Strain localization, granulite formation and geodynamic setting of ‘hot orogens’: a case study from the Eastern Ghats Province, India

Strain localization, granulite formation and geodynamic setting of ‘hot orogens :a case study from the Eastern Ghats Province, India

SAIBAL GUPTA*Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India

The Eastern Ghats Province underwent major orogenic events in the Neoproterozoic–Cambrian period: 980–930, 900–650 and 550–500Ma.At each time interval, deformation occurred synchronous with high-grade metamorphism. The first event was characterized by distributedstrain throughout the entire province, while strain and thermal anomalies during the later orogenies were confined to the province boundaries.In the first case, pre-orogenic rifting caused ultrahigh-temperature metamorphism at the base of the crust, and was closely followed by crustalshortening related to the collision of the granulite belt with the Indian craton. The thermal anomaly persisting from the rifting event, followedby the thermal relaxation associated with crustal shortening led to prolific melt production and transfer of heat producing elements (HPE) intothe middle and upper parts of the thick post-collisional crust. Heating and associated melting caused rheological weakening of the crustal sec-tion, and explains why strain was distributed across the entire thermally perturbed zone. Erosion removed a substantial portion of the HPE-rich upper crust, and deposited the detritus in cratonic sedimentary basins to the west. Subsequently, the rheologically stronger Eastern GhatsProvince crust could effectively transmit stresses and concentrate them along pre-existing zones of weakness near the province boundaries.Progressive thrusting in these domains led to consistent loading of the footwall, even as it underwent thermal relaxation. Since both strainand heating were associated with the footwall of pre-existing discontinuities, the ‘hot orogen’ so formed was also spatially restricted. Copy-right © 2011 John Wiley & Sons, Ltd.

Received 15 December 2010; accepted 13 July 2011

KEY WORDS hot orogens; Eastern Ghats; strain localization; rheological weakening; granulite; Neoproterozoic

1. INTRODUCTION

Classical models attempting to explain the thermal evolutionof orogenic belts that formed in response to compressivestresses within the earth (e.g. England and Thompson,1984) predict that the peak metamorphic temperatureswithin such belts are attained on the uplift path followingthe attainment of peak pressures, describing the so-called‘clockwise’ metamorphic P-T paths. Such models are foundto be particularly appropriate for explaining the origin oforogens by continental collision. The increase in tempera-ture in collisional orogens is attributed to ‘thermal relaxa-tion’ of the crust as a consequence of enhanced heatproduction by decay of radioactive elements. In contrast,many ancient orogens preserve P-T paths that are ‘counter-clockwise’, with the stabilization of peak metamorphic min-eral assemblages occurring synchronously with increasing

pressure (i.e. depth of burial). The origin of such belts, thatwere already ‘hot’ during the course of burial, cannot be de-scribed by simple models of continental collision. Much ofthe concern about such ‘hot orogens’ has therefore centredon identifying a suitable geodynamic setting (e.g. Sandifordand Hand, 1998; Collins, 2002a; Collins and Richards,2008; Chardon et al., 2011) that can account for the sourceof the heat, and the focusing of shortening deformation intothe thermally perturbed zone.

Collins (2002a) recognized one such ‘hot orogen’ in thePalaeozoic Lachlan Fold Belt in eastern Australia, and attrib-uted its origin to repeated ‘tectonic switching’ between exten-sion and contraction. He called such orogens ‘extensionalaccretionary orogens’ (Collins, 2002b), and suggested thatthey originated in the back-arc of the overriding plate duringthe process of subduction. These orogens were believed tooriginate along retreating subduction boundaries that weredominated by protracted lithospheric extension, with onlytransient contractional deformation. Heating was attributedto the extensional process, while contraction occurred in re-sponse to periodic subduction of buoyant lithospheric com-ponents such as oceanic plateaus. Hyndman et al. (2005)

*Correspondence to: S. Gupta, Department of Geology and Geophysics, IndianInstitute of Technology, Kharagpur 721 302, India.E-mail: [email protected]

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Copyright © 2011 John Wiley & Sons, Ltd.

GEOLOGICAL JOURNALGeol. J. (2011)Published online in Wiley Online Library(wileyonlinelibrary.com). DOI: 10.1002/gj.1328

have also suggested that the hot, thin and consequently weakback-arc lithosphere could also concentrate shortening dur-ing continental collision following subduction. In suchcases, the relative rate of thickening and heat transfer woulddetermine the sense (clockwise or counter-clockwise) of theP-T-t path (Brown, 2007).

Both the above types, i.e. the extensional accretionaryorogens of Collins (2002a) and the inverted back-arc basinsdiscussed by Hyndman et al. (2005), are linked to conver-gent plate boundaries. Of these, the latter setting is favourablefor the formation of ‘hot’ orogens, as some locales associatedwith subduction, such as back-arcs, are domains of anoma-lously high heat flow, and are known to localize deformation.A third category of orogens that were apparently ‘hot’ in thecourse of compressive deformation have also been documented;these orogens appear to be entirely intracratonic in nature, andare formed in response to reworking of pre-existing continental,and sometimes, orogenic crust. Such intra-cratonic ‘hot orogens’have been reported from central Australia (e.g. Sandiford andHand, 1998). For such orogens, explaining the source ofthe heat, the stresses that triggered orogeny and the reasonsfor localization of deformation at the site of the thermal per-turbation form important issues that need to be addressed.

This paper describes the geological evolution of a part ofa granulite terrane in the eastern part of the Indian shield,known as the Eastern Ghats Belt. For some time, this belt hasbeen the focus of considerable attention from metamorphicpetrologists (see Dasgupta and Sengupta, 2003, and referencestherein), and painstaking research over the past decadehas also generated geochronological constraints for themajor thermal events. Of late, structural information is alsoavailable from critical parts of the terrane (see Chetty,2010), and integration of the available data suggests that apart of the Eastern Ghats Belt, known as the Eastern GhatsProvince, was a ‘hot orogen’ at least twice (or perhaps thrice)in its geologic history. The conditions existing during thespecific periods are first summarized and then assessed, and itis argued that the reasons for the ‘hot orogenesis’ during theearliest episode are very different from that during subsequentevents. It is also demonstrated that following the initial ‘hotorogeny’, the rheological character of the crust in the EasternGhats Province changed dramatically, and this is reflectedin the manner of strain localization during the subsequentorogenic episodes.

2. GEOLOGICAL BACKGROUND

The Eastern Ghats Belt is a multiply deformed, polymetamor-phosed granulite facies terrane that lies on the eastern fringesof the Archaean craton of peninsular India, and was supposedlyformed during an Indo-Antarctica collisional event in theProterozoic (e.g. Grew and Manton, 1986; Bhowmik, 1999;

Mezger and Cosca, 1999; Dobmeier and Raith, 2003;Dasgupta and Sengupta, 2003). The belt extends linearly ina NE–SW direction, and contains several lithologic domainsparallel to its trend (Narayanaswami, 1975; Nanda andPati, 1989; Ramakrishnan et al., 1998; Figure 1). The west-ernmost part of the belt comprises charnockites, enderbites,basic granulite and enclaves of metasedimentary migmatites,and is referred to as the Western Charnockite Zone (WCZ).The WCZ is separated from a dominantly supracrustal gran-ulite suite to the east by a mega-scale lineament that has beencharacterized as a shear zone (the Sileru Shear Zone, SSZ;Chetty and Murthy, 1998). A chain of alkaline complexes(prominently those at Rairakhol, Khariar, Koraput, Kunavaram,Jojuru, Elchuru and Uppalapadu) is located approximately alongthe SSZ (Figure 2), suggesting that it served as a locus formagmatism (Chetty and Murthy, 1998). However, sincemany of these complexes were subsequently reported to bedeformed and metamorphosed (Gupta and Bose, 2004;Gupta et al., 2005), the SSZ is now considered to be apost-emplacement shear. East of the SSZ, the supracrustalgranulite suite includes two zones of similar lithologicalconstitution, dominated by sillimanite-bearing gneisses withintercalated calc-silicates, quartzites, high-Mg–Al granulitesand rare marbles; these are referred to as the Western andEastern Khondalite Zones (WKZ and EKZ, respectively;Figure 1). A central Charnockite–Migmatite Zone (CMZ),consisting of extensively migmatized supracrustal granulites(including sillimanite gneisses) intruded by porphyriticgranitoids, is located between the WKZ and the EKZ, andextends to the north of the WCZ. Unlike the WCZ–WKZcontact, the boundaries between the other lithologic domainsare transitional (Ramakrishnan et al., 1998). Apart from theporphyritic granitoids and the enderbite suite, intrusivebodies such as anorthosites lie in the western part of thegranulite belt, while alkaline complexes appear to be alignedin the proximity of the boundary with the craton.Detailed geological investigations over the last two decades,

coupled with a wealth of new geochronological information onthe timing of the varied magmatic components and metamor-phic events within the terrane, has led to a new subdivisionof the Eastern Ghats Belt into distinct crustal provinces anddomains (Figure 2; Dobmeier and Raith, 2003). Theseprovinces and domains are characterized by disparate geolog-ical histories and were metamorphosed in the granulite faciesat different times (Gupta, 2004). The largest of these pro-vinces, designated as the Eastern Ghats Province (EGP), isa dominantly supracrustal domain that includes the WKZ,CMZ and the EKZ. This province underwent widespread gran-ulite facies metamorphism in the Grenvillian (~980–930Ma)time, with a Neoproterozoic–Cambrian thermal overprint(Mezger and Cosca, 1999). In the north, the Eastern GhatsProvince is juxtaposed directly against Palaeo-Archaeangranites (Rajesh et al., 2009) and amphibolite facies

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Copyright © 2011 John Wiley & Sons, Ltd. Geol. J. (2011)DOI: 10.1002/gj

metamorphic rocks of the Bastar Craton. This contact hasbeen considered by some workers (e.g. Biswal et al., 2000,2007; Gupta et al., 2000; Bhadra et al., 2004) to be a suturezone resulting from collision tectonics. South of this contact,the EGP abuts against the enderbites and charno-enderbitesof the WCZ. Geochronologic data indicates that magmatismand metamorphism in the WCZ north of the Godavari Basinis entirely Archaean in age (2.7 and 2.5Ga respectively;Kovach et al., 2001; Simmat and Raith, 2008). On this basis,this part of the WCZ was identified as a distinct, Archaeanage, granulite terrane called the Jeypore Province. Unlike

the EGP–craton boundary to the north, there is little detailedgeological work across the EGP–Jeypore Province boundary(i.e. the Sileru Shear Zone), and the tectonic status of thisprovince boundary is as yet uncertain. The geologicalhistory of the Eastern Ghats Belt south of the GodavariBasin was interpreted to be more complex (see Dobmeierand Raith, 2003 for details); the present study does notconcern itself with this region, and this is therefore notdiscussed further.

This study traces the geological evolution of the EGPthrough the Neoproterozoic, and it is suggested that the

Figure 1. Geological map of the Eastern Ghats Belt (after Ramakrishnan et al., 1998). Inset map shows the location of the Eastern Ghats Belt in peninsularIndia. Note that the Sileru Shear Zone forms a tectonic contact to the east of the WCZ. Contacts between the other lithologic domains are transitional.

(WCZ: Western Charnockite Zone; WKZ: Western Khondalite Zone; EKZ: Eastern Khondalite Zone; CMZ: Charnockite–Migmatite Zone).

