Interpretation of stratigraphy and structure of the ...

Interpretation of stratigraphy and structureof the Neoarchaean Dharwar Supergroup of rocksin Chitradurga area, Dharwar Craton

ABHINABA ROY1, H M RAMACHANDRA

2 and SILADITYA SENGUPTA3,*

1Formerly, Geological Survey of India, Kolkata, India.

2Formerly, Geological Survey of India, Bengaluru, India.3Geological Survey of India, DGCO, New Delhi, India.*Corresponding author. e-mail: [email protected]

MS received 7 August 2019; revised 15 November 2019; accepted 25 November 2019

The Neoarchaean Dharwar Supergroup of rocks in the Chitradurga area unconformably overlie theMesoarchaean Peninsular Gneissic Complex in the west and are tectonically juxtaposed with Jav-agondanahalli Schist Belt in the east. The rocks of the supergroup have been divided into olderBababudan and younger Chitradurga Groups. We support the recent division of the Bababudan rocksinto a lower conglomerate–sandstone facies association and an upper sandstone–mudstone facies asso-ciation indicating tidal Cat depositional environment. The Talya Conglomerate sequence at the base ofthe Chitradurga Group is inferred to represent a fault-controlled debris Cow deposit. The basin opensout to the east where sedimentation and volcanism took place on an uneven basement surface. TheVanivilas and Ingaldhal Formations likely represent contemporaneous and overlapping sequencesindicative of facies variation in space. The KM Kere Conglomerate at the base of the Hiriyur For-mation represents a facies series comprising a sequence of volcanic–pyroclastic–volcaniclastic–epiclastassociation. We propose a four-fold stratigraphic classiBcation with introduction of a new ‘Kantara-manahalli Formation’, placed above the Vanivilas and Ingaldhal Formations and below the HiriyurFormation. The interpretation of multiple deformed nature of Dharwar Supergroup of rocks and thedominance of the second deformation (D2) is supported. The initial irregularities on basement surfaceand the F1 folds have significant role in fold superposition and outcrop patterns. The intra- and inter-formational ductile shear zones have dominant sinistral transcurrent component. Structural studies areconclusive of simple shear (D2b) superposed on intense pure shear (D2a) indicative of an overalltranspressional type of horizontal tectonics.

Keywords. Chitradurga Schist Belt; Dharwar Craton, India; Neoarchaean; structure; stratigraphy.

1. Introduction

The western part of the Archaean Dharwar Craton(generally known as the Western Dharwar Cratonor WDC) in south India has received considerableattention of Precambrian geologists over the lastseveral decades. BrieCy, the Dharwar craton is

believed to comprise of two contrasting cratonicblocks, the Western Dharwar Craton (WDC) andthe Eastern Dharwar Craton (EDC) having dif-ferent greenstone belts characteristics, metamor-phic signature, age data and nature of the gneissesand granitoids and the two are separated by eitherthe ductile shear zone, east of the Chitradurga Belt

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or the Closepet Granite (Swami Nath et al. 1976;Kaila et al. 1979; Drury and Holt 1980; Rollinsonet al. 1981; Swami Nath and Ramakrishnan 1981;Chadwick et al. 1992, 2000, 2007; Jayananda et al.2000; Ramakrishnan and Vaidyanadhan 2008;Rama Rao et al. 2015). On the contrary, Maibamet al. (2011), based on their study of zircon Pb–Pbage data of metasedimentary rocks from bothWDC and EDC challenged the idea of contrastingevolutionary trends in the two crustal blocks andconsidered that both WDC and EDC evolved as asingle terrain. The 3.4–3.1 Ga old PGC and olderSargur Complex rocks are more abundantlyexposed in the WDC and formed the basement fordeposition of Dharwar supracrustals. Contempo-rary evolutionary models for different componentsof the craton based on abundant geochemical andgeochronological data have been presented byJayananda et al. (2013, 2015).In brief, the WDC comprises 3.4–3.1 Ga old

Archaean type TTG gneisses known as PeninsularGneiss Complex (PGC) that contain mappable tosmall scale enclaves of older supracrustals groupedunder the Sargur Schist Complex. These are believedto have formed the basement for deposition of theNeoarchaean Dharwar Supergroup, a granite–green-stone association that evolved between 3.0 and 2.6Ga. The Dharwar Supergroup has historically beendivided into an older BabubadanGroup and youngerChitradurga Group that are intruded by 2.61 Gaintrusive granites (Jayananda et al. 2006).The Chitradurga Schist Belt (CSB, or Chi-

tradurga–Gadag Superbelt, Ramakrishnan andVaidyanadhan 2008) is an important component ofthe WDC and as deBned in this paper, refers to theDharwar Supergroup of rocks forming a N–S toNNW–SSE trending granite–greenstone beltextending over a length of 400 km from Gadag in thenorth to Srirangapatna in the south (Bgure 1). TheCSB shares a tectonic contact on its eastern marginwith the Javagondanahalli (JGHalli) belt having 2.74Ga Sm–Nd age of its amphibolite unit (Jayanandaet al. 2011; Sengupta and Roy 2012). The westernmargin of the CSB is marked by well-developedbasement cover unconformable relationship betweenthe BababudanGroup of the CSB and the PeninsularGneissic Complex attested by the presence of quartz-pebble conglomerate (SwamiNath et al. 1976). Abovethis unconformity, a stable, platformal sequence ofthe Bababudan Group forming the lower part of theCSB has been deposited and is unconformably suc-ceeded by rocks of the younger Chitradurga Group inthe east (Srinivasan and Ojakangas 1986).

This paper presents a review of the existing data,presentation of new observations and discussion ofcertain aspects of stratigraphy and structure of theCSB in the Chitradurga area (study area). This areaoccupies the central part of the N–S to NNW–SSEtrending,*400 km long CSB. The CSB in the studyarea has a maximum width of about 40 km andexposes the entire stratigraphic succession of theDharwar Supergroup comprising the older Bababu-dan and younger ChitradurgaGroups of rocks. It alsocontains the regional scale fold structure knownas the‘ChitradurgaFold’ and provides excellent sections forstudy of lithological characters, mesoscopic folds andfoliations developed in different types of rocks of theDharwar Supergroup. The discussion on certainaspects of the CSB is augmented by unpublished dataof the authors on the above aspects recorded fromcritical Beld areas. The paper in particular includes adiscussion of structures in the Talya Conglomeratesequence at the base of theChitradurgaGroup and itsimportance in tectonic evolution of the DharwarSupergroup; stratigraphic character of the Kuru-maradikere (KMKere)Conglomerate sequence at thebase of the Hiriyur Formation of the ChitradurgaGroup, and a discussion on its volcaniclastic nature;proposal for a new formation, the Kantaramanahalli(KRHalli) Formation within the Chitradurga Groupbased on interpretation of geological map and struc-tural data; and the role of shear zones marginal to theCSB in its evolution.This paper does not elaborate onthe PGC and Sargur-type supracrustal enclaves(Ghattihosahalli belt) occurring as the basement tothe west of Chitradurga Belt, nevertheless, it can berecorded here that we Bnd that the GhattihosahalliBelt is a shear belt and the major D2 sinistral shearaAecting the western margin of the Chitradurga Beltalso aAected the older PGC and Ghattihosahalli Belt(will be discussed elsewhere separately). The base-ment nature of the PGC in relation to DharwarSupergroup of rocks can be observed at a few sectionsmainly in the western margin of CSB, withinthe antiformal cores of the Chitradurga Fold andSriranakatte Dome.

2. Lithological and depositional charactersof the Dharwar Supergroup of rocksin the study area

The Dharwar Supergroup of rocks in the study areainclude those belonging to Babudan and Chi-tradurga Groups and details of lithological com-ponents of the two groups are given in Chadwick

98 Page 2 of 21 J. Earth Syst. Sci. (2020) 129:98

et al. (1981) and Sheshadri et al. (1981) and Srini-vasan and Ojakangas (1986). The details given inthese references are only brieCy reproduced in thefollowing sections augmented by data from selectedrecent publications.

2.1 The Bababudan Group

The Bababudan Group of rocks in its entirety isexposed only in the western part (Bgure 1) in alinearly disposed NNW–SSE trending belt, detaileddescription of lithological assemblage has beengiven in Chadwick et al. (1981) and in Sheshadriet al. (1981). These are deposited unconformablyover basement Peninsular Gneisses and rocks ofthe Sargur Complex (Ghattihosahalli Belt). Thebasal unconformity is represented by the Ner-alakatte oligomictic conglomerate that grades intoquartzite of quartz-arenitic composition. The con-glomerate is followed in the younging direction(eastwards) successively by a sequence of amyg-dular metabasalt, quartzite (mainly quartz-areniticand very rarely arkosic), metabasalt, minor bandsof metaultramaBc, phyllite and muscovite-sericiteschist, minor gabbro and sheets of quartzite (alsomainly quartz-arenite composition). The abovesequence of rocks is delimited in the east by theTalya conglomerate sequence forming the base ofthe Chitradurga Group. It is considered that thecontact between the Bababudan and ChitradurgaGroups represents a syn-depositional fault respon-sible for the upliftment of Bababudan Group ofrocks causing truncation of its deposition to furthereast. The consideration of a fault controlled depo-sition of the Talya Conglomerate is evidenced bythe facts that (i) Talya conglomerate sequence doesnot simply overlie the underlying BababudanGroup of rocks but it transects the lower sequenceat a low angle and Bnally abuts against the base-ment gneiss in the north and (ii) large boulders ([2m) of quartzites of Bababudan Group occur asclasts within the Talya Conglomerate whichimplies that the Bababudan rocks have alreadyconsolidated and acted as a provenance for rapiddeposition of such an ill sorted material (furtherdetailed discussion in 2.2.1.1). This fault has sub-sequently been reactivated into a ductile shearzone during later deformation since for a largestrike length the conglomerate is found sheared.It has recently been shown (Bhattacharya et al.

