveresolved that this lobe is comprised of 37 lavaflows. It extends 344 km in the east–west and156 km in the north–south directions around theSeoni, Jabalpur, Mandla, Dindori and Amarkan-tak areas (Fig. 2). The landscape is covered by flat-topped plateaus (Maikala) and ridges that oftenform small mesas and buttes. The contact betweenthe base of the Traps and the underlying sedimentaryLameta beds is at 364 m above mean sea level nearJabalpur, and the maximum elevation of the lava-flow sequence is 1177 m at Badargarh Mountainnear Amarkantak. Overall, the lava pile is around900 m thick, and major topographical breaks occurat elevations of about 450, 600 and 900 m. Theselava flows are deeply incised by the westwards-draining River Narmada. The eastern Deccan outlieris bounded by Precambrian rocks (Saucers) in thesouth, and Gondwana sediments in the NE and NWparts. Rocks belonging to the Mahakoshal Grouplie below the lava flows near the Jabalpur area. The

LAVA-FLOW PALAEOMAGNETIC MEASUREMENTS IN THE DVP

Fig. 2. Map showing (a) the location of the eastern Deccan volcanic province and (b) the Mandla lobe (modified after Shrivastava et al. 2012) and layout of the traverses (A–B,B–C and D–E). The filled red circles with numbers represent lithologs. Single or multiple lava flows in each litholog is assigned with a number that represents the respectivelava flows (maintaining the order of superposition and thickness) and their formational affinity with the western Deccan basalts (shown in red, blue, green and yellow).Abbreviations: 9, Lapeta Bargi; 13, Jodhpur Pindrai; 16, Bara Simla; 18, Nagapahar; 26, Matka South; 27, Matka North; 28, Deori; 29, Barkhera Guraiya; 36, Bikrampur; 37,Karopani Pahar; 38, Mohtara; 39, Manikpur; 42, Badargarh Mountain; 44, Karanjia; 45, Kapildhara; 46, Keonch Amarkantak; 52, Mohan Tola; 53, Mandla Bridge; 54,Sahsradhara; 55, Khairi; CIS, Central Indian Shear Zone.

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Quaternary sediments (alluvium) are limited to thoseareas where the river becomes widened and the Dec-can basalt is completely covered by alluvial sedi-ments. The outlier is tectonically controlled byrift-bounded basinal fault systems such as theSon–Narmada Fault System to the north and theTapti Fault (Fig. 2) in the southern flank, and bythe Central Indian Suture Zone towards the SE part(Murthy & Mishra 1981; Nair et al. 1996). TheSon–Narmada Fault System comprises the Son–Narmada North Fault (SNNF) and the Son–Nar-mada South Fault (SNSF), forming an east–west-orientated rift known as the Narmada Rift (see fig.1 in Shrivastava et al. 2012). The rift zone is charac-terized by deposition of a 1000 m-thick pile of Qua-ternary sediments. The Deccan basalt in the northand south of the Chindwara Amarkantak area is con-trolled by these basinal faults (see fig. 1 in Shrivas-tava et al. 2012). Long-distance stratigraphiccorrelation of lava flows or formations (a packageof lava flows) over the Deccan Province remainsproblematic. Deshmukh et al. (1996) stated that theeastern Ambenali Formation (analogous to theAmbenali Formation of the Western Ghats) and theeastern low-Ti formation (may correspond to thePanhala Formation of the Western Ghats) have alarge areal extent in central and eastern areas.Peng et al. (1998) reported isotopic and elementalgeochemistry of lava-flow samples from a 690 m-thick lava pile at Mhow, a 620 m-thick pile atChikaldhara and a 230 m-thick pile at Jabalpur,and suggested that the Ambenali Formation and afew flows of the Bushe and Khandala Formationsmay be present in the NE Deccan (Mandla lobe).However, Subbarao et al. (1999) concluded thatdirect correlations are difficult owing to a confus-ing stratigraphic order of flows, the available iso-topic composition and, in some areas, differentmagnetic polarities. The Trap–basement contactlies at 364 m asl in the Mandla lobe and, based onregional mapping and detailed petrographical stud-ies coupled with a lateral tracing of the flows, these37 lava flows were grouped into six chemical types(Pattanayak & Shrivastava 1999; Shrivastava &Pattanayak 2002; Shrivastava & Ahmad 2005;Shrivastava et al. 2014). Based on the geographicaldistribution and order of superposition of the flowsin the Mandla lobe, they further suggested that theolder flows occur in the west of the outlier at theSeoni Jabalpur Sahapura sector, whereas the youn-ger flows are confined to the Dindori Amarkantaksector in the east (Fig. 2).

