Journal of Petrology Advance Access originally published online on February 4, 2005
Journal of Petrology 2005 46(6):1085-1119; doi:10.1093/petrology/egi011
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Mesoproterozoic Reworking of Palaeoproterozoic Ultrahigh-temperature Granulites in the Central Indian Tectonic Zone and its Implications
1 DEPARTMENT OF GEOLOGY AND GEOPHYSICS, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR-721 302, INDIA
2 MINERALOGISCH–PETROLOGISCHES INSTITUT, DER UNIVERSITÄT BONN, POPPELSDORFER SCHLOß, D-53115 BONN, GERMANY
RECEIVED OCTOBER 4, 2003; ACCEPTED DECEMBER 14, 2004
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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In the southern periphery of the Sausar Mobile Belt (SMB), the southern component of the Central Indian Tectonic Zone (CITZ), a suite of felsic and aluminous granulites, intruded by gabbro, noritic gabbro, norite and orthopyroxenite, records the polymetamorphic evolution of the CITZ. Using sequences of prograde, peak and retrograde reaction textures, mineral chemistry, geothermobarometric results and petrogenetic grid considerations from the felsic and the aluminous granulites and applying metamorphosed mafic dyke markers and geochronological constraints, two temporally unrelated granulite-facies tectonothermal events of Pre-Grenvillian age have been established. The first event caused ultrahigh-temperature (UHT) metamorphism (M1) (T
950°C) at relatively deeper crustal levels (P 9 kbar) and a subsequent post-peak near-isobaric cooling P–T history (M2). M1 caused pervasive biotite-dehydration melting, producing garnet–orthopyroxene and garnet–rutile and sapphirine–spinel-bearing incongruent solid assemblages in felsic and aluminous granulites, respectively. During M2, garnet–corundum and later spinel–sillimanite–biotite assemblages were produced by reacting sapphirine–spinel–sillimanite and rehydration of garnet–corundum assemblages, respectively. Applying electron microprobe (EMP) dating techniques to monazites included in M1 garnet or occurring in low-strain domains in the felsic granulites, the UHT metamorphism is dated at 2040–2090 Ma. Based on the deep crustal heating–cooling P–T trajectory, the authors infer an overall counterclockwise P–T path for this UHT event. During the second granulite event, the Palaeoproterozoic granulites experienced crustal attenuation to 6·4 kbar at T 675°C during M3 and subsequent near-isothermal loading to 8 kbar during M4. In the felsic granulites, the former is marked by decomposition of M1 garnet to orthopyroxene–plagioclase symplectites. During M4, there was renewed growth of garnet–quartz symplectites in the felsic granulites, replacing the M3 mineral assemblage and also the appearance of coronal garnet–quartz–clinopyroxene assemblages in metamorphosed mafic dykes. Using monazites from metamorphic overgrowths and metamorphic recrystallization domains from the felsic granulite, the M4 metamorphism is dated at 1525–1450 Ma. Using geochronological and metamorphic constraints, the authors interpret the M3–M4 stages to be part of the same Mesoproterozoic tectonothermal event. The result provides the first documentation of UHT metamorphism and Palaeo- and Mesoproterozoic metamorphic processes in the CITZ. On a broader scale, the findings are also consistent with the current prediction that isobarically cooled granulites require a separate orogeny for their exhumation. KEY WORDS: Central Indian Tectonic Zone; UHT metamorphism; counterclockwise P–T path; monazite chemical dating
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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The majority of orogens are tectonic collages of a number of elongated lithotectonic domains with contrasting tectonothermal histories (e.g. Grenville orogen: Rivers et al., 1989
; Eastern Ghats Mobile Belt: Dobmeier & Raith, 2003). The key to unravelling ancient orogenic processes is, thus, to identify these domains and to reconstruct the metamorphic P–T–t paths of rocks within them. Careful reconstruction of metamorphic P–T–t paths in these domains is expected to reveal their polycyclic nature. Such polymetamorphic history has been documented from basement inliers in some orogens (e.g. Chewore Inliers, in the Zambezi belt, Zimbabwe: Goscombe et al., 1998; Ungava orogen, Canada: St-Onge & Ijewliw, 1996). One of the locales where polymetamorphic rocks could exist as a distinct metamorphic belt is the so-called allochthonous polycyclic domain in an orogen (Rivers et al., 1989). The present study is from one such allochthonous polycyclic domain in the Sausar Mobile belt (SMB), which constitutes the southern component of the composite Central Indian Tectonic Zone (CITZ) (Fig. 1). In recent reconstructions of East Gondwanaland, the CITZ is recognized as an important Proterozoic collisional zone, along which the North Indian Block (NIB: Eriksson et al., 1999; comprising the Aravalli–Bundelkhand Provinces) and the South Indian Block (SIB; comprising the Singhbhum, Bastar and Dharwar Provinces) were amalgamated during the Palaeoproterozoic to form the Indian subcontinent (Yedekar et al., 1990; Jain et al., 1991; Mishra et al., 2000). However, there is insufficient petrological and geochronological evidence in support of this. The recent discovery of a high-pressure upper amphibolite–granulite-facies domain (locally referred to as the Ramakona–Katangi granulite (RKG) domain, Fig. 1) in the northern part of the SMB has led to the suggestion that this belt marks a major, Grenville-aged, collisional event during the final amalgamation of the SIB and the NIB (Bhowmik & Roy, 2003; Bhowmik & Spiering, 2004). The present study is from another such domain [Bhandara Balaghat granulite (BBG) domain, Fig. 1] in the southern part of the SMB. The authors have used reaction textures, mineral chemistry, geothermobarometric results and petrogenetic grid considerations from felsic granulites, aluminous granulites and mafic dyke markers, and geochronological data, to elucidate polymetamorphic events, separated in age by 500 Ma. In the process, a Palaeoproterozoic ultrahigh-temperature (UHT) metamorphism has been recognized for the first time in the CITZ. The implications of these new findings in the context of the evolutionary history of orogens in general, and of the CITZ in particular, are discussed. Mineral abbreviations are after Kretz (1983).
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GEOLOGICAL SETTING |
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TOPABSTRACTINTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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The BBG domain is an allochthonous tectonic sheet between the low-grade (greenschist-facies) Sausar Group of rocks in the north and the cratonic domain of low- to medium-grade felsic gneisses of the Amgaon gneissic complex on the south (Bhowmik & Pal, 2000
; Bhowmik & Roy, 2003; Fig. 2a). Both the northern and the southern margins of the BBG domain are highly tectonized (Fig. 2a). The BBG domain is lensoidal in shape, nearly 190 km long and 4–20 km wide, and tapers towards both east and west (Fig. 1). The lithological ensemble can be subdivided into four distinct components (Fig. 2a): (1) a large part of the domain is occupied by a migmatitic felsic gneiss (locally with garnet) of tonalitic to granodioritic composition; (2) enclaves of garnet–cordierite gneiss, iron-formation granulite, quartzite, aluminous granulite and felsic granulite occur within the felsic gneiss; (3) a mafic–ultramafic magmatic suite of metagabbro, metanoritic gabbro, metanorite and metaorthopyroxenite occurs as concordant sheets in the felsic gneiss; (4) mafic dykes of metagabbronorite and metaolivine gabbro (termed Md1) and amphibolite (termed Md2).