HOT OROGENESIS IN THE EASTERN GHATS PROVINCE


EGP was a ‘hot orogen’ several times during this period. It isargued that the geodynamic setting in the two cases was dis-tinct, and that the interplay between strain localization andthermal evolution was a natural consequence of thelithospheric strength variations effected within the EGPlithosphere in the course of its geologic history.

3. THERMAL EVENTS IN THE EASTERN GHATSPROVINCE

Since the primary factor associated with the formation of‘hot’ orogens is heat, the geological history of the EGP isreviewed in the context of the documented thermal episodesin the late Mesoproterozoic–Neoproterozoic. Based on thereported ages for the various metamorphic events in theEGP, four major thermal intervals can be isolated, of whichthree were associated with shortening. The metamorphicevidence for each thermal episode is reviewed, and followedsubsequently by a discussion on the causes and conse-quences of each event.

3.1. Thermal Event 1 (TE-1): UHT metamorphism (1250–1100 or ~1000Ma?)

The record of the first major thermal event in the EGP ispreserved in very unusual but spectacular high-Mg–Alassemblages and calc-silicate granulites. Importantly, theserare assemblages were not restricted to specific domains,but were reported from across the EGP (Figure 2)—Paderu(Lal et al., 1987; Pal and Bose, 1997); Araku (Sengupta et al.,1991); Anantagiri (Sengupta et al., 1990); Vizianagram(Kamineni and Rao, 1988); Anakapalle (Sengupta et al.,1997; Rickers et al., 2001a); Chilka Lake (Sen et al.,1995), Rayagada (Shaw and Arima, 1996); Rajamundry(Dasgupta et al., 1995). This spatial distribution indicates thatalthough evidence for the ultrahigh-temperature (UHT) meta-morphism is only preserved in local pockets, the event affectedthe entire EGP. The Mg–Al granulites occur as pods or lenseswithin the surrounding lithologies, and their precise field rela-tionship is indistinct. Indeed, some of the Mg–Al granulitesoccur as xenoliths within mafic granulites, and may well be ex-otic with respect to the associated lithologies (Rickers et al.,2001a). Unfortunately, there is little available information

Chennai

o84 Eo80 Eo22 N

Chilka Lake

o18 N

Rajamundry

VizianagramAnakapalle

Paderu-Araku-Anantagiri

Rayagada

Bolangir

Khariar

Rairakhol

Koraput

Angul

Krishna Province

Jeypore Province

RengaliProvince

B A S T A R

C R A T O N

D H A R W A R

C R A T O NEastern Ghats

Province

Bhubaneswar

B A Y O F B E N G A L

G o d a v a r i

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UHT metamorphism

Alkaline ComplexMassif anorthosite

Figure 2. Subdivision of the Eastern Ghats Belt into provinces (after Dobmeier and Raith, 2003). The Eastern Ghats Province (focus of this study) is shownbound by a bold line. Localities with documented ultrahigh-temperature (UHT) metamorphism (shown by stars) are distributed across the belt. Locations of the

alkaline complexes at Rairakhol, Khariar and Koraput, and the massif anorthosite complexes at Chilka Lake and Bolangir are also shown.

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on the nature of the deformation accompanying this phase ofmetamorphism.The assemblages diagnostic of high temperature and low

pressure are Zn-poor spinel + quartz, sapphirine + quartzand complex Fe–Ti–Al oxide solid solution in Mg–Al gran-ulite, and wollastonite + scapolite in calc-silicate granulite(see Dasgupta and Sengupta, 2003, and references therein).This phase of metamorphism in the EGP was designated asM1, with estimated peak conditions of 8–10 kbar and~1000 �C (Dasgupta and Sengupta, 1995, 2003). The retro-grade path following the M1 peak is generally proposed tobe one of near-isobaric cooling, although a few studiessuggest an initial phase of isothermal decompression (e.g.Lal et al., 1987; Sengupta et al., 1997).Determining the absolute age of the UHT event has

proved more difficult, as in most cases, the minerals usedto date granulite metamorphism in the EGP grew after theinitial UHT event, during the succeeding M2 granulite event(e.g. Mezger and Cosca, 1999). An initial estimate of thetiming of M1 metamorphism was obtained from detailedU–Th–Pb monazite geochronometry (Simmat and Raith,2008), by dating of monazites hosted in garnet containedwithin the high Mg–Al granulites and metapelitic gneisses.The dates show a broad range, and suggested that the ageof UHT metamorphism possibly lies between 1250 and1100Ma. However, later studies by Upadhyay et al. (2009),Das et al. (2011) and Bose et al. (2011) have revealed thatmetapelites from various parts of the EGP preserve a broadrange of U–Pb zircon ages ranging from 1800–500Ma.While all these workers considered the older zircon ages tobe detrital, Upadhyay et al. (2009) considered all ages youn-ger than 1200Ma to be metamorphic; by implication, theearliest (UHT) metamorphic event was placed around1200Ma. Das et al. (2011) placed the same event at ca.1000Ma, based on monazite inclusions within orthopyrox-ene associated with sapphirine, a definitively UHT assem-blage. Chemical dating of similar monazite inclusions inorthopyroxene from paragneisses of the EGP yield agesbetween 1030 and 1020Ma (Bose et al., 2011), compatiblewith the age inferred by Das et al. (2011).

3.2. Thermal Event 2 (TE-2): granulite facies metamor-phism (980–930Ma)

The most prominent thermal event in the EGP was M2granulite facies metamorphism, during which the UHT gran-ulites were reworked at P-T conditions estimated at 8–8.5 kbarand 850 �C (see Dasgupta and Sengupta, 2003, and referencestherein). Unlike the M1 event that is only preserved in selectedlithologies, M2 metamorphism was pervasive and can be iden-tified in all pre-existing lithologies within the belt. This eventwas accompanied by regional deformation and penetrative fab-ric formation, and the peak metamorphic assemblages either

grow synchronous with, or outlasted penetrative deformation(Mukhopadhyay and Bhattacharya, 1997; Gupta et al., 2000).Structural studies indicate that the regional deformationwas compressive in nature, being associated with isoclinalfolding and thrust-related shearing (e.g. Halden et al., 1982;Bhattacharya et al., 1994; Dobmeier and Raith, 2000; Guptaet al., 2000; Bhadra et al., 2004). Orientation of the fabricrelated to this compressive event varies from NE–SW,south-easterly dipping in the major part of the orogen, toWNW–ESE trending in the northern part of the EGP (Sarkaret al., 2007).

Peak metamorphic assemblages in the metapelites thatdominate the EGP commonly contain orthopyroxene +sillimanite + garnet + quartz. The orthopyroxene–sillimaniteassociation appears to have developed at the expense of ear-lier cordierite-bearing assemblages; Das et al. (2011) arguethat the corresponding prograde P-T path involved loadingwith/without heating. Cordierite reappears as a consequenceof the breakdown of this assemblage (Kamineni and Rao,1988; Sengupta et al., 1990; Dasgupta et al., 1995; Mohanet al., 1997), and together with the corresponding breakdownof garnet to symplectitic intergrowths of orthopyroxene andcalcic plagioclase in quartzofeldspathic gneisses and maficgranulites (e.g. Dasgupta et al., 1991; Gupta et al., 2000),are commonly cited as evidence of near-isothermal decom-pression to mid-crustal levels. This retrograde M2 trajectorytherefore appears to be distinctly different from that follow-ing the M1 peak. The timing of the M2 metamorphic peak isalso reasonably well constrained, between 980–930Ma(Grew and Manton, 1986; Paul et al., 1990; Shaw et al.,1997; Mezger and Cosca, 1999). An even more precise esti-mate for the age of the M2 metamorphic event has beenobtained by SHRIMP U–Pb analyses on zircon grains fromthe Panirangini area of the Araku Valley, that yield a concor-dant age of 953 � 6Ma (Das et al., 2011).

A major feature of M2 metamorphism is the syn-tectonicintrusion of voluminous porphyritic granitoid bodies (e.g.Angul, Salur, Sunabheda) and anorthosite complexes (e.g.Bolangir, Chilka Lake, Jugsayapatna, Turkel). The grani-toids were all emplaced between 985 and 955Ma, as con-strained from near-concordant U–Pb ages (Grew andManton, 1986; Paul et al., 1990; Kovach et al., 1998), ac-companied penetrative deformation at the peak of M2 meta-morphism (Mukhopadhyay and Bhattacharya, 1997) and aretherefore invariably deformed. The granitoids exhibit pro-nounced S-type characteristics (Krause, 1998), and testifyto an intracrustal origin. Some workers (e.g. Sen and Bhatta-charya, 1997) have suggested that the granitoids in theChilka Lake area were products of biotite and muscovite de-hydration melting reactions. Apart from the granitoids, theBolangir anorthosite complex intruded granulite facies coun-try rocks near the northern boundary of the EGP at933� 32Ma (Krause et al., 2001), concomitant with N–S



directed compressive deformation (Dobmeier, 2006). TheChilka Lake anorthosite body likewise intruded around983� 2.5Ma (Chatterjee et al., 2008), again testifying tothe presence of a hot, melt-laden crust during Grenvillianorogenesis in the EGP.

3.3. Neoproterozoic thermal events (TE-3): granulite andamphibolite facies metamorphism (900–650Ma)

TE-3 is used to collectively refer to a number of high-grademetamorphic events that affected the Eastern Ghats Provincethrough the Proterozoic. Unlike TE-1 and TE-2 that affectedthe entire province, these later thermal events were morelocalized. The most prominent of these events occurred inthe Chilka Lake area in the northern EGP, in the vicinityof the anorthosite body. Krause et al. (2001) had earlierdated the ferrodiorites associated with the anorthosite bodyto be about 792Ma, and on this basis, suggested the associ-ated anorthosite to be of the same age. This appears to be inconflict with the age obtained by Chatterjee et al. (2008),and indicates that the anorthosites and the associated ferro-diorites may not necessarily be genetically linked. Pervasivecompressive deformation and granulite facies metamorphismoccurred between 690 and 660Ma (Dobmeier and Simmat,2002). Sengupta et al. (2008) deduced metamorphic condi-tions of 5.6� 1 kbar, 650� 50 �C for this event, based onstudies on calc-silicate rocks located in the contact aureoleof the anorthosite. Earlier, Sarkar et al. (2007) had inferredsimilar P-T conditions for the Angul area; this was tenta-tively correlated with a 700Ma event in the Rengali Prov-ince to the north. This event in Angul was considered to bea separate tectonic event unrelated to earlier Grenvilliangranulite facies metamorphism (Sarkar et al., 2007).