Methods

To obtain precise palaeomagnetic data, orien-tated rock samples were collected from 37 lavaflows. Field criteria, megascopic characters and

petrological nomenclature proposed by Pattanayak& Shrivastava (1999) and Shrivastava & Ahmad(2005) were followed. On the basis of reconnais-sance surveys, three traverses, A–B (Rukher–Sivni: Fig 3a), B–C (Sivni–Amarkantak: Fig 3b)and D–E (Nainpur–Shahpura: Fig 3c) were per-formed to cover the maximum topographical reliefand to provide the overall best resolution of themagnetostratigraphy of the lava flows in the area.Sample locations were selected as a function oflithology and degree of weathering. For palaeomag-netic sampling, criteria discussed by Van der Voo(1990) have been followed. Rock samples were ori-entated with the help of a Brunton compass, and atleast two horizontal levels, the north direction andthe specimen identity were marked before the sam-ples were plucked from the lava flows (Fig. 4a, b). Aminimum of three and a maximum of six rock sam-ples were collected from each lava flow (Fig. 4c).For the suitability of the palaeomagnetic samples,fresh rock samples were selected from which atleast four cores and eight standard size specimenswere prepared (Fig. 4d, f ). Palaeomagnetic investi-gations were carried out on 158 orientated rock sam-ples collected from 42 sites (Table 1) of the Mandlalobe. Standard cylindrical cores were cut from handsamples in the laboratory, and 959 cylindrical spec-imens (2.5 cm in diameter and 2.2 cm in length)were prepared. In all, 21 litholog/sections (Fig. 2)were selected for the collection of orientated rocksamples across the A–B, B–C and D–E traverses(Fig. 3a, b, c), where single litholog sections holdone or multiple lava flows. Orientated rock samplesfor similar lava flows (i.e. the 1st, 4th, 6th, 10th and26th) were collected from more than one site at dif-ferent locations and altitudes for cross-verificationof the palaeomagnetic results, and also for a bettercorrelation of lava-flow stratigraphy and magneto-stratigrphy of the area. Prior to the palaeomagneticinvestigations, magnetic susceptibility for all thespecimens was measured using a Bartington magne-tic susceptibility meter (MS-2B). Natural remanentmagnetization (NRM) directions were measuredwith a JR-5A spinner (3 pT sensitivity) magnetome-ter. To isolate characteristic remnant magnetizationdirections (ChRM) from the specimens, alternatingfield (AF) and thermal demagnetizations were car-ried out using a Molspin AF demagnetizer and ther-mal demagntizer (Model Magnon International TD700; Magnon GmbH), respectively. The thermaldemagnetizations (THD) were carried out in 14steps at 100, 200, 300, 350, 400, 450, 500, 530,560, 580, 600, 630, 680 and 7008C, respectively. Inorder to monitor the magnetic mineralogical changesdue to thermal demagnetizations, the susceptibilityof each specimen was measured after each thermaltreatment. The stepwise thermal demagnetizationand susceptibility of the basaltic samples revealed

Fig. 3. Lava-flow stratigraphy and lithological sections along: (a) A–B (Rukher Sivni).

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Fig. 3. (Continued) (b) B–C (Sivni Amarkantak); and

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Fig. 3. (Continued) (c) D–E (Nainpur Shahpura) traverses. Black, dark grey, white and light grey indicate the formational affinity with the western Deccan basalts asdetermined by Shrivastava et al. (2014). Fm, Formation. Maintaining the order of superposition, the numbers within the bars are assigned to the respective lava flows and theirformational affinity with the western Deccan basalts (shown with black, dark grey, white and light grey). Numbers within the circle marked over the bar indicate the section/lithog number. The three digit numbers, written over the bar, represent their height (altitude, in metres) above sea level (asl).

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changes in the intensity decay patterns, attributed tothe formation of a secondary component. The alter-nating field demagnetizations (AFD) were also car-ried out in 14 steps at 3.6, 5.0, 7.5, 10, 15, 20, 25,30, 35, 40, 50, 60, 80 and 100 mT. Based on pilotresults, a few steps were selected for blanket studiesat 0, 25, 30 and 35 mT in the case of AF demagnet-ization, and at 0, 300, 350 and 4008C in the case ofthermal demagnetization. Vector demagnetizationdiagrams (Zijderveld 1967) for each sample wereanalysed using principal component analysis(Kirschvink 1980). Site-mean directions were calcu-lated using Fisher (1953) statistics. Lava flows wereconsidered to be horizontal because the dips of the

Deccan Trap lava flows were not detectable at thescale of our sites and the results were therefore nottilt-corrected. The Remasoft (version 3.0) softwareof Chadima & Hrouda (2006) and the PaleomagneticAnalysis Program (version 4.2) of Chunfu Zhang(Zhang & Ogg 2003) were used for the palaeomag-netic data analysis.

Palaeomagnetic results

Prior to demagnetization, NRM studies were carriedout for all the sites and the results obtained wereplotted over an equal-area projection. NRM intensi-ties of various flows collected from the Nagapahar,

Fig. 4. Systematic sample collection and laboratory treatment showing: (a) the highly fractured lava-flow section;(b) the marking of the north direction and horizontal level; (c) the orientated block samples; (d) coring in thelaboratory; (e) core samples; and (f) standard size specimens.