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The BBG domain records five phases of deformation (BD1–BD5, where B refers to the BBG domain), the earliest of which is preserved as relict high-T granulite facies banding (BS1), demarcated by alternate light- and dark-coloured migmatitic layers in the felsic and aluminous granulites (Figs 3 and 4). BD2 is preserved as a rare BS2 fabric in the felsic granulite (Fig. 4). This was followed by a strong ductile shear zone deformation (BD3) that produced southerly verging isoclinal folds (BF3) and a strong mylonitic fabric (BS3) (Fig. 4). The mafic dykes Md1 were folded by BF3. A southerly tectonic transport at relatively high temperatures during BD3 is indicated by sigma-type asymmetrical orthopyroxene porphyroclasts and the southerly vergence of the BF3 folds. Subsequent deformation (BD4) produced narrow, steep, ductile shear-zone fabrics that are mostly restricted to the margins of the BBG domains. Md2 mafic dykes are folded only by BF4. Geological mapping across the BBG domain–Sausar Group supracrustal contact (Fig. 1) showed that the BS4 fabric could be correlated with the earliest deformational fabric in the latter. The terminal deformation BD5 produced cross-folds both in the Sausar Group rocks and rocks in the BBG domain.
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The samples of felsic granulites have been collected from two structurally equivalent locations from the southern part of the BBG domain: (1) Larsara in the east; (2) Dongariya in the west (Fig. 2a). In both the locations, felsic granulites are interlayered with metagabbros and iron-formation granulites. Aluminous granulites and Md1 have been sampled from the Larsara area only (Fig. 2b). The felsic granulites occur as
750 m long and 100 m wide northeast–southwest-trending bodies, bounded on both sides by the metabasites. The mylonite foliation, BS3, which is best developed in the felsic granulites strikes northeast–southwest and dips moderately (35–45°) towards the northwest. Aluminous granulite occurs as 10 m long and 5 m wide lensoidal bodies within the felsic granulites, in close proximity to the metagabbros. Md1 occurs as thin veins, stringers (1–2 cm wide) and bands (50 m wide) within the felsic granulites. The BD3 deformation largely obliterated its intrusive relationship. However, discordant relationships in the form of thin veins and apophyses of the basic rock are still recognizable in some low-strain domains (Fig. 2b). Sample locations for petrological studies in the Larsara area are shown in Fig. 2b. In the Dongariya area, samples of felsic granulites were taken from an identical BS3 foliation domain. From each locality, a number of samples have been collected [numbered as B220(1), B220(2), etc. for location B220, for example]. A total of 15 samples (nine felsic granulites, four aluminous granulites and two Md1) were selected for detailed study after scrutinizing 30 samples. The mineral associations in these samples are listed in Table 1.
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PETROGRAPHY |
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TOPABSTRACTINTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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Felsic granulite
The felsic granulite preserves a porphyroblastic assemblage of garnet, orthopyroxene, quartz, mesoperthite, plagioclase/mesoantiperthite with minor amounts of monazite, zircon and rare apatite (Fig. 5a–c). In order to differentiate them from later-generation parageneses, the porphyroblastic garnet, orthopyroxene and plagioclase are referred to as garnet1, orthopyroxene1 and plagioclase1, respectively. Garnet1 contains inclusions of biotite, quartz (Fig. 5a) and plagioclase. Biotite is totally absent in the leucosome that contains quartz, mesoperthite and plagioclase with scattered grains of garnet1 and orthopyroxene1.
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Garnet1 is partially rimmed by a symplectite of orthopyroxene2–plagioclase2, mostly as a collar around garnet (Figs 4 and 5a), against quartz. In some cases, the symplectite advances well within the garnet interior (Fig. 5a). The symplectites in the pressure shadow zones around garnet1 are aligned parallel to the BS2 fabric (Fig. 4), which implies that the garnet breakdown is broadly synkinematic with respect to BD2. The orthopyroxene2–plagioclase2 symplectite is replaced by a coronal variety of garnet (garnet2) interwoven with granular quartz (Fig. 5d). Garnet2 is preferentially localized as an overgrowth on garnet1 (Fig. 5d). Garnet2 is compositionally distinct from garnet1 (discussed later). Another type of garnet in the felsic granulite is of rather small size, equant in shape (Fig. 5c), and is compositionally similar to garnet2. This garnet overgrows the mylonitic foliation BS3. By analogy, garnet2 is taken to be post-BD3.
Aluminous granulites
A porphyroblastic garnet (garnet1)–mesoperthite–rutile–quartz ± sillimanite ± plagioclase ± spinel (spinel1) association is present in the leucocratic layers of the aluminous granulites (Figs 3, 6a and b). Garnet1 includes scattered grains of biotite1 and sillimanite1 (Fig. 6a), whereas mesoperthite contains rare inclusions of spinel1 (Fig. 6b). Rutile occurs both within garnet and also in the matrix, often in coarse aggregates. Late biotite–plagioclase intergrowths replace garnet1 against perthite.
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The mineral association in the melanocratic bands is garnet–spinel–sillimanite–sapphirine–plagioclase–perthite–biotite–corundum, in the total absence of quartz (Figs 3 and 6c–f). Porphyroblastic garnet (garnet1) contains inclusions of biotite1 that is also present in the matrix. Sapphirine, spinel1 and sillimanite1 are often rimmed by a coarse coronal variety of garnet, designated as garnet2 (Fig. 6c and d) (see later). Porphyroblastic sillimanite (Sil1) additionally occurs as coarse idioblastic minerals in the melanocratic matrix. Idioblastic corundum, containing rare inclusions of spinel1, is separated from garnet2 by an intergrowth of spinel2–sillimanite2 ± biotite2 (Fig. 6e). In the latter case, spinel2 is preferentially concentrated at the interface of corundum, whereas sillimanite2 occurs around garnet. Biotite2–spinel2–sillimanite2 symplectites also occur as kelyphitic rims around garnet2 (Fig. 6f).
Mafic dyke1
In the metamorphosed mafic dyke, Md1, BD3 has produced a flattened fabric, defined by elongate magmatic pyroxenes and plagioclase (Fig. 7). Coronal garnet ± quartz ± clinopyroxene-bearing symplectites occur around flattened and recrystallized grains of orthopyroxene, clinopyroxene, plagioclase and also ilmenite (Fig. 7).