2015) that the sedimentary succession of theBababudan Group in the study area can be placed in

two distinct facies associations; a conglomer-ate–sandstone facies association at the base and asandstone–mudstone facies association in the upperpart of the succession. The lower conglomer-ate–sandstone facies association comprises oligomic-tic quartz–pebble conglomerate, pebbly sandstoneand conglomerate–sandstone alternations collec-tively termed the Neralakatte Conglomerate(Bgure 2a). It has been interpreted that this faciesassociation represents subaerial to subaqueous mass-Cow deposits and hyper-concentrated subaqueoussediment gravity-Cow deposits in an alluvial fan-fandelta setting. The upper sandstone–mudstoneassociation includes sharp based, mature sandstone,heterolithic sandstone–mudstone and mudstone andthe facies architecture strongly resembles a gradedBning-upward sequence of modern tidal Cat. It hasalso been inferred that the above rocks represent theoldest signature of open marine tidal sedimentationrecorded from Precambrian in peninsular India. Royand Bhattacharya (2014) and our unpublished datashow that the Neralakatte Conglomerate is charac-terized by a consistent N–S to NNW–SSE strikingsubvertical composite (Sd1/Sd2) foliation, a conspic-uous low plunging (5–20� towards 0�–342�) pebbleelongation and well developed stretching lineations.The above structures are superimposed upon by alater shear-related deformation (D2b) as evident fromthe development of shear bands superposed on earlyfoliations. Themap pattern of the BababudanGroupof rocks along with that of the overlying Talya con-glomerate sequenceof theChitradurgaGroupdisplayan overall S-shaped large scale fold structure havingsubvertical NNW striking axial plane with low tomoderate plunge.The Neralakatte Conglomerate is overlain by an

amygdular metabasalt unit now represented byschistose amphibolite. This amphibolite unitdeBnes the boundary between the two sedimentaryfacies sequences of the Bababudan Group describedabove. The amygdules in the metabasalt show anassemblage of quartz with or withour calcite andhave acted as good strain markers as they are Cat-tened on the schistosity plane (S2a). The mineralassemblage in the metabasalt includes amphibole(Fe-pargasitic hornblende), plagioclase (oligoclase)and chlorite (ripidolite) with minor amounts ofsphene, rutile, epidote, albite, carbonate and opa-que minerals. Relict clinopyroxenes (augite) areoccasionally preserved within amphiboles. Horn-blende occurs both in the groundmass and as coarseporphyroblasts, whose growth outlasted S2 foliationdevelopment (Bgure 2b). Earlier foliation (S1) is

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very strongly crenulated and mostly transposed tolater foliation (S2a) representing the subverticalNNW striking regional schistosity of the fold belt.The mineral assemblages indicate lower amphibo-lite facies metamorphism.A few bands of metaultramaBcs and metagabbro

occur possibly as conformable intrusives ortectonically emplaced bodies within the uppersandstone–mud facies rocks. The metaultra-maBcs show a metamorphic mineral assemblageincluding porphyroblasts of anthophyllite (+/–cummingtonite) Fe–Mg amphibole and talc set in

a matrix of actinolite (-tremolite), pycnochlorite,ilmenite, rutile, sphene and chromiferous mag-netite (Bgure 2c). Clinopyroxene (diopsidicaugite) occurs as occasional relics withinamphibole. Microscopic structures deBne threestrong fabric elements; an early schistosity (S1),transposed schistosity (S2a) and strong shearbands (Sb), the latter largely overprinting theearlier fabrics (Bgure 2d and e). The porphy-roblast formation outlasted S2a, but predates theshearing event. The adjoining quartzite alsoshows evidences of shearing. Thus the

Figure 1. Geological map of Chitradurga Schist Belt marking the study area and disposition of different lithostratigraphic units(after GSI).


Figure 2. (a) Two sets of deformation fabric (Sd1 and Sd2) at acute angle in Neralakatte quartz pebble Conglomerate ofBababudan Group. (b) Hornblende porphyroblast, whose growth outlasted Sd2 foliation in amphibolite of Bababudan Group.(c) Microsection showing porphyroblast-cum-porphyroclasts of anthophyllite/cummingtonite in a matrix of actinolite(-tremolite), pycnochlorite, ilmenite, rutile, sphene and chromiferous magnetite in metaultramaBc rock of Bababudan Group.(d) Microsection showing shear fabric (Sd2b) superposing on an Sd2a crenulation cleavage in metaultramaBc rock of BababudanGroup. (e) Microsection showing well developed CS fabrics in sheared metabasalt of Bababudan Group. (f) Conglomerate-greywacke couplet within Talya Conglomerate having bedding deBned by alternate clast-rich and clast-free zones, at the basalpart of Chitradurga Group.


Figure 2. (g) Rounded ellipsoidal Granitoid cobble and tabular quartzite boulder with variably sized other clasts in matrix-supported Talya Conglomerate; note that the large tabular boulder of quartzite got sinistrally folded along with the matrix.(h) Microsection showing very well developed Sd2 crenulation cleavage in the matrix of Talya Conglomerate at the base ofChitradurga Group. (i) Ductile shearing (d2b) indicated by development of shear bands over planes of Cattening deformation(d2a). (j) Asymmetric elongated lensoid quartzite clasts in Talya Conglomerate developed due to sinistral shearing; yellow lines:S2 cleavage, black lines: long axis of the elongated clasts and blue lines: orientation of shear band. (k) Sketch showing eAect ofCattening superposed by sinistral shearing in Talya Conglomerate resulting in sinistral folding of the schistosity (S1kS2) andasymmetric bending of long axes of the pebbles having tapering ends and development of shear bands (Sb). (l) Sinistralasymmetric mesoscopic folds in matrix of Talya Conglomerate.


maBc–ultramaBc assemblage shares these defor-mation structures with the associated sedimentsand may represent shallow to moderate crustallevel emplacement of a differentiated originaltholeiitic liquid.

2.2 The Chitradurga Group

The Chitradurga Group of rocks is depositedunconformably over the Bababudan Group of rocksin an unbroken easterly succession in the same area(Bgure 1). The basal unconformity is represented bythe Talya polymict conglomerate that is followedupwards in succession by other members of theVanivilas, Ingaldhal and Hiriyur Formations. Asmentioned earlier, lithological details of rock typesconstituting the above formations are given inSheshadri et al. (1981) and Chadwick et al. (1981) andonly relevant unpublished data of the authors andinterpretations are included in the following sections.

2.2.1 Vanivilas Formation

2.2.1.1 Talya Conglomerate: The Talya Conglo-merate is a matrix supported conglomerate wherethe clasts consist mainly of pebbles and boulders ofgranite, quartzite and vein quartz together withminor amounts of BIF, basalt and shale fragmentsand the matrix is made up of abundant feldsparalong with chlorite, biotite and quartz (Bgure 2g).The quartzite boulders are as big asmore than 2m inlength. The relatively less altered nature of feldspargrains and lack of sorting may suggest rapid depo-sition in a fault-controlled basin in a cold climaticenvironment.The Talya Conglomerate comprises a sequence of

conglomerate–greywacke and greywacke mudstonealternations with the conglomerate being up to 30m thick and unsorted in nature. It forms a coupletwith a 40 m thick greywacke showing diffusedcontact (Roy et al. 2012; Bhattacharyya et al.2015) (Bgure 2f). In the thickest part of the sedi-mentary succession, about 28 such couplets havebeen identiBed with predictable thinning and Bningupward trend (e.g., Roy et al. 2012; Bhattacharyyaet al. 2015). Such conglomerate–greywacke cou-plets have been interpreted to be deposits formedby an energy dissipating mass Cow. Developmentof such thinning and Bning upward succession mayimply deposition in a fault-controlled sinkingbasin. Chadwick et al. (1992) interpreted thepolymict conglomerate to have been deposited in

alluvial or shallow-water fans and as debris Cows,whereas the associated heteroliths were possiblydeposited by turbidity currents emerging fromshallow marine fans. A few prismatic clasts in theconglomerates, well within the bed, show near ver-tical orientation with deformed sedimentary layers inthe matrix at the base and at the top of the clasts.Rarely some of the clasts are striated on the

surface (this study; Ojakangas et al. 2014; Roy andBhattacharya 2014; Bhattacharya et al. 2015). Suchorientation of clasts with deformed laminations attheir base has been interpreted as dropstones rep-resenting glacial environment (Ojakangas et al.2014). The clasts show all evidences of reworkingwhatever might have been the provenance andenvironment of deposition. In glaciomarine con-glomerate, the striations on clasts/dropstones resultfrom the shear movement of ice sheets, and hencethe population of such striated pebbles/clasts areexpected to be abundant. But in case of Talya con-glomerate such a feature is scarce and negligible. Onthe contrary, the possibility of a fan-delta to sub-marine conglomerate status for this horizon mightbe more likely. Surlyk (1984) has explained con-glomerate deposition along scarps in a tilted faultblock situation (Bgure 5). The steep slope or thescarp surface is possibly generated by basin marginblock fauting. Upward Bning basin Bll as discussedby Bhattacharyya et al. (2015) further substantiatesuch an interpretation (cf. Postma 1984; EthridgeandWestcott 1984). The conglomerate sequence hasbeen subjected to intense polyphase deformationand low grade greenschist facies metamorphism(Bgure 2h). In view of strong multiphase deforma-tion aAecting the Talya sedimentary succession it isdifBcult, if not impossible, to reconstruct the originalbedding vs. pebble/clast orientation.Dropstones areout-sized clasts, which occur near the top of the bedwith deformed striations at their base. In the presentcase, the clasts occur well inside the bed and thedeformed laminations at their base are of tectono-metamorphic origin. From the above considerationsthe glacial nature of some of the clasts cannot betaken as conclusive.Following strong Cattening deformations (D1 and