A thermal overprint within the time-span for TE-3 hasalso been identified in the Koraput area, where the presenceof an alkaline complex (Sarkar et al., 1989) suggests a phaseof Neoproterozoic rifting and extension. The complex lies3 km east of the Sileru Shear Zone and cuts across an earliergranulite facies fabric in the host rocks (Gupta et al., 2005).The intrusion age is disputed; Sarkar et al. (1989) inferred anage of 856 � 18Ma from Rb–Sr whole-rock studies, whileBhattacharya and Basei (2010) suggest an age of 917Mafrom U–Pb zircon studies. However, according to Hippeet al. (2008), magmatic zircons are absent in the complex,with the low Zr content being inadequate to achieve Zr sat-uration in such alkaline magmas. Following crystallizationof the alkaline complex, there was an initial phase of hydra-tion and amphibolite facies metamorphism, after which thealkaline complex was also metamorphosed along with itscountry rocks under granulite facies conditions (~8 kbar,800 �C; Gupta et al., 2005; Nanda et al., 2008). The meta-morphic imprint accompanied and outlasted an associatedshear deformation that affected the western fringe of the

EGP and the eastern boundary zone of the Jeypore Provinceto the west. The shearing event and the succeeding metamor-phic imprint was considered by Nanda et al. (2008) to be en-tirely intracontinental. The prograde P-T path associatedwith this event indicates a heating followed by loading tra-jectory. Peak pressures and temperatures were followed byisothermal decompression indicating rapid uplift. Hippeet al. (2008) inferred an age range anywhere between880–700Ma for the metamorphic imprint, based on meta-morphic zircons that were interpreted to have formed bybreakdown of biotite during granulite facies metamorphism.Thus, while the age of the rifting corresponding to alkalinemagmatism remains uncertain, an age of around 880Ma oryounger is indicated for the later granulite facies metamor-phism (Hippe, 2006; Nanda et al., 2008). Interestingly, thisage is consistent with the 900Ma age inferred for hydrationand zircon growth during a late metamorphic event in thePanirangini area, further to the east (Das et al., 2011).

3.4. Thermal Event 4 (TE-4): Neoproterozoic–Cambrianmetamorphism (550–500Ma)

In most parts of the Eastern Ghats Province, a ‘thermal dis-turbance’ is also recorded during the Pan-African time(Neoproterozoic–Cambrian, 550–500Ma) and is only recog-nized in the form of reset mineral ages, some late magmaticrocks and zircon growth in late apatite–magnetite veins(Mezger and Cosca, 1999). This period, however, has as-sumed importance in the light of the geological studies con-ducted along the contact between the EGP and the BastarCraton. Gupta et al. (2000) had documented that along theEGP–craton boundary in the north, hot granulites had beensyn-tectonically thrust onto the ‘cold’ cratonic foreland,leading to partial melting of cratonic rocks in the immediatecontact, and a decrease in metamorphic grade further west-ward. This ‘inverted metamorphic’ zonation was accentu-ated by sequential fabric development in the cratonicforeland, with hotter rocks along the contact with hangingwall granulites developing penetrative fabrics earlier thanthose further to the west (Bhadra et al., 2004). However,Bhadra et al. (2004) noted that the last phase of movementalong the contact was associated with a different movementvector, lower metamorphic temperatures and deformation ofunmetamorphosed cratonic sediments along the contactzone. Later, Simmat and Raith (2008) documented a well-defined monazite age population in the period 530–470Mafrom strongly sheared granulites located along the contactzone between the EGP and the Bastar Craton, interpretingthat the final phase of movement along this boundary oc-curred at this time. A Pan-African overprint was alsodetected in a series of Mesoproterozoic alkaline complexes(Khariar, Kunavaram, Jojuru, Elchuru and Uppalapadu)aligned along the boundary between the EGP and the craton

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(Aftalion et al., 2000; Upadhyay, 2008 and referencestherein). Biswal et al. (2007) had also obtained similar ages(~511–552Ma) from the Khariar alkaline complex in thenorthern part of the area, although they interpreted that mag-matism had also occurred syntectonically with movement onthe boundary shear zone, a point not supported by the stud-ies of Aftalion et al. (2000) and Upadhyay et al. (2006).Thus, it appears that granulite facies conditions at this timewere restricted to the boundary shear zone (Gupta et al.,2000). Importantly, further to the east, in the central andeastern part of the EGP, the thermal event at this time wascomparatively weak (Mezger and Cosca, 1999).

4. DISCUSSION

The above categorization of the thermal episodes recorded inthe magmatic, metamorphic and geochronologic datasetavailable for the EGP serves to highlight an important aspectof the thermotectonic evolution of the granulite province. Itdemonstrates that the Eastern Ghats Province was thermallyperturbed at several different times during the late Mesopro-terozoic to early Cambrian, but the structural and metamorphicsignature of the earlier (>930Ma) and later (900–500Ma)events appear to be very different. The 980–930Ma granulitemetamorphism (i.e. TE-2) and associated fabrics can be identi-fied in all parts of the EGP; indeed, the presence of this‘Grenvillian signature’ forms the basis for the distinct identityof the EGP as a province (Dobmeier and Raith, 2003). UnlikeTE-2, subsequent granulite facies metamorphic events andtheir associated deformation (manifested as fabrics) did notaffect the entire province, but were apparently spatially andtemporally restricted. The difference in crustal responsebetween the TE-2 and subsequent thermal events has beendocumented in the areas around Angul, Chilka Lake,Koraput and Deobhog. In all of these localities, penetrativefabric formation accompanied an early phase of (Grenvillian)granulite facies metamorphism; all these localities separatelyexperienced granulite facies metamorphism, deformation andfabric formation at later times in the mid-late Neoproterozoic.The effects of these later events are confined to these specificdomains and are not recorded elsewhere in the EGP. The TE-2 thermal imprint, on the other hand, can be detected over theentire province, and that the strain related to deformation ac-companying this event led to penetrative fabric formationacross the EGP. If the age data for the different events are ro-bust, it would appear that that the rheology of the EGP crustduring the TE-2 granulite event was drastically different fromthat during the later high-grade events, with its intrinsicstrength increasing so as to be able to partition strain into dis-crete domains during the later events. In the context of the pres-ent study, an attempt has been made to try and identify the

cause for the dramatic increase in strength of the EGP litho-sphere during the Neoproterozoic.

4.1. Thermal Event-1—causes and consequences

The distribution of UHT metamorphic domains in the East-ern Ghats Province indicates that the first thermal eventwas caused by a tectonic event that affected the entireregion, but not the flanking Jeypore Province. On a globalplatform, there has been considerable speculation on the tec-tonic setting associated with UHT metamorphism, but as yet,there is no consensus on a single, specific model (see Harley,2004, 2008; Brown, 2007; Kelsey, 2008, for recent reviews).While some models have attempted to explain the high tem-peratures as resulting from elevated crustal heat productionfollowing crustal thickening (e.g. McKenzie and Priestley,2008; Tsunogae and Santosh, 2011), numerical modellingof the phenomenon generally shows a temperature deficit(e.g. Burg and Gerya, 2005) and implies that UHT condi-tions cannot be attained within the crust by such a mecha-nism (Kelsey, 2008). The extremely high temperatures arebest explained by an additional heat flux from the mantle,possibly by replacement of the lithospheric mantle with hot,convecting asthenospheric material. This can occur either bydelamination of the mantle lithosphere as a result of gravita-tional instability following convergence (e.g. Houseman et al.,1981; Garzione et al., 2008; Ducea, 2011; Gutiérrez-Alonsoet al., 2011), or by lithospheric extension and thinning, withthe mantle lithosphere thinning more rapidly than the crust(e.g. McKenzie, 1978; Sandiford and Powell, 1986; Crosbyet al., 2010). The former situation has been suggested forregions such as the Southern Alps and the Alboran Sea(Houseman andMolnar, 2001), while the latter has been docu-mented in the Labrador Sea margin (Sclater et al., 1980).

The two competing models (shortening vs. extension)may theoretically be distinguished by the nature of the retro-grade trajectory associated with the metamorphic imprint(e.g.Marotta et al., 2009). Crustal thickening inevitably leadsto enhanced topography followed by erosion that should bepreserved in the form of isothermal decompression (ITD)in the retrograde P-T trajectory. On the other hand, extensionwith pronounced thinning of the mantle lithosphere will leadto prograde heating followed by cooling from peak tempera-tures with little associated decompression. If the mode of ex-tension is asymmetric (as in the Basin and Range Province),cooling from peak temperatures in zones of pronounced lith-ospheric thinning and constant crustal thickness will be iso-baric (Sandiford and Powell, 1986).

The shape of the retrograde P-T path following UHTmetamorphism in the EGP is, however, ambiguous. In mostUHT localities, peak metamorphic temperature was gener-ally followed by isobaric cooling (IBC), but the post-peaktemperature path in a few localities (e.g. at Anakapalle)



has also been inferred to follow an ITD trajectory (Senguptaet al., 1997). This is not necessarily contradictory, sincenear-isobaric cooling may simply imply a faster rate of cool-ing than uplift, and need not necessarily imply isostatic equi-librium (Loosveld and Etheridge, 1990). In such a case,however, an initial phase of isobaric cooling will be fol-lowed by decompression, similar to that observed for theEGP (e.g. Dasgupta and Sengupta, 2003). Isothermal de-compression is indeed recorded on the retrograde path, butfor the TE-2 thermal event. The viability of a tectonic modelfor TE-1 is therefore dependent on its proximity in time withthe TE-2 event.

4.2. TE-1 and TE-2: temporally separated events or acontinuum?

Like TE-1, TE-2 also affected the entire Eastern GhatsProvince but was associated with compressive deformation.Any model for TE-2 needs to explain the source of the heat,and the reason why deformation that accompanied crustalshortening was penetrative in nature. A simple solution tothe ‘heat’ problem is to consider that the elevated tempera-tures associated with TE-2 are sustained by the persistenceof the thermal anomaly generated during TE-1. Since thethermal time constant for the lithosphere is around 50Ma,the perturbation generated by TE-1 rifting can only persistinto TE-2 if the two events were sufficiently closely spacedin time (i.e. <50Ma, Sandiford, 1999). As summarized ear-lier, there is considerable uncertainty about the timing ofTE-1, with estimates varying from 1200Ma (e.g. Simmatand Raith, 2008; Upadhyay et al., 2009) to 1000Ma (Boseet al., 2011; Das et al., 2011). If the earlier age (1200Ma)is accepted, TE-1 and TE-2 would be separated by a periodof over 200 million years and cannot be considered part ofthe same tectonic cycle. In such a case, an obvious problemto be addressed is why two major thermal anomalies shouldrecur in precisely the same region of the crust at separatepoints in time, apart from reasons of pure coincidence. Fur-ther, since metamorphic textural associations during TE-2suggest reactions that involve melting, the EGP crust needsto melt after already experiencing melt extraction duringTE-1. To re-melt an already ‘refractory crust’ (that has expe-rienced melting before), higher temperatures would be re-quired during TE-2 compared to TE-1. Such ‘ultrahigh’metamorphic temperatures are not recorded during TE-2,which makes this possibility increasingly improbable. Fromtheoretical arguments, therefore, it appears more likely thatthat TE-2 closely followed TE-1 (at around 1000Ma), assuggested by Das et al. (2011) and Bose et al. (2011). Thiswould imply that the older zircon ages obtained in theEGP are essentially detrital ages, and that TE-1 and TE-2represent a continuum in time.