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MINERAL CHEMISTRY |
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TOPABSTRACTINTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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The chemical compositions of the coexisting mineral phases in samples of felsic granulite, aluminous granulite and Md1 were determined using a CAMECA SX-51 electron microprobe at the laboratory of the Geological Survey of India at Faridabad, and a Cameca Camebax Microbeam Electron Microprobe at the University of Bonn, Germany. The operating conditions for both the instruments were set as 1 µm beam diameter, 15 kV accelerating voltage and 12 nA specimen current. The PAP correction scheme was used. Natural and synthetic minerals were used as standards. Representative mineral compositions are given in Tables 2–5. Mineral analyses along compositional profiles are not given here. X-ray element mapping of selected textural sites in one sample was carried out using a Jeol Superprobe at the University of Cologne, Germany. The operating conditions were set as 20 kV accelerating voltage and 40 nA specimen current.
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Garnet
Felsic granulite
Representative chemical analyses are given in Table 2. The cores of garnet1 show large inter-sample variation in composition from Prp31Grs06Alm62Sps01 to Prp35–36 Grs03–04Alm60Sps01 (Fig. 8a). The lowest pyrope content in garnet1 is noted in sample B223A(2). In the same sample, the core of garnet1, which is mantled by orthopyroxene2–plagioclase2 symplectite (Figs 4 and 5a), and smaller garnets occurring as relicts in the symplectite haloes (Fig. 5a) record even lower pyrope contents (Fig. 8a). By contrast, garnet2 overgrowth on garnet1 is enriched in grossular and depleted in pyrope (Prp23 Grs11Alm65Sps01 to Prp28Grs09Alm62Sps01) (Fig. 8a). The highest grossular content is noted in garnet2 that has overgrown the recrystallized plagioclase grains in the matrix (Fig. 5c) (Sample No. B223A(2), Anal. No. A-36).
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X-ray element mapping of garnet1 in Fig. 5a shows that a large part of porphyroblastic garnet1 is compositionally homogeneous with respect to Mg and Fe (Fig. 9a and b). There is, however, a sharp increase in Ca all along the rim of garnet1 at the contact with garnet2 and also locally inside garnet1, where the symplectic plagioclase2 advanced well within the interior (Fig. 9c).
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Compositional profiling of garnet along a traverse A–B (Fig. 9d and e) across two garnet grains is shown in Fig. 10a. Both the garnet grains show progressive rimward enrichment in grossular and concomitant depletion in pyrope and almandine contents. The high-grossular and low-pyrope content of garnet2 immediately right of the contact is obvious. Such a compositional variation across a natural garnet–garnet couple, involving two end-member garnet1 and garnet2 compositions, can be explained by the operation of a very complex Ca–Mg–Fe diffusion, that provides clues regarding the time-scales of orogenic processes (Ganguly et al., 1996
). This aspect will be treated in a separate publication.
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Aluminous granulites
Cores of porphyroblastic garnet1 and coarse garnet2 are uniformly pyrope-rich and grossular-poor (Prp35–41 Grs03–02Alm55–61Sps01) (Table 2). Rims of garnet1 are depleted in pyrope and enriched in almandine (Prp25–30 Grs04Alm65–72Sps01). A similar composition is noted for garnet2 in contact with spinel2–sillimanite2–biotite2 symplectite. Garnet2 in contact with included spinel1 shows Fe–Mg compositional variation depending on its grain size and that of the associated spinel1. Coarse garnet2 (grain diameter in the range of 1–1·7 mm) in contact with small spinel1 is depleted in XMg (XMg = Mg/Mg + Fe2+) by 0·03–0·06 units, relative to garnet2 cores away from spinel1 (Fig. 8b). Smaller garnet2 (grain diameter in the range of 0·3–0·4 mm) in contact with coarser spinel1 (in Fig. 6c) shows even larger depletion in XMg (by 0·09 unit) (Fig. 10b).
Mafic dyke1
Coronal garnet in Md1 is compositionally homogeneous with uniformly high almandine and grossular and relatively lower pyrope contents (Prp19–20Grs20–22 Alm58–59Sps01) (Table 2).
Orthopyroxene–clinopyroxene
Felsic granulite
Cores of porphyroblastic orthopyroxene1 show large inter-sample variation in XMg (0·54–0·61) and Altot (Altot = AlIV + AlVI) (0·06–0·25) (Table 3). The sample with the highest XMg also records the highest alumina in orthopyroxene1 (Fig. 8c). In sample B223A(2), the coarse orthopyroxene2 cores are more magnesian (XMg = 0·57–0·58) and aluminous (Altot = 0·09–0·10) relative to orthopyroxene1 cores (XMg = 0·54, Altot = 0·06) (Fig. 8c). In general, orthopyroxene2 has similar XMg, but shows variation in Altot-content (from 0·10 to 0·06). The latter varies with grain size (smaller grains at 0·06–0·07) and from core (0·10) to rim (0·07).
In Fig. 8d, the variation of XMg in cores of coexisting orthopyroxene1 and garnet1 is plotted; this shows positive covariation. The sample containing the most magnesian garnet is also characterized by the most magnesian, and also the most aluminous, orthopyroxene.
Mafic dyke1
Megacrystic orthopyroxene is magnesian (XMg = 0·56) and low in alumina (Altot = 0·03–0·04) (Table 3). There is slight rimward fall in Altot contents (0·04 in core to 0·03 in rim). Megacrystic clinopyroxene in comparison is more aluminous (Altot = 0·06–0·07) and magnesian (XMg = 0·72–0·78). There is small rimward depletion in Al-content of clinopyroxene in contact with coronal garnet. Coronal clinopyroxene is compositionally similar to that of megacrystic clinopyroxene rim.
Plagioclase
Felsic granulite
Cores of plagioclase1 range in composition from An25 to An29, whereas cores of plagioclase2 are more calcic (An34) (Table 4). The latter shows depletion in An-content towards the rims (An29) against garnet2. Reintegrated mesoantiperthite is of the composition An27Ab50Or23 [Anal. No. R(3), Table 4].
Aluminous granulites
The composition of plagioclase varies in the range An17–31.
Mafic dyke1
Megacrystic plagioclase is reversely zoned, with XAn systematically increasing from An60 in the core to An73 in rim (Table 4); however, the An-content falls sharply (An41) against coronal garnet.
Perthite
Aluminous granulites
Reintegration of mesoperthite composition was carried out with a broad beam (30 µm beam diameter). Regardless of its mode of occurrence, the pre-exsolution composition of the alkali feldspar is calculated as Or47–51Ab44–47An6 [Anal. Nos R(1), R(2); Table 4].
Spinel and sapphirine
Aluminous granulites
In the aluminous granulites, spinel1 included in garnet2 and in mesoperthite in the leucocratic layers shows sharply different composition (Fig. 8b; Table 5). The latter is the most ferroan, with XMg value of 0·25 [Sample No. B220D (5), Anal. No. B-1]. Irrespective of the sample, spinel1 included within garnet2 is always magnesian (XMg = 0·39–0·52) (Fig. 8b; see Table 5 also). A relatively ferroan composition is observed in coarser spinels (grain diameter in the range of 0·06–0·08 mm), whereas smaller spinels (grain diameter in the range of 0·02–0·03 mm) are the most magnesian (Fig. 8b). Spinel1 contains 6–12 mol % gahnite. Spinel2, on the other hand, has a slightly higher gahnite content (max. 14 mol %) and intermediate XMg (0·31–0·34).