Table 1. Palaeomagnetic results for the Mandla lava flows, with sections, flows, traverses and altitudes

Sites/sections Lava flow Latitude Longitude Traverse Altitude (m) N NO D I a95 K

Badargarh Mountain 37 228 44′ 0.027′′ 818 46′ 0.116′′ B–C 1130 3 12 343 211 17 202Badargarh Mountain 36 228 59′ 0.815′′ 818 39′ 0.056′′ B–C 1080 3 12 27 38 7 148Badargarh Mountain 35 228 59′ 0.832′′ 818 39′ 0.015′′ B–C 1043 3 12 49 55 14 44Badargarh Mountain 34 228 46′ 500′′ 818 43′ 969′′ B–C 954 5 31 103 73 39 41Mohtara 33 228 47′ 780′′ 818 22′ 167′′ B–C 900 4 29 151 44 17 25Mohtara 32 228 47′ 735′′ 818 22′ 217′′ B–C 876 6 30 178 50 16 227Manikpur 31 228 43′ 0.181′′ 818 25′ 0.990′′ B–C 696 3 12 223 249 7 272Manikpur 30 228 43′ 0.74′′ 818 25′ 0.112′′ B–C 952 3 12 42 32 21 140Badargarh Mountain 29 228 59′ 0.550′′ 818 38′ 0.773′′ B–C 969 3 12 222 212 4 430Khairi 28 228 36′ 0.091′′ 808 28′ 0.918′′ D–E 488 3 20 157 68 17 28Sahasatradhara 27 228 37′ 0.87′′ 808 20′ 0.20′′ D–E 433 5 27 326 215 25 24Mohtara 26 228 47′ 811′′ 818 22′ 277′′ B–C 855 4 20 176 23 21 14Mandla Bridge 26 228 36′ 12′′ 808 21′ 41′′ D–E 441 5 31 159 25 9 156Mohan Tola 25 228 34′ 74′′ 808 20′ 78′′ D–E 475 4 29 189 74 9 47Karanjia 24 228 42′ 641′′ 818 34′ 091′′ B–C 885 3 12 203 10 14 41Mohtara 23 228 47′ 829′′ 818 22′ 303′′ B–C 844 5 30 166 44 17 30Mohtara 22 228 47′ 861′′ 818 22′ 329′′ B–C 817 4 29 211 32 31 9.4Barkhera Guraiya 21 238 10′ 462′′ 808 38′ 563′′ B–C 643 3 12 58 16 8 108Karopani Pahar 20 – – B–C 960 4 30 307 250 21 11Karanjia 19 228 42′ 995′′ 818 25′ 309′′ B–C 893 3 13 58 26.7 6 253Karopani Pahar 18 228 51′ 94′′ 818 12′ 63′′ B–C 810 4 25 111 63 22 127Keonchi Amk 17 228 40′ 20′′ 818 43′ 61′′ B–C 985 3 12 357 225 14 29Karopani Pahar 16 228 52′ 818 12.5′ B–C 775 4 25 158 32 11 33Mohtara 15 228 48′ 99′′ 818 20′ 43′′ B–C 760 3 25 82 17 25 24Lapeta Bargi 14 238 00′ 400′′ 798 52′ 576′′ A–B 590 3 12 57 232 4 447Lapeta Bargi 13 238 00′ 399′′ 798 52′ 517′′ A–B 534 3 12 211 26.5 7 161Jodhpur Pindari 12 238 05′ 34′′ 798 53′ 004′′ B–C 535 3 28 302 7 40 4Lapeta Bargi 11 238 00′ 315′′ 798 52′ 547′′ A–B 518 3 26 119 26 36 7Dhanwahi 10 228 59′ 78′′ 808 08′ 59′′ B–C 573 4 48 301 255 22 13Jodhpur Pindari 10 238 05′ 380′′ 798 58′ 919′′ B–C 510 5 28 132 224 19 13Lapeta Bargi 9 238 00′ 271′′ 798 52′ 592′′ A–B 495 4 26 231 27 29 11Lapeta Bargi 8 238 00′ 221′′ 798 52′ 594′′ A–B 465 5 19 254 38 29 18Lapeta Bargi 7 238 00′ 185′′ 798 52′ 580′′ A–B 438 4 31 195 26 35 14Nagapahar 6 238 04′ 31′′ 808 04′ 56′′ B–C 528 3 48 338 234 13 33Jodhpur Pindari 6 – – B–C 465 3 36 342 225 6.5 106Nagapahar 5 238 04′ 66′′ 808 04′ 79′′ B–C 498 3 23 143 63 6.7 99Matka South 4 238 10′ 148′′ 808 32′ 40′′ B–C 620 3 21 350 215 15 27Bara Simla 4 238 10′ 16′′ 798 58′ 45′′ B–C 447 5 15 334 230 15 20Matka North 3 238 10′ 873′′ 808 31′ 938′′ B–C 610 3 12 233 0.18 9.5 93Matka South 2 238 10′ 588′′ 808 31′ 941′′ B–C 620 5 24 350 232 20 15Matka South 1 238 10′ 706′′ 808 31′ 883′′ B–C 593 4 16 352 217 14 23Nagapahar 1 238 05′ 28′′ 808 04′ 51′′ B–C 456 5 32 342 227 23 30

Abbreviations: N, number of orientated block samples; No, number of the specimens used in the calculation of the mean direction; D and I, mean declination and inclination (in specimen coordinate) of the eachlava flow; a95, half-angle of the cone of 95% confidence about the mean direction; K, the Fisher (1953) precision parameter.