If TE-1 and TE-2 are indeed part of a continuum, asargued above, the penetrative nature of fabric formation dur-ing deformation accompanying TE-2 is easily explained. Inthis case, rifting would be closely followed by crustal/litho-spheric shortening. The ‘hot’ EGP lithosphere (followingTE-1) would be ‘thermally softened’ (Thompson et al.,2001) and therefore inherently susceptible to reactivationduring subsequent crustal shortening (Sandiford, 1999;Sandiford and Hand, 1998). Crustal thickening during short-ening deformation may lead to additional melting at the baseof the overthickened crust, with the production of S-typegranitoids (Krause, 1998). The Pb-isotopic signature of theorthogneisses in the EGP indicate derivation from a mixtureof Archaean and Proterozoic material (Rickers et al.,2001b), testifying to the presence of Archaean crust belowthe supracrustals. Furthermore, the granitoids serve to advectmore heat, along with their substantial heat producing ele-ment (HPE) content (Senthil Kumar et al., 2007) into themiddle and upper crust. Burial of hot crust following a rift-ing event has also been suggested as a possible cause for ris-ing temperatures in the middle to lower crust of the BrokenHill Block, leading to granulite facies metamorphism(Forbes et al., 2008). In the case of the Eastern GhatsProvince, it is therefore suggested that the extreme thermalanomaly associated with the preceding rifting event hadnot completely decayed during the onset of TE-2; this, alongwith the anomalously high heat production in the EGP rocks(Senthil Kumar et al., 2007) and the heat advected by thegranitoids were responsible for sustaining granulite faciesconditions in the middle and lower crust during TE-2(Figure 4A). This ‘thermally weak’ crust accommodatedcrustal shortening by penetrative fabric formation acrossthe entire terrane.

4.3. Geodynamic setting during the TE-1/TE-2 continuum

TE-1 is best explained by lithospheric thinning during riftingof continental crust (Figure 3). This model explains a num-ber of features of UHT metamorphism in the EGP. The ther-mal anomaly generated by rifting will be restricted to thezone of pronounced thinning of the mantle lithosphere, andwill not affect the flanks or ‘shoulders’ of the rift zone.The Jeypore Province, which forms the western ‘shoulder’of the rift zone (Figure 3B), therefore did not experienceany thermal aberration at this time. Within the rift zone,extremely high temperatures are generated by thinningand removal of the underlying mantle lithosphere. If exten-sion was asymmetric, the crust would maintain near-normalthickness in the most thermally perturbed zone, andwould consequently experience only isobaric cooling on theretrograde path.The geodynamic setting related to the subsequent crustal

shortening event in Grenvillian time (TE-2) must necessarily

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be speculative, but is most likely linked to plate marginstresses related to continental collision. The collision mayinvolve the entire Eastern Ghats Belt (i.e. including theJeypore Province) and the Bastar-Dharwar Craton, as sug-gested by Upadhyay (2008). In such a case, the shorteningin the EGP, along with the generation of the granitoids,may possibly be explained by the formation and closure ofa back-arc basin. An alternative explanation may lie in thecontiguity of the EGB with the Rayner Complex of EastAntarctica in Neoproterozoic time (Mezger and Cosca,1999; Dobmeier et al., 2006). The Grenvillian event in theRayner Complex has been correlated with a prolonged(990–900Ma) Neoproterozoic thermal event in the northernPrince Charles Mountains of Antarctica (Boger et al., 2000)that was possibly related to the closure of an ocean basin tothe south of this area (Kelly et al., 2002). In such a case, thestresses related to the collisional plate margin would have tobe transmitted inland, and concentrated in the thermally per-turbed and rheologically weak lithosphere of the combinedEGP-Rayner continental fragment. Although such a modelcannot be overruled, the first model is preferred in this study,as available evidence suggests that the Archaean Indian cra-ton is a distinct lithospheric entity from the granulites of theEastern Ghats Belt, and that the contact between them is a

suture (e.g. Gupta et al., 2000; Upadhyay, 2008; Vijayakumarand Leelanandam, 2008).

Rifting and UHT metamorphism followed directly byshortening and granulite facies metamorphism of pre-existing continental crust would lead to considerable modifi-cation of the crust in the affected region. High temperaturessustained over a period of ~100Ma would be expected tolead to extensive melting of the lower crust, with the gener-ation of prolific amounts of granitic magma (Figures 3B and4A). Thus, a crustal section through the EGP following TE-1and TE-2 would contain a HPE-depleted, UHT granulitezone at the base, a partially HPE-scavenged mid-crust andan increasing proportion of granitoids rich in high heat-producing elements (HPE) towards shallower crustal levels(Figure 4B).

4.4. Post-TE-2 evolution of the EGP crust—a test of theproposed model

The post-TE-2 crustal profile for the EGP (Figure 4B) sug-gested above is necessarily model-driven and speculative,but has the potential to explain why the EGP crust may havestrengthened following TE-2. Transfer of a significantamount of HPE into the middle and upper crust would serve

CRUST

LITHOSPHERIC MANTLE

Eastern Ghats Province(hot)

Jeypore Province(cold)B.

UHT metamorphism

HPE-richgranitoids

CRUST

LITHOSPHERIC MANTLE

A.

Figure 3. Schematic cross-sectional representation of the tectonic setting during TE-1. A. Undeformed lithosphere prior to rifting. B. Initiation of rifting, withdetachment faulting associated with asymmetric extension in the crust, and lithospheric thinning of the underlying mantle. The underlying asthenosphereupwells, leading to heating, ultrahigh-temperature metamorphism and granitoid genesis at the base of the Eastern Ghats Province crust. Note that the western

shoulder of the rift, assumed to be the Jeypore Province, is unaffected by both the rifting and its thermal anomaly.



to strengthen the underlying crustal section, since buriedsources of radioactive heating are more effective at weaken-ing the crust than those nearer the surface (Pyskelwec andBeaumont, 2004). If the high heat-producing layer is subse-quently removed from the crust altogether (e.g. by erosion),this would lead to further strengthening of the crustal section.The test of the proposed model, however, lies in demonstrat-ing the existence of a lower crust that has undergone signifi-cant depletion in the heat producing elements. This is clearlyimpossible to verify directly, but may be inferred from obser-vations at the currently exposed surface, and from the sedi-mentary record of the basins lying west of the granulite belt.

The transfer of melts from a partially molten lower crustinto middle and upper crustal regimes is a very efficientmechanism for removal of incompatible elements from deepcrustal levels. Since the major heat producing elements(U, Th and K) are also incompatible, they would also beincorporated into melts generated during crustal anatexis.During TE-2, there is widespread emplacement of suchcrustally-derived charnockite/granitoid bodies (the S-typegranitoids of Krause, 1998) that comprise a significant partof the exposed present-day EGP crust (see Figure 1). U,

Th and K abundances in these rocks are known to be signif-icantly high (Senthil Kumar et al., 2007), indicating thatthey were major carriers of these elements. It is to be notedthat the present-day exposure level corresponds to a depthof about 25 km at the time of emplacement of these intru-sives; this represents the mid-crustal level of the overthick-ened crust that must have existed during TE-2. Thus, it canbe concluded that after TE-1, TE-2 further accelerated thetransfer of heat producing elements into the middle of thethickened crust (i.e. the present exposure level); it is logicalto infer that a major proportion of the HPE may have beencarried further upward to even higher structural levels.Following TE-2, the retrograde metamorphic P-T trajec-

tory suggests isothermal decompression, compatible witherosional unroofing of the over-thickened crust. The meta-morphic record suggests removal of over 10 km of uppercrustal material (Figure 4B). The most puzzling aspect isthe identity of the repository into which the eroded uppercrust of the EGP was deposited. West of the JeyporeProvince of the Eastern Ghats Belt, there are a number ofintracratonic Proterozoic sedimentary basins including thePranhita-Godavari, Abhujmar, Ampani, Indravati, Chhatisgarh

A. Eastern Ghats Province(hot, penetratively deformed)

Upper crustal layer

HPE-rich granitoid

Granulite facies metamorphism

UHT layer from TE-1

Bastar Craton Jeypore Province

Mesoproterozoicsediments

B.

UHT layer from TE-1

Bastar Craton Jeypore Province

Eastern Ghats Province

HPE-scavenged mid-crust

Neoproterozoic sediments derived from EGP

Older Mesoproterozoicsediments

Figure 4. Schematic cross-section depicting lithospheric response during and following TE-2. A. Initiation of the hot orogeny immediately following TE-1,with compressive stresses leading to shortening in the EGP. The heat producing element (HPE)-rich granitoids move up, and may form a layer close to uppercrustal levels. The entire zone is still hot from TE-1 rifting and thermal relaxation following crustal thickening. Strain is concentrated and penetratively distrib-uted within the EGP, resulting in pervasive fabric formation and granulite facies metamorphism (hatched area) of the middle and lower crust. B. Post-orogenic(i.e. TE-2) state. Following crustal thickening, the upper crustal layer and underlying HPE-rich granitoid layer are stripped off by erosion and deposited in thecratonic basins to the west. Consequently, the newly formed granulites are partially exhumed. Since a part of the heat producing layers are removed, the lith-

osphere will cool and strengthen with time.

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and Khariar basins (Chaudhuri et al., 1999) that are favour-ably located and may have served as receptacles for detritusderived from an elevated EGP in the east. Recent radiomet-ric age data, however, suggest that these basins were initi-ated in the Mesoproterozoic (Patranabis-Deb et al., 2007;Das et al., 2009), derived their detritus from the BastarCraton (Wani and Mondal, 2009, 2011) and closed byaround ~1000Ma (Basu et al., 2008). This would imply thatthere is apparently no record for the unroofing of the EGP inthe Proterozoic sedimentary basins of Peninsular India.However, even within these basins, there are indisputablyundeformed Neoproterozoic clastics that overlie (oftendeformed) Mesoproterozoic successions unconformably(e.g. Saha and Chaudhuri, 2003; Ghosh and Saha, 2003;Mishra, 2011; Figures 4A and B). There is also somecontroversy about the stratigraphic position of the tuffaceoushorizon used to date the closure of the Chhatisgarh Basin(Patranabis-Deb et al., 2007), with some workers suggestingthat the dated (~1000Ma) unit actually underlies a consider-able part of the succession (Mukherjee and Ray, 2010).Indeed, Grenvillian ages have been obtained by K–Ar datingof glauconites within some of these later rocks (Chaudhuriand Howard, 1985; Conrad et al., 2010). Thus, althoughsedimentary basins existed to the west of the granulite beltfrom the Mesoproterozoic, at least some appear to havepersisted into the Neoproterozoic. The EGP detritus was inall likelihood deposited within these basins. It is, neverthe-less, pertinent to remember that Grenvillian ages are not verycommon in the detrital record of these intracratonic basins.It can be concluded that following TE-2, a part of the

upper crust was eroded from the top of the EGP anddeposited in the cratonic basins to the west. Based on the un-usually high proportion of HPE-rich charnockites/granitoidsobserved at the current exposure level, it is suggestedthat the fraction of the upper crust removed by erosionmust have contained comparable (to the present-dayexposed EGP crust), if not higher, proportions of high heatproducing elements. The proposed model, therefore,appears to be robust in the light of existing evidence. TheEGP crust therefore became stronger in the aftermath ofdeformation, metamorphism and erosion following theTE-2 event.

4.5. Strain partitioning during the Neoproterozoic thermalevents (TE – 3)

As mentioned earlier, following TE-2, deformation andhigh-grade metamorphism in the Eastern Ghats Provincewere localized rather than penetrative, suggesting a signifi-cant and fundamental change in the rheology of the EGPcrust after TE-2. Following compressive deformation duringTE-2, episodic extensional phases are also documentedwithin the EGP, most prominently in the form of the

Koraput Alkaline Complex, and the widespread emplace-ment of mafic dykes. Subsequent compressive (and trans-pressive) deformation accompanied high-grade granulitefacies metamorphism at various times within the Neoproter-ozoic (the TE-3 events), but these are confined to the north-ern and western margins of the EGP. Importantly, in allthese cases, metamorphic reworking of the earlier granuliteswas also restricted to the vicinity of the province boundaries.The most important problem with the TE-3 events is there-fore to account for the localization of both strain and high-grade metamorphism in specific parts of the EGP.

