(PDF) Tectonic restoration of the Precambrian crystalline rocks along the west coast of India: Correlation with eastern Madagascar in East Gondwana

The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U–Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil–Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsaratanana Complex). In the eastern domain, the period of early crust formation is extended to the Paleo–Mesoarchean (3.32–3.15 Ga) and a supracrustal sequence (Fenerivo Group), deposited at 3.18 Ga and metamorphosed at 2.55 Ga, is identified. In the central domain, a Neoarchean period of high-grade metamorphism and anatexis that affected both felsic (Betsiboka Suite) and mafic gneisses (Tsaratanana Complex) is documented. We propose, therefore, that the Antananarivo domain was amalgamated within the Greater Dharwar Craton (India + Madagascar) by a Neoarchean accretion event (2.55–2.48 Ga), involving emplacement of juvenile igneous rocks, high-g...

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Precambrian Research 252 (2014) 191–208 Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres Tectonic restoration of the Precambrian crystalline rocks along the west coast of India: Correlation with eastern Madagascar in East Gondwana S. Rekha a,∗ , A. Bhattacharya a , N. Chatterjee b a b Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA a r t i c l e i n f o Article history: Received 29 December 2013 Received in revised form 27 June 2014 Accepted 14 July 2014 Available online 4 August 2014 Keywords: Antongil–Antananarivo Coorg granulites Western Dharwar Craton Monazite geochronology Bemarivo Belt Gondwanaland a b s t r a c t New structural–mineralogical data and U–Th-total Pb monazite chemical ages in 27 samples in a 430 km long corridor along the west coast of India are combined with existing data to reconstruct the tectonic set up of the Meso/Neoarchean crystalline rocks in the Western Dharwar Craton (WDC). The data helps to delineate two NW-trending Paleoproterozoic ductile shear zones that limit the southern and the northern margins of the WDC. The southern shear zone (metamorphic age: 2.3–2.4 Ga) separates the greenschist facies supracrustal belts (2.5 and 3.3 Ga), foliated granitoids (2.5 and 2.9 Ga) and amphibolite facies anatectic gneisses (>3.0 Ga) of the WDC from the >2.9 Ga granulite facies ortho/para-gneisses of the Coorg Block. This shear zone is correlated with the ∼2.4 Ga Betsimisaraka suture zone in east-central Madagascar that demarcates the accretion zone between the Antongil Block (≈WDC) and the granulite facies lithologies of the Antananarivo domain (≈Coorg Block). The northern shear zone system (metamorphic age: 2.2–1.8 Ga) extending NW into Madagascar possibly exists as a hitherto undiscovered tectonic zone forming the basement of the Mesoproterozoic Sahantaha Formation underlying the Neoproterozoic Bemarivo Belt supracrustals in NE Madagascar. Within the WDC, the Meso/Neoproterozoic ages retrieved from poorly-defined margins in monazite are uncommon, dispersed within the craton, and do not define localized zones within the craton. The chemical ages of metamorphic monazites formed at greenschist/amphibolite facies conditions preclude metamorphism–deformation associated with accretion of crustal blocks within the WDC during the Rodinia assembly. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Palaeomagnetic studies indicate that Madagascar and India were contiguous (Fig. 1; top-right inset) prior to the Cretaceous break up of Gondwanaland (Meert and Lieberman, 2004; Torsvik et al., 2000). The present day landmass of Madagascar comprises crustal fragments from East Gondwana (India, Australia and Antarctica) and West Gondwana (East Africa) (Collins and Pisarevsky, 2005; De Wit, 2003; Lawver and Scotese, 1987) that accreted during the Late Neoproterozoic and the Early Paleozoic (Blasband et al., 2000; Collins and Pisarevsky, 2005; Kröner et al., 2000; McWilliams, 1981; Meert et al., 1995; Stern, 1994; Unrug, 1996; Veevers, 2004). Tucker et al. (1999) proposed, based on U–Pb ∗ Corresponding author. Tel.: +91 7598145803. E-mail addresses: rekha eas@yahoo.com, georekha@gmail.com (S. Rekha). http://dx.doi.org/10.1016/j.precamres.2014.07.013 0301-9268/© 2014 Elsevier B.V. All rights reserved. zircon ages, that the Antongil Block in NE Madagascar and the anatectic Peninsular gneisses and granitoids of the Western Dharwar Craton (WDC) in India (Beckinsale et al., 1980; Bhaskar Rao et al., 1991; Meen et al., 1992; Peucat et al., 1995; Taylor et al., 1984) constituted a coherently evolved crustal domain prior to the Cenozoic rifting of the Gondwana supercontinent. This suggestion is endorsed by later workers (Paquette et al., 2003; Rekha et al., 2013b; Schofield et al., 2010; Thomas et al., 2009; Tucker et al., 2011a). If parts of northeast Madagascar and western India shared coherent evolution before the break-up of Gondwana, the crustalscale shear zones that pre-date the Cretaceous lithosphere dismemberment should be traceable across the facing coastlines of the two landmasses. Several crustal-scale shear zones are identified in South India (Bhaskar Rao et al., 1996, 2003; Brandt et al., 2011; Ghosh et al., 2004; Meißner et al., 2002; Peucat et al., 2013; Raith et al., 1999; Santosh et al., 2012; Tomson et al., 192 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 1. Simplified geological map showing major shear zones in south India. Inset maps show the continents making up the East and West Gondwanaland at 500 Ma after Sommer et al. (2003) (top-right) and the location of south central India (bottom-right). Rectangular box outlines the Phonda–Kasaragod corridor along the western coast of India. Closepet granite is shown by ‘+’ sign. 2013) (Fig. 1) and in Madagascar (BGS et al., 2008; Collins, 2000, 2006; Collins et al., 2003a,b,c; Collins and Windley, 2002; Cox et al., 2004; De Waele et al., 2009; Raharimahefa and Kusky, 2006, 2009; Tucker et al., 2011a,b) (Fig. 2), but linking the shear zones across the facing coast lines has been ambiguous. The Betsimisaraka suture zone is a key geologic feature in east-central Madagascar. Kröner et al. (2000) and Collins and Windley (2002) suggest that the Betsimisaraka suture zone demarcating the contact between the Antananarivo domain and the Antongil Block is a polychronous subduction-related orogen whose formation initiated during Neoproterozoic subduction (740–630 Ma) and culminated with terminal collision at 560–490 Ma. On the other hand, Tucker et al. (2011a) opine that the Antananarivo domain (in the west) and the Antongil–Masora Block (in the east) accreted together in the late Archean (c. 2.55–2.48 Ga), and the Neoproterozoic metasediments and intrusives in the Betsimisaraka suture zone post-date the Archean accretion. The Betsimisaraka suture zone is predicted to extend into western India, but its location within India is controversial (Collins and Windley, 2002; Ishwar-Kumar et al., 2013; Raharimahefa and Kusky, 2010; Raval and Veeraswamy, 2003; Windley et al., 1994). The Betsimisaraka suture zone