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Bara Simla, Jodhpur Pindari, Bikrampur, KaropaniPahar, Keonchi Amarkantak, Mohan Tola, MandlaBridge, Sahashradhara and Khairi sections (Fig.3a, c) varied from 0.03 to 70.43 A m21, with amean intensity of 9.26 A m21. These values show nosystematic variation from one lava flow to another.The maximum intensity was found in the specimenscollected from the Mandla Bridge section, where afresh lava flow is exposed in the Narmada riverbed. The Koenigsberger ratio (Q ratio ¼ NRM/kH, where k is the magnetic susceptibility and H isthe magnitude of Earth’s magnetic field in thestudy area) was calculated and a value of obtained7.2, which indicates the suitability of the rocks forpalaeomagnetic investigation. Further, an isother-mal remanent magnetization (IRM) study was car-ried out for the Mandla lavas, and the majority ofthe IRM data (see fig. 5a, b, c, d in Pathak 2015)showed a saturation value of around 200 mT. TheIRM curves saturating in a field of 200 mT indicatethat the titano-magnetite is the major magnetic min-eral responsible for the ChRM in the samples. TheNRM mean directions of the normal and reversepolarities were calculated separately for all the spec-imens. The NRM mean direction of the specimensrepresenting normal polarity were isolated as hav-ing a declination (D) of 3388 and an inclination(I ) of 2368(a95 ¼ 5.1; N0 ¼ 234 specimens, wherea95 is the half-angle of the cone of 95% confidenceabout the mean direction and N is the number ofspecimens), and similarly the mean direction ofthe specimens of reverse polarity was isolated asD ¼ 1538 and I ¼ 2788 (a95 ¼ 4.2; N0 ¼ 194 spe-cimens). The NRM measurements of the specimenscollected from the Matka South, Matka North,Lapeta Bargi, Dhanwahi, Mohtara, Karanjia, Bar-khera Gauriya, Manikpur and Badargarh Mountainsections were plotted on an equal-area projection.However, the NRM directions of these sectionswere found to be more scattered than in the Nagapa-har, Bara Simla, Jodhpur Pindari, Bikrampur, Karo-pani Pahar, Keonchi Amarkantak, Mohan Tola,Mandla Bridge, Sahashradhara and Khairi sections.Prior to the palaeomagnetic investigations, mag-netic susceptibility for all of the specimens wasmeasured using a Bartington magnetic susceptibilitymeter (MS-2B). Stereographic projections (Fig. 5a,b, c, d), Zijderveld diagrams (Fig. 6) and intensitydecay patterns for the Mandla lava flows were plottedafter application of the AF and thermal demagnetiza-tion. The stereographic projections, where palaeo-magnetic results are plotted simultaneously (Fig.5a, d), are used to understand the palaeomagneticdirections and demagnetization behaviour duringAFD and THD. During the demagnetizations (inmost of the lava flows), it was noticed that the second-ary viscous component was removed in the majorityof the specimens by the application of a 10–15 mT

peak AF field, and ChRM was found between the15 and 60 mT fields (Fig. 5a, b, c, d). The NRM inten-sity was reduced to 10% by the application of 80 mTand, in the majority of the samples, the intensity wasreduced to zero in the 100 mT AF field. The straightline (Fig. 6) passing through the origin in theZijderveld diagrams indicates the isolation of a pri-mary component. Thermal demagnetization spectraon the representative samples indicate the isolationofthe ChRM directions (Fig. 5a, b, c, d) within the ther-mal bracket of 200–5008C, and the removal ofthe weak viscous component by the application of1508C. AF demagnetization was found to be moresuitable for the isolation of ChRM rather than forthermal demagnetization (Fig. 5a, b, c, d). Out of 37lava flows studied, 10 showed a transitional direc-tion: therefore, it was not possible to resolve thestable direction. The mean ChRM of normal polaritylava flows (i.e. the 1st, 2nd, 4th, 6th, 17th, 27th and37th) was isolated as D ¼ 344.48 and I ¼ 2238(a95 ¼ 6.3; K ¼ 58.6; N ¼ 10 flows, where K is theprecision parameter). The mean ChRM of the reversepolarity lava flows (i.e. the 16th, 23rd, 26th, 32nd,33rd, 34th and 35th) was isolated as D ¼ 164.58and I ¼ 36.78 (a95 ¼ 11.7; K ¼ 36.6; N ¼ 7 flows).However, the overall normal mean direction of theMandla lava flows was isolated as D ¼ 344.58 andI ¼ 2308 (a95 ¼ 8.2; K ¼ 72.6; N ¼ 17 flows),and the corresponding VGP position was derived aspalaeolatitude 48.078 N and palaeolongitude 282.68E. The present VGP was plotted along with theVGP of the Deccan Super Pole (Vandamme et al.1991).

Discussion

Present flow-by-flow palaeomagnetic measure-ments (Table 1) indicates multiple polarity eventsin the Mandla region. Magnetic polarity resultswith respect to each lava flow were plotted againstthe altitude (Fig. 7), where lava flows representnormal (in black), reverse (in white) and transitional(in grey) polarity directions. It clearly indicates thatmost of the flows have reverse direction, and anormal–reverse–normal type of configuration hasbeen found in the Mandla region (Fig. 7). However,an exact correlation with a previously reported nor-mal–reverse–normal model (C30n–C29r–C29n)proposed by Courtillot et al. (1986) and Vandammeet al. (1991) needs further validation with respectto available recent ages (Fig. 8) and lava-flow strat-igraphy of the Mandla lobe (Shrivastava et al.2015). Lower lava flows (1st–6th) show normalpolarity directions, except for the 3rd and 5thlava flows (Fig. 8), which represent transitionaland reverse directions, respectively. These lowerlava flows are correlatable with C29n (Fig. 8) asthe 1st and 4th lava-flow 40Ar/39Ar ages are

Fig. 5. Representative stereographic projections for AFD and THD results for the specimens collected from: (a) the1st, 2nd, 4th, 5th and 6th lava flows.