D2a), the conglomerate sequence has been subjectedto ductile shearing (D2b) and thus represents amoderate to high strain zone (Bgure 2i, j, k) showingconsistent sinistral asymmetric folding (Bgure 2kand l). This shear zone development along the TalyaConglomerate horizon is congruous with the overalldeformation pattern of the schist belt. Localizationof simple shear strain is possibly inCuenced by


extreme heterogeneity in the composition andtexture of the conglomerate and its location at or closeto a basin margin pre-existing fault/discontinuity.While the soft matrix accommodated most of thestrain, the spheroidal/ellipsoidal clasts were sub-jected to external rotational strain with only little orno internal crystal-plastic strain. This is very evi-dent from variable orientation of the clasts on astrongly deformed matrix.

2.2.1.2 Other members of the Vanivilas Forma-tion: The Talya Conglomerate is followed upwardsin the east by other members of the VanivilasFormation. These include shallow marine depositsof quartzite, carbonate, manganiferous chert andphyllite and deeper marine facies of BIF and minorbasaltic volcanics. There are rare reports of a pebblyhorizon associated with quartzite overlying thereworked basement gneiss in this formation from theSiranakatte dome area (e.g., Naha et al. 1995). Thebasal quartzite is exposed also in the northern andnorthwestern parts of theCSBoverlying the gneissicbasement near Kandavadi area. The rocks of theVanivilas Formation were deposited over a highlyuneven erosional surface of the basement granitegneiss as evident from the disposition of rocks of theVanivilas Formation in the Siranakatte area (Nahaet al. 1995). The Siranakatte dome is an example of abasement highwhich remained exposed above the sealevel during the deposition of the overlying quartzite,pebbly sandstone, dolomitic carbonate and BIF unitsof the Vanivilas Formation. It is quite likely that theTalya Conglomerate sequence restricted to the west-ern part of the CSB in Chitradurga area is contem-poranious with the shallow water quartzite-carbonitesequence in the central part of the Vanivilas Forma-tion, the former being deposited as a fault-controlleddebris Cow deposit with the latter representing astable facies association deposited over a gneissicbasement.

2.2.2 Ingaldhal Formation

The IngaldhalFormation is exposed in the inner partof the ‘Chitradurga Fold’ in the central part of thestudy area comprising mainly maBc volcanic rockswith subordinate intermediate and felsic varieties,minor argillites and marker BIF horizons. Pyro-clastic volcanics in the sequence include volcanicbreccias, agglomerate, lapilli tuA and tuA. Varioliticand spherulitic structures occur in some locations

indicative of mixing between different basic magmacomponents. Pillowed basalts constitute an impor-tant component of the sequence. A thick layer ofoccasionally amygdular metabasalt (known in ear-lier literature as ‘Jogimaradi Traps’) occurs withinsequence intrudedby small veins of the younger 2605Ma old Chitradurga Granite. These are interlayeredwith several Banded Iron Formation, bands the roleof which in the stratigraphic interpretation is dis-cussed in a later section of this paper. The rocks ofthe volcanic sequence and associated sediments aremetamorphosed and display schistose fabric withvariable intensity.Detailed observations of these rocksshow their structural conformity with those reportedfromwell studied sections elsewhere in the study area.

2.2.3 Hiriyur Formation

The Ingaldhal Formation is overlain in the east bywhatwas originally described as a thick sedimentarypile interspersed with minor volcanics (Sheshadriet al. 1981), with the sedimentary pile representedby a greywacke–argillite suite of rocks containingseveral interbeds of polymict conglomerate and BIFintercalations. The associated volcanics and pyro-clastics include those dominantly of basic composi-tionwithminor acidic component.Our observationsshow that many of the greywacke–argillites in factare volcanic or volcaniclastic in nature, the originalcharacteristic features of which are mostly obliter-ated due to later deformation and greenschist faciesmetamorphism.The basal part of the Hiriyur Formation as

described originally by Sheshadri et al. (1981) isconstituted by the major polymict conglomeratemember termed the KM Kere conglomerate thatseparates rocks of the older Ingaldhal Formation tothe west from those of the Hiriyur Formation in theeast. Our recent studies show that the KM Kereconglomerate in fact represents a very importantvolcanic-pyroclastic-epiclastic horizon in the CSBin the study area and deserves a formational statusin the stratigraphy. A detailed description of thisrock unit and its stratigraphic status are discussedbelow.

2.2.4 Facies series nature of the KM KereConglomerate sequence of the HiriyurFormation

The KM Kere Conglomerate sequence deBnesthe disconformity at the base of the Hiriyur


Formation overlying the Ingaldhal Formation of theChitradurga Group in the stratigraphic scheme pro-posed by Sheshadri et al. (1981). These authors haveshown that the conglomerate unit of the sequencecontains generally rounded pebbles ranging in sizefrom a fewmm to about 20 cm, most being in the 4–6cm range. The clasts include those of massive andschistose lavas, banded iron formation, black chert,striped jasper, granite, quartz-sericite schist, rhyo-lite,metagabbro and vein quartz that are supposed tohave been derived from the lower Ingaldhal Forma-tion apart from those of (basement) gneisses andgranite. Presence of greywacke–argillite and tuAa-ceous matrix in the conglomerate has been reported.The pebble composition, density and sizes have beenobserved to varywidelywith the sequence dominatedat places by welded tuAs. Presence of interbandednon-pebbly phyllites with partings of sandy and cal-careous material is also reported. Chadwick et al.(1981) generally concur with above description of theKM Kere conglomerate. Mukhopadhyay and Baral(1985) have commented on the close association ofKM Kere conglomerate with the agglomeratic hori-zon in the west and in the presence of subrounded orrounded volcanic bombs in the conglomerate set in aphyllitic matrix.Our observation has shown that the KM Kere

Conglomerate sequence in fact represents a faciesseries comprising interlayered epiclastics, vol-caniclastics and volcanics. The volcanics includethose of explosive and non-explosive origin. It isrecorded that in different sections of KM KereConglomerate sequence either one of the epiclas-tic, volcaniclastic or volcanic components domi-nate or at places be the only type that isexposed. Similar sequences have been reportedfrom other geological ages and setting in differentparts of the world. Such sequences are charac-terized by close spatial association, interlayering,gradation and even intermixing between epiclas-tic, volcaniclastic and pyroclastic components.Importantly the inherent difBculty in ascribing anappropriate term to a component rock in such asequence has been heavily debated (Fisher 1961;Le Maitre et al. 2002 – the IUGS classiBcationscheme; Dimroth et al. 1980 – and other papersin this special edition of Precambrian Research;Schmid 1981; Williams et al. 1982; Fisher andSchmincke 1984; Cas and Wright 1988; Whiteand Houghton 2006; Manville et al. 2009). Aspyroclastic rocks are products of explosive vol-canism, and include airfall, Cow, surge and lahardeposits, they invariably show gradation to

volcaniclastics, and in turn to epiclastics. Thesein general represent deposits formed by air orwater action that have sourced their load frommainly juvenile pyroclastic eruption. But thedepositional process would involve other kinds ofpre-existing rocks too as sources, resulting inmixing of pyroclastic and epiclastic components.The problem is especially acute while dealingwith Precambrian deposits where deformation,metamorphism and secondary alteration havedestroyed, modiBed or obscured many of originaldepositional, textural and mineralogical features.These facts underlie the complexity in recognitionand classiBcation of rocks comprising the KMKere Conglomerate sequence.Our observations of the KM Kere sequence show

that there is wide variation in composition, shape,size and degree of assortment of clasts and matrixalong both strike and dip. Clasts include those ofacid and basic pyroclasts, metabasalt, metagabbro,rhyolite, BIF, quartzite, argillite, chert, jasper andvein quartz. Bomb and lapilli sized juvenile vol-canic fragments of acid and basic compositionsoccur in recognizable modal proportions even inapparently epiclastic members of the sequence.Tuffaceous and volcanic matrix as also of siliceous,argillic and rarely carbonate compositions arepresent. Graded bedding in certain layers showsBning upwards to east. Individual mineral grainsgenerally measure less than a cm across andinclude dominantly quartz along with feldspars,muscovite, pyrite, magnetite and other undeBnedopaques, and rare jasper. Juvenile clast compo-nents of quartz and feldspar are euhedral, subhe-dral or angular in nature. Clast shapes appear to berelated to their source. Those derived from sedi-mentary sources including BIF, metapelite, quart-zite and vein quartz as also rarely of granite andgneissic sources show subrounded and subangularshapes. Pyroclast fragments of both basic andacidic compositions show complexly welded crystaland lithic fragments that have largely retainedtheir magmatic viscous shapes and structures.Rhyolite clasts are typically subangular to angular.The interlayered epiclastic, pyroclastic and

volcaniclastic units in the KM Kere sequenceimperceptibly grade in to each other in manyplaces and individual litho units pinch out alongstrike quite frequently. It is often difBcult to traceany genetic type of band for more than a few tensof metres and often for much less along strike.Several thin pyroclast layers are cobanded withepiclastic layers and distinguishing pyroclasts


from volcaniclasts is also problematic in manyplaces.Further eastwards in the sequence tensofmetrethick bands of metabasalt, variolitic metabasalt,acid pyroclast, rhyolite occur with less frequent andthinner layers of volcaniclasts and epiclasts. Ametagabbro sheet, also several tens of metres widewith long strike length, occurs in this area.It is interpreted that a repetitive cycle of explosive

and non-explosive volcanism, interrupted by shortcycles of intermixed epiclast deposition took placeduring evolution of the KM Kere Conglomeratesequence. It signiBes a unique volcanic-sedimentarydeposition environment during evolution of theChitradurga Group of rocks in the study area.