was correlated with the Moyar shear zone (Windley et al., 1994), the Palghat–Cauvery shear zone (Collins and Windley, 2002; Raharimahefa and Kusky, 2010) and the Moyar–Bhavani shear zone (Raval and Veeraswamy, 2003) (Fig. 2). On the other hand, Ishwar-Kumar et al. (2013) propose that the Betsimisaraka suture zone extends as a curvilinear suture outcropping within India as the Karwar–Kumta shear zone in the north (K) that is continuous with the Coorg shear zone (K) in the south (Fig. 2). The authors contend that the Betsimisaraka–Karwar–Kumta–Coorg suture zone is a polychronous Meso/Neoproterozoic (1.3–0.9 Ga) belt along which the Mesoarchean Antananarivo crustal domain (comprising the Antananarivo, the Karwar and the Coorg Blocks) in the west and south is accreted to the WDC. The uncertainty in linking the shear zone across Madagascar and India stems from the profound lack of structural, metamorphic and chronologic information in the crustal domains along the western coast of India, where the shear zones in Madagascar are presumed to extend within western India. Another aspect that may have contributed to the imprecise correlation among the regional scale shear zones is that the evolutionary history of crustal domains in Madagascar were superposed by Neoproterozoic-Early Cambrian ductile deformation, anatexis and plutonism related to the final assembly of Gondwana. The superposition is absent along the west coast of India being distally located from the zone of amalgamation between East and West Gondwana (Rekha et al., 2013b). The objective of this study is to address the ambiguity by reconstructing the Paleoarchean to Paleoproterozoic deformation, metamorphism and chronologic history of the crystalline rocks along the 430 km long corridor along the west coast of India strategically located such that the crustal domain stretches across the zone where the Betsimisaraka suture zone is expected to extend within India (Fig. 2). To reconstruct the tectonics of the WDC and the craton-limiting regional shear zones we combined the recently published geological and chronologic data (Rekha et al., 2013b; Rekha and Bhattacharya, 2013, 2014; Ishwar-Kumar et al., 2013; Santosh et al., 2013) with new structural-chronologic information in the southern part of the craton and U–Th-total Pb chemical ages S. Rekha et al. / Precambrian Research 252 (2014) 191–208 193 Fig. 2. Proposed shear zones linking India and Madagascar within the framework of East Gondwana. The Phonda–Kasargod corridor is indicated by the gray-shaded rectangular area in the version proposed by Ishwar-Kumar et al. (2013). Acronyms used for shear zones in India are the same as in Fig. 1; TL for Tapti Lineament. BS – Betsimisaraka suture, RSZ – Ranotsara shear zone, ASZ – Angavo shear zone, AIHSZ – Angavo-Ifanadiana high-strain zone, AHGSZ – north-trending high grade shear zone, TSZ – Tranomaro shear zone, BOB – Bemarivo Belt. of monazite from 27 samples in the corridor. Based on these new findings, we discuss the extension of the shear zones in east-central Madagascar, especially the Betsimisaraka suture zone, within India. 2. The Bhatkal–Kasargod corridor The northern sector (north of Bhatkal) in the corridor (Fig. 3) is dominated by the lithodemic units of the WDC, e.g. the Peninsular gneisses comprising migmatitic tonalite–trondjhemite–granodiorite gneisses (TTGs), greenschist facies supracrustal rocks comprising phyllites, banded iron formations, meta-mafic/ultramafics and meta-quartzites of the N/NNW-trending Shimoga schist belt, and deformed granitoid plutons intrusive into the basement gneisses and supracrustal rocks (Rekha et al., 2013b; Rekha and Bhattacharya, 2013, 2014). U–Pb and Pb–Pb zircon ages, monazite chemical ages, and whole rock Sm–Nd ages (Rekha et al., 2013b and the references there-in) suggest that the TTG gneisses are the oldest lithodemic unit (>3.1 Ga) in the WDC. The supracrustal rocks of the Shimoga schist belt sensu stricto are considered equivalent to the Neoarchean Bababudan Group, the oldest unit of the Dharwar Supergroup (Ramakrishnan and Vaidyanadhan, 2008). The WDC granitoids are emplaced in two age intervals, e.g. 2.4–2.6 Ga and 2.9–3.0 Ga (Rekha et al., 2013b, and references there-in). South of Bhatkal (Fig. 3), the area is dominated by WDC gneisses and granitoids, and rocks of the Coorg massif comprising mafic granulites and anatectic quartzofeldspathic gneisses that possess multiple tectonic fabrics, and foliated charnockite–enderbite with demonstrably fewer tectonic fabrics (Fig. 4). The foliations in the high-grade gneisses and deformed granitoids in and neighboring the northern fringe of the Coorg massif granulites are sub-vertical and WNW-trending (Fig. 4a). Sandwiched between the amphibolite/greenschist facies lithologies of the WDC in the north (domain I) and the granulites in domain III is a zone of anatectic non-granulite facies gneisses (domain II) characterized by recumbent folds superposed by W/WNW-trending open and upright folds (Fig. 4a). Domain II (Fig. 4a) in the south is limited by a WNWtrending line that separates garnet-bearing anatectic gneisses in the south from the garnet-free WDC lithologies in the north. The line broadly coincides with the orthopyroxene-in isograd (Peucat et al., 2013; Tomson et al., 2013). In the north, domain II is limited by a NNW-trending line that marks the northernmost boundary of the W/WNW trending folds in anatectic gneisses exclusive to domain II. 2.1. Domain I: the craton fringe In the Peninsular gneisses, the earliest foliation SM1 defined by leucosome layers in biotite ± hornblende matrix is isoclinally folded, and the composite of axial planar foliation (SM2 ) and SM1 is variably transposed parallel to the penetrative foliation SM3 foliation (Mukhopadhyay, 1986; Naha et al., 1991, 1995, 1996; Rekha et al., 2013b). The gently to moderately dipping SM3 foliation in the anatectic gneisses (Fig. 4b) describes asymmetric, open, gently-plunging folds (DM4 ) with sub-vertical axial planes trending N/NNW (Fig. 4c). The DM4 structures are locally superposed by open and upright cross folds (DM5 ) with W/WNW-trending axial planes (Fig. 4d). Phyllite, schist and micaceous quartzite of the Shimoga schist belt are characterized by five fabric-forming events (Rekha et al., 2013b). The pervasively developed fabric in the schists/phyllites that constitutes the form surface for mesoscopic folds (DM4 ) in domain I is the crenulation cleavage SM3 . SM3 has a gentle to moderate northward dip in this domain (Fig. 4e, cf. Rekha et al., 2013b). The overprinting DM4 folds in the Shimoga schist belt are tight to 194 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 3. Planar and linear structures in the Phonda–Kasargod corridor. The structures in the corridor north of Bhatkal are from Rekha et al. (2013a); the structures in the Bhatkal–Kasargod sector (outlined) are from this study (Fig. 4; details in text). Open circle indicates locations of monazite-dated samples. Cartoon depicts the spatial variation in structures along the corridor (not to scale). NSZ and