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Fig. 5. (Continued) (b) the 7th–16th lava flows.

Fig. 5. (Continued) (c) the 17th–27th lava flows.

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Fig. 5. (Continued) (d) the 28th–37th lava flows of the Mandla lobe. Solid and open circles represent projections inthe lower and upper hemispheres, respectively.

Fig. 6. Representative Zijderveld plots showing the decay of magnetization using AFD and THD techniques forspecimens collected from the 1st, 2nd, 4th, 6th, 9th, 10th, 17th, 20th, 23rd, 25th, 26th, 28th 32nd and 33rd lavaflows (specimen identity along with the lava flow is given). Circles filled with black and grey colours representhorizontal (H) and vertical (V) components, respectively. All plots are shown in specimen coordinates system.

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63.15 + 1.15 and 64.98 + 1.19 Ma, respectively(Shrivastava et al. 2015). A reverse polarity isobtained for most of the lava flows. However, tran-sitional directions were also recorded for the major-ity of the lava flows, such as the 9th, 11th, 13th and14th lava flows of the Lapeta Bargi section; the 10thand 12th lava flows for the Jodhpur Pindari section;the 15th lava flow of the Mohtara section; and the21st lava flow of the Barkhera Guraiya section.However, the 7th, 12th and 27th flows of the Keon-chi Amarkantak, Karopani Pahar and Sahashrad-hara sections show magnetic anomalies (Fig. 8).Magnetic anomalies for the 9th–15th lava flows(Fig. 8) indicate a weakening of the magnetic fields,probably due to a polarity transition from normal toreversal during the deposition of these lava flows.The age of the 23rd lava flow is 60.23 + 0.57 Ma(Shrivastava et al. 2015) and represents reverse ano-malies. It correlates with the thick C26r, whichseems unmatched with the previously reported mag-netostratigraphic results for the Deccan Traps. The31st lava flow is correlated with the C28r, as its pla-teau age is 64.07 + 0.61 Ma. Further, the top ofthe lava flow (i.e. the 37th) in the Badargarh Moun-tain section represents a normal polarity that is

correlatable with C28n. It is also supported by Scho-bel et al. (2014), who stated that the Mandla lavaflows are younger than the Malwa lava flows. Anattempt has been made to establish a magnetostrati-graphic correlation of lava flows, primarily based onaltitude, from the eastern Deccan volcanic province(Fig. 9) and with the published magnetic polarityresults from the western and northern DeccanTraps (Malwa region). In the Mahabaleshwar andPune regions, normal polarity (C29n) was reported(Fig. 9) at an altitude of .1000–1400 m (Rao &Bhalla 1981; Courtillot et al. 1986; SreenivasaRao et al. 1985; Schobel et al. 2014). However, inthe Badargarh Mountain section, normal polaritywas also observed at an altitude of 1130 m. The nor-mal polarity (C30n) found at lower altitudes,.200–500 m, in the Pratapgarh, Mohw and Kun-dam areas (Fig. 9) is, perhaps, correlatable withthe normal polarity of lava flows recorded fromthe Jodhpur Pindrai, Bara Simla, Nagapahar, Dhan-wahi, Matka South, Matka North and Deori areas.The altitude-based correlation of lava packages forsuch a vast area seems to have inherent limitationsowing to the disorder in the stratigraphic heightsof the lava packages. Therefore, geochemical

Fig. 7. Magnetic polarity of lava flows plotted against altitude for A–B (Rukher–Sivni), B–C (Sivni–Amarkantak)and D–E (Nainpur–Shahpura) traverses. The order of superposition of lava flows is represented by numericnumbers and their normal, reverse and transitional magnetic polarities are shown with squares filled with black,white and grey, respectively.

similarities between lava flows from differentregions, available ages of lava flows and their corre-lation with the geomagnetic polarity timescale(GPTS) (Cande & Kent 1995; Gradstein et al.2012) have been considered as key criteria for mag-netostratigraphic correlations. Field criteria, such asthe presence of vesicles on lava-flow tops, breaks inslope, the presence of intertrappeans or bole beds,weathering patterns, the degree of lateritization,joint patterns and the nature of lava flows, havebeen used to identify an individual flow unit (seetable 1 in Pattanayak & Shrivastava 1999). Flow-by-flow palaeomagnetic results, when interpretedin conjunction with the physical and chemical strat-igraphy, have shown that the structural complexity

in the lava-flow sequence lies between Jabalpurand Dindori. The juxtaposition of the distinctmagnetic-polarity-bearing groups of lava flows hasbeen noticed in the Deori (flows 1–4 abetted againstflows 5–14) and Dindori areas. At Dindori andtowards its south, the distinct magnetic-polarity-bearing groups of lava packages (flows 15–27 andflows 28–37) are juxtaposed (Fig. 10). Field evi-dence, such as the missing lava flows near Deori,the presence of a hot-water spring at the southernend of the Nagapahar Fault, a straight linear seg-ment of the Narmada River that follows the faultplane near Dindori and the sudden topographicalbreaks near the Badargarh Amarkantak areas (emi-nences and depressions), support the idea of the