3. Stratigraphic models proposedfor the Dharwar Supergroup of rocksin the study area (Chitradurga area)

Several stratigraphic models have been proposedfor the Dharwar Supergroup of rocks in the studyarea (Chitradurga area), including those of SwamiNath et al. (1976), Sheshadri et al. (1981), Rad-hakrishna and Vasudev (1977), Mukhopadhyayet al. (1981), Mukhopadhyay and Baral (1985),Chadwick et al. (1981, 2007), Burhanuddin et al.(1990) and Mohakul and Singh (2010). A slightlymodiBed version of stratigraphy proposed for theDharwar Supergroup of rocks in the study area(Chitradurga area) by Sheshadri et al. (1981),based on mapping data of the Geological Survey ofIndia, is given below (table 1). This stratigraphicmodel has been widely used by workers in theChitradurga area.It may be mentioned that the stratigraphy in the

Chitradurga area can be conveniently discussed interms of disposition of the marker Banded IronFormation (BIF) with reference to other lithologi-cal sequences. The authors present here a sche-matic cartoon of the disposition of the differentlithounits in the Chitradurga area including theregional ‘Chitradurga Fold’ deBned by the markerBIF bands that are well exposed in the central partof the study area (Bgure 3). The ‘ChitradurgaFold’ has been mapped as a second generation (F2)southerly closing regional antiform having steepsoutherly plunge of fold axis (Mukhopadhyay andBaral 1985). Based on study of preserved way upcriteria in appropriate lithologies, the fold can beinterpreted to be true anticlinal in nature meaningthe oldest stratigraphic unit is preserved in the coreof the fold with younger lithologies successively

away from the core of the fold. Three major BIFmarkers have been identiBed in this part (Chad-wick et al. 1981) two of which (BIF-I and BIF-II)are arcuate and deBne the regional ‘ChitradurgaFold’, whereas the third marker BIF (BIF-III) isexposed as an approximately N–S trending straightband occurring in the eastern part of theChitradurga area (Bgure 3). The two arcuatemarker BIF bands deBning the ‘Chitradurga Fold’are also known as the ‘inner arc BIF’ and the thirdBIF band in the eastern part of the Chitradurgaarea is known as ‘outer arc BIF’ as described inMukhopadhyay and Baral (1985).The ‘Jogimaradi Traps’ (a set of mainly

metabasic rocks), occurs stratigraphically beneaththe BIF-I as deBned above. It forms the core of theregional antiformal ‘Chitradurga Fold’ and hasbeen placed in the Ingaldhal Formation by She-shadri et al. (1981) in their stratigraphicscheme (table 1) that is younger to the VanivilasFormation. However, Chadwick et al. (1981) con-sider the ‘Jogimaradi Traps’ to represent theBababudan Group. The BIF-I, according toChadwick et al. (1981), can be discontinuouslytraced from the central part of Chitradurga area(regional ‘Chitradurga Fold’ area) further tonorthwest (Bgure 3). They also interpret that theBIF-II, occurring stratigraphically above theJogimaradi Traps can be traced from the centralpart of the Chitradurga area further northwest tothe Kandavadi area (Bgure 3) and also along thewestern margin of the Chitradurga area that limitsthe extent of the CSB as well. This would make therocks occurring stratigraphically above BIF-I andbelow BIF-II to be a part of the Vanivilas Forma-tion in the scheme of Sheshadri et al. (1981), whohowever place this sequence of rocks in theIngaldhal Formation.Chadwick et al. (1981) state that BIF-III, on the

eastern margin of the Chitradurga area can betraced only discontinuously in the area to south-east of the ‘Chitradurga Fold’ arc (Bgure 3). Intheir scheme the sequence of rocks stratigraphi-cally above BIF-II and below BIF-III comprisingmetavolcanics including variolitic and pillowedmetabasalts, pillow breccias, undeBned pyroclasts,phyllites, thin cherts; the polymict KM KereConglomerate and acid volcanic rocks and bandedtuAs, constitutes a separate stratigraphic unit thatis not formally named by them. On the other hand,Sheshadri et al. (1981) have included the abovesequence as a part of the Ingaldhal Formation.Both the above authors place rocks occurring


stratigraphically above the KM Kere Conglomer-ate under the youngest Hiriyur Formation of theChitradurga Group of rocks.

The complexity and differences in the abovetwo schemes are evident that have promptedSheshadri et al. (1981) to comment that the

Figure 3. Schematic block diagram showing disposition of the different lithounits in the central part of Chitradurga area (studyarea).

Table 1. Stratigraphic classiBcation of Neoarcheaean Dharwar Supergroup in Chitradurga area (Sheshadri et al. 1981).

Chitradurga

Group

Hiriyur

Formation

Greywacke–argillite suite with basic to intermediate volcanics, banded ferruginous chert and

polymict conglomerate (Aimangala and Hosakere)

KM Kere and GR Halli Conglomerates

��Disconformity��Ingaldhal

Formation

Basic (including ‘Jogimaradi Traps’, intermediate and acid lavas and pyroclastics with

interbeds of banded pyritiferous chert and argillite

Chloritic phyllite, Banded ferruginous chert

Vanivilas

Formation

Banded manganiferous chert and phyllite, Limestone and dolomite,

Chlorite–biotite–garnet phyllite, Quartzite and quartz schist

��Unconformity Polymictic Talya conglomerate��Bababudan

Group

Amygdular metabasalt closely interbedded with cross-bedded and ripple marked quartzite,

quartz–biotite–cholorite–garnet schist (locally with actinolitic hornblende, chloritoid, carbonate and white

mica) and sheets of ultramaBc (talc–tremolitechlorite–carbonate schist and serpentinite) and thin beds of

ironstone

��Unconformity Oligomictic Neralakatte Conglomerate��Basement

rocks

Peninsular Gneiss (containing enclaves of rocks of the Sargur Schist Complex)


variations in volcanic facies have caused prob-lems of lithostratigraphic correlation in differentparts of the Chitradurga area that need to beresolved by detailed mapping. Views broadlysimilar to that of Chadwick et al. (1981) on thestratigraphy of the Chitradurga area have beenexpressed by Burhanuddin et al. (1990) based on1:25,000 scale mapping in the central part of theChitradurga area. Mukhopadhyay et al. (1981)who have worked out the structure in thesouthern (Dodguni area) and northern (Chi-tradurga area) parts of the Chitradurga schistbelt attempted to provide a common strati-graphic scheme for the schist belt. They, how-ever, mention that as large parts of the schist beltstill needed to be studied on modern lines, theirpicture may need modiBcation and elaborationbased on more detailed data. They also implythat, even taking into account their structuralframework for the area, disparity in distributionof litho units in different parts of the Chitradurgaarea (possibly due to lateral facies variation) doescause difBculty and confusion in stratigraphiccorrelation.

3.1 New stratigraphic model proposedfor the Dharwar Supergroup inChitradurga area

In the stratigraphic model of Sheshadri et al.(1981), the basal Vanivilas Formation of theChitradurga Group is followed upwards in theyounging direction by the Ingaldhal Formation,which in turn is overlain by the Hiriyur Forma-tion. The Ingaldhal Formation, well exposedaround Chitradurga, consists mainly of metaba-salt with intercalated bands of BIF, minoramount of metapelite and acid volcanic/tuAs. Atno location, the Vanivilas Formation is in contactwith the Ingaldhal Formation. These two forma-tions are exposed in mutually exclusive domainsputting constraints in establishing their relativestratigraphic order. From our studies it is difBcultto subscribe to the earlier view that the IngaldhalFormation is younger to and overlies the Vani-vilas Formation. We propose that these two for-mations share a transitional relationship. Ourdata based on tracing of marker horizons andstructures in different geological sections indicatethat the Ingaldhal and Vanivilas Formations weredeposited broadly contemporaneously but devel-oped on two disparate settings – rocks of theVanivilas Formation representing a near shore

platformal sedimentation whereas the Ingaldhalrock assemblages including the well known ‘Jogi-maradi Trap’ evolved in a deeper waterenvironment.In contrast to earlier views of Chadwick et al.