SSZ together constitute SMSZ. open, asymmetric and upright with N/NNW trending axial planes and regionally curved hinge zones plunging gently toward NNW and SSE (Fig. 4f). By contrast, DM5 folds are also open and upright, with WNW-trending sub-vertical axial planes and fold axes plunging gently in an arc between E and ESE (Fig. 4g). The DM5 folds are locally developed in domain I, but become prominent southwards. The planar fabrics in the granitoids are weakly perceptible and fewer than in the Peninsular gneisses and the WDC supracrustals. At least two sets of tectonic fabrics are observed in biotite-rich granitoids. The youngest of the two fabrics trends N/NNW; the fabric is disjunctive (often locally developed), sub-vertical, locally axial planar to crenulations and mesoscopic folds (Fig. 4h) defined by biotite segregations. Since supra-solidus and high-temperature deformation microstructures (Paterson et al., 1989; Vernon et al., 2004) are lacking in these granitoids, the planar fabrics are inferred to be low-T deformation features. S. Rekha et al. / Precambrian Research 252 (2014) 191–208 195 Fig. 4. (a) Structural map and (b–k) stereographic projections of planar and linear structures in the lithodemic units of the Bhatkal–Kasargod sector. (a) Map divided into domains I, II and III based on lithology and structural criteria (boxed area and legend from Fig. 3). Stereographic projections for the WDC Peninsular gneisses in domain I showing contoured pole girdles for S planes (darker shades of gray enclose higher contours) and poles of F fold axes (filled squares): (b) SM3 at 3, 6 and 12% intervals (n = 36, Max = 22%) and FM3 (n = 5), (c) SM4 at 6, 12 and 24% intervals (n = 19, Max ∼ 47%) and FM4 (n = 13), (d) SM5 at 7, 14, 28 and 56% intervals (n = 16, Max = 75%) and FM5 (n = 10). Projections for the phyllites/schists in the Shimoga schist belt of domain I (symbols as in b–d): (e) SM3 at 1, 2, 4, 8 and 16% intervals (n = 169, Max = 22%) and FM3 (n = 27), (f) SM4 at 4, 8, 16 and 32% intervals (n = 28, Max ∼ 36%) and FM4 (n = 22), (g) SM5 at 6, 12 and 24% intervals (n = 16, Max = 33%) and FM5 (n = 14). The subscripts of S and F for the Shimoga Belt are designated to be equivalent to the Peninsular gneisses (in reality, e.g., SM5 should represent the fifth tectonic fabric in the schists/phyllites). (h) Projection for the deformed granitoids in domain I showing poles of early (n = 11, open circles) and later fabrics (≈ SM4 , n = 15, filled circles). Projections for the gneisses in domain II: (i) poles of northward (n = 39, open circles) and southward (n = 32, open squares) gently-dipping gneissic layers, the form surface describing recumbent folds; the dashed line represents the best-fit girdle, (j) poles of recumbent fold axial planes at 2, 4, 8 and 16% intervals (n = 64, Max = 24%), and FM5 axial planes (n = 10, filled circles) and fold axes (n = 7, filled squares); the dash–dot line represents the best-fit girdle. (k) Projection for the granulites in domain III showing poles of the shear zone fabric (≈ SM5 ) and fold axis lineations in quartzofeldspathic gneisses (open squares: planes, n = 38; open triangles: lineations, n = 12) and metapelites (filled squares: planes, n = 32; filled triangles: lineations, n = 9). 2.2. Domain II: the sandwich zone Anatectic biotite gneisses (Fig. 5a and b) devoid of magmatic/metamorphic orthopyroxene dominate domain II. Unlike the domain I Peninsular gneisses in which leucosomes predate or are synchronous with DM1 , the domain II anatectic gneisses exhibit late diatexite leucosomes that truncate the early SM1 stromatic layers (Fig. 5b). Mesoscopic recumbent folds on the SM4 foliation exclusive to this domain (Fig. 5a) are associated with gently-dipping extensional shears (Fig. 5c). W/WNW-trending upright folds (DM5 ) with gently-plunging axes are superposed on the recumbent folds (Fig. 4i and j), and extensional shears mark the last deformation phase. These WNW-trending folds become increasingly tighter and more common as domain III is approached. 2.3. Domain III: the DM5 Manjeshwar–Sulya Shear Zone (MSSZ) Domain III comprises an interleaved ensemble of the WDC gneisses, anatectic granulite facies gneisses (dominantly garnet–sillimanite gneisses and mafic granulites) and foliated charnockites/enderbites characterized by a penetrative WNWtrending sub-vertical foliation (Figs. 4k and 5d) and discrete mylonite zones. Pre-existing fabrics in the gneisses are largely obliterated, or drawn into parallelism with the WNW-trending fabric. The leucosome layers in the granulite facies lithologies describe steeply plunging reclined folds (Fig. 5e) with the fold axis sub-parallel to the down-dip stretching lineation (Fig. 4k). Mesoscopic S–C fabrics and , ı and winged porphyroclast of feldspar indicate a dextral sense of shear on the monophase shear foliation. A set of NNW/N-trending sinistral shears (Fig. 5f) and WNW-trending dextral shears (Figs. 5g and h) formed synchronously with the mylonitic shear foliation. The orthogneisses host rare couple-of-cm wide melt pods in these shear zones (Fig. 5f). The common occurrence of steeply-plunging reclined folds sub-parallel to stretching lineations, and the lack of sheath folds suggest that the DM5 deformation was dominated by a strike-slip 196 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 5. Photographs showing field relations in domains II (a–c) and III (d–h). All photos except (c) and (h) represent plan views. Pen is 15 cm long. Pen-head and hammer-head point north. Larger and shorter half-arrows are for the first order and second order shears, respectively. (a) Recumbent folds on gneissic layering. Note the open, upright folds with gently-plunging folds on the sub-horizontal foliation. (b) Domain II biotite gneiss showing diatexite leucosomes that truncate pre-DM5 structures. (c) Gentle south-dipping extensional shears in anatectic biotite gneiss in domain II. (d) Stromatitic leucosomes in granulite facies gneisses in the Coorg Block. (e) Steeply-plunging reclined folds in DM5 low-strain domain. (f) Locally-developed sinistral N-trending shears and shear-hosted leucosome in high-grade gneisses. The shear zone tapers out along strike in the leucosome-free zone indicating melt emplacement was synchronous with deformation. (g) Same features as in (f). Note the sigmoid nature of the en echelon leucosomes. (h) WNW-trending shears in deformed granitoid with reverse-dextral sense of movement. S. Rekha et al. / Precambrian Research 252 (2014) 191–208 197 Fig. 6. Back-scattered electron (BSE) images showing textural relations in the rocks of domain III (bold broken line in each image shows the trace of the shear zone fabric). (a) Garnet overgrowth on the chlorite-defined DM5 mylonite fabric in Peninsular gneiss. (b) Mylonite in Peninsular gneiss showing pre-tectonic garnet. This garnet has a post-tectonic mantle overgrowth (not visible in image). Note that epidote overgrows the fabric. (c) DM5 chlorite replacing former high-T garnet + hornblende assemblages in the Coorg Block. (d, e) DM5 biotite ± hornblende