Following TE-2, the EGP crust became fundamentallystronger and capable of transmitting far-field stresses, withthe deformation occurring only along pre-existing weakzones. Pre-existing weak zones are known to localize intra-cratonic deformation, provided they penetrate the mantlepart of the lithosphere (e.g. Van Wees and Stephenson,1995; Ziegler et al., 1995, 1998; Van Wees and Beekman,2000; Pysklywec and Beaumont, 2004). Such susceptibleweak zones in the EGP are represented either by mantle-penetrating rift zones (such as at Koraput), or by the originaldiscontinuities that confined the EGP sedimentary basin andwere inverted during the crustal shortening accompanyingTE-2. These domains are now represented by the provinceboundaries of the EGP. Thus, stresses originating as a conse-quence of tectonic activity far removed from the western andnorthern boundaries of the EGP may have concentrated de-formation in these domains. Collision-related stresses arecertainly the most likely source, as these can be transmittedfor distances of the order of 1600 km (Ziegler et al., 1995,1998). Although no synchronous collision has yet been iden-tified either to the west of the EGP, or to the east, in the oncecontiguous Rayner Province of East Antarctica (see Harley,2003), the possibility of distant plate boundary stresses be-ing transmitted through the now-strong EGP crust, and be-ing localized along the comparatively weaker provinceboundary zones remains the most likely cause of theTE-3 events.

The localization of strain in susceptible province bound-ary zones was probably initiated by thrusting on pre-existingdiscontinuity planes. This, in turn, caused crustal duplicationwith an associated thermal perturbation in the vicinity of thediscontinuity. Thermal relaxation following overthrustingmay result in granulite facies metamorphism in the middleand lower part of the thickened crustal block (England andThompson, 1984). Explaining the heating followed by load-ing P-T trajectory during metamorphism, as observed in theKoraput area, is, however, more difficult. A possible solu-tion can be devised by taking into account the time lag be-tween initiation of the shortening process and the onsetof erosion and cooling. It has been suggested earlier (e.g.Richardson and England, 1979) that such a time lag isexpected in regions where the crust is thickened rapidly,



leading to the initial development of a dense crustal root as aconsequence of metamorphic reactions. The dense crustalroot would subdue topography even following developmentof the overthickened crust. Richardson and England (1979)suggested that time scales of the order of 20Ma wererequired to reverse the density change by thermal relaxation;this reduction in crustal density would generate the topogra-phy that drives erosion. The heating followed by loadingtrajectory can be explained in thrust systems that operatewithin this time scale.

The overall shortening in an orogenic belt is accommo-dated by movement on several successive thrusts. A blockin the footwall of two successive thrusts can theoreticallyexperience a heating followed by loading trajectory. This isdemonstrated schematically in Figure 5 for a two-layeredcrustal block that is initially in thermal equilibrium(Figure 5A). An initial phase of overthrusting (along F1 inFigure 5B) would cause a step-like temperature profile attime t= t0. A point P in the lower block would thus experi-ence instantaneous loading (corresponding to depth d1) attime t= t0, but would tend to heat and achieve a highertemperature with time (t= t1). If, within the phase of thermalrelaxation following the initial thrusting, a second thrust F2develops with P again in the footwall (Figure 5C), the refer-ence point P will experience further loading (since d2> d1)and continue to heat and evolve towards the steady-statetemperature for that depth and time (t= t2). The prograde tra-jectory will therefore be one of heating followed by loading.Such a sequence of thermal evolution is only possible in thefootwall domain of a thrust that is already in a state of ther-mal relaxation following an earlier phase of overthrusting.Thus, it is imperative that the two (or more) thrusts operatewithin the time scales of conductive relaxation of the crust.Moreover, since the model is exclusively developed forcontinental crust, it is compatible with intra-continentalorogenic episodes, and invoking an association with plateboundary processes is not necessary.

Heating followed by loading trajectories have also beendocumented in other areas, as in Central Australia, and havealso been attributed to intracratonic deformation. The ther-mal anomalies in these regions have been attributed to the‘fast convective thinning’ of an overthickened lithosphericmantle root, leading to its replacement by hot, convectingasthenosphere. Such a process causes rapid heating at thebase of the crust, even as thickening continues, therebygenerating a heating followed by loading prograde metamor-phic trajectory (Loosveld, 1989a, b; Loosveld and Etheridge,1990). Other non-uniformitarian explanations, such asgravitational spreading of the overthickened crust leadingto gravitational instability and sinking of the underlyingmantle lithosphere (e.g. Houseman and Gemmer, 2007),have also been proposed. Such models have been succes-sively applied to the Tibetan Plateau (England and Molnar,

1997), and the Basin and Range Province of the southwestUnited States (Flesch et al., 2000). While some features ofsuch models may possibly be applicable in the present case,the associated formation of an extensional sedimentary ba-sin, as dictated by these models, is not observed. Further-more, all these models would be incapable of confining thethermal anomaly to a small part of the crust, as observedduring TE-3 events in the EGP. The model proposed in thiswork has the merit of confining the thermal anomaly to thefootwall region of the thrust system; this can explain whythe metamorphic episode does not affect a major part ofthe province.

4.6. Thermal Event-4—causes and consequence

Like TE-3, TE-4 is also characterized by strongly localizeddeformation, specifically along the boundary between theEastern Ghats Province and the Dharwar-Bastar Craton.Many recent studies suggest that this thermal event reflectsthe collision and amalgamation of India into the Indo-Antarctica continent, in the latest Neoproterozoic–Cambriantime (e.g. Bhadra et al., 2004; Dobmeier et al., 2006; Biswalet al., 2007). The localization of deformation during TE-4along the boundary zone with the craton is therefore compar-atively easy to explain. The mechanism of strain localizationmust be essentially similar to that during TE-3—the contactshear zone representing a weak plane that focused theaccompanying deformation, leading to heating and loadingof the boundary zone. Post-amalgamation heating documen-ted on either side of the contact (Gupta et al., 2000; Daset al., 2008) confirms the involvement of an additional heatsource following juxtaposition of the two terranes. As in theearlier case, progressive thrusting in the boundary zonewithin the time-span of thermal relaxation following theinitial thrusting can explain both the source of heat and therestricted nature of the metamorphic imprint.TE-4, therefore, was also associated with intra-continental

orogenesis that was triggered by far-field plate boundarystresses. The effect of the kinematics associated with thisevent, however, was to transport hanging wall granulites ofthe EGP further to the west over the cratonic foreland. Assuggested by Upadhyay (2008), this would cause the over-riding EGP thrust sheet to bury the original Grenvillian su-ture between the granulite belt and the Indian craton. It isfurther suggested, on the basis of the inferences drawn fromthis study that the Neoproterozoic sedimentary basins thatcontain the bulk of the sedimentary detritus derived fromthe EGP following TE-2, also currently lie below the granu-lites as a consequence of this Neoproterozoic–Cambrianmovement. This would not only account for the scarcity ofGrenvillian ages in the cratonic foreland, as suggested byUpadhyay (2008), but also for the paucity of Neoproterozoicsedimentary detritus in these cratonic basins.

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Dep

th

Temperature

A.

B.

C.

P

F1

F1

PF1

F1

F2

F2

Dep

th

Temperature

d1

t0

t1

Dep

th

Temperature

d2

t0

t1

t2

Upper crust

Lower crust

Upper crust

Lower crust

Upper crust

Lower crust

Upper crust

Lower crust

Upper crust

Lower crust

Figure 5. Schematic representation of the formation of a ‘hot’ orogen during TE-3, shown for a hypothetical two-layered crust. The blocks on the left representthe crustal section, while the boxes on the right show the corresponding geothermal profile. Note that the model is also applicable for the ‘hot’ orogeny duringTE-4.A. Pre-orogenic condition with a stable crustal section and associated geotherm. B. Shortening (orogenic) phase, with the crust being doubled by thrustingalong a pre-existing discontinuity F1. At time t= t0, immediately following thrusting, the thermal profile shows a characteristic saw-tooth form. At time t = t1, theequilibrium profile evolves to higher temperatures for the lower block. P represents a reference point in the overthrust block that experiences instantaneousburial to depth d1, and heating tending to the higher temperature corresponding to the stable geothermal profile at time t = t1. C. As thermal relaxation (heating)continues in the lower block, a second thrust F2 cuts through the section, increasing the depth of burial of point P from d1 to d2 at time t = t2. The temperature atpoint P now tries to evolve towards the new steady-state profile at t2, and registers further increase in temperature. Thus, point P experiences heating followed by

loading.



4.7. Hot orogeny in the Eastern Ghats Province—indicators of an extensional accretionary orogen?

The protracted Neoproterozoic evolution of the EasternGhats Province, with the documented periods of ‘hot orogen-esis’, can possibly be interpreted as having formed in a back-arc setting, and may be argued to represent an extensionalaccretionary orogen (Collins, 2002a, b). This would re-quire the existence of a long-lived, Pacific-type active conti-nental margin to the west of the EGP (as indicated by thewestward vergence of compressional structures). As men-tioned earlier, such a margin possibly existed alongthe present interface between the EGP granulites and theDharwar-Bastar Craton, and is now preserved as a fossilsuture zone (see Gupta et al., 2000; Leelanandam et al.,2006; Upadhyay, 2008). The ‘long-lived’ nature of such amargin is supported from a few palaeomagnetic studiesarguing that India was in all probability an isolated entitythrough much of the Neoproterozoic (see Collins andPisarevesky, 2005). The evidence that ‘tectonic switching’(extension–compression–extension–compression) occurredrepeatedly within the belt also supports the extensionalaccretionary orogen model proposed by Collins (2002b).The EGP may therefore be a deep crustal analogue of theLachlan Fold belt of southeast Australia, for which themodel was first proposed.

The extensional accretionary model may adequately rep-resent the geodynamic setting during the TE-1/TE-2 contin-uum. A problem arises from the lack of evidence for anyarc-related magmatism in the EGP within the stipulated timeperiod, apart from the megacrystic granitoid bodies thatintruded during TE-2. The bulk of the EGP crust, in fact,is of Palaeoproterozoic age, though Archaean componentsare also identified (Rickers et al., 2001b). Subduction ofcontinental crust may inhibit production of calc-alkalinemagmas (Brown, 2007); however, this is characteristic of‘cold’, as opposed to ‘hot’ subduction regimes. Also, thetime estimated for the shortening episodes in extensionalaccretionary orogens is generally small (about 15m.y., Collins,2002b). In contrast, in the EGP, TE-2 continued for an inter-val of about 50m.y. (980–930Ma). Nevertheless, the riftingin the inferred back-arc setting during TE-1, followed bycollisional orogeny during TE-2 suggest that the Grenvillian‘hot orogen’ can probably be adequately represented by themodel of Collins (2002b), or even more appropriately,that of Hyndman et al. (2005). However, during TE-3 andTE-4, these models appear to fail completely, since thiswould involve invoking plate boundaries in various partsof the EGP at different times through the Neoproterozoic.In addition, TE-3 and TE-4 are not associated with anymajor magmatism, either arc-related or intracrustal. Theregionally restricted nature of the orogeny at these times,moreover, further suggests that the classical ‘hot

orogen’ model would not be applicable to the EGP atthese times.