(1981) and recently of Mohakul and Singh (2010),we believe that the basic volcanics of IngaldhalFormation of the Chitradurga Group cannot beequated with those of the Bababudan Group asexposed in the western part of the study area. Thevolcanic sequence in the above Bababudan Groupis interbanded with shallow-level, basin marginoligomictic conglomerate–quartzite assemblage,whereas the volcanic sequence of the IngaldhalFormation comprises of volcanic and a range ofpyroclastic rocks associated characteristically withsulphide bearing BIF and euxenic shales, repre-senting deep marine environment. Also our datashows that (Bgure 3) the marker BIF-I describedearlier pinches out some distance northwest of the‘Chitradurga Fold’ closure and the continuity ofthe marker BIF-II (Bgure 3) is also patchy and itsrecognition made difBcult due to no-outcrop andthick soil cover in the same direction. In fact, theBIF-II can not be traced with any degree of cer-tainity (Bgure 3) to continue to the western marginof the study area where the sequence of BababudanGroup of rocks is exposed. The basic volcanics withassociated quartzites of Kandavadi area are possi-ble time equivalents of Ingaldhal Formation, con-trary to the idea of these belonging to BababudanGroup since the Ingaldhal volcanics likely to con-tinue in Kandavadi area and our study indicatesthat the Bababudan rocks are restricted to the westof the Talya Conglomerate (Bgure 3). However, inlight of the present review, further detailed map-ping of the rocks of the Kandavadi area is neededto bring out their precise stratigraphic status.Sheshadri et al. (1981) have shown that the

Ingaldhal Formation of the Chitradurga Group isoverlain in the east by the Hiriyur Formation, thedisconformity represented by the KM Kere Con-glomerate. The KM Kere Conglomerate (discussedin an earlier section of this paper) comprises asequence of epiclast–volcaniclast–pyroclastic rocks.The KM Kere Conglomerate and Talya Conglom-erate sequences are not in contact with each otherin any part of the study area. The Talya Con-glomerate sequence is restricted to the western partof the study area and is not repeated in the east byfolding. It is delimited in its eastern margin by aprominent N–S to NNW–SSE trending ductileshear zone superposed on the second deformation


of the Dharwar Supergroup of rocks in the studyarea. The KM Kere Conglomerate sequence, how-ever, is restricted to the eastern part of the studyarea. The lithological differences between theabove two sequences (both sequences described indetail in earlier sections of this work) too are highlycontrasting and no correlation between the twois possible.Thus, the differences in various existing strati-

graphic models proposed for the Dharwar Super-group of rocks in the Chitradurga area (study area)and our observation in different sections of thestudy area led us to propose a modiBed strati-graphic sequence wherein the Chitradurga Groupcan be divided into four formations. Apart from theexisting three formations in the scheme of She-shadri et al. (1981), a new formation, here namedas the ‘Kantaramanahalli Formation’ is beingproposed by us. It was earlier mentioned that basedon the geometry and disposition of the lithounits,Vanivilas Formation and Ingaldhal Formation aretime equivalents, representing a proximal anddistal facies. This formation is made up of anargillite-wacke sequence with some discontinuousbands of conglomerate and BIF. Our data and map

patterns as given in Bgure 3 show the Kantara-manahalli Formation to stratigraphically overliethe Vanivilas Formation in the south and theIngaldhal Formation in the north, hence beingyounger to both those formations. It is juxtaposedalong a zone of Shear/Fault with the (older) TalyaConglomerate sequence in the west. It is overlainby the younger KM Kere conglomerate (seedescription in an earlier section of this paper) ofHiriyur Formation in the east along (Bgure 3) aN–S to NNW–SSE trending fault/discontinuityzone termed the Medikeripura high strain zone byChadwick et al. (2007). This contact zone in themore southerly continuation of the Hiriyur For-mation in the study area is marked by emplace-ment of deformed gabbroic sheets. Hence theMedikeripura high strain zone or ductile shear zonerepresents a terrane boundary where the originalintrabasinal fault-cum-disconformity between theIngaldhal and Hiriyur Formations has beenreworked during deformation of the DharwarSupergroup of rocks.Our newly proposed stratigraphic sequence for

the Dharwar Supergroup of rocks in the study areais given below:


4. Structure of the Chitradurga Schist Belt

Structural characters of the Dharwar Supergroupof rocks have been studied in different parts of theCSB over the past decades and are described in theworks of Mukhopadhyay et al. (1981), Mukhopad-hyay and Ghosh (1983), Mukhopadhyay and Baral(1985), Chadwick et al. (1981, 2000, 2003, 2007),Drury (1983), Naha et al. (1995), Mukhopadhyayand Srinivasan (2003), Roy et al. (2008), Senguptaand Roy (2012) and unpublished works of theGeological Survey of India. Recently new sets ofstructural data have been generated particularly inthe western part and their significance have beendiscussed (Roy et al. 2012; Roy and Bhattacharya2014).The rocks of the Dharwar Supergroup in the

study area comprising the older Bababudan andyounger Chitradurga Groups (Bgures 1 and 3)show imprints of at least three phases of deforma-tion (Mukhopadhyay et al. 1981; Mukhopadhyayand Baral 1985), associated with greenschist grademetamorphism (Sheshadri et al. 1981; Chadwicket al. 1981; Naha et al. 1995 and references therein).In general, there is no apparent discordance in thedeformational features amongst the Bababudanand Chitradurga Group of rocks. Though theintensity of deformation varies in different rocktypes, there is a commonality of structural char-acteristics shared by rocks of both the groupsthereby maintaining an apparent structural unity.Primary sedimentary and volcanic structures arepreserved in different parts of the area that help inrecognizing the younging direction despite thedeformation and metamorphism. As mentioned inan earlier section of this work, presence of markerBanded Iron Formations (BIF) in many parts ofthe area has enabled tracing of lithounits for con-siderable strike lengths in deciphering the mappattern, study of folds and other structural andtectonic features.The paper presents some new observations and

data on the patterns of folding and shearing of therocks of the study area including their geometry onmicro, meso and macroscopic scales and also ondistribution and eAect of strain in two major con-glomerate horizons, the oligomict NeralakatteConglomerate and the polymict Talya conglomer-ate. Attempts are made to interprete and explainthe available structural data including thoserecorded by the authors. The following discussionis based on relevant aspects of the above data andinterpretations.

4.1 Nature of major folding in the study area

The structure in the Chitradurga area as workedout in detail by Mukhopadhyay et al. (1981) andMukhopadhyay and Baral (1985) has resulted inrecognition of the major arcuate folded structure inthe central part of the Chitradurga area named bythem as the ‘Chitradurga Fold’. It is deBned bydisposition of two sets of dominant BIF bands,including an inner (older) and an outer (younger)set of BIF associated with metavolcanics (mainlybasic) and minor metasediments. They have shownthat the ‘Chitradurga Fold’ is a second generation(F2) southerly closing, very steeply plunging,nearly vertical fold and that there are no regionalfolds of the Brst generation (F1) preserved in anypart of the Chitradurga area (Bgure 3).We interpret that the regional structure of the

central part of the Chitradurga area can best bedeBned as a series of second generation (F2) culmina-tions (diverging plunges) and depressions (convergingplunges), possibly guided by basement highs and lowsof the depositional basin, giving rise to gentle tomoderate northerly or southerly plunging, F2 foldshaving nearly upright to steep easterly dipping axialplanes in general. The general shallow to moderateplunge of the folding is also responsible for the longlinear N–S to NNW–SSE disposition of the belt. Wealso interpret the large scale second generation (F2)‘ChitradurgaFold’ in the central part of the studyarea(Mukhopadhyay and Baral 1985) as having formedfrom possible extreme accentuation of basement highdue to E–Wshortening resulting in an antiformal coreof the gneissic basement. Further this zone witnessedsyntectonic (during the second deformation alsoresulting in the formation of F2 folds) emplacement ofthe Chitradurga Granite (see Bgure 4a). The syntec-tonic emplacement of the granite during D2 is evi-denced by its elongated lensoid disposition restrictedin south by the core of the major Chitradurga F2

antiform, the presence of magmatic stage deformationfabric (MSDF) deBned by alignment of feldspar crys-tals, superposed by only phase of solid state deforma-tion (recovery-recrystallisation) fabric subparallel toS2, absence of any pre-D2 foliation, elongation of themaBc microgranular enclaves subparallel to S2, sheet-like tabular intrusions observed in the northwesternpart and presence of D2b-shearing at places. On theotherhand, the elongatedSiranakattedomal structurein the southern part of the study area plunges gentlytowardsNNWin its northern part and towards SSE inthe southern part. As a result of converging plunges ofthe Siranakatte dome in its north and theChitradurga


Fold in its south along the same axial planar zonewithminor disharmony between them, a broad hour-glasslike outcrop pattern has developed as seen in Bgure 3.