Sapphirine in the aluminous granulite is compositionally between the 221 and 793 (molar MgO:Al2O3:SiO2 ratio) end-members without any Fe3+ and is highly magnesian (XMg = 0·73) (Table 5).
Biotite
Felsic granulite
Included biotite in garnet1 in the felsic granulite is titaniferous (TiO2 = 3·63–4·01 wt %) and magnesian (XMg = 0·73) (Table 5).
Aluminous granulites
In the aluminous granulites, included biotite within garnet1 is even more titaniferous (TiO2 = 4·89 wt %) and magnesian (XMg = 0·81) (Table 5). Biotite contains 0·12 wt % ZnO.
Summary
The observed inter-sample chemical trends in the felsic granulites reflect original bulk compositional control on the progress of different mineral reactions involving garnet1 and orthopyroxene1. These reactions are likely to have buffered the mineral compositions under restricted range of P–T conditions of metamorphism (see Fitzsimons & Harley, 1994). By contrast, the intra-specimen compositional variation of garnet and orthopyroxene at near-fixed bulk composition [e.g. in sample B223A(2)] possibly indicates subsequent changes in P–T conditions of metamorphism.
In the aluminous granulites, both intra- and inter-sample compositional variations indicate a reversal of the Fe–Mg compositional relationship between spinel and garnet, even at the scale of a thin section, giving rise to the compositional relationship XMg(Spl1) > XMg(Grt2) for the melanocratic layers and XMg(Spl1) < XMg(Grt1) for the leucocratic layers. Such compositional reversals between garnet and spinel are known from both experimental and natural rock data (reviewed by Fitzsimons, 1996) and may result from bulk compositional variation, retrograde re-equilibration and pressure variations. In this study, the authors observe considerable Fe2+–Mg exchange between coexisting garnet2 and spinel1, the extent of diffusion being largely controlled by the grain size of the exchanging phases. Based on this observation, it is predicted that the original spinel1 was compositionally Fe-rich relative to the garnet. The authors, therefore, consider the XMg of the phases in the aluminous granulites to decrease in the following order: biotite–sapphirine–garnet–spinel. In the following section, they deduce the sequence of mineral reactions in the studied rocks using textural and compositional criteria. For the latter, compositions of the coexisting phases in the aluminous granulites are plotted in the SiO2–FB–MB ternary system (projected from sillimanite, K-feldspar and melt) (Fig. 11a), where FB and MB represent Fe- and Mg-rich biotite (after McDade & Harley, 2001).
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SEQUENCE OF MINERAL REACTIONS |
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TOPABSTRACTINTRODUCTIONGEOLOGICAL SETTINGPETROGRAPHYMINERAL CHEMISTRYSEQUENCE OF MINERAL REACTIONSP-T CONDITIONS OF METAMORPHISMELECTRON MICROPROBE DATING OF...RESULTSDISCUSSIONREFERENCES |
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The development of migmatitic banding, stabilization of the porphyroblastic garnet1–orthopyroxene1–perthite association, and the presence of biotite, plagioclase and quartz inclusions in garnet1, are consistent with the progress of the dehydration–melting reaction
 | (R1) |
The leucocratic layers in the gneiss can be considered to represent at least a part of the melt, with some peritectic phases (see, e.g. Moraes et al., 2002). The reaction has been experimentally studied by many workers (Vielzeuf & Montel, 1994; Patiño Douce & Beard, 1995; Stevens et al., 1997; Vielzeuf & Schmidt, 2001; Nair & Chacko, 2002). In the studied rocks, those with a high Ti-content in relict biotite, highly aluminous orthopyroxene1 and pyrope-rich garnet1 are consistent with ultrahigh temperatures of metamorphism (T 
950°C) for reaction (R1) (Nair & Chacko, 2002).
In the aluminous granulites, textural indications for the reaction leading to the stabilization of garnet1 are not clear. However, by analogy with the felsic granulites, a similar biotite dehydration–melting reaction, involving additionally early sillimanite at high temperatures, can be predicted to account for the development of leucocratic layers with abundant mesoperthite and dark restitic layers. Abundant rutile in the aluminous granulites could be produced from the Ti liberated from biotite during melting (see Stevens et al., 1997).
In the next stage of mineralogical evolution, an assemblage of spinel1–sapphirine was formed in the aluminous granulites. In the total absence of cordierite, quartz and orthopyroxene, this assemblage can be produced by the reaction
 | (R2) |
. Compared with previous studies (e.g. Hensen & Harley, 1990; Mouri et al., 1996), garnet and spinel switch positions in this reaction. Reaction (R2) has a high dP/dT slope, progresses to the right with increasing temperature, and is located at T > 900°C (McDade & Harley, 2001). The compositional characteristics of biotite and spinel suggest that the gahnite content in spinel1 was contributed by the reacting biotite. It is interesting to note that at this stage of mineral reaction history, quartz was removed from the matrix of the restite, obviously indicating progressive silica undersaturation.
Inclusions of sapphirine, sillimanite1 and spinel1 in garnet2 (Fig. 6c and d) and the appearance of corundum containing inclusions of spinel1 in the aluminous granulites and chemographic support (Fig. 11a) can be attributed to the simplified reaction
 | (R3) |
for the reverse compositional relation, XMg(Spl) > XMg(Grt)). The authors have used the ferruginous spinel composition in the leucocratic layers to deduce reaction (R3), assuming that the spinel occurring in contact with other ferromagnesian phases (such as garnet) in the restite re-equilibrated during the subsequent evolution of the rock. Reaction (R3) progresses to the right with cooling and/or loading and suggests further silica undersaturation. The rocks studied here, therefore, provide an evolutionary link between silica-saturated bulk composition and undersaturated ones, primarily brought about by melting and removal of silica (McDade & Harley, 2001).
Development of a coarse symplectite of spinel2–sillimanite2–biotite2 between garnet2 and corundum (Fig. 6e and f) is related to the simplified reaction
 | (R4) |
), where the melt provides the water necessary to stabilize biotite. Even if sapphirine is absent, reaction (R4) implies reversal of the reaction (R3). Extensive exsolution in alkali feldspar in both the aluminous granulites and felsic granulites, producing mesoperthite, can be correlated with this cooling event.