Fig. 8. Flow-wise magnetostratigraphic correlation of the present results with the published geochemical flowstratigraphy of Shrivastava et al. (2014) for the Mandla lobe. 40Ar/39Ar ages determined by Shrivastava et al.(2015) for the eight lava flows are marked with open black circles (within the stratigraphic column on the left-handside of the figure). The 40Ar/39Ar plateau ages for the Mandla lavas are shown by filled circles and +2s horizontalbars. The Mandla lavas correlate geochemically with the upper formations (Mahabaleshwar, Ambenali) found in theSW of the thick western sequence, whose ages (shown by open circles) were reported by (1) Chenet et al. (2007),mean of four analyses and (2) Widdowson et al. (2000), mean of four analyses; and with the Rajahmundry lavaflows in the SE, whose ages (3) are from Knight et al. (2003), mean of eight analyses. The main sequence of Deccanlava flows was erupted over a period of ,1 myr in two intense phases (Chenet et al. 2009) that bracket theCretaceous–Palaeogene boundary (K/PB) at approximately 66 Ma. Deccan activity began with a smaller phase 1eruption (not shown) close to 68 Ma. All reported ages were calculated relative to standard FCs (Fish Canyonsanidine) (28.201 Ma: Kuiper et al. 2008) for comparison with the GPTS of Gradstein et al. (2012).

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Fig. 9. Magnetostratigraphic correlation of the Mandla lavas (along the Sivni–Amarkantak (B–C) traverse) with the northern and southern Deccan Traps. Data from Schobelet al. (2014) for the northern Deccan Trap profiles, and from Rao & Bhalla (1981), Sreenivasa Rao et al. (1985) and Courtillot et al. (1986) for the southern Deccan Trapprofiles, were used in the present correlation. C/T Boundary, the Cretaceous–Tertiary boundary.

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presence of faults in this area (Fig. 10). The verticalshift of magnetically distinct lava packages at differ-ent sectors in the outlier contravenes the idea of asmall regional dip (Vandamme et al. 1991; Van-damme & Courtillot 1992): thus, favouring the pres-ence of four NE–SW-trending post-Deccan faults.Physical stratigraphic, petrographical (Shrivastava& Pattanayak 2002; Shrivastava & Ahmad 2005),major oxide (see fig. 4a, c and table 9 in Pattanayak& Shrivastava 1999), trace elemental and isotopiccompositional (see figs 3i–iv, 4, 5a–c, 6a–c andtables 3, 4 & 5 in Shrivastava et al. 2014) breaksfor abetted lava flows match with the presently doc-umented palaeomagnetic polarity reversals. Whenthese breaks are traced out from section to section,they exhibit shift in heights of approximately300 m. near the Kundam Deori and Dindori areas.Present magnetic chron reversal heights, when con-sidered in conjunction with field, petrographical,chemical, geophysical and seismotectonic models(see figs 5, 6 & 8 in Shrivastava & Pattanayak2002), are supportive of the findings that four faultstrending NE–SW are present in the Mandla lobe(Figs 2 & 10). Further, present palaeomagneticreversals indicate a significant vertical shift of the5th lava flow in adjacent sections, suggesting thepresence of a NE–SW-trending normal fault atNagapahar that coincides with the fault (see fig. 1in Shrivastava et al. 1999) in the south of Jabalpur,

as was also revealed by reduced travel times in deepseismic-sounding (DSS) studies (Kaila et al. 1989).Tectonic activity is also inferred near the MatkaNorth and Deori sections, where the 1st, 2nd and3rd lava flows abetted against lava flows of theMatka South section. Further to the east of Deori,major topographical breaks were observed at theBarkhera Guraiya section, where, Poladpur- andBushe-like lava flows (i.e. the 33rd, 27th, 26th,25th, 23rd and 18th) have been found at consi-derably higher altitudes. A DSS crustal profile sug-gests that the Jabalpur Mandla crustal block is ahorst-type structure (see fig. 5 in Shrivastava &Pattanayak 2002). The Narmada–Son Lineamentappears to represent a weak zone in the Indian con-tinental crust. The two deep-seated faults that runfrom the surface, cutting the Moho, are evident(Kaila 1988) from the Hirapur–Mandla DSS pro-file to the north of Jabalpur. Kaila (1988) inferreda near-surface fault to the south of Jabalpur. Rajen-dran & Rajendran (1998, 1999) reported rift pillowsin the Narmada Fault System (NFS). Mahadevan &Subbarao (1999), however, stressed that rift pillowsare absent below the Narmada South Lineament:therefore, lower crustal underplating led to thePrecambrian faults, and numerous feeder dykes pro-vided the tectonic milieu for the stress concen-tration. Kayal (2000) clearly indicated that theNarmada South Fault to the south of Jabalpur

Fig. 10. Abutment of lava flows of different magnetic polarities when plotted over lithological sections along theB–C traverse, which indicate the presence of four normal post-Deccan faults at the Nagapahar, Kundam Deori,Dindori and Badargarh Amarkantak areas.

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activated at the crust–mantle depth by compression.The Hirapur–Mandla DSS profile (Kaila 1988)unveiled a structural configuration across the Nar-mada Rift System. The high gravity anomalybetween Jabalpur and Mandla is attributed to anigneous intrusion in the upper crust or density anom-alies in the upper mantle (Kaila et al. 1989; Verma& Banerjee 1992).