4.8. Diverse geodynamic settings for hot orogenies

The most interesting aspect of the Neoproterozoic evolutionof the EGP is that the region experienced orogenesis while‘hot’ at different times. As argued above, the elegant ‘exten-sional accretionary’ orogen model of Collins (2002b) canpossibly apply to the TE-1/TE-2 continuum, but cannot ex-plain TE-3 and TE-4 events. Indeed, it appears that theEGP preserves a record of at least two separate geodynamicsituations that are compatible with the formation of ‘hotorogens’.The first type is exemplified by the TE-1TE-2, where a

post-rift lithosphere is shortened. The entire rift-affectedzone is thermally perturbed and therefore, rheologicallyweak. Any subsequent strain on such a block is thereforedistributed across the entire ‘hot’ and weak section, leadingto the formation of a ‘hot orogen’. In this case, the orogenis wide and characterized by penetrative fabric formation.The most important difference between the first ‘hot’

orogeny (TE-2), and the second and third episodes (TE-3and TE-4) is the nature in which strain was partitioned inthe former and latter cases. During the second and thirdorogenies, strain was localized along pre-existing weakzones in the crust. This suggests that by the time of the lattertwo orogenies the EGP lithosphere had become significantlystronger and was capable of transmitting stresses over largedistances. This indicates another mechanism for the forma-tion of a hot orogen, specifically in previously cooled andstrong lithospheric sections. If the footwall domain of anoverthrust that is heating by thermal relaxation undergoesloading by progressive thrusting at higher structural levels,within a short time span following the initial overthrustand prior to the onset of erosion, a hot orogen will develop.Fabric formation and high-grade metamorphism in such a lo-cale will be restricted to the heated, rheologically weakeneddomain in the footwall of the initial overthrust. Spatially re-stricted (i.e. narrow) ‘hot orogens’ can then be formed in dis-tinctly intracratonic settings.

5. CONCLUSIONS

The Eastern Ghats Province underwent major orogenicevents in the Neoproterozoic–Cambrian time: 980–930,900–650 and 550–500Ma. At each time, the event was char-acterized by deformation occurring in synchroneity withhigh temperature metamorphism in the crust. The first eventwas characterized by distributed strain throughout the entireprovince, resulting in pervasive fabric formation throughoutthe EGP. In contrast, strain and thermal anomalies during the

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later orogenies were confined to the vicinity of crustal-scaleweak zones. In the earlier case, pre-orogenic rifting led tolithospheric mantle delamination and ultrahigh-temperaturemetamorphism at the base of the crust. This was closely fol-lowed by crustal shortening related to the collision of thegranulite belt with the Archaean Indian craton. The thermalanomaly persisting from the rifting event, followed by thethermal relaxation associated with crustal shortening led toprolific melt production and emplacement of HPE-rich char-nockites/granitoids at mid- to upper crustal levels. The result-ing heating caused rheological weakening of the crustal sec-tion, and the subsequent Grenvillian (i.e. 980–930Ma)orogeny led to strain being distributed across the entire ther-mally perturbed zone. Following this event, a major propor-tion of the HPE was transferred into the middle and uppercrust. Erosion removed a substantial portion of the latter,and deposited the detritus in cratonic sedimentary basins tothe west. Subsequently, the EGP crust and lithosphere wasstrengthened, and could effectively transmit stresses, and con-centrate them along pre-existing zones of weakness, e.g.along the margins of the inverted basin, or along the craton–mobile belt boundary. Progressive thrusting in these domainsled to consistent loading of the footwall, even as it underwentthermal relaxation following crustal thickening. Since bothstrain and lithospheric thickening are associated with the foot-wall of pre-existing discontinuities, the ‘hot orogen’ so formedis also spatially restricted.

ACKNOWLEDGEMENTS

SG thanks the Guest Editors of the Special Issue, ProfessorsM. Santosh and S. Dagupta, for the invitation to contributeto the volume. The paper benefited substantially from the com-ments of an anonymous reviewer and the editorial handling ofProf. Dasgupta. The Chief Editor, Prof. Ian Somerville, is alsothanked for meticulous editing of the manuscript before sub-mission. The ideas expressed in this paper are partially an out-come of an ongoing DST-AISRF sponsored research projectno. INT/AUS/P-28/09.

REFERENCES

Aftalion, M., Bowes, D.R., Dash, B., Fallick, A.E. 2000. Late Pan-Africanthermal history in the Eastern Ghats terrane, India, from U–Pb and K–Arisotopic study of the Mid-Proterozoic Khariar alkali syenite Orissa.Geological Survey of India Special Publication 57, 26–33.

Basu, A., Patranabis-Deb, S., Schieber, J., Dhang, P.C. 2008. Strati-graphic position of the ~1000Ma Sukhda tuff (Chhatisgarh Supergroup,India) and the 500Ma question. Precambrian Research 167, 383–388.

Bhadra, S., Gupta, S. Banerjee, M. 2004. Structural evolution across theEastern Ghats Mobile Belt–Bastar craton boundary, India: hot over coldthrusting in an ancient collision zone. Journal of Structural Geology26, 233–245.

Bhattacharya, S., Sen, S.K., Acharya, A. 1994. The structural setting ofthe Chilka Lake granulite–migmatite–anorthosite suite with emphasison the time relation of charnockites. Precambrian Research 66, 393–409.

Bhattacharya, S., Basei M. 2010. Contrasting magmatic signatures in theRairakhol and Koraput alkaline complexes, Eastern Ghats Belt, India.Journal of Earth System Science 119, 175–181.

Biswal, T.K., Jena, S.K., Datta, S., Das, R., Khan, K. 2000. Deformationof Terrane Boundary Shear Zone (Lakhna Shear Zone) between EasternGhats Mobile Belt and Bastar Craton in Balangir and Kalahandi Districts,Orissa. Journal of the Geological Society of India 55, 367–380.

Biswal, T.K., De Waele, B., Ahuja, H. 2007. Timing and dynamics of thejuxtaposition of the Eastern Ghats Mobile Belt against the BhandaraCraton, India: a structural and zircon U–Pb SHRIMP study of the fold-thrust belt and associated nepheline syenite plutons. Tectonics 26,TC4006, doi: 10.1029/2006TC002005.

Bhowmik, S.K. 1999. Multiple episodes of tectonothermal processes in theEastern Ghats granulite belt. Proceedings of the Indian Academy ofSciences (Earth and Planetary Science) 106(3), 131–146.

Boger, S.D., Carson, C.J., Wilson, C.J.L., Fanning, C.M. 2000.Neoproterozoic deformation in the Radock Lake region of the northernPrince Charles Mountains, east Antarctica: evidence for a single pro-tracted orogenic event. Precambrian Research 104, 1–24.

Bose, S., Dunkley, D.J., Dasgupta, S., Das, K., Arima, M. 2011. India–Antarctica–Australia–Laurentia connection in the Paleoproterozoic–Mesoproterozoic revisited: evidence from new zircon U–Pb and monazitechemical age data from the Eastern Ghats Belt India. Geological Societyof America Bulletin, doi: 10.1130/B30336.1.

Brown, M. 2007. Metamorphic conditions in orogenic belts: a record ofsecular change. International Geology Review 49, 193–234.

Burg, J.P., Gerya, T.V. 2005. The role of viscous heating in Barrovianmetamorphism of collisional orogens: thermomechanical models andapplication to the Lepontine Dome in the Central Alps. Journal ofMetamorphic Geology 23, 75–95.

Chardon, D., Jayananda, M., Peucat, J. 2011. Lateral constrictional flowof hot orogenic crust: Insights from the Neoarchaean of south India, geo-logical and geophysical implications for orogenic plateaux. GeochemistryGeophysics Geosystems 12, Q02005, doi: 10.1029/2010GC003398.

Chatterjee, N., Crowley, J.L., Mukherjee, A., Das, S. 2008. Geochronol-ogy of the 983-Ma Chilka Lake Anorthosite, Eastern Ghats Belt,India: implications for pre-Gondwana tectonics. Journal of Geology116, 105–118.

Chaudhuri, A.K., Howard, J.D. 1985. Ramgundam sandstone: a middleProterozoic shoal bar sequence. Journal of Sedimentary Petrology 55,392–397.

Chaudhuri, A.K., Mukhopadhyay, J., Deb, S.P., Chanda, S.K. 1999.The Neoproterozoic cratonic successions of peninsular India. GondwanaResearch 2, 213–225.

Chetty, T.R.K. 2010. Structural architecture of the northern compositeterrane, the Eastern Ghats Mobile Belt, India: implications for Gondwanatectonics. Gondwana Research 18, 565–582.

Chetty, T.R.K., Murthy, D.S.N. 1998. Regional tectonic framework of theEastern Ghats Mobile Belt: a new interpretation. Geological Survey ofIndia Special Publication 44, 39–50.

Collins, A.S., Pisarevesky, S.A. 2005. Amalgamating East Gondwana: theevolution of the circum-Indian orogens. Earth Science Review 71, 221–270.

Collins, W.J. 2002a. Hot orogens, tectonic switching, and creation of con-tinental crust. Geology 30, 535–538.

Collins, W.J. 2002b. Nature of extensional accretionary orogens. Tectonics21(4), 10.1029/2000TC001272.

Collins, W.J., Richards, S.W. 2008. Geodynamic significance of S-typegranites in circum-Pacific orogens. Geology 39(7), 559–562.

Conrad, J.E., Hein, J.R., Chaudhuri, A.K., Patranabis-Deb, S.,Mukhopadhyay, J., Deb, G.K., Beukes, N.J. 2010. Constraints on thedevelopment of Proterozoic basins in central India from 40Ar/39Aranalysis of authigenic glauconitic minerals. Bulletin Geological Societyof America, doi: 10.1130/B30083.1

Crosby, A.G, White, N.J., Edwards, G.R., Shillington, D.J. 2010. Self-consistent strain rate and heat flow modelling of lithospheric extension:application to Newfoundland–Iberia conjugate margins. PetroleumGeoscience 16(3), 247–256.



Das, S., Nasipuri, P., Bhattacharya, A., Swaminathan, S. 2008. Thethrust contact between the Eastern Ghats Belt and the adjoining Bastarcraton (Eastern India): evidence from mafic granulites and tectonic impli-cations. Precambrian Research 162, 70–85.

Das, K., Yokoyama, K., Chakraborty, P.P., Sarkar, A. 2009. Basal tuffsand contemporaneity of the Chhatisgarh and Khariar basins based on newdates and geochemistry. Journal of Geology 117, 88–102.

Das, K., Bose, S., Karmakar, S., Dunkley, D.J., Dasgupta, S. 2011. Mul-tiple tectonometamorphic imprints in the lower crust: first evidence of ca.950Ma (zircon U–Pb SHRIMP) compressional reworking of UHT alumi-nous granulites from the Eastern Ghats Belt, India. Geological Journal46(2–3), 217–239.

Dasgupta, S., Sengupta, P. 1995. Ultrametamorphism in Precambriangranulite terrains—evidence from Mg–Al granulites and calc-granulitesof the Eastern Ghats, India. Geological Journal 30, 307–318.