An important observation related to the next stage of mineralogical evolution in the felsic granulite is that the orthopyroxene2–plagioclase2 symplectite at the margin of garnet1 against quartz is aligned along BS2 (Fig. 4). Orthopyroxene2 and relict garnet1 in the symplectites are Mg- and Al-rich, and ferroan, respectively, relative to orthopyroxene1 and garnet1 occurring away from the symplectites (Fig. 8d). These textural and compositional features attest to the reaction
 | (R5) |
Development of garnet2–quartz symplectite at the expense of plagioclase2 and orthopyroxene2 as a metamorphic overgrowth on compositionally reset garnet1 (Fig. 5d), and the compositional characteristics of the phases, signify backward movement of reaction (R5) in the felsic granulite in response to cooling, loading or a combination of both at a later stage. Since garnet2 overgrew recrystallized plagioclase formed by deformation, BD3 (Fig. 5c), the authors argue that garnet growth post-dated this deformation. Coeval with garnet2 formation in the felsic granulite, coronal garnet appeared in Md1 (Fig. 7) according to the reactions
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P–T CONDITIONS OF METAMORPHISM |
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Table 6 lists the results of thermobarometric computations using various methods. For the assemblage garnet–orthopyroxene–plagioclase–quartz in the felsic granulites, the authors employed the formulation of Pattison et al. (2003)
that uses a convergence technique and accounts for late Fe–Mg exchange. For comparison, results obtained from the THERMOCALC program (ver. 3.1) (Holland & Powell, 1998) are given. Reintegrated mesoperthite compositions from the aluminous granulites, occurring both as inclusions within garnet1 and in the matrix, when considered in the ternary feldspar diagram of Fuhrman & Lindsley (1988) gives a temperature of 950°C (Fig. 12a). Using the core compositions of the porphyroblastic phases, P–T values of 9 ± 1 kbar, 900 ± 50°C were obtained for M1 from the felsic granulites (Fig. 12b). Therefore, the peak metamorphic M1 P–T conditions in the study area are taken as 9 kbar, 950°C. This implies that the granulites of the BBG domain join the select group of UHT metamorphosed rocks (Harley, 1998). Such high temperatures are consistent with the predicted biotite dehydration–melting reactions in both the felsic and aluminous granulites.
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The P–T conditions and P–T path of evolution of the studied rocks can be further evaluated with the help of petrogenetic grids in the system KFMASH. The authors have constructed a partial petrogenetic grid around the invariant point [Crd, Opx] (Fig. 11b), using balanced univariant reactions (see Table 7) and the compositions of the studied phases. Melt composition is taken from Carrington & Harley (1995)
. The sequential progress of the reactions (R2)–(R4) in the studied rocks depicts a counterclockwise P–T trajectory comprising heating (M1), loading and cooling (M2) (Fig. 11b).
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M2 metamorphic conditions can be further constrained from the coronal garnet2 (core)–corundum–spinel1–sillimanite1 and garnet2 (rim)–corundum–spinel2–sillimanite2 assemblages using the calibration of Shulters & Bohlen (1989)
, which gives a temperature range from 910 to 700°C at 9 kbar pressure, respectively (Table 6). This range of temperature corresponds to the M2 cooling event.
M3 metamorphic conditions are estimated from orthopyroxene2–plagioclase2 symplectite and adjoining garnet composition in the presence of quartz. The results range from 6·6 kbar, 700°C (Pattison et al., 2003) to 6·1 kbar, 650°C (Holland & Powell, 1998). The authors have, therefore, taken an average P–T condition of 6·4 kbar, 675°C for this stage of metamorphism (Fig. 12c). This implies that the orthopyroxene2–plagioclase2 symplectite in the felsic granulite was possibly formed in response to decompression, and not by heating.
Application of the same methods for the composition of garnet2 in the felsic granulite, and for coronal garnet in the mafic dyke1, fails to distinguish between the T conditions of M4 and those of M3 (Table 6). This is clearly related to the problem of Fe–Mg diffusion's blocking temperature in coexisting garnet and orthopyroxene. However, the pressure estimate is approximately 1·5 kbar higher than that of M3 (Fig. 12d and e; Table 6). Given the higher grossular content of garnet2 and the depletion in An-content of plagioclase at the immediate contact, the authors interpret this difference in the pressure estimate as real (implying loading), and not an artefact of barometric computation.
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ELECTRON MICROPROBE DATING OF MONAZITE |
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Samples and analytical procedure
Following the procedure outlined by Suzuki & Adachi (1991)
and Montel et al. (1996), the authors have dated the metamorphic stages by electron probe analysis of monazite. Coarse monazite grains (100–140 µm grain diameter), occurring in four textural settings in the felsic granulite, were selected for this purpose. These are as follows. (1) Type 1 monazite, which occurs as inclusions within porphyroblastic garnet1, and is expected to be protected from significant post-peak re-equilibration (Fig. 13a, Grain A; Table 8). (2) Type 2 monazite, which occurs in orthopyroxene2–plagioclase2 symplectite domains (Figs 4 and 13b; Table 8); Grain B of this textural type occurs in contact with a compositionally zoned garnet (Fig. 9d); Grain B1 occurs as narrow, curvilinear grains in the same symplectite domain. (3) Type 3 monazite occurs as large grains in the strain shadow domains, away from the influence of BS3 mylonite fabric (Fig. 4). (4) Type 4 monazite occurs in the BS3 mylonite fabric (Fig. 4).
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All analyses were carried out with a Camebax Microbeam Electron Microprobe at the University of Bonn, Germany. The instrumental operating conditions and the analytical procedures were outlined by Dobmeier & Simmat (2002)
. The data are presented both as spot chemical ages in individual monazite grains and also by the Chemical Th–U–total Pb Isochron Method (CHIME method after Suzuki et al., 1994; Cocherie et al., 1998). |
RESULTS |
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A total of 183 measurements on 11 grains were carried out (Table 8). Grain A, belonging to Type 1 monazite, shows euhedral crystal outline with concentric zonation (Fig. 13a). Th, U, Pb profiling along direction A–B indicates that the colour variation is primarily due to Th-zoning, with the brightest regions related to the highest Th concentrations (Fig. 14a). The analysed spots show variations in Th content from 5·66 to 11·01 wt %. In all the spots, the Pb content (0·64–1·29 wt %) is significantly above the detection limit. Spot chemical ages show a concordant age population in the range 1970–2177 Ma (Fig. 15a). Using this dataset, the calculated CHIME ages give a rather tightly constrained age of 2089 ± 14 Ma for the formation of Grain A (Fig. 16a).