Palaeomagnetic reversals found in the Mandlalava flows correspond to a thick reverse chronof the Western Ghats and the northern DeccanTraps. Athavale (1970) pointed out that, in theMandla region, the boundary between the mainreversed basaltic sequence and the overlying normalsequence is located at 350 m above the average alti-tude of 600 and 425 m asl (above sea level), which isalso where it was observed in the western DeccanVolcanic Province. Interestingly, the existence ofanother reversal-normal or relatively rapid pilingof an additional 350 m of lava flows at Amarkantakmight be responsible for such a polarity bias. How-ever, the fact that the thickness of the lava packagesbetween the Lameta beds and at Amarkantak greatlyresemble those observed near Jabalpur, outline thatthe Amarkantak region was plausibly uplifted. Hor-izontal correlations are particularly difficult in thewest of the traverse, especially between Jabalpurand Kundam. However, it has, in particular, beennoticed in the palaeomagnetic investigations thatsimilar lava flows (i.e. the 1st, 4th, 6th and 26th)show the same polarity at different localities andaltitude (Fig. 3b, c): thus, strengthening the lava-flow stratigraphy of Pattanayak & Shrivastava(1999) and Shrivastava et al. (2014). Using palaeo-magnetic measurements of the flows near Jabalpur,Kundam and Lakhnadon, and considering all avail-able data, Vandamme & Courtillot (1992) sug-gested two possibilities: (i) the existence of twomajor faults with vertical offsets of about 100 m;or (ii) the presence of a synform structure of smoothcylindrical symmetry. Verma & Banerjee (1992)stated that this area lies within the tectonic frame-work of the Narmada–Son Lineament.

Shrivastava et al. (2014) have established thatthe Mandla lavas are chemically and isotopicallysimilar to the Poladpur, Ambenali and Mahaba-leshwar Formation lavas of the Western Ghats,and therefore should be considered as a extensionof such lavas in the Mandla region: therefore, theexistence of Mahabaleshwar-like, Ambenali-likePoladpur-like and Bushe-like lavas should benoted in this area. The majority of the lava flowsin this area have an affinity to the Poladpur Forma-tion and are widespread with a substantial geograph-ical extent. Northeastern Deccan lava flows are inthe same stratigraphic order as the SW DeccanTraps (i.e. Bushe, Poladpur, Ambenali and Maha-bleshwar.) However, in the Khajurwar and Karanjia

sections, the Bushe-like lava flows are sandwichedbetween the Poladpur-like flows, which do not fol-low the same stratigraphic order. Mahoney et al.(2000) suggested that Bushe-like lava flows havepossibly had local feeder vents. These lava flowsmight have been derived from some local sources.The 1st, 2nd and 3rd lava flows show correlationwith the Mahabaleshwar Formation and occur at alower stratigraphic level (Fig. 3b). This means thatthe younger lava flows are at a lower stratigraphicheight, indicating tectonic disturbance (Fig. 2 &10). These lava flows show a shift in stratigraphicheight of approximately 150 m near Nagapahar,and around 300 m near the Kundam Deori and Din-dori areas. Further, Mandla lava flows have beencorrelated with the lava flows of the WesternGhats in order to resolve its possible correlationwithin the stratigraphic framework of the mainDVP. Present magnetostratigraphic results of theMandla lobe (Fig. 11) were also compared with thegeochemical logs of Devey & Lightfoot (1986) andthe magnetostratigraphy in the south of the WesternGhats (e.g. Wensink 1973). At higher altitudes in theMandla lobe, mainly Mahabaleswar-like lava flowsshow a normal polarity. The transitional lava-flowunits at lower altitudes (of Mahabaleswar-likelava) in the Mandla lava pile of the eastern DVPwere emplaced during reverse polarity, similar tothat proposed by Chenet et al. (2008) for the Maha-baleshwar Poladpur Ghat section of the westernDeccan province. Transitional directions in theMahabaleswar Formation were found in most ofthe sections of the western Deccan Traps, as wellin the Mandla lobe (Fig. 11). Wensink & Klootwijk(1971) stated that the magnetic polarity of the Maha-baleswar Formation matches well with the magneticpolarity directions of the Mandla lobe. The presentmagnetic polarity directions at higher altitudes(1090–1150 m) are also correlatable with the palae-omagnetic results of Chenet et al. (2008) from theMahabaleshwar Poladpur Ghat Section (Fig. 11).In these locations, the Mahabaleshwar PoladpurGhat section and the Mandla lobe have a similarmagnetic polarity (normal) and lava flows are geo-chemically correlatable (e.g. Mahabaleshwar-likelava flows in the Mandla area). However, in the Man-dla region, normal polarity at higher altitudes is con-fined to only the topmost lava flows in BadargarhMountain section. Further, it has been found thatalmost all the previous magnetostatigraphic studiesunanimously indicated that the major portion of theAmbenali and Poladpur formations erupted in thereverse polarity chron, and no normal polarity lavaflows were recorded at the lowermost altitudes.Most of the magnetostratigraphic sections are con-sistent with the normal–reverse–normal modeland many contain only the upper part of the sequencewith the reverse-normal transition. Vandamme et al.

(1991) proposed a further five locations (e.g. Kan-dala, Mahableswar, Kolhapur, Phonda and Amboli)in the Western Ghats where normal/reverse loca-tions seemed to be almost identical (Fig. 11). Chenetet al. (2008) found reversed polarity for the Poladpurand Ambenali formations, as well as for the lower-most flows of the Mahabaleswar Formation. Morerecently, Jay et al. (2009) reported that the 29r–29n palaeomagnetic reversal is found at the base ofthe Mahabaleshwar Formation in the five mostsoutherly traverses.