4.2 Superposition of folds and interferencepatterns in the study area

The classiBcation of fold interference patterns byRamsay (1967) is based on the assumption that laterfolds are shear folds and are superposed on earliercylindrical folds.This kinematicmodel of shear foldingis not fully applicable to fold development of theDharwar Supergroup of rocks in the study area sincethe early F1 folds are extremely non-cylindrical innature and later superimposed F1 folds have resultedfrom Cexural mechanism. The interference patternsobserved in the present case are thus closely compa-rable with those produced by Cexural refoldingexperiments of analogue materials (Ghosh et al.1992, 1993; Grujic 1993). It may be mentioned herethat Ghosh et al. (1992) considered that the geometryof superposed folds depends to a large extent on theshape of the early folds and proposed four modes ofsuperposedbucklingof a competent layer embedded inan incompetent host. Although our observations arerestricted to small scale folds, Brst generation folds(F1) are verywell preserved in the inner and outerBIF(BIF-I&BIF-II) bands of the southerly closing secondgeneration (F2) ‘Chitradurga fold’. The Brst genera-tion (F1) folds range in size from hand specimen tooutcrop scale and rarely in dimensions greater than50 m (Bgure 4b and c). F1 folds are also clearly rec-ognizable in most of the BIF bands in all parts of thestudy area. We subscribe to the view of Mukhopad-hyayandBaral (1985) that the pattern of theF1minorfolds in the inner and outer BIF bands of ‘Chitradurgafold’ does not support the contention of Naqvi (1973)that the twoBIFbands represent two limbs of an earlylarge scale isoclinal structure.F1 folds are conspicuously tight to isoclinal and

non-cylindrical in nature (Bgure 4c and d). The cur-vature of the hinge line varies from 0� to as much as180�where the fold takes the shape of a perfect sheathor eyed fold while the axial plane remains planar(plane non-cylindrical fold) giving rise to ellipticaloutcrop pattern. Sheath folds are usually consideredto have evolved as a result of progressive shear in ashear zone, or where F2 folds are superposed on F1, orin cases where F2 folding is accompanied by a largeamount of stretching normal to overall orientation oflayering producing acute domes and basins withnearly 180� curvature of hinge lines. We interpret

that sheath folds in the study area havenot developeddue to any of the above-mentioned mechanisms. Onthe other hand, we consider that the sheath foldsrepresent a single generation structure (F1) resultingfrom extreme sub-vertical stretching perpendicularto themaximumshortening andoverall orientation ofbedding. Initial irregularity (non-linearity) of thehinge lines at an early stage of buckling, followed bycoalescence ormergingof the oppositelyplunging foldhinges and further accentuation of the irregularitieshas caused extreme stretching of the hinge lines toproduce sheath folds. Thus they could be interpretedto have resulted from pure shear (buckling followedby homogeneous shortening) mechanism.Folds in competent layers show predominantly

Class 1C and occasionally near similar (Class 2)geometry (as in Ramsay 1967). The axial planarcleavage and grain fabrics indicate a combination ofbuckling and homogeneous Cattening mechanismsresponsible for fold formation. They show accommo-dation structures indicative of appreciable compe-tence contrast between BIF layers during folding.Boudinage structure, shown by competent siliceouslayers, is developed in extensional domains, that is, onthe limbs of tight or isoclinal folds, at high or rightangle to the direction of shortening. Superposition ofF2 folds on early boudins has produced folded boudinsand on early folds has produced various fold interfer-ence patterns even on outcrop scale (Bgure 4e and f).This includes dominantly Type 3 and occasionallyType 2-fold interference patterns (as given in Ramsay1967) since the F1 folds are mostly tight or isoclinal innature. Rarely dome-basin Type 1 interference struc-ture hasdevelopedwhere the early fold is less tight andgentle in nature.F1 sheath folds have been deformed by later F2

folds. Superposition of F2 and F3 on earlier F1 foldshas been discussed in detail by Mukhopadhyay andBaral (1985). There is no structural gap within thedifferent formations of the Chitradurga Group ofrocks in the study area. The structural pattern ismainly deBned by F2 folds and the associated domi-nant planar fabric S2, with earlier folds and cleavagesoccasionallypreservedas relict structures (Bgure 4g).

4.3 Strain characteristics of deformationprocess in the study area deducedfrom pebble deformation in Neralakatteand Talya Conglomerates

Pebble shapes in deformed conglomerate have longbeen used to estimate the Bnite strain in rocks by


Figure 4. (a) Moderate to steep southeasterly plunging Chitradurga fold deBned by the Ingaldhal Formation in the N, incontrast with low (to moderate) NNW plunging folds deBned by the Vanivilas Formation assemblages in the south, togetherforming a regional scale non-cylindrical structure. (b) Tight isoclinal dextral F1 fold with high amplitude: wavelength ratiosuperposed by gentle F2 sinistral folding in BIF of the inner arc of the main Chitradurga fold, Ingaldhal Formation ofChitradurga Group. (c) Superposition of gentle F2 warps on isoclinal early (F1) folds in BIF; spaced S2 cleavage is perpendicularto the F1 axial plane. (d) Plane noncylindrical nature of the F1 mesofold in BIF showing curvature of hinge; Ingaldhal Formation.(e) Superposition of wide hinged F2 fold over boudins of early generation (D1) in BIF of Ingaldhal Formation, from the mainChitradurga fold area. (f) Type-III superposition pattern (of Ramsay 1967) in BIF of Ingaldhal Formation. (g) Well developed S2cleavage and ptygmatitic folding of the thin competent psammitic bands in chlorite phyllite layers intercalating with BIF ofIngaldhal Formation.


employing different methods of strain measure-ments. It has been shown that two main aspectswhich are important in this context are viscositycontrast between pebbles and matrix and pebbleconcentration (Gay 1968, 1969; Bilby et al. 1975;Gay and Fripp 1976; Freeman 1987; Mandal et al.2003; Vitale and Mazzoli 2005). Theoretical andobservational data indicate that a high concentra-tion of pebbles, even with large viscosity contrast,would bring the eAective mean viscosity ratio closeto 1, implying that the pebble strain would be thesame as the bulk strain. Gay (1968) showed that ina multi-object system, the number and the volumeof the objects relative to the matrix have a bearingon the eAective viscosity. He noted that eAectivemean viscosity ratio (Rm) that would control thebulk strain of the rock, rapidly decreases withincreasing object concentration and approaches thevalue of 1 in a densely packed system.The stratigraphic status and a general descrip-

tion of the two important conglomerate horizons inthe Dharwar Supergroup of rocks in the study area,the Nerlakate (at the base of the BababudanGroup) and Talya (at the base of the ChitradurgaGroup) Conglomerates, has been presented inearlier sections. These two conglomerates greatlydiffer in their pebble-matrix ratios, pebble con-centration, type of pebbles and their initial shapes,viscosity contrast, nature of pebbles and also ofmatrix. The interpretation of Gay (1968) men-tioned above holds good for Neralakatte oligomic-tic conglomerate (dominated by quartz pebbles inargillitic matrix) where the average concentrationof pebbles exceeds 45% by volume. The pebblesshow strong parallelism with the subverticalschistosity plane (XY plane of the strain ellipsoid),

represented by a transposed cleavage plane (S2) inthe matrix and a strong low plunging stretchinglineation (X-axis of the pebbles). Measurements ofpebble axes indicate Cattening type of plane strain(pure shear) deformation where the ratio of axesX: Y: Z varies from 5:3:1 to 5:4:2, the averagebeing 7:5:2.In contrast, the Talya polymictic conglomerate

is characterized by low concentration of pebbles(\20% by volume) comprising granite, gneiss,quartzite, vein quartz, shale and occasional basal-tic clasts ranging in size from pebble through cob-ble to boulder. These clasts show high viscositycontrast with the component wacke-argillitematrix and thereby show strong heterogeneity instrain. Whereas the granite, gneiss and vein quartzclasts are rounded to subrounded ellipsoidal inshape, the quartzite clasts are elongate and longtabular in nature. This is due to inherent aniso-tropy/bedding plane present in quartzite clasts.They are at times mistaken as boudinaged quart-zite bands. Statistically, the XY planes of the clastsare oriented parallel to matrix schistosity indicat-ing Cattening type of strain (pure shear) duringearly stages of deformation (F1 and F2). Thematrix schistosity is either a composite (S1/S2)plane or a transposed surface (S2) and the pebblesare deformed predominantly on this plane. Super-posed on this Cattening strain, the clasts are fur-ther deformed during shear-related deformation(D2b) in the area. Asymmetric S-folds and shearbands (Sb) deCecting the S1/S2 composite plane areindicative of sinistral shear of strike slip nature.The average strike of the shear bands isN50W–S50E and the dip is sub-vertical. Pebblesand clasts are further reoriented due to shearingshowing strong obliquity with S1/S2 plane. Thepebbles/clasts have attained asymmetric or sig-moidal shapes due to overprinting of simple shearon pure shear. The NNW–SSE striking axial planarcrenulation cleavage (S2) is oriented clockwise withrespect to shear bands.It is thus clear from the above discussion that

the conglomerate clasts were subjected to twostages of successive strain to give rise to the Bnalshape of the objects. The Brst stage strain, a pureshear strain, accompanying D1/D2 deformationwas the dominating one producing strong Catten-ing on a plane perpendicular to E–W/ENE–WSWshortening of the belt and strong pebble lineationplunging gently towards NNW parallel to thedirection of elongation of the belt. The secondstage strain, which is relatively less in intensity

Figure 4. (Continued.)


was superposed on the Cattened and/or elongatedellipsoidal pebbles/clasts to modify them intoasymmetrical or sigmoidal shape at certain places.This superposition of simple shear over pure sheardeformation is in conformity with the bulk kine-matic pattern of the schist belt as a whole. Intranspressional type of deformation with simulta-neous pure shear and simple shear, the magnitudeof simple shear component should be less (Das-gupta et al. 2012). In the absence of detailed strainmeasurements, it is difBcult to determine if thebulk strain was of transpressional type or anoverprinting strain in two stages.