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plot (after Suzuki et al., 1994
on PbM
during WDS-scans and following the approach of Dobmeier & Simmat (2002)The back-scattered electron image of grain B, belonging to Type 2 monazites, shows three distinct compositional domains from core to rim (Fig. 13b). (1) An ovoid relatively homogeneous core (Domain 1, Fig. 13b) is present, showing broadly uniform Th and Pb concentrations of 7·10–9·05 and 0·79–0·96 wt %, respectively (Fig. 14b). Spot chemical ages from this domain range from 1958 to 2208 Ma (Fig. 15b). Using the CHIME method, the 17 analysed spots give a tightly constrained age of 2086 ± 16 Ma (Fig. 16b). (2) An inner concentric, Th-zoned rim with locally preserved euhedral outline is present in Grain B (Domain 2, Figs 13b and 14b–d). This domain resembles Type 1 monazites described above. Profile E–F shows that the domain is thinly banded close to its contact with the previous domain, and there is a thick outer rim, best developed in its lower part (Fig. 14d). Spot chemical ages from this domain range from 1924 to 2299 Ma (Fig. 15b), which give a CHIME chemical age of
2040 ± 17 Ma (Fig. 16c). This age is nearly 40 Myr younger relative to the previous domain. Consequently, Domain 1 of Grain B is considered to be an inherited older core. (3) An outermost homogeneous dark rim (Domain 3, Fig. 13b) of substantially lower Pb (0·20–0·48 wt %) and also Th (4·12–5·89 wt %) concentrations is present (Fig. 14b and c). The boundary between this domain and Domain 2 is sharp—typically a few microns thick, as shown in the two compositional profiles A–B and C–D (Fig. 14b and c)—and has truncated the concentric zoning of Domain 2 (Fig. 13b). Considering the sharpness of the boundary between the domains and the occurrence of Domain 3 in direct contact with garnet2, the authors interpret the formation of Domain 3 as a consequence of re-metamorphism (M4), and not due to Pb-diffusion (Braun et al., 1998; Cocherie et al., 1998; Crowley & Ghent, 1999). This domain gives distinct Mesoproterozoic spot chemical ages in the range 1318–1648 Ma (Fig. 15b). Calculated CHIME monazite ages give a tightly constrained age of 1525 ± 13 Ma (Fig. 16d). Type 3 monazite (Grain G, Fig. 13c; Table 8) also shows a homogeneous core that gives a CHIME age of 2048 ± 14 Ma (Figs 15c and 16e); this has a Mesoproterozoic metamorphic overgrowth (Fig. 15c). Type 4 monazites, excepting Grain D, show consistent Mesoproterozoic age (Table 8). Grain D shows a relict Palaeoproterozoic core and rim of Mesoproterozoic age (Table 8). An isochron drawn through these monazite compositions gives an age of 1450 ± 9 Ma (Fig. 16f).
Summarizing, the monazite grains of variable compositional characteristics in different textural settings in the studied rocks bear the imprint of a Mesoproterozoic (1450–1525 Ma) metamorphism superimposed on a Palaeoproterozoic (2040–2090 Ma) event. Based on (a) the occurrence of Type 1 monazites as shielded inclusions within garnet1 and (b) the presence of concentric Th-zonation in the former and also in Domain 2 of Type 2 monazites, the authors interpret a Palaeoproterozoic age for the UHT metamorphism, M1. In contrast, the Mesoproterozoic ages, which are retrieved from metamorphic overgrowths, and the BS3 mylonite domain mark the M4 metamorphism. These results will be combined with textural, compositional and thermobarometric data to constrain the integrated metamorphic history of the studied complex, and its implication.
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DISCUSSION |
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This study demonstrates that the allochthonous BBG domain at the southern periphery of the CITZ records two distinct granulite-facies tectonothermal events, separated by a time gap of approximately 500 Myr. Geothermobarometric data and interpretation of reaction textures in the context of appropriate petrogenetic grids constrain the earlier UHT granulite-facies metamorphism (M1) at P
9 kbar, T 950°C, followed by a subsequent near-isobaric cooling event (M2), which was terminated at 700°C (Fig. 17a). Considering that near isobaric cooling from TMax is a natural consequence of thermal relaxation of the perturbed geotherm, the M1–M2 metamorphic stages can be considered to belong to the same UHT metamorphic event. Based on the partial KFMASH petrogenetic grid, and the sequential operation of reactions (R2)–(R4), the authors infer an overall counterclockwise P–T path for rocks metamorphosed during the UHT event based on the deduced deep crustal heating–cooling trajectory (Fig. 17a) (Waters, 1989; Dasgupta et al., 1997; Sengupta et al., 1999). Electron microprobe dating of monazites constrains an age of 2040–2090 Ma for this UHT metamorphic event. Our results, therefore, provide the first tight constraint on the presence of an older crust, and a Palaeoproterozoic crustal history in the rocks leading to cratonization (stabilization through isobaric cooling) of the CITZ. Similar Palaeoproterozoic UHT metamorphism on a counterclockwise P–T path has been documented from elsewhere (Australia: Goscombe, 1992; Labrador: Currie & Gittins, 1988), and this suggests a global thermal perturbation at this time (Condie, 2000; Windley, 2003).
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The isobarically cooled deep crustal UHT granulites were subsequently affected by decompression down to 6·4 kbar at 675°C during M3 and loading to 8 kbar during M4. Electron microprobe dating of monazite gives an age of 1450–1525 Ma for M4. This implies that the isobarically cooled granulites were residing at lower-crustal depths (corresponding to 9 kbar metamorphic pressure) for approximately 500 Myr before being partially exhumed by the later Mesoproterozoic tectonothermal event. The mafic dykes were emplaced within this time interval and were affected by the later event, M4. M3 could not be dated directly. However, M3 with its decompressive retrograde P–T path appears to be unrelated to the Palaeoproterozoic cooling of M2. The authors would, therefore, consider M3 and M4 to be part of the same Mesoproterozoic tectonothermal event (Fig. 17b). This interpretation supports the prediction of Harley (1989)
that isobarically cooled lower-crustal granulites must await a separate orogeny for exhumation. The overall P–T path of the Mesoproterozoic metamorphism remains indeterminate because the prograde arm cannot be characterized. Nevertheless, the granulites were still at depths corresponding to 8 kbar pressure during Mesoproterozoic time, and their final exhumation required further tectonothermal events. There is an increasing body of evidence that similar Mesoproterozoic granulite-facies metamorphism is more common (East Antarctica: Kelly et al., 2002; Eastern Ghats Belt, India: Mezger & Cosca, 1999; Kovach et al., 2001; Simmat, 2003, quoted by Dobmeier & Raith, 2003) than originally believed.
The tectonothermal history of the granulite complex of the BBG domain, deduced in this study, contrasts sharply with that from the northern granulite (RKG) domain of the SMB (Fig. 17c and d) (Bhowmik & Roy, 2003; Bhowmik & Spiering, 2004). The latter is characterized by a clockwise P–T trajectory of possible Grenvillian age (Fig. 17c and d). These two granulite domains are separated by the greenschist–amphibolite-facies Sausar Group (Fig. 1) metamorphosed during the ca. 1000 Ma Grenvillian event (Lippolt & Hautman, 1994; Pandey et al., 1998). It may be recalled that the BD4–BD5 deformations in the BBG granulites studied here are also recorded in the Sausar Group rocks. This raises the possibilities that (a) these two deformations are of Grenvillian age, (b) the two granulite domains and the Sausar Group rocks were juxtaposed during this collisional event along the CITZ, and (c) the BBG granulites were exhumed to shallower crustal levels at this time and (d) the Grenvillian orogeny appears to be responsible for the formation of the Indian subcontinent through collision of the SIB and NIB (Fig. 1) along the CITZ. On a larger scale, the Central Indian Tectonic Zone appears to record nearly 1000 Myr of multistage crustal evolutionary history in the Proterozoic.