replacing former high-T assemblage including orthopyroxene in the Coorg granulites. (f) Randomly-oriented chlorite, occasionally associated with blue–green amphibole, overgrows high-grade minerals in the Coorg granulites. sense-of-shear with a down-dip vorticity vector (Ghosh et al., 2003). The orientations of the conjugate pair of N-trending sinistral and WNW-trending dextral shears formed synchronously with shearing suggest that deformation strain was transpressional in nature. Weakening of the deformation strain and the strain field northwards is manifested by small-scale W/WNW-trending upright folds on gently-dipping extensional shear fabrics in domain II and in the southern parts of domain I. The temperature of the WNW-trending DM5 fabric varies across the three domains. In most parts of domains I and II, the DM5 fabric is weakly developed except for couple of meters wide highstrain zones that truncate the WDC lithologies. In these high-strain 198 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 zones, chlorite–muscovite and actinolite–chlorite assemblages in pelitic and mafic phyllites/schists, respectively, in the Shimoga schist belt attest to greenschist facies conditions during DM5 deformation. In the gneisses and granitoids, the DM5 fabric defined by shape-preferred aggregates of biotite ± chlorite ± muscovite replace coarse-grained polygonized aggregates of feldspar, and occasionally hornblende. In domain III, DM5 mylonites defined by chlorite ± biotite ± actinolite aggregates wrap around feldspar clasts showing core-mantle structure. Garnet in the mylonite occurs in two modes, e.g. pre-tectonic ellipsoidal garnets within chlorite aggregates, and post-tectonic garnets (and epidote) overgrowing the mylonite fabric (Fig. 6a and b). The growth of post-tectonic garnet–epidote at the expense of chlorite–plagioclase–quartz assemblage suggests prograde metamorphism at greenschist facies conditions. In zones south of this location, locally aligned aggregates of biotite ± hornblende replacing orthopyroxene and garnet in gneisses and granitoids define the DM5 fabric (Fig. 6c–f). The DM5 fabric-defining hornblende grains are commonly replaced by randomly-oriented chlorite–plagioclase intergrowths (Fig. 6e). In the Coorg massif granulites, pervasive DM5 re-orientation of early granulite facies fabric occurred at amphibolite facies. Meltfilled DM5 N/NNW-trending shears (Fig. 5f) in the WDC gneisses corroborate the prevalence of anatectic conditions, but the syn-DM5 anatexis did not necessarily occur at granulite facies conditions. Northwards in domain III, and in domains I and II, the DM5 deformation occurred at greenschist facies conditions. The temperature of DM5 deformation within the WNW-trending shear zone waned considerably northwards from the Coorg massif granulites. The decrease in temperature correlates with northward decrease in DM5 deformation strain manifested by the greater preservation of pre-DM5 structures, zonal development of DM5 fabric, and the progressively open nature of DM5 folds. In summary, we suggest the following: (a) With the exception of the WDC gneisses that experienced pre-DM3 amphibolite facies anatexis-deformation, the Peninsular gneisses (DM3 , DM4 ), the supracrustal belts (DM1 –DM4 ) tectonically juxtaposed (post-DM2 , pre-DM4 ) to the gneisses (Rekha et al., 2013b), and the felsic plutons emplaced into the gneiss-supracrustal rock composite occurred at greenschist facies conditions (Rekha et al., 2013b; this study); (b) the NW through N–NE trending curvilinear tectonic trend within the WDC is correlated with asymmetric, non-planar and noncylindrical DM4 folds characterized by steeply-dipping axial planes and gentle to moderately plunging fold axes (Rekha et al., 2013b; this study); (c) the DM4 trend is truncated by two craton-limiting, WNW-trending, steep-dipping regional shear zones (Fig. 3), e.g. the South Maharashtra Shear Zone (SMSZ) in the north (Fig. 3; Rekha and Bhattacharya, 2013, 2014) and the Manjeshwar–Sulya shear zone (MSSZ) in the south (Fig. 4; cf. Chetty et al., 2012); (d) while the amphibolite facies supracrustals hosted in the SMSZ evolved along a counter clockwise metamorphic P–T path (Rekha and Bhattacharya, 2013, 2014), the prograde metamorphic temperatures during shearing in the MSSZ decreased northwards from amphibolite facies temperatures at the Coorg massif granulite margin to greenschist facies temperatures northwards in the WDC lithologies. 3. Results of Th–U-total Pb monazite age determination Out of 300 samples examined, 27 samples in the corridor (Fig. 3) yielded monazites with Th, U and Pb concentrations adequate for chemical age determination. The sample wise age populations (Inline Supplementary Table S1) and probability density plots based on 620 spot ages are presented in Figs. 7 and 8. Monazites in phyllites/schists in the WDC supracrustal belts are too small (typically Fig. 7. Probability–density plots of monazite ages in (a) the Shimoga and Goa schist belts, and the Peninsular gneisses and granitoids of the WDC, (b) the mylonite sample (PT-5Ay) and granulite facies gneisses of the Manjeshwar–Sulya shear zone in the south, and (c) schists and granitoids of South Maharashtra shear zone in the north. Number of samples analyzed (N), and ‘n’ is the number of spot ages. Lithology wise population ages and 2 errors are in Ma. Monazite analyses and chemical ages are in Inline Supplementary Table S1. <5 ␮m equivalent diameter) and low in Th, U, Pb abundance (close to detection limit) for realistic age determination. In the Shimoga schist belt, a single garnet-bearing chlorite schist (MAK-69A) with coarse (20–150 ␮m diameter) monazites having relatively high Th, U and Pb concentrations was dated (Inline Supplementary Table S1). Inline Supplementary Table S1 can be found online at http://dx.doi.org/10.1016/j.precamres.2014.07.013. The samples were analyzed using CAMECA SX-100 electron probe microanalyzer in the Department of Geology and Geophysics, S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 8. (a) Probability–density plots of monazite ages (this study) from the WDC lithologies in domains I, II and III (blue line) compared with those obtained from the WDC lithologies north of Bhatkal after Rekha et al. (2013a) (red discontinuous line). Probability–density plots of existing U–Pb zircon ages (magenta dotted line) from the WDC lithologies (Raith et al., 1999; Meißner et al., 2002; Peucat et al., 2013) are also shown. Dates younger than 2 Ga are excluded. (b) Probability density plots of monazite spot ages (this study) from the Coorg granulites in domain III (blue line) and U–Pb zircon ages (magenta dotted line) from the Coorg Block (Santosh et al., 2013) are shown. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) Indian Institute of Technology, Kharagpur, India, CAMECA SX-FIVE in the Department of Earth Sciences, Indian Institute of Technology, Mumbai, and JEOL JXA 8200 Superprobe in the Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts. Analytical protocols for Th–U-total Pb age determinations in monazites (Montel et al., 1996) are provided in Rekha et al. (2013b) for analyses with CAMECA SX-100 and SX-FIVE, and Chatterjee et al. (2011) for analysis with JEOL JXA-8200 Superprobe. PT-25 was analyzed with the different instruments to check for consistency in the results of the Th, U and Pb analysis and age determinations. The cumulative probability–density of the spot ages was computed using Isoplot/Ex (Ludwig, 2003). Only spot ages with 2 errors <6% of the absolute values were included in the statistical analysis (cf. Rekha et al., 2013b; Prabhakar, 2013). Monazites in the WDC gneisses, granitoids and schist (MAK-69) are typically 30–100 ␮m in diameter and chemically homogeneous in Th, U, Pb and Y, except for chemically distinct thin rims (<5 ␮m wide). The thin rims were not analyzed because the beam-induced damage around the analyzed spots exceeded the rim width. Monazites in the WDC lithologies share sharply-defined non-reactive margins with the adjacent silicate phases. 199 Monazites in individual WDC samples are isochronous and yield mean population ages with 2␴ errors typically < 4%, and in many instances < 2% of the mean population age (Table 1). The spot ages in metamorphic monazites from the WDC samples taken together are clustered in four age groups, 3.1–3.5 Ga, 2.9–3.0 Ga, 2.4–2.6 Ga and 2.2–2.3 Ga, identical to the estimates of Rekha et al. (2013b) (Fig. 8a). The oldest Meso/Paleoarchean ages are retrieved exclusively from the Peninsular gneisses (Fig. 7a and Inline Supplementary Table S1). In granitoids, the mean age populations in monazite cluster at 2.9–3.0 Ga, and 2.5 Ga (Londa and Quepem plutons) (Fig. 7a, Table 1). The monazite-dated samples in the Shimoga schist belt show four distinct age populations, e.g. 3322 ± 30 Ma, 3141 ± 31 Ma, 2615 ± 10 Ma and 2383 ± 21 Ma (Fig. 7a, Table 1). Metamorphic monazite in the garnetiferous quartz–chlorite schist (MAK-69A) yield bi-modal age populations, e.g. 2550 ± 34 Ma and 2381 ± 22 Ma (Table 1). Monazites in the MSSZ hosted mylonite sample (PT-5Ay) yielded statistically-resolved age clusters (Ludwig, 2003) at 2970 ± 61 Ma, 2431 ± 88 Ma and 2249 ± 37 Ma (Fig. 7b and Table 1). The larger errors associated with the ages of these populations is due to the fewer spot ages obtained from the monazites (Fig. 9a and b). In contrast to the WDC lithologies, monazites in the retrogressed Coorg massif granulites (Fig. 9c–g) are larger (up to 200 ␮m diameter; long axis up to 300 ␮m long) and complexly-zoned in Th and Y with diffuse or gradational boundaries between the inner chemical domains (Fig. 9c–g). Sharp boundaries are generally restricted to the interfaces separating the youngest rims mantling the patchy chemically zoned grain interiors (Fig. 9e). These monazites share reactive margins with adjacent silicate/oxide minerals. The chemically-zoned monazites in the retrogressed Coorg massif granulites yielded three statistically-resolved age populations at 3279 ± 17 Ma, 3022 ± 9 Ma and 2473 ± 18 Ma (Fig. 7b). Rare monazite veins in PT-25 (arrow, Fig. 9g) yielded 2.3 Ga, and margins of polychronous monazites (Fig. 9e–g) yielded younger Neoarchean ages. The younger monazite ages in the Coorg massif granulites overlap with the ages obtained from monazites in the mylonite PT-5Ay (Fig. 9b). In the Pernem–Phonda sector of the corridor, metamorphic monazites exhibit complexly zoned interiors that are either mantled by chemically-homogeneous younger zones, or the interiors occur as dissected rafts within chemically homogeneous grains (Rekha and Bhattacharya, 2013, 2014). The dissected rafts and grain interiors are Neoarchean and Early Paleoproterozoic (2.6–2.4 Ga). In the southern part of the shear zone, the rims of metamorphic monazites are Early Paleoproterozoic (2.3–2.2 Ga); northwards the monazite rims are younger, e.g. Late Paleoproterozoic (1.8–1.9 Ga) and Early Mesoproterozoic, 1.6–1.8 Ga (Fig. 7c). The general northwards decrease in the metamorphic age in the shear zone suggests long-lived accretion along the northern margin of the craton (Rekha and Bhattacharya, 2014). 4. Discussion Extrapolation of results of high-T experiments on intracrystalline Pb diffusion in monazites (1000–1300 ◦ C; Cherniak et al., 2004; Gardès et al., 2006, 2007) to lower temperature suggest the loss of inherited Pb by intra-crystalline diffusion in monazite is negligible below 700–750 ◦ C. For example, ∼10 ␮m diameter monazite grains may shed only ∼1% of inherited Pb by volume diffusion at 700 ◦ C in several billions of years, and at higher temperature ∼800 ◦ C, Pb retention is >99% in monazite grain 100 ␮m in diameter (Cherniak et al., 2004). Alternatively, fluids aid in monazite growth in digenetic, metamorphic and magmatic conditions (Braun et al., 1998; Bingen and van Breemen, 1998; Budzyn et al., 2010; 200 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Table 1 Latitude/longitude, lithology, brief petrography, occurrence and mean population age (±2) of monazite dated samples in Phonda–Kasargod sector (sample locations in Fig. 3). Sample number Location Lat/Long South Maharashtra shear zone KS-13B N 16◦ 16.24′ E 73◦ 48.97′ Rock type Brief mineralogy Monazite occurrence Un-mix/weighted average age ± 2 (in Ma) Deformed pegmatite Dynamically recrystallized perthitic Kfs and Qtz with many small post-tectonic Grt grains Length: 20–40 ␮m with few grains upto 400 ␮m; mostly euhedral; the grains are patchy and disintegrated; occurs as inclusions in recrystallized quartz and K-feldspar and at quartz–K-feldspar boundaries Length: 10–40 ␮m; monazite parallel to the schistosity; euhedral to subhedral; rare compositional zoning; occurs at quartz–biotite and quartz–plagioclase contact and overgrowing the fabric-defining biotite Length: 20–30 ␮m; euhedral to subhedral; occurs as inclusions in quartz, plagioclase and at quartz–biotite boundaries Length: 10–30 ␮m; euhedral to subhedral; occurs in the biotite–plagioclase–quartz matrix, rarely with in garnet 1535 ± 22 (24), 1685 ± 18 (64), 1925 ± 76 (12) n = 17 KS-35 N 16◦ 03.24′ E 73◦ 45.14′ Grt–Bt schist Bt–Pl–Kfs–Qtz. Post-tectonic Grt overgrowing the fabric SV-21 N 16◦ 05.26′ E 73◦ 34.85′ Grt–Bt schist Bt–Qtz–Pl–Kfs (with minor Hbl). Small Grt appears to be pre/syn-tectonic INS-I INS-III N 15◦ 51.63′ E 73◦ 50.30′ Grt–Bt schist Bt–Pl–Qtz with rare late Chl. Post-tectonic Grt Mylonite Bt–Ms–Qtz. Qtz mostly occur as ribbon Western Dharwar Craton USP-2 N 15◦ 40.02′ E 73◦ 55.01′ USP-3 ZEN-44D N 15◦ 31.98′ E 74◦ 05.71′ Chl–Bt schist Chl–Bt–Qtz–Pl. Fabric defined by Chl–Bt aggregates ZEN-31B N 15◦ 18.78′ E 74◦ 10.32′ Polymict conglomerate GA-73A N 15◦ 20.06′ E 74◦ 16.50′ Deformed Granitoid Chl–Bt–Qtz–Cal–Ms matrix warping around the Pl–Qtz rich tonalitic and Bt–Qtz schist clasts Qtz–Pl–Kfs GA-111C N 15◦ 09.97′ E 74◦ 04.18′ Mylonite JD-19 N 15◦ 09.02′ E 74◦ 28.70′ Gabbro KK-31A N 15◦ 06.38′ E 74◦ 22.57′ Deformed granitoid Qtz–Pl–Kfs NJ-17 N 15◦ 03.04′ E 74◦ 20.00′ Deformed granite Qtz–Pl–Kfs. The relict magmatic Pl grains still preserve the orientation of magmatic flow direction KK-4A N 14◦ 54.27′ E 74◦ 12.23′ Chl–Ms–Qtz