Dasgupta, S., Sengupta, P. 2003. Indo-Antarctica correlation: a perspec-tive from the Eastern Ghats Belt. In: Proterozoic East Gondwana:Supercontinent Assembly and Breakup, Yoshida, M., Windley, B.F.,Dasgupta, S. (eds) Geological Society, London, Special Publications206, 131–143.

Dasgupta, S., Sengupta, P., Fukuoka, M., Bhattacharya, P.K. 1991.Mafic granulites from the Eastern Ghats, India: further evidence for ex-tremely high temperature crustal metamorphism. Journal of Geology99, 124–133.

Dasgupta, S., Sengupta, P., Ehl, J., Raith, M., Bardhan, S. 1995. Reac-tion textures in a suite of spinel granulites from the Eastern Ghats Belt,India: evidence for polymetamorphism, a partial petrogenetic grid in thesystem KFMASH and the roles of ZnO and Fe2O3. Journal of Petrology36, 435–461.

Dobmeier, C. 2006. Emplacement of Proterozoic massif-type anorthositeduring regional shortening: evidence from the Bolangir anorthosite com-plex (Eastern Ghats Province, India). International Journal of EarthScience 95, 543–555.

Dobmeier, C., Raith, M. 2000. On the origin of ‘arrested’ charnockitiza-tion in the Chilka Lake area, Eastern Ghats Belt, India. GeologicalMagazine 137, 27–37.

Dobmeier, C.J., Simmat, R. 2002. Post-Grenvillean transpression inthe Chilka Lake area, Eastern Ghats Belt—implications for thegeological evolution of peninsular India. Precambrian Research 113,243–268.

Dobmeier, C.J., Raith, M. 2003. Crustal architecture and evolution of theEastern Ghats Belt and adjacent regions of India. In: Proterozoic EastGondwana: Supercontinent Assembly and Breakup, Yoshida M., WindleyB.F., Dasgupta S. (eds). Geological Society, London, Special Publica-tions 206, 145–168.

Dobmeier, C., Lütke, S., Hammerschmidt, K., Mezger, K. 2006.Emplacement and deformation of the Vinukonda meta-granite (EasternGhats, India)—implications for the geological evolution of peninsularIndia and for Rodinia reconstructions. Precambrian Research 146,165–178.

Ducea, M.N. 2011. Fingerprinting orogenic delamination. Geology 39(2),191–192.

England, P.C, Thompson, A.B. 1984. Pressure–temperature–time paths ofmetamorphism. I. Heat transfer during evolution of regions of thickenedcontinental crust. Journal of Petrology 25, 894–928.

England, P.C., Molnar, P. 1997. Active deformation of Asia; from kine-matics to dynamics. Science 278, 647–650.

Flesch, L.M., Holt, W.E., Haines, J.A., Shen-Tu, B. 2000. Dynamics ofthe Pacific–North American plate boundary in the western United States.Science 287, 834–836.

Forbes, C.J., Betts, P.G., Giles, D., Weinberg, R. 2008. Reinterpretationof the tectonic context of high-temperature metamorphism in the BrokenHill Block, NSW, and implications on the Palaeo- to Meso-Proterozoicevolution. Precambrian Research 166, 338–349.

Garzione, C.N., Hoke, G.D., Libarkin, J.C., Withers, S., MacFadden,B., Eiler, J., Ghosh, P., Mulch, A. 2008. Rise of the Andes. Science320, 1304–1307.

Ghosh, G., Saha, D. 2003. Deformation of the Proterozoic SomanpalliGroup, Pranhita-Godavari valley, South India—implication for a Mesopro-terozoic basin inversion. Journal of Asian Earth Sciences 21, 579–594.

Grew, E.S., Manton, W.I. 1986. A new correlation of sapphirine granulitesin the Indo-Antarctic metamorphic terrain: late Proterozoic dates from theEastern Ghats Province of India. Precambrian Research 33, 123–137.

Gupta, S. 2004. The Eastern Ghats Belt, India—a new look at an old oro-gen. In: Uniformitarianism revisited—comparison between ancient andmodern orogens of India. Geological Survey of India Special Publica-tions 84, 75–100.

Gupta, S., Bose, S. 2004. Deformation history of the Kunavaram Complex,Eastern Ghats Belt, India: implications for alkaline magmatism along theIndo-Antarctica suture. Gondwana Research 7(4), 1228–1335.

Gupta, S., Bhattacharya, A., Raith, M., Nanda, J.K. 2000. Pressure–temperature–deformational history across a vestigial craton–mobile beltboundary: the western margin of the Eastern Ghats Belt at Deobhog,India. Journal of Metamorphic Geology 18, 683–697.

Gupta, S., Nanda, J., Mukherjee, S., Santra, M. 2005. Alkaline magma-tism versus collision tectonics in the Eastern Ghats Belt, India: constraintsfrom structural studies in the Koraput Complex. Gondwana Research 8(3), 403–419.

Gutiérrez-Alonso, G., Murphy, J.B., Fernández-Suárez, J., Weil, A.B.,Franco, M.P., Gonzalo, J.P. 2011. Lithospheric delamination in thecore of Pangea: Sm–Nd insights from the Iberian mantle. Geology 39,155–158.

Halden, N.M., Bowes, D.R., Dash, B. 1982. Structural evolution of mig-matites in granulite facies terrane: the Precambrian crystalline complexof Angul, Orissa, India. Philosophical Transactions of the Royal Societyof Edinburgh (Earth Science) 73, 109–118.

Harley, S. 2003. Archaean–Cambrian crustal development of East Antarctica:metamorphic characteristics and tectonic implications. In: ProterozoicEast Gondwana: Supercontinent Assembly and Breakup, Yoshida, M.,Windley, B.F., Dasgupta, S. (eds). Geological Society, London, SpecialPublications 206, 203–230.

Harley, S. 2004. Extending our understanding of ultrahigh temperaturecrustal metamorphism. Journal of Mineralogical and PetrologicalSciences 99, 140–158.

Harley, S. 2008. Refining the P-T records of UHT crustal metamorphism.Journal of Metamorphic Geology 26, 125–154.

Hippe, K. 2006. Aufbau der U–Pb-Datierungsmethode und ihre Anwendungauf Zirkone des Alkalikomplexes von Koraput, Eastern-Ghats-Provinz.Unpublished diploma thesis, Free University of Berlin, Indien.

Hippe, K., Hammerschmidt, K., Dobmeier, C.J. 2008. Evidence of meta-morphic zircon growth in Zr-depleted nepheline syenite. GeophysicalResearch Abstracts 10, EGU2008-A-09472.

Houseman, G.A., McKenzie, D.P., Molnar, P. 1981. Convective instabil-ity of a thickened boundary layer and its relevance for the thermal evolu-tion of continental convergence belts. Journal of Geophysical Research86(B7), 6115–6132.

Houseman, G.A., Molnar, P. 2001. Mechanisms of lithospheric renewalassociated with continental orogeny. In: Continental Reworking andReactivation, Miller J.A., Holdsworth, R.E., Buick, I.S., Hand, M.(eds). Geological Society, London, Special Publications 184, 13–37.

Houseman, G.A., Gemmer, L. 2007. Intra-orogenic extension driven bygravitational instability: Carpathian–Pannonian orogeny. Geology 35(12), 1135–1138.

Hyndman, R.D., Currie, C.A., Mazzotti, S.P. 2005. Subduction zonebackarcs, mobile belts, and orogenic heat. GSA Today 15, 4–10.

Kamineni, D.C., Rao, A.T. 1988. Sapphirine granulites from Kakanuruarea, Eastern Ghats, India. American Mineralogist 73, 692–700.

Kelly, N.M., Clarke, G.L., Fanning, C.M. 2002. A two-stage evolution ofthe Neoproterozoic Rayner Structural Episode: new U–Pb sensitive highresolution ion microprobe constraints from the Oygarden Group, KempLand, East Antarctica. Precambrian Research 116, 307–330.

Kelsey, D. 2008. On ultrahigh-temperature crustal metamorphism. GondwanaResearch 13, 1–29.

Kovach, V.P., Berezhnaya, N.G., Salnikova, E.B., Narayana, B.L.,Divakara Rao, V., Yoshida, M., Kotov, A.B. 1998. U-Pb zircon ageand Nd isotope systematics of megacrystic charnockites in the EasternGhats Granulite Belt, India, and their implications for East Gondwanareconstruction. Journal of African Earth Science 27, 125–127.

Kovach, V.P., Simmat, R., Rickers, K. 2001. The Western CharnockiteZone of the Eastern Ghats Belt, India—an independent crustal province

s. gupta


of late Archaean (2.8Ga) and Palaeoproterozoic (1.7–1.6Ga) terrains.International Symposium and Field Workshop on the Assemblyand Breakup of Rodinia and Gondwana, Osaka, 26–30 October 2001.Gondwana Research 4, 666–667.

Krause, O. 1998. Die petrogenetische Bedeutung der porphyrischenGranitoide fu/r die Krustenentwicklung des Eastern Ghats Belt (Indien).PhD Thesis, Universität Bonn: Germany.

Krause, O., Dobmeier, C., Raith, M.M., Mezger, K. 2001. Age of em-placement of massif-type anorthosites in the Eastern Ghats Belt, India:constraints from U–Pb zircon dating and structural studies. PrecambrianResearch 109, 25–38.

Lal, R.K., Ackermand, D., Upadhyay, D.H. 1987. P-T-X relation-ships deduced from corona textures in sapphirine–spinel–quartzassemblages from Paderu, southern India. Journal of Petrology 28,1139–1168.

Leelanandam, C., Burke, K., Ashwal, L.D., Webb, S.J. 2006. Proterozoicmountain building in peninsular India: an analysis based primarily onalkaline rock distribution. Geological Magazine 143, 195–212.

Loosveld, R.J.H. 1989a. The synchronism of crustal thickening and highT/low Pmetamorphism in theMount Isa Inlier, Australia 1. An example, thecentral Soldiers Cap belt. Tectonophysics 158, 173–190.

Loosveld, R.J.H. 1989b. The synchronism of crustal thickening and lowpressure-facies metamorphism in the Mount Isa Inlier, Australia 1.Fast convective thinning of mantle lithosphere during crustal thickening,Tectonophysics 158, 191–218.

Loosveld, R.J.H., Etheridge, M.A. 1990. A model for low-pressure faciesmetamorphism during crustal thickening. Journal of Metamorphic Geology8, 257–267.

Marotta, A.M., Spalla, M., Gosso, G. 2009. Upper and lower crustal evo-lution during lithospheric extension: numerical modelling and naturalfootprints from the European Alps. In: Extending a continent: Architec-ture, Rheology and Heat Budget, Ring U., Wernicke B. (eds.). GeologicalSociety, London, Special Publications 321, 33–72.

McKenzie, D.P. 1978. Some remarks on the development of sedimentarybasins. Earth and Planetary Science Letters 40, 25–32.

McKenzie, D., Priestley, K. 2008. The influence of lithospheric thicknessvariations on continental evolution. Lithos 102, 1–11.

Mezger, K. Cosca, M.A. 1999. The thermal history of the Eastern GhatsBelt (India), as revealed by U–Pb and 40Ar–39Ar dating of metamorphicand magmatic minerals: implications for the SWEAT correlation.Precambrian Research 94, 251–271.