5. Conclusion

A review of data and interpretations available forthe Dharwar Supergroup of rocks from the Chi-tradurga area in the Western Dharwar Craton andfrom arguments presented in this paper from ourunpublished data lead us to the following broadconclusions on different aspects of the DharwarSupergroup of rocks that add to our understandingof the Dharwar Craton.An early stage of crustal stretching accompanied

by limited rifting initiated the basin formation ofthe Dharwar Supergroup of rocks in the study area(Bgure 5). Sedimentation and volcanism occurredin the tectonically active basin that opened up insuccessive pulses towards east, punctuated by thedeposition of major conglomerate horizons. In thestudy area, the older Bababudan Group of rocks,with the Neralakatte Conglomerate at the base isrestricted to the western part and is overlain byfault-controlled deposits of the Talya Conglomer-ate forming the base of the younger ChitradurgaGroup. The basin opens out to the east wheresedimentation and volcanism took place on an

uneven basement surface marked by the presenceof prominent basement highs, for example, theSiranakatte dome in the southern part of the studyarea (Bgures 3 and 5). The Talya polymict con-glomerate of the Chitradurga Group is alsorestricted to the western part of the study area andis interpreted to represent a growth-fault deposit.This conglomerate sequence represents a debrisCow deposit, which is strongly tectonised wherethe clasts are deformed in both shape and orien-tation. Although deeper marine facies sedimentshave been deposited in the eastern part, the pres-ence of basement highs led to the deposition ofshallow marine sedimentation around them. TheKM Kere Conglomerate represented by a vol-canic–pyroclast–volcaniclast–epiclast associationforms an important stratigraphic horizon repre-senting the base of the Hiriyur Formation(Bgure 5).Generally, accepting the stratigraphic scheme as

proposed by Sheshadri et al. (1981), we propose afour-fold classiBcation of the Chitradurga Groupby introducing an additional formation, namely theKantaramanahalli (KR Halli) Formation, occuringabove the Ingaldhal (and Vanivilas) and below theHiriyur Formations. The KR Halli Formation isexposed in the antiformal axial depression domainof the large scale, strongly non-cylindrical foldrepresented by the southerly plunging anticlinal‘Chitradurga Fold’ in the north and the northerlyplunging Sriranakatte anticline in the south. Ascould be established from our lithological andstructural studies it is suggested that Vanivilas andIngaldhal Formations likely represent contempo-raneous and overlapping sequences indicativeof facies variation in space.Though the intensity of deformation varies in

different constituent rocks structural featuresdeveloped are comparable in both Bababudan and

Figure 5. Schematic diagram showing the crustal stretching accompanied by limited rifting that initiated the basin formationand deposition of the Dharwar Supergroup of rocks progressed from west to east in the study area.


Chitradurga Groups of rocks indicative ofstructural unity. Development of shear zones/highstrain zones are conBned along inherent weak zonesin the belt, such as the basement-cover contactzone (Oligomictic Neralakatte conglomerate) andoriginal fault zones denoted by Talya conglomerateboth in the western part of the study area andalong the Medikeripura High Strain Zone (MHA ofChadwick et al. 1981) in the eastern part.Structural data show presence of three episodes

of deformation of which the second generationstructures are the most dominant ones deBning theregional NNW–SSE trending regional structuralpattern of the belt. This is in conformity with theobservations of Mukhopadhyay et al. (1981),Mukhopadhyay and Ghosh (1983), Mukhopadhyayand Baral (1985) and Sengupta and Roy (2012).Superposition of successive generation of structuresis well documented. Structural features are mainlyductile in nature and have developed at shallow tomoderate crustal depth (*8 km).Integration of structural data including shape

and orientation of folds, strong Cattening type ofdeformation of conglomerate clasts, superposedstructures and interference pattern, foliationcharacteristics, and geometry and kinematics ofshear zones, a horizontal tectonic model is stronglysupported with attendant E–W to ENE–WSWregional shortening and N–S to NNW–SSE elon-gation giving rise to the present shape of the belt,as also proposed by several workers mentionedearlier.Structural interpretation shows that transcur-

rent/strike slip movement (D2b) slightly postdatesthe second generation shortening event (D2a),which may be explained in a domain of continuumhorizontal oblique compression. Emplacement ofelongate (granitic) plutonic bodies along most ofthe thrust and strike-slip shear zones (ductile orbrittle–ductile) in the Chitradurga area furthersupports a horizontal tectonic model. However, asfar as it can be constrained from our understandingof the Chitradurga area, the plate tectonic modelfor the WDC appears to be not very well con-strained. The mid-crustal level craton-wide imbri-cate fold thrust belt model for the ChitradurgaSchist Belt (including a part of the study area)(Chadwick et al. 2007) is quite rational but needssupport from structural data from many otherparts of the craton. Although a fold-thrust modelcan be reasonably applied along the eastern mar-gin, the model is untenable along the westernmargin and also in the central part of the belt.

Higher metamorphic grade PGC (along with oldersupracrustals) is overlain, both stratigraphicallyand structurally, by low metamorphic gradeDharwar supracrustals (Bababudan Group), whichargues against a thrust model. Similarly, thealternative speculative models proposed involvingsagduction and mantle plume or the lateral con-structional Cow (LCF) do not Bnd support fromBeld evidences.

Acknowledgements

We acknowledge with thanks the contribution of anumber of workers, especially of Geological Surveyof India, in shaping the concept of evolution of theChitradurga Schist Belt. Critical review along withconstructive comments and suggestions providedby two anonymous reviewers on an earlier versionof the manuscript have greatly helped in improvingthe quality of the paper. We are indebted to Prof DMukhopadhyay for detailed discussions and guid-ance in organization of the paper. Sincere thanks toArya Ghosh of Geological Survey of India for herhelp and cooperation in taking the photomicro-graphs of microsections.

References

Bhattacharya H N, Bhattacharya B, Pal S and Roy A 2015Late Archaean tidalites from western margin of Chi-tradurga greenstone belt, southern India; Precamb. Res.257 109–113.

Bhattacharyya H N, Roy Abhinaba, Pal S and BhattacharyyaB 2015 Evolution of Chitradurga greenstone belt in theframe of Archaean granite-greenstone terrain of Karnataka;Unpublished DST Major Project Report (2011–2015),Presidency University, Kolkata.

Bilby B A, Eshelby J D and Kundu A K 1975 The change ofshape of a viscous ellipsoidal region embedded in a slowlydeforming matrix having a different viscosity; Tectonophys.28(4) 265–274.

Burhanuddin M, Chandrashekhraih K C, Laxmana B K andManjunatha 1990 Geology of central part of ChitradurgaSchist Belt, Chitradurga District, Karnataka, UnpublishedGeol. Surv. Ind. report.

Cas R A F andWright J V 1988 Volcanic Successions: Modernand Ancient, Chapman & Hall, London, 528p.

Chadwick B, Ramakrishnan M and Viswanatha M N 1981 Thestratigraphy and structure of the Chitradurga region: Anillustration of cover–basement interaction in the lateArchaean evolution of the Karnataka craton, southernIndia; Precamb. Res. 16 31–54.

Chadwick B, Vasudev V N, Krishna Rao B and Hegde G V1992 The Dharwar supergroup: Basin development andimplications for Late Archaean tectonic setting in western


Karnataka, southern India; In: The Archaean: Terrains,Processes and Metallogeny Publ. (eds) Glover J E and Ho S,University of Western Australia 22 3–15.

Chadwick B, Vasudev V N and Hegde G V 2000 The Dharwarcraton, southern India, interpreted as the result of lateArchaean oblique convergence; Precamb. Res. 99 91–101.

Chadwick B, Vasudev V N and Hegde G V 2003 TheChitradurga schist belt and its adjacent plutonic rocks,NW of Tungabhadra, Karnataka: A duplex in the lateArchean convergent setting of the Dharwar craton; J. Geol.Soc. India 61 645–663.

Chadwick B, Vasudev V, Hegde G V and Nutman A P 2007Structure and SHRIMP U/Pb zircon ages of granitesadjacent to the Chitradurga schist belt: Implications forNeoarchean convergence in the Dharwar craton, southernIndia; J. Geol. Soc. India 69 5–24.

Dasgupta N, Mukhopadhyay D and Bhattacharyya T 2012Analysis of superposed strain: A case study from barrconglomerate in the south Delhi Fold Belt, Rajasthan,India; J. Struct. Geol. 34 30–42.

Dimroth E, Donaldson J A and Veizer J 1980 Early Precam-brian volcanology and sedimentology in the light of therecent; Precamb. Res. 12(1–4) 1–470.

Drury S A 1983 A regional tectonic study of the ArchaeanChitradurga greenstone belt, based on LANDSAT inter-pretation; J. Geol. Soc. India 24 167–184.

Drury S A and Holt R W 1980 The tectonic framework of thesouth India craton: A reconnaissance involving LANDSATimagery; Tectonophys. 65 111–115.

Ethridge F G and Westcott W A 1984 Tectonic setting,recognition and hydrocarbon reservoir potential of fan-deltadeposits; In: Sedimentology of gravels and conglomerates(eds) Koster E H and Steel R J, Canadian Soc. Petrol. Geol.Memoir 10 213–235.

Fisher R V 1961 Proposed classiBcation of volcanoclasticsediments and rocks; Geol. Soc. Am. Bull. 72 1409–1414.

Fisher R V and Schmincke H U 1984 Pyroclastic Rocks;Springer-Verlag, Berlin, 472p.

Freeman B 1987 The behaviour of deformable ellipsoidalparticles in three-dimensional slow Cows: Implications forgeological strain analysis; Tectonophys. 132 297–309.

Gay N C 1968 Pure shear and simple shear deformation ofinhomogeneous viscous Cuids: Theory; Tectonophys. 5211–234.

Gay N C 1969 Analysis of strain in the Barberton MountainLand, eastern Transvaal using deformed pebbles; J. Geol.77 377–396.

Gay N C and Fripp R E P 1976 The control of ductility on thedeformation of pebbles and conglomerates; Phil. Trans.Roy. Soc. London A 283 109–128.