In order to exact a magnetostratigraphic cor-relation of the Deccan Traps, it is necessary toclosely examine the magnetostratigraphic timescalebetween 60 and 67 Ma from the published GPTSof Gradstein et al. (2012). Further, identificationof C30n–C29r is most important for the magneto-stratigraphic correlation, as the major part of the2000 m-thick Western Ghats (e.g. Vandamme &Courtillot 1992) lava flows were erupted within

the reversed C29r (700 kyr) duration (Gradsteinet al. 2012). The available ages for the strati-graphically controlled, approximately 900 m-thickMandla lobe enable their correlation with thegeomagnetic polarity timescale (Gradstein et al.2012). Of late, Shrivastava et al. (2015) have notdetected any statistically significant age differencefrom the bottom to the top (range 63–65 Ma) ofthe lava flows for the composite Mandla section,and have calculated a weighted mean age of63.9 + 0.3 Ma. These lava flows are significantlyyounger than the majority of the main Deccan vol-canic activity documented from the Western Ghats(67–65 Ma). Recent 40Ar/39Ar ages (Schobelet al. 2014) reported for the western and southernrims of the Malwa Plateau are 67.12 + 0.44 Ma,which suggests that the Malwa lavas stated toerupt during C30n. Based on these age determina-tions, it is concluded that the Mandla lava flows(63–65 Ma) are younger in age compared to the

Fig. 11. Magnetostratigraphic, together with chemical stratigraphic, correlations (shown with dash lines) of theMandla lava flows with the well-established magnetostratigraphy and chemical stratigraphy of Wensink &Klootwijk (1971), Wensink (1973) and Chenet et al. (2008).

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Malwa lava flows (67.12 Ma) in the central DeccanTraps. Magnetic polarity results for the 1st, 4th,11th, 23rd, 27th, 31st and 37th lava flows fromMandla area (Fig. 8), when correlated with theirrespective 40Ar/39Ar ages (Shrivastava et al.2015) and the GPTS (Cande & Kent 1995; Grad-stein et al. 2012), suggest that a new magneto-stratigraphy configuration is resolved, coincidentalwith C29n–C28r–C28n. However, these magneto-stratigraphic results (Fig. 8) are younger thanthe previously reported magnetic configurationC30n–C29r–C29n for the entire Deccan Traps(Vandamme & Courtillot 1992). The present nor-mal–reverse–normal configuration of the Mandlalobe suggests that these flows are significantly youn-ger than the majority of the main Deccan Trapslava flows documented from the Western Ghats(67–65 Ma).

Conclusion

† The lava pile in the Mandla lobe is structurallycomplex as four post-Deccan normal faultsnear the Nagapahar, Kundam Deori, Dindori,and the Badargarh Mountain Amarkantak areasare present, across which offsets of approxi-mately 150 m have been measured.

† To some extent, the magnetic polarity bias (tran-sitional direction) found in the present studymight be the result of the combined effects oftectonic disturbance in the area, lesser availabil-ity of the unaltered lava flows and their altitude-based correlation.

† Considering the highly wavy palaeo-surfacesand faulting due to post-Deccan isostatic adjust-ments over a distance of more than about 800 kmalong the strike length, there is the possibilityof disorder in the stratigraphic heights of thelava packages, which, therefore, constrains thealtitude-based correlation of lava packagesover such a vast area.

† The magnetostratigraphic correlation of theMandla lava flows with that of the main DVPis mainly based either on: (a) the magnetic polar-ity correlation as a function of altitude; or (b)the available 40Ar/39Ar ages of the Mandlalava flows (Shrivastava et al. 2015). Previousaltitude-based correlation of the Mandla lavasfits into the normal–reverse–normal model(C30n–C29r–C29n) of Courtillot et al. (1986)and Vandamme et al. (1991). But, a later corre-lation model based solely on new 40Ar/39Arages from Shrivastava et al. (2015) fits wellwith the GPTS (Cande & Kent 1995; Gradsteinet al. 2012), pointing to the entire Mandlalava packages having been laid down in theC29n–C28r–C28n chrons. This later correlation

is considered to be more reliable as it lies wellwithin the GPTS of Gradstein et al. (2012).

† The Mandla lavas erupted at different timescompared to the SW part of the province and,in view of present palaeomagnetic results, itis suggested that the Mandla lavas eruptedfrom different feeder system(s). The present nor-mal–reversal–normal configuration of the Man-dla lavas suggests that they are significantlyyounger than the majority of the main DVPsequences documented from the Western Ghats(67–65 Ma).

† Overall, the normal mean direction of the Man-dla lava flows was isolated and the VGP positionwas derived as a palaeolatitude of 48.078 N and apalaeolongitude of 282.68 E. Based on a compar-ison of VGP derived from the present study withthat of the Deccan Super Pole, it is inferred thatthe entire Deccan lava packages were eruptedover short duration.

We acknowledge Department of Science of Technology,Govenment of India, New Delhi for financial supportthrough Research Project Grant No. ESS/16/286/2006.Authors acknowledge volume editor and anonymous re-viewers for valuable comments and suggestions.

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