Mishra, D.C. 2011. Long hiatus in Proterozoic sedimentation in India:Vindhyan, Cuddapah and Pakhal basins—a plate tectonic model. JournalGeological Society of India 77, 17–25.

Mohan, A., Tripathi, P., Motoyoshi, Y. 1997. Reaction history of sapphi-rine granulites and a decompressional P-T path in a granulite complexfrom the Eastern Ghats. Proceedings of the Indian Academy of Sciences(Earth and Planetary Science) 106(3), 115–129.

Mukherjee, A., Ray, R.K. 2010. An alternate view on the stratigraphicposition of the ~1Ga Sukhda Tuff vis-à-vis chronostratigraphy ofthe Precambrians of the Central Indian Craton. Journal of Geology118, 325–332.

Mukhopadhyay, A.K., Bhattacharya, A. 1997. Tectonothermal evolutionof the gneiss complex at Salur in the Eastern Ghats belt of India. Journalof Metamorphic Geology 15, 719–734.

Nanda, J., Gupta, S., Dobmeier, C.J. 2008. Metamorphism of theKoraput Alkaline Complex, Eastern Ghats Province, India—evidencefor reworking of a granulite terrane. Precambrian Research 165,153–168.

Nanda, J.K., Pati, U.C. 1989. Field relations and petrochemistry of thegranulites and associated rocks in the Ganjam-Koraput sector of theEastern Ghats Belt. Indian Minerals 43, 247–264.

Narayanaswami, S. 1975. Proposal for charnockite–khondalite system inthe Archaean Shield of Peninsular India. Geological Survey of IndiaMiscellaneous Publication 23, 1–16.

Pal, S., Bose, S. 1997. Mineral reactions and geothermobarometry in asuite of granulite facies rocks from Paderu, Eastern Ghats GranuliteBelt: a reappraisal of the P-T trajectories. In: Eastern Ghats Granulites,Sen, S.K. (ed.). Proceedings of the Indian Academy of Sciences (Earthand Planetary Science) (Special Volume) 106, 77–89.

Patranabis-Deb, S. Bickford, M.E., Hill, B., Chaudhuri, A.K., Basu, A.2007. SHRIMP ages of zircon in the uppermost tuff in the Chhatisgarhbasin in Central India require ~500Ma adjustment in Indian Proterozoicstratigraphy. Journal of Geology 115, 407–415.

Paul, D.K., Ray Barman, T.K., McNaughton, M.J., Fletcher, I.R., Potts,P.J., Ramakrishnan, M., Augustine, P.F. 1990. Archaean–Proterozoicevolution of Indian charnockites: isotopic and geochemical evidence fromgranulites of the Eastern Ghats Belt. Journal of Geology 98, 253–263.

Pysklywec, R.N., Beaumont, C. 2004. Intraplate tectonics: feedbackbetween radioactive thermal weakening and crustal deformation drivenby mantle lithospheric instabilities. Earth and Planetary Science Letters221, 275–292.

Rajesh, H.M., Mukhopadhyay, J., Beukes, N.J., Gutzmer, J., Belyanin,G.A., Armstrong, R.A. 2009. Evidence for an early Archaean granitefrom Bastar craton, India. Journal of the Geological Society of London166(2), 193–196.

Ramakrishnan, M., Nanda, J.K., Augustine, P.F. 1998. Geological evo-lution of the Proterozoic Eastern Ghats Mobile Belt. Geological Survey ofIndia Special Publication 44, 1–21.

Richardson, S.W., England, P.C. 1979. Metamorphic consequences ofcrustal eclogite production in overthrust orogenic zones. Earth andPlanetary Science Letters 42, 183–190.

Rickers, K., Raith, M.M., Dasgupta, S. 2001a. Multistage reaction tex-tures in xenolithic high Mg–Al granulites at Anakapalle, Eastern GhatsBelt, India: examples of contact polymetamorphism and infiltration-driven metasomatism. Journal of Metamorphic Geology 19, 91–107.

Rickers, K., Mezger K., Raith, M.M. 2001b. Evolution of the continentalcrust in the Proterozoic Eastern Ghats Belt, India and new constraints forRodinia reconstruction: implications from Sm–Nd, Rb–Sr and Pb–Pbisotopes. Precambrian Research 112, 183–210.

Saha, D., Chaudhuri, A.K. 2003. Deformation of the Proterozoic succes-sions in the Pranhita-Godavari basin, south India—a regional perspective.Journal of Asian Earth Sciences 21, 557–565.

Sandiford, M., 1999. Mechanics of basin inversion. Tectonophysics 305,109–120.

Sandiford, M., Powell, R., 1986. Deep crustal metamorphism during con-tinental extension: modern and ancient examples. Earth and PlanetaryScience Letters 79, 151–158.

Sandiford, M., Hand, M. 1998. Controls on the locus of intraplate defor-mation in central Australia. Earth and Planetary Science Letters 162,97–110.

Sarkar, A., Nanda, J.K. Paul, D.K.; Bishui, P.K., Gupta, S.N. 1989. LateProterozoic alkaline magmatism in the Eastern Ghats Belt: Rb–Sr isoto-pic study on the Koraput Complex, Orissa. Indian Minerals 43, 265–272.

Sarkar, M., Gupta, S., Panigrahi, M.K. 2007. Disentangling tectoniccycles along a multiply deformed terrane margin: structural and metamor-phic evidence for mid-crustal reworking of the Angul granulite complex,Eastern Ghats Belt, India. Journal of Structural Geology 29, 802–818.

Sclater, J.C., Royden, L., Hoyrath, F., Burchfiel, B.C.S., Semken, S.,Stegena, L. 1980. The formation of the intra-Carpathian basins as deter-mined from subsidence data. Earth and Planetary Science Letters 51,139–162.

Sen, S.K., Bhattacharya, S., Acharya, A. 1995. A multi-stage pressure–temperature record in the Chilka Lake granulites: the epitome of meta-morphic evolution of the Eastern Ghats, India? Journal of MetamorphicGeology 13, 287–298.

Sen, S.K., Bhattacharya, S. 1997. Dehydration melting of micas in theChilka Lake khondalites: the link between the metapelites and granitoids.Proceedings of the Indian Academy of Sciences (Earth and PlanetaryScience) 106, 277–297.

Sengupta, P., Dasgupta, S., Bhattacharya, P.K., Fukuoka, M.,Chakraborty, S., Bhaowmik, S. 1990. Pretectonic imprints in sapphi-rine granulites from Anantagiri, Eastern Ghats, India, and their implica-tions. Journal of Petrology 31, 971–996.

Sengupta, P., Karmakar, S., Dasgupta, S., Fukuoka, M. 1991. Petrologyof spinel granulites from Araku, Eastern Ghats, India and a petrogeneticgrid for sapphirine-free rocks in the system FMAS. Journal of MetamorphicGeology 9, 451–459.

Sengupta, P., Sanyal, S., Dasgupta, S., Fukuoka, M., Ehl, J., Pal, S.1997. Controls of mineral reactions in high-grade garnet–wollastonite–



scapolite-bearing calc-silicate rocks: an example from Anakapalle,Eastern Ghats, India. Journal of Metamorphic Geology 15, 551–564.

Sengupta, P., Dasgupta, S., Dutta, N.R., Raith, M.M., 2008. Petrologyacross a calcareous rock–anorthosite interface from the Chilka LakeComplex, Orissa: implications for Neo-Proterozoic crustal evolution ofthe northern Eastern Ghats Belt. Precambrian Research 162, 40–58.

Senthil Kumar, P., Menon, R., Reddy G.K. 2007. The role of radiogenicheat production in the thermal evolution of a Proterozoic granulite-faciesorogenic belt: Eastern Ghats (Indian shield). Earth and Planetary ScienceLetters 254, 39–54.

Shaw, R.K., Arima, M. 1996. High temperature metamorphic imprintfrom calc-granulites of Rayagada, Eastern Ghats, India: implications ofisobaric cooling path. Contributions to Mineralogy and Petrology 126,169–180.

Shaw, R.K., Arima, M., Kagami, H., Fanning, C.M., Shiraishi, K.,Motoyoshi, Y. 1997. Proterozoic events in the Eastern Ghats GranuliteBelt, India: evidence from Rb–Sr, Sm–Nd systematics, and SHRIMPdating. Journal of Geology 105, 645–656.

Simmat, R., Raith, M.M. 2008. Th–U–Pb monazite geochronometry ofthe Eastern Ghats Belt, India: timing an spatial disposition of poly-metamorphism. Precambrian Research 162, 16–39.

Thompson, A.B., Schulmann, K., Jezek, J., Tolar, V. 2001. Thermallysoftened continental extensional zones (arcs and rifts) as precursors tothickened orogenic belts. Tectonophysics 332, 115–141.

Tsunogae, T., Santosh, M. 2011. Sapphirine + quartz assemblage from theSouthern Granulite Terrane, India: diagnostic evidence for ultrahigh-temperature metamorphism within the Gondwana collisional orogen.Geological Journal 46(2–3), 183–197.

Upadhyay, D. 2008. Alkaline magmatism along the southeastern marginof the Indian shield: implications for regional geodynamics and con-straints on craton-Eastern Ghats Belt suturing. Precambrian Research162, 59–69.

Upadhyay, D., Raith, M., Mezger, K., Bhattacharya, A., Kinny, P.D.2006. Mesoproterozoic rifting and Pan-African continental collision inSE India: evidence from the Khariar alkaline complex. Contributions toMineralogy and Petrology 151, 434–456.

Upadhyay, D., Gerdes, A., Raith M.M. 2009. Unraveling sedimentaryprovenance and tectonothermal history of high-temperature metapelites,using zircon and monazite chemistry: a case study from the Eastern GhatsBelt, India. Journal of Geology 117, 665–683.

Van Wees, J.-D., Stephenson, R.A. 1995. Quantitative modeling of basinand rheological evolution of the Iberian basin (Central Spain): implica-tions for lithosphere dynamics of intraplate extension and inversion.Tectonophysics 252, 163–178.

Van Wees, J.-D., Beekman, F. 2000. Lithosphere rheology duringintraplate basin extension and inversion—inferences from automatedmodeling of four basins in western Europe. Tectonophysics 320, 219–242.

Vijaya Kumar, K., Leelanandam, C. 2008. Evolution of the EasternGhats Belt, India: a plate tectonic perspective. Journal Geological Societyof India 72, 720–749.

Wani, H., Mondal, M.E.A. 2009. Petrochemistry of sandstones fromNeoproterozoic basins of the Bastar craton, Central Indian Shield: impli-cations for paleoweathering provenance and tectonic history. Island Arc18, 352–374.

Wani, H., Mondal, M.E.A. 2011. Evaluation of provenance, tectonic set-ting, and paleo-redox conditions of the Mesoproterozoic–Neoproterozoicbasins of the Bastar craton, Central Indian Shield: using petrography ofsandstones and geochemistry of shales. Lithosphere 3(2), 143–154.

Ziegler, P.A., Cloetingh, S., Van Wees, J.D 1995. Dynamics of intra-platecompressional deformation: the Alpine foreland and other examples.Tectonophysics 252, 7–59.

Ziegler, P.A., van Wees, J.-D., Cloetingh, S. 1998. Mechanical controlson collision-related compressional intraplate deformation. Tectonophysics300, 103–129.

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Strain localization, granulite formation and geodynamic setting of ‘hot orogens’: a case study from the Eastern Ghats Province, India