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ACKNOWLEDGEMENTS |
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We acknowledge the financial assistance from the DST (Grant No. ESS/23/VES/129/2000) and DAAD (S.K.B.), IIT, Kharagpur (A.B.S.), Mineralogisch–Petrologisches Institüt (B.S.) and DFG (M.M.R.). The work was completed when SKB was in the Mineralogisch–Petrologisches Institut, Bonn, as a visiting fellow under INSA–DFG fellowship. Part of the analytical work was also carried out in the Geological Survey of India, for which we thank N. C. Pant and S. Shome for extending help during microprobe analysis and back-scattered electron image photography. X-ray element maps were generated in the University of Cologne, for which we thank Markus Klein. The manuscript has benefited greatly from stimulating discussions with Somnath Dasgupta. We would also like to thank two anonymous reviewers for thorough and constructive reviews, and Richard Arculus for editorial assistance.
* Corresponding author. E-mail: santanu{at}gg.iitkgp.ernet.in
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REFERENCES |
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Bhowmik, S. K. & Pal, T. (2000). Petrotectonic implication of the granulite suite north of the Sausar mobile belt in the overall tectonothermal evolution of the Central Indian mobile belt. Geological Survey of India Unpublished Progress Report.
Bhowmik, S. K. & Roy, A. (2003). Garnetiferous metabasites from the Sausar Mobile Belt: petrology, P–T path and implications for the tectonothermal evolution of the Central Indian Tectonic Zone. Journal of Petrology 44, 387–420.
Bhowmik, S. K. & Spiering, B. (2004). Constraining the prograde and retrograde P–T paths of granulites using decomposition of initially zoned garnets: an example from the Central Indian Tectonic Zone. Contributions to Mineralogy and Petrology 147, 581–603.[Web of Science]
Braun, I., Montel, J. M. & Nicollet, C. (1998). Electron microprobe dating of monazites from high-grade gneisses and pegmatites of the Kerala Khondalite Belt, southern India. Chemical Geology 146, 65–85.[CrossRef][Web of Science]
Carrington, D. P. & Harley, S. L. (1995). Partial melting and phase relations in high-grade metapelites: an experimental petrogenetic grid in the KFMASH system. Contributions to Mineralogy and Petrology 120, 270–291.[Web of Science]
Cocherie, A., Legendre, O., Peucat, J. J. & Kouamelan, A. N. (1998). Geochronology of polygenetic monazites constrained by in situ electron microprobe Th–U-total lead determination: implications for lead behaviour in monazite. Geochimica et Cosmochimica Acta 62, 2475–2497.[CrossRef][Web of Science]
Condie, K. C. (2000). Episodic continental growth models: afterthoughts and extensions. Tectonophysics 322, 153–162.[CrossRef][Web of Science]
Crowley, J. L. & Ghent, E. D. (1999). An electron microprobe study of the U–Th–Pb systematics of metamorphosed monazite: the role of Ph diffusion versus overgrowth and recrystallization. Chemical Geology 157, 285–302.[CrossRef][Web of Science]
Currie, K. L. & Gittins, J. (1988). Contrasting sapphirine parageneses from Wilson Lake, Labrador and their tectonic implications. Journal of Metamorphic Geology 6, 603–622.[Web of Science]
Dasgupta, S., Ehl, J., Raith, M. M., Sengupta, P. & Sengupta, P. (1997). Deep crustal contact metamorphism around the Chimakurthy mafic–ultramafic Complex, Eastern Ghats Belt, India. Contributions to Mineralogy and Petrology 129, 182–197.[CrossRef][Web of Science]
Dobmeier, C. & Raith, M. M. (2003). Crustal architecture and evolution of the Eastern Ghat Belt and adjacent regions of India. In: Yoshida, M., Windley, B. W. & Dasgupta, S. (eds) Proterozoic East Gondwana: Supercontinent Assembly and Breakup. Geological Society, London, Special Publications 206, 145–168.
Dobmeier, C. & Simmat, R. (2002). Post-Grenvillian transpression in the Chilka Lake area, Eastern Ghats Belt: implications for the geological evolution of peninsular India. Precambrian Research 113, 243–268.[CrossRef][Web of Science]
Eriksson, P. G., Mazumder, R., Sarkar, S., Bose, P. K., Altermann, W. & van der Merwe, R. (1999). The 2·7–2·0 Ga volcano-sedimentary record of Africa, India and Australia: evidence for global and local changes in sea level and continental freeboard. Precambrian Research 97, 269–302.[CrossRef][Web of Science]
Fitzsimons, I. C. W. (1996). Metapelitic migmatites from Brattstrand Bluffs, East Antarctica: metamorphism, melting and exhumation of the mid crust. Journal of Petrology 37, 395–414.
Fitzsimons I. C. W. & Harley, S. L. (1994). The influence of retrograde cation exchange, P–T estimates and a convergence technique for the recovery of peak metamorphic conditions. Journal of Petrology 35, 543–576.
Fuhrman, M. L. & Lindsley, D. H. (1988). Ternary-feldspar modeling and thermometry. American Mineralogist 73, 201–215.[Abstract]
Ganguly, J., Chakraborty, S., Sharp, T. & Rumble, D., III (1996). Constraint on the time scale of biotite grade metamorphism during Acadian orogeny from a natural garnet–garnet diffusion couple. American Mineralogist 81, 1208–1216.[Abstract]
Goscombe, B. (1992). High-grade reworking of central Australian granulites: metamorphic evolution of the Arunta complex. Journal of Petrology 33, 917–962.
Goscombe, B., Armstrong, R. & Barton, J. M. (1998). Tectonometamorphic evolution of the Chewore inliers: partial re-equilibration of high-grade basement during the pan-African orogeny. Journal of Petrology 39, 1347–1384.[CrossRef][Web of Science]
Harley, S. L. (1989). The origin of granulites: a metamorphic perspective. Geological Magazine 126, 215–247.[Abstract]
Harley, S. L. (1998). On the occurrence and characterization of ultrahigh-temperature crustal metamorphism. In: Treloar, P. J. & O'brien, P. J. (eds) What Drives Metamorphism and Metamorphic Reactions? Geological Society, London, Special Publications 138, 81–107.
Hensen, B. J. (1987). P–T grids for silica-undersaturated granulites in the systems MAS (n + 4) and FMAS (n + 3): tools for the derivation of P–T paths of metamorphism. Journal of Metamorphic Geology 5, 255–271.[Web of Science]
Hensen, B. J. & Harley, S. L. (1990). Graphical analyses of P–T–X relations in granulite facies metapelites. In: Ashworth J. R. & Brown, M. (eds) High Temperature Metamorphism and Crustal Anatexis. London: Unwin Hyman, pp. 19–56.
Holland, T. J. B. & Powell, R. (1998). An internally consistent thermodynamic dataset for phases of petrological interest. Journal of Metamorphic Geology 16, 309–343.[CrossRef][Web of Science]
Jain, S. C., Yedekar, D. B. & Nair, K. K. K. (1991). Central Indian shear zone: a major Pre-cambrian crustal boundary. Journal of Geological Society of India 37, 521–531.