schist Chl–Ms-defined and Qtz-defined layers warping around the large Qtz clast KK-59 N 14◦ 31.62′ E 74◦ 33.82′ Chl–Bt schist MAK-5 N 14◦ 05.51′ E 74◦ 22.57′ Bt-defined and Qtz-defined layers warping coarse Pl grains Opx–Pl Chl–Bt–Qtz. The fabric defined by shape preferred aggregates of Chl + Bt and elongated Qtz grains Quartzo–feldspathic Ms–Bt–Qtz–Pl. The fabric defined by the shape schist preferred aggregates of Ms and Bt and elongated Qtz grains Length: 10–30 ␮m; anhedral and elongated; occurs as elongated grains parallel to the schistosity defined by biotite–muscovite–quartz matrix Length: 10–50 ␮m; subhedral to anhedral; elongated; mostly occur in schistose matrix as overgrowing the chlorite–biotite aggregates and also as elongated grains along the grain boundaries of quartz and chlorite–biotite aggregates Length: 10–30 ␮m; anhedral; irregular and disintegrated grains; occurs in the matrix defined by chlorite, biotite and quartz Length: 20–50 ␮m; subhedral to anhedral; occurs as inclusions in recrystallised quartz and plagioclase and along the phase boundaries of quartz–plagioclase and K-feldspar Length: 15–25 ␮m; subhedral to anhedral; occurs in the biotite–quartz matrix over growing the fabric Length: 10–20 ␮m; euhedral to subhedral; mostly occur in plagioclase matrix Length: 60–150 ␮m; mostly anhedral with irregular patchy zones; occurs as inclusions in polygonized quartz and along the grain contacts with quartz and K-feldspar Length: 40–60 ␮m; mostly anhedral and porous; occurs as inclusions in deformed quartz and along the phase boundaries of quartz, plagioclase and K-feldspar Length: 10–40 ␮m; mostly anhedral and rarely euhedral; occurs as grains overgrowing the chlorite–muscovite and quartz defined layers Length: 10–30 ␮m; mostly anhedral and elongated; occurs as elongated grains along with the fabric defining chlorite–biotite aggregates Length: 20–60 ␮m; subhedral to anhedral with rare patchy chemical zoning; occurs as inclusions in quartz and plagioclase and in grain contacts with quartz, plagioclase and biotite 1744 ± 21 (29), 1816 ± 16 (71) n = 26 2131 ± 31 n = 10 2231 ± 14 n = 34 2534 ± 26 (41), 2712 ± 63 (59) n=5 2640 ± 60 n=5 2518 ± 57 (80), 2153 ± 94 (20) n=5 2295 ± 85 (14), 2592 ± 46 (28) 2967 ± 23 (58) n = 14 2111 ± 56 (33), 2582 ± 63 (67) n=6 2026 ± 39 (49), 2282 ± 77 (51) n=8 2860 ± 86 (49), 3082 ± 90 (51) n=9 2627 ± 55 (13), 2908 ± 46 (29), 3108 ± 32 (58) n = 23 2921 ± 110 (29), 3104 ± 84 (71) n=8 2614 ± 110 n=2 2623 ± 11 (75), 3148 ± 33 (15), 3324 ± 30 (10) n = 20 201 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Table 1 (Continued) Sample number Location Lat/Long Rock type Brief mineralogy Monazite occurrence Un-mix/weighted average age ± 2 (in Ma) MAK-69A N 13◦ 22.40′ E 75◦ 12.88′ Garnetiferous Qtz–Chl schist Chl–Qtz. Chl defined fabric. Very large grains of Grt 2381 ± 22 (71), 2550 ± 34 (29) n = 15 MAK-130A N 13◦ 17.56′ E 74◦ 47.25′ Deformed granitoid Bt–Pl–Qtz MAK-152 N 13◦ 06.29′ E 74◦ 52.86′ Deformed granitoid Bt–Pl–Qtz SKP-1 N 13◦ 02.78′ E 74◦ 47.85′ Deformed granitoid Bt–Pl–Kfs–Qtz with rare Amphibole MNG-1 MNG-4 N 12◦ 51.82′ E 74◦ 47.54′ Gneiss VLC-11 N 12◦ 52.68′ E 74◦ 56.83′ Deformed granitoid Qtz–Pl–Kfs defined leucocratic layer and Bt–Qtz–Pl–Kfs defined melanocratic layer Bt–Pl–Kfs–Qtz with rare Ms PT-15 N 12◦ 57.51′ E 75◦ 12.24′ Gneiss Bt–Pl–Qtz–Kfs Length: 20–150 ␮m; mostly anhedral; occurs mostly along the grain boundaries of recrystallized quartz and also along the interface of quartz and chlorite Length: 20–140 ␮m; euhedral to subhedral with complex chemical zoning; occurs as inclusions in deformed quartz, perthite, overgrowing the biotite defined fabric, along the grain contacts with quartz, plagioclase and biotite Length: 30–200 ␮m; mostly euhedral with complex chemical zoning; occurs as inclusions in quartz and plagioclase and along the phase boundaries of quartz, plagioclase, biotite Length: 20–40 ␮m; anhedral with patchy chemical zoning; occurs as inclusions in quartz, along the phase boundaries of quartz, plagioclase, biotite Length: 20–40 ␮m; anhedral with patchy chemical zoning; occurs mostly along the phase boundaries of quartz, plagioclase, biotite Length: 50–300 ␮m; subhedral to anhedral with complex chemical zoning; occurs mostly along the phase boundaries of biotite, plagioclase and quartz, also as inclusions in biotite and quartz Length: 20–100 ␮m, few grains > 200 ␮m in long axis; anhedral with complex chemical zoning; occurs as inclusions in quartz and plagioclase and also along the grain boundaries of quartz and feldspar and along the phase boundaries of quartz, plagioclase and biotite Manjeshwar–Sulya shear zone N 12◦ 43.69′ PT-32B E 75◦ 06.34′ Deformed granitoid Pl–Kfs–Qtz with rare Bt PT-25 N 12◦ 33.26′ E 75◦ 11.31′ Granulite gneiss Opx–Bt–Pl–Qtz PT-5Ay N 12◦ 40.45′ E 75◦ 26.04′ Mylonite PT-21A PT-21C N 12◦ 34.45′ E 75◦ 19.13′ Granulite gneiss Qtz ribbons and Chl/Hbl aggregates defining the mylonitic foliation warp around Opx, Grt, Pl granulite assemblage Opx–Grt–Pl–Bt–Apt–Qtz Length: 15–80 ␮m; mostly subhedral with patchy chemical zoning; occurs as inclusions in quartz and as along the grain contacts with quartz and biotite. Length: 20–80 ␮m, few grains upto 300 ␮m in long axis; mostly anhedral, rounded to elliptical with complex chemical zoning; occurs as inclusion in plagioclase and in fabric-defining biotite aggregates. Length: 50–140 ␮m; subhedral to anhedral with patchy chemical zoning; occurs as inclusions in plagioclase clasts with an epidote–apatite corona and as corona mantling apatite. Length: 30–300 ␮m; mostly subhedral, rounded to elliptical with complex chemical zoning; occurs as inclusion in quartz, plagioclase, ortho-pyroxene and garnet, and elongated parallel to the biotite flakes. 3044 ± 12 n = 54 2985 ± 13 n = 65 2923 ± 82 n=6 3009 ± 40 n = 12 2965 ± 31 n = 21 3189 ± 19 (56), 3299 ± 67 (29), 3503 ± 130 (16) n = 15 2898 ± 48 (80), 3151 ± 78 (20) n=5 2268 ± 39 (8), 2519 ± 22 (21), 2867 ± 44 (21), 3032 ± 23 (51) n = 64 2249 ± 37 (47), 2431 ± 88 (13), 2970 ± 61 (40) n = 15 2550 ± 50 (3), 2886 ± 76 (2), 3048 ± 11 (82), 3283 ± 17 (13) n = 159 Values in parenthesis in the last column correspond to percentage of spot ages in the population for which the mean ±2 values are provided. n = total number of spots ages. Mineral abbreviations after Kretz (1983). Cabella et al., 2001; Hawkins and Bowring, 1999; Hoisch et al., 2008; Janots et al., 2011; Kempe et al., 2008; Poitrasson et al., 2000; Pyle and Spear, 2003; Rasmussen et al., 2005; Rasmussen and Muhling, 2007; Rekha et al., 2013a). Summarizing, at T > 800 ◦ C, both intracrystalline diffusion and fluid-aided dissolution–precipitation may operate in monazite, but at lower temperatures, intra-crystalline diffusive re-setting of monazite age is unlikely (Cherniak et al., 2004; Gardès et al., 2006, 2007). Thus, monazite dating is ideally suited to constrain low-T metamorphic events because of the ability of monazite to grow readily by fluid-assisted precipitation (Rasmussen et al., 2001; Rasmussen and Muhling, 2007; Janots et al., 2009; Rekha et al., 2013a). Zircon, on the other hand, in view 202 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 9. Textures and X-ray element maps of monazites in domain III. (a, b) PT-5Ay mylonite and (c–g) PT-21C and PT-25 Coorg granulites. (a) Monazite within plagioclase clast mantled by epidote–apatite corona. (b) Monazite partially mantling apatite defining DM5 fabric. (c) Zoned monazite as inclusion in plagioclase. The monazite comprises ∼3.1 Ga low-Th, Y domain that shares diffuse margin with ∼2.9 Ga higher-Th domains. (d) Zoned monazite in apatite/biotite defining DM5 fabric with spot ages tightly constrained between 3.0 and 3.1 Ga. (e) Zoned monazite hosted in DM5 biotite with older 3.0–3.1 Ga interior mantled by Neoarchean ages (∼2.5 Ga) along grain margin. (f) Plagioclase-hosted zoned monazite with 2.9–3.0 Ga interior mantled by 2.5–2.8 Ga domains along grain margin. The two domains share diffuse margins. (g) Zoned monazite with three distinct age populations at 2.9–3.0 Ga, 2.5–2.6 Ga and 2.3 Ga hosted in DM5 biotite. 