Ghosh S K, Mandal N, Khan D and Deb S 1992 Modes ofsuperposed buckling in single layers controlled by initialtightness of early folds; J. Struct. Geol. 14 381–394.

Ghosh S K, Mandal N, Sengupta S, Deb S and Khan D 1993Superposed buckling in multilayers; J. Struct. Geol. 1595–111.

Grujic D 1993 The inCuence of initial fold geometry on type 1and type 2 interference patterns: An experimentalapproach; J. Struct. Geol. 15 293–307.

Jayananda M, Chardon D, Peucat J J and Capdevila R 20062.61 Ga potassic granites and crustal reworking in thewestern Dharwar craton, southern India: Tectonic,

geochronologic and geochemical constraints; Precamb.Res. 150(1–2) 1–26.

Jayananda M, Chardon D, Peucat J J and Fanning C M 2015Paleo- to Mesoarchean TG accretion and continentalgrowth in the western Dharwar craton, southern India:Constraints from SHRIMP U–Pb zircon geochronology,whole-rock geochemistry and Nd–Sr isotopes; Precamb.Res. 268 295–322.

Jayananda M, Jahn B, Gireesh R V and Bora S 2011Geochronologic and isotopic constraints on the accre-tionary relationships of western and eastern blocks of theDharwar craton across Huliyar–Sira corridor: Implica-tions for late Archean tectonics; International Sympo-sium on Precambrian Accretionary Orogens and FieldWorkshop in the Dharwar Craton; Geol. Soc. India,pp. 51–53.

Jayananda M, Moyen J F, Martin H, Peucat J J, Auvray Band Mahabaleswar B 2000 Late Archaean (2550–2520 Ma)juvenile magmatism in the eastern Dharwar craton, south-ern India: Constraints from geochronology, Nd–Sr isotopesand whole rock geochemistry; Precamb. Res. 99225–254.

Jayananda M, Peucat J J, Chardon D, Krishna Rao B,Fanning C M and Corfu F 2013 Neoarchean greenstonevolcanism and continental growth, Dharwar craton, south-ern India: Constraints from SIMS U–Pb zircon geochronol-ogy and Nd isotopes; Precamb. Res. 227 55–76.

Kaila K L, Roy Chowdhury K, Reddy P R, Krishna V G, HariNarain, Subbotin S I, Sollogub V B, Chekunov A V,Kharetchko G E, Lazarenko M A and Ilchenko T V 1979Crustal structure along Kavali–Udipi proBle in the IndianPeninsular Shield from deep seismic sounding; J. Geol. Soc.India 20 307–333.

Le Maitre R W, Streckeisen A, Zanettin B, Le Bas M J, BoninB, Bateman P, Bellieni G, Dudek A, Efremova S, Keller J,Lamere J, Sabine P A, Schmid R, Sorensen H and WoolleyA R 2002 Igneous rocks: A classiBcation and glossary ofterms, Recommendations of the International Union ofGeological Sciences, Subcommission of the Systematics ofIgneous Rocks; Cambridge University Press.

Maibam B, Goswami J and Srinivasan R 2011 Pb–Pb zirconages of Archaean metasediments and gneisses from theDharwar Craton, southern India: Implications for theantiquity of the eastern Dharwar craton; J. Earth Syst.Sci. 120(4) 643–661.

Mandal N K, Samanta S K, Bhattacharyya C and Chakra-borty C 2003 Deformation of ductile inclusions in a multipleinclusion system in pure shear; J. Struct. Geol. 251359–1370.

Manville V, Segschneider B, Newton E, White J D L,Houghton B F and Wilson C J N 2009 Environmentalimpact of the 1.8 ka Taupo eruption, New Zealand:Landscape responses to a large-scale explosive rhyoliteeruption; Sedim. Geol. 220(3–4) 318–336.

Mohakul J P and Singh B 2010 Report on specialized thematicmapping of the western shear zone of Chitradurga schistbelt between Mayakonda in the north and madadkeri in thesouth along with mapping of Mayakonda belt: Unpublishedprogress report of Geol. Surv. Ind. FS 2003–2005.

Mukhopadhyay D and Baral M C 1985 Structural geometry ofthe Dharwar rocks near Chitradurga; J. Geol. Soc. India 26547–566.


Mukhopadhyay D, Baral M C and Ghosh D 1981 A tectonos-tratographic model of Chitradurga schist belt; J. Geol. Soc.India 22 22–31.

Mukhopadhyay D and Ghosh D 1983 Superposed deformationin Dharwar rocks in southern part of the Chitradurga schistbelt, Karnataka; In: Precambrians of south India (eds)Naqvi S M and Rogers J J, Mem. Geol. Soc. India 4275–292.

Mukhopadhyay D and Srinivasan R 2003 Dharwar craton ofsouth India: A record of billion years of early history; In:Advances in Precambrian of Central India (eds) Roy A andMohabey D M, Gondwana Geological Magazine, Spec. Vol.7.

Naqvi S M 1973 Geological structure and aeromagnetic andgravity anomalies in the central part of Chitradurga schistbelt, Mysore, India; Geol. Soc. Am. Bull. 84 1721–1732.

Naha K, Mukhopadhyay D, Dastidar S and Mukhopadhyay RP 1995 Basement–cover relations between a granite gneissbody and its metasedimentary envelope: A structural studyfrom the Early Precambrian Dharwar tectonic province,southern India; Precamb. Res. 72 283–429.

Ojakangas R W, Srinivasan R, Hegde V S, Chandrakant S Mand Srikantia S V 2014 The Talya Conglomerate: AnArchean (*2.7 Ga) Glaciomarine Formation, WesternDharwar Craton, southern India; Curr. Sci. 106(3)387–396.

Postma G 1984 Slumps and their deposits in fan delta frontand slope; Geology 12(1) 27–30.

Radhakrishna B P and Vasudev V N 1977 The EarlyPrecambrian of the southern Indian shield; J. Geol. Soc.India 18 525–541.

Rama Rao J V, Balakrishna B, Murty N V S, Ajaykumar P,Ramakrishna Rao M V, Acharya R S and Sankaram SP 2015 Comprehensive view from geophysical signaturesover Chitradurga Schist Belt, Karnataka; J. Geol. Soc.India 86(4) 489–499.

Ramakrishnan M and Vaidyanadhan R 2008 Geology of India;Geol. Soc. India 1 556p.

Ramsay J G 1967 Folding and Fracturing of Rocks; McGraw-Hill, New York, 568p.

Rollinson H R, Windley B F and Ramakrishnan M 1981Contrasting high and intermediate pressures of metamor-phism in the Archaean Sargur schists of southern India;Contrib. Mineral. Petrol. 76(4) 420–429.

Roy A, Bhattacharya H N, Bhattachary B and Pal S 2012Chitradurga schist belt of Dharwar craton revisited:

Evidences in favour of polyphase deformation and ductileshearing along the western margin of the belt; Abstract:Rock Deformation Structure II, pp. 103–105.

Roy A and Bhattacharya H N 2014 Overprinting of simpleshear strain on pure shear deformation: Evidences from thewestern margin of the Chitradurga schist belt of Dharwarcraton; Abstract: Rock Deformation Structure III,pp. 57–60.

Roy A, Sengupta S and Mandal A 2008 Synchronous devel-opment of mylonite and pseudotachylyte: An example fromthe Chitradurga Eastern Margin Shear Zone, Karnataka; J.Geol. Soc. India 72 447–457.

Schmid R 1981 Descriptive nomenclature and classiBcation ofpyroclastic deposits and fragments: Recommendations ofthe IUGS subcommission on the systematics of igneousrocks; Geology 9 41–43.

Sengupta S and Roy A 2012 Tectonic amalgamation of crustalblocks along Gadag–Mandya Shear Zone in DharwarCraton of southern India; J. Geol. Soc. India 80(1)447–457.

Sheshadri T S, Chaudhuri A, Harinadha Babu P and Chaya-pathi N 1981 Precambrian supracrustals of southern Kar-nataka; Mem. Geol Surv. India 112 163–198.

Srinivasan R and Ojakangas R W 1986 Sedimentology ofquartz-pebble conglomerates and quartzites of the ArcheanBababudan Group, Dharwar Craton, south India: Evidencefor early crustal stability; J. Geol. 94(2) 199–214.

Surlyk F 1984 Fan delta to submarine fan conglomerate of theVulgian–Valginian Wollaston Fortland Group, East Green-land (eds) Koster E H and Steel R J, Canadian Soc. Petrol.Geol. Memoir 10 359–382.

Swami Nath J, Ramakrishnan M and Viswanatha M N 1976Dharwar stratigraphic model and Karnataka craton evolu-tion; Rec. Geol. Surv. India 107(2) 149–175.

Swami Nath J and Ramakrishnan M 1981 Early Precambriansupracrustals of southern Karnataka; Mem. Geol. Surv.India 112 1–350.

Vitale S and Mazzoli S 2005 InCuence of object concentrationon Bnite strain and eAective viscosity contrast: Insightsfrom naturally deformed packstone; J. Struct. Geol. 272135–2149.

White J D L and Houghton B F 2006 Primary volcaniclasticrocks; Geology 34(8) 677–680.

Williams H, Turner F J and Gilbert C M 1982 Petrography –

An Introduction to the Study of Rocks in Thin Sections; 2ndedn, W. H. Freeman and Company, San Francisco, 626p.

Corresponding editor: N V CHALAPATHI RAO


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