Kelly, N. M., Clarke, G. L. & Fanning, C. M. (2002). A two-stage evolution of the Neoproterozoic Rayner Structural Episode: new U–Pb sensitive high resolution ion microprobe constraints from the Oygarden Group, Kemp Land, East Antarctica. Precambrian Research 116, 307–330.[CrossRef][Web of Science]
Kovach, V. P., Simmat, R., Rickers, K., Berezhnaya, N. G., Salnikova, E. B., Dobmeier, C., et al. (2001). The Western Chamockite Zone of the Eastern Ghats Belt, India—an independent crustal province of late Archaean (2·8 Ga) and Palaeoproterozoic (1·7–1·6 Ga) terrains. International Symposium and Field Workshop on the Assembly and Breakup of Rodinia and Gondwana, Osaka, 26–30 October 2001. Gondwana Research 4, 666–667.[CrossRef]
Kretz, R. (1983). Symbols for rock-forming minerals. American Mineralogist 68, 277–279.[Abstract]
Lippolt, H. J. & Hautmann, S. (1994). 40Ar/39Ar ages of Precambrian manganese ore minerals from Sweden, India and Morocco. Mineralium Deposita 18, 195–215.
McDade, P. & Harley, S. L. (2001). A petrogenetic grid for aluminous granulite facies metapelites in the KFMASH system. Journal of Metamorphic Geology 19, 45–59.[CrossRef][Web of Science]
Mezger, K. & Cosca, M. A. (1999). The thermal history of the Eastern Ghats Belt (India), as revealed by U–Pb and 40Ar–39Ar dating of metamorphic and magmatic minerals: implications for the SWEAT correlation. Precambrian Research 94, 251–271.[CrossRef][Web of Science]
Mishra, D. C., Singh, B., Tiwari, V. M., Gupta, S. B. & Rao, M. B. S. V. (2000). Two cases of continental collisions and related tectonics during the Proterozoic period in India: insights from gravity modelling constrained by seismic and magnetotelluric studies. Precambrian Research 99, 149–169.[CrossRef][Web of Science]
Montel, J.-M., Fcret, S., Veschambre, M., Nicollet, C. & Provost, A. (1996). Electron microprobe dating of monazite. Chemical Geology 131, 37–53.[CrossRef][Web of Science]
Moraes, R., Brown, M., Fuck, R. A., Camargo, M. A. & Lima, T. M. (2002). Characterization and P–T evolution of melt-bearing ultrahigh-temperature granulites: an example from the Anápolis–Itauçu Complex of the Brasília Fold Belt, Brazil. Journal of Petrology 43, 1673–1705.
Mouri, H., Guiraud, M. & Hensen, B. J. (1996). Petrology of phlogopite–sapphirine-bearing Al–Mg granulites from Ihouhaouene in Ouzzal, Hoggar, Algeria: an example of phlogopite stability at high temperature. Journal of Metamorphic Geology 14, 725–738.[CrossRef][Web of Science]
Nair, R. & Chacko, T. (2002). Fluid-absent melting of high-grade semi-pelites: P–T constraints on orthopyroxene formation and implications for granulite gneiss. Journal of Petrology 43, 2121–2141.
Pandey, B. K., Krishna, V. & Chabria, T. (1998). An overview of Chotanagpur gneiss–granulite complex and adjoining sedimentary sequences, Eastern and Central India. In: International Seminar on Precambrian Crust in Eastern and Central India. UNESCO–IUGS–IGCP-368, pp. 131–135.
Patiño-Douce, A. E. & Beard, J. S. (1995). Dehydration melting of biotite gneiss and quartz amphibolite from 3 to 15 kbar. Journal of Petrology 36, 707–738.
Pattison, D. R. M., Chacko, T., Farquhar, J. & McFarlane, C. R. M. (2003). Temperatures of granulite facies metamorphism: constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange. Journal of Petrology 44, 867–900.
Rivers, T., Martignole, J., Gower, C. F. & Davidson, A. (1989). New tectonic divisions of the Grenville Province. southeast Canadian sheild. Tectonics 8, 63–84.[Web of Science]
Sengupta, P., Sen, J., Dasgupta, S., Raith, M., Bhui, U. K. & Ehl, J. (1999). Ultra-high temperature metamorphism of metapelitic granulites from Kondapalle, Eastern Ghats Belt: implications for the Indo-Antarctic correlation. Journal of Petrology 40, 1065–1087.[CrossRef][Web of Science]
Shulters, J. C. & Bohlen, S. R. (1989). The stability of hercynite and hercynite–gahnite spinels in corundum or quartz-bearing assemblages. Journal of Petrology 30, 1017–1031.
Simmat, R. (2003). Identifizierung hochgradig metamorpher Provinzen des Eastern Ghats Belt in Indien anhand einer EMS-Studie von Monazit-Altersmustern. Ph.D. thesis, Universität Bonn.
St-Onge, M. R. & Ijewliw, O. J. (1996). Mineral corona formation during high-P retrogression of granulitic rocks, Ungava orogen, Canada. Journal of Petrology 37, 553–582.
Stevens, G., Clemens, J. D. & Droop, G. T. R. (1997). Melt production during granulite-facies anatexis: experimental data from ‘primitive’ metasedimentary protoliths. Contributions to Mineralogy and Petrology 128, 352–370.[CrossRef][Web of Science]
Suzuki, K. & Adachi, M. (1991). Precambrian provenance and Silurian metamorphism of the Tsubonosawa paragneiss in the South Kitakami terrane, Northeast Japan, revealed by the chemical Th–U-total Pb isochron ages of monazite, zircon and xenotime. Geochemical Journal 25, 357–376.[Web of Science]
Suzuki, K., Adachi, M. & Kajizuka, I. (1994). Electron microprobe observations of Pb diffusion in metamorphosed detrital monazites. Earth and Planetary Science Letters 128, 391–405.[CrossRef][Web of Science]
Vielzeuf, D. & Montel, J. M. (1994). Partial melting of metagreywackes. Part I: fluid-absent experiments and phase relationships. Contributions to Mineralogy and Petrology 117, 375–393.[CrossRef][Web of Science]
Vielzeuf, D. & Schmidt, M. W. (2001). Melting relations in hydrous systems revisited: application to metapelites, metagreywackes and metabasalts. Contributions to Mineralogy and Petrology 141, 251–267.[Web of Science]
Waters, D. J. (1989). Metamorphic evidence for the heating and cooling path of Namaqualand granulites. In: Daly, J. S., Cliff, R. A. & Yardley, B. W. D. (eds) Evolution of Metamorphic Belts. Geological Society, London, Special Publications 43, 357–363.
Windley, B. F. (2003). Continental growth in the Proterozoic: a global perspective. In: Yoshida, M., Windley, B. F. & Dasgupta, S. (eds) Proterozoic East Gondwana: Supercontinent Assembly and Breakup. Geological Society, London, Special Publications 206, 23–33.
Yedekar, D. B., Jain, S. C., Nair, K. K. K. & Dutta, K. K. (1990). The Central Indian Collision Suture. In: Precambrian of Central India. Geological Survey of India, Special Publications 28, 1–37.
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