2.3 Ga spot ages are retrieved in irregular low-Th monazite vein (arrow) cutting across the older age domains. S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Fig. 10. Compilation of existing U–Pb zircon ages and U–Pb–Th chemical ages in monazite in the corridor (data source: Ishwar-Kumar et al., 2013; Rekha et al., 2013a; Santosh et al., 2013). K–Ar ages after Ishwar-Kumar et al. (2013). The Karwar–Kumta suture zone proposed by Ishwar-Kumar et al. (2013) is shown by a continuous double line for reference. of its inability to respond by intra-crystalline diffusion and growth at the low temperatures are likely to remain passive to these low-T events (Gordon et al., 2009; Harlov et al., 2007; Kapp et al., 2005; Rasmussen et al., 2005; Schärer et al., 1999; Whitney et al., 2003). 4.1. Significance of monazite ages in the MSSZ The Mesoarchean monazite ages in domain I WDC gneisses and granitoids (Rekha et al., 2013b, this study) continue into domain III as far south as the Manjeshwar–Sulya (Fig. 10), although the DM1 –DM4 structures in WDC are either transposed or re-oriented parallel to the WNW-trending DM5 shear zone (Figs. 3, 4). Apparently the growth of monazite synchronous with and post-dating the DM5 was impeded within MSSZ because either the permeating inter-granular fluids were chemically infertile for monazite precipitation and/or the lack of pore connectivity inhibited fluid transport to the monazite nucleation zones (Rekha et al., 2013a). Gently to moderately plunging and upright DM4 asymmetric folds with steeply-dipping curvilinear N-trending axial planes dominate the structural geometry of the WDC lithologies in domain I (Figs. 3 and 4a, c, f). The trend is interrupted by locally-developed 203 WNW-trending DM5 shears that become more intense southwards in domains II, and especially in domain III. Eastwards of the corridor the DM4 folds become tighter and the N-trending SM4 fabric becomes penetrative as the curvilinear accretion zone between the East and the West Dharwar Cratons (Figs. 1 and 2), broadly coinciding with the N-trending Closepet pluton, is approached. U–Pb (zircon) emplacement age of the syn-DM4 Closepet pluton lies between 2.45 and 2.55 Ga (Friend and Nutman, 1991; Jayananda et al., 2000; Nutman et al., 1996). Apparently the DM4 structures are broadly Late Neoarchean (2.5 Ga) in age. Since the DM4 structures are transposed and obliterated by the DM5 WNW-trending shear zone in domain III, the transpressional orogen is likely to be younger than the EDC-WDC (DM4 ) accretion. The DM5 WNW-trending MSSZ that hosts both the WDC lithologies and the Coorg massif granulites could be an internal feature within the WDC. If so, the Coorg granulites should be integral to the WDC and may constitute the lower crustal equivalent of the craton (cf. Peucat et al., 2013; Tomson et al., 2013). Alternatively, the MSSZ could be a terrain boundary along which the WDC lithologies accreted with the Coorg Block that did not share coherent evolutionary history with the WDC lithologies until the two terrains accreted along the orogen (Santosh et al., 2013). Below we discuss some of the features relevant to the debate. First, granulite facies lithologies are lacking within the WDC, and only occur interleaved with the WDC lithologies within the MSSZ (Fig. 3). Second, the DM5 deformation is weakly-developed in the craton interior and reported exclusively from areas (Sirankatte, Honakere) located in the southern part of the WDC (Naha et al., 1986, 1990, 1993). If the Coorg massif granulites were indeed lower crustal equivalents of the WDC lithologies, it is difficult to explain why the intense DM5 deformation prominent in the lower crustal analogs is absent in the WDC interior. Instead, a simpler explanation would be to suggest that the DM5 deformation at the craton margin was a consequence of accretion of the WDC lithologies vis-à-vis the WDC with the Coorg massif granulites. It appears therefore that the Coorg granulites are not lower crustal equivalent of the WDC lithologies. Instead, the disparately evolved WDC and the Coorg granulites constitute separate crustal blocks that accreted along the MSSZ (Figs. 3 and 4). Santosh et al. (2013) consider the 2.9–3.3 Ga Coorg massif granulites constitute an exotic block with no record of ∼2.5 Ga metamorphism, and unrelated to the WDC lithologies in the north or the ensemble of high grade gneisses of the Southern Granulite Terrane (SGT). Our results are in agreement with the conclusion of Santosh et al. (2013), and contradict the suggestion by Peucat et al. (2013) that the granulites comprising the lower crustal analogs of WDC extend up to the Moyar shear zone further to the south (Fig. 1). 4.2. Status of the proposed Karwar–Kumta–Coorg shear zone Ishwar-Kumar et al. (2013) suggest that the Karwar–Kumta shear zone continuous with the Coorg shear zone (≈ Manjeshwar–Sulya shear zone, this study) is Neo/Mesoproterozoic in age (Fig. 2), related to the Rodinia assembly, and is the extension of the Betsimisaraka suture zone in east-central Madagascar into India. Below we summarize evidence that suggests this interpretation may not be valid. First, U–Pb zircon ages and U–Th-total Pb chemical ages in monazites – both existing and those presented in this study – are identical across the proposed Rodinia suture (Karwar–Kumta shear zone, Ishwar-Kumar et al., 2013) (Fig. 10). The identical ages as well as the similarity in lithology and structure across the proposed suture zone are unlikely if the crustal blocks with disparate evolutionary history were accreted along the shear zone. Second, U–Pb ages in zircon and monazite from samples within the proposed Rodinia suture cluster into age populations, e.g. >3.0 Ga, 2.9–3.0 Ga, 2.4–2.6 Ga and 2.4–2.2 Ga, with no younger ages reported (Fig. 10). Significant in this context is the 2.9–3.0 Ga 204 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 age obtained from chemically-homogeneous metamorphic monazite overgrowing the penetrative schistosity in the sample located adjacent the proposed shear zone (Fig. 10). If the accretionary shear zone formed during the Rodinia assembly, one would expect that at the temperature inferred for the accretion zone (500 ◦ C, 15 kbar; Ishwar-Kumar et al., 2013), Late Proterozoic monazites to have grown in locales of high strain and thermal anomaly (Fig. 10). The absence of these younger metamorphic monazites within the proposed shear zone suggests that the Karwar–Kumta shear zone is unlikely to be related to the Rodinia assembly. Third, the chemical age of post-tectonic monazite in garnet–chlorite schist sample MAK-69A from the Shimoga schist belt is 2.3 and 2.5 Ga. If this schistosity continues northward into the deformed Bondla ultramafic complex (Figs. 3 and 10; Ishwar-Kumar et al., 2013), it appears reasonable to assume that the deformation of the complex is Early Paleoproterozoic/Neoarchean rather than Mesoproterozoic in age. Fourth, the DM5 tectonic fabric in the MSSZ post-dates and obliterates the curvilinear DM4 structures in the WDC (Figs. 3 and 4). Since the tectonic fabric (DM5 ) in the MSSZ is younger than the DM4 tectonic fabric in the Karwar–Kumta high-strain zone, the two shear zones cannot be considered time equivalent as suggested by Ishwar-Kumar et al. (2013). Finally, the domain south of the MSSZ comprises foliated garnet-bearing charnockite–enderbite, anatectic garnet–sillimanite (± cordierite ± orthopyroxene) metapelite gneisses, garnet ± orthopyroxene quartzofeldspathic gneisses and mafic granulites, and garnet–scapolite–wollastonite bearing calc-silicate gneisses. If the MSSZ was continuous with the Karwar–Kumta shear zone (Ishwar-Kumar et al., 2013), then the granulite facies lithologies should dominate the lithologies in the Karwar Block west of the Karwar–Kumta shear zone (Fig. 10). Our studies suggest that these lithologies are notably absent within the Karwar Block, which is dominated by non-garnetiferous and orthopyroxene-free >3.0 Ga Peninsular gneisses and 2.9–3.0 Ga blastoporphyritic granitoids typical of the WDC; both lithologies are notably absent in the Coorg Block. The disparity in lithologies and age precludes the possibility of MSSZ being continuous with the Karwar–Kumta shear zone. The lack of Neoproterozoic age in the Phonda–Kasargod corridor (Fig. 10) suggest that the Betsimisaraka suture, if it were Neoproterozoic/Early Palaeozoic age (Collins and Windley, 2002; Kröner et al., 2000), does not extend into India, within the length of the corridor. If the suture were continuous with the Karwar–Kumta shear zone as suggested by Ishwar-Kumar et al. (2013), then the Betsimisaraka suture should be ∼2.5 Ga in age as suggested by Tucker et al. (2011a). But for this reconstruction to be valid, the Karwar–Kumta Block (Fig. 10) should comprise granulite facies lithologies (≈ Antananarivo Block, NE Madagascar). Because granulites are absent in the Karwar–Kumta Block, and the monazite and zircon ages across the high strain zone within the block are identical (Fig. 10), we consider that this suggestion is unlikely to be tenable. Possibly, the Karwar–Kumta shear zone (2.5 Ga in age) may have formed contemporaneous with the WDC-EDC accretion and the syn-tectonic emplacement of the Closepet granite at 2.5 Ga, and therefore, the Karwar–Kumta high strain zone is a feature internal to the Antongil-WDC crustal domain. 4.3. Timing of the Coorg Block – WDC accretion Ideally, constraining the age of an accretion event is best achieved by dating monazite grown syntectonically with the accretion fabric. However, in coarse-grained rocks, determining monazite paragenesis in relations to fabrics is tortuous because the fabric, more commonly than not, is widely spaced and may not intersect or host the small monazite grains. Thus, although monazite grown distal from the fabric may record the accretion event, dates obtained in these monazites cannot be demonstrably linked to the accretion fabric. The problem is alleviated in mylonite zones because in these zones of high deformation strain, paragenetic relations of monazites in relation to the mylonitic fabric can be better ascertained. Monazite ages obtained in the three samples PT-5Ay (Fig. 9a and b), PT-21c (Fig. 9c–e) and PT-25 (Fig. 9f and g) are from monazite grains hosted within the WNW-trending high strain zones. PT-5Ay is a mylonite with a chlorite-defined mylonitic fabric overgrown by a prograde epidote–garnet assemblage (Fig. 6a and b), whereas PT-21C and PT-25 are enderbite from the Coorg Block deformed at amphibolite facies condition (Fig. 6c–g). Two age populations (2.2 and 2.4 Ga) are obtained from the monazite grains that partly mantle fabric-defining apatite in PT-5Ay (Fig. 9b). In the same sample, chemically homogenous monazite with an epidote–apatite corona yields mostly 2.9 Ga ages and rare 2.5 Ga ages along the grain margin (Fig. 9a). In PT-21C, monazite aligned parallel to the mylonitic fabric and with post-tectonic overgrowth yields two distinct age populations, e.g., 3.0 Ga in diffuse chemical domains in the grain interior, and younger 2.5 Ga ages at the grain margin (Fig. 9c–e). In PT-25, monazite in veins (Fig. 9g) post-tectonic with respect to the accretion fabric yields 2.3 Ga. The gamut of monazite ages suggest that the minimum age of Coorg Block-WDC accretion is 2.2 Ga, while the MSSZ post-dates the 2.5 Ga EDC-WDC accretion (Bhaskar Rao et al., 1992; Chadwick et al., 2000; Chardon and Jayananda, 2008; Friend and Nutman, 1991; Moyen et al., 2003a,b; Peucat et al., 2007; Taylor et al., 1988). The evidence together suggests that the MSSZ formed between 2.2 and 2.5 Ga. Peucat et al. (2013) consider that the younger Paleoproterozoic ages (2.2–2.3 Ga) resulted from post-accretion cooling. However, textural evidence (Figs. 6a, b and 9a, b) suggests that the WDC-Coorg Block accretion correlates with prograde heating in the shear zone. Tectonic cartoons show the possible sequences of EDC-WDC accretion at 2.5 Ga and the Neoarchean to Paleoproterozoic accretion of the Greater Dharwar Craton at its southern and northern margins (Fig. 11). 4.4. Coorg Block – WDC accretion zone: the Madagascar connection To ascertain if the Neoarchean accretion zone in the southern margin of the WDC continued westward into Madagascar, the following three crustal domains in east-central Madagascar are important (Fig. 12a), e.g. the Mesoarchean Antongil and Masora Blocks, the Neoarchean Antananarivo domain, and the Paleoproterozoic (2.4–2.5 Ga) accretion zone in the general location of the Betsimisaraka suture zone separating the two domains (Tucker et al., 2011a,b). Rekha et al. (2013b) correlated the lithodemic units in the WDC with those in the Antongil Block, e.g. the 2.4–2.6 Ga Goa schist belt ≈ the Mananara Group; the 2.5 Ga Quepem granitoid ≈ the Masoala Suite; the 3.1 Ga Shimoga schist belt ≈ the Fenerivo Group and the 3.1 Ga Peninsular gneiss suite ≈ the Nosy Boraha suite. The high-grade orthogneisses and foliated charnockite/enderbites in the Antananarivo domain (Collins and Windley, 2002; Kröner et al., 2000; Tucker et al., 1999) are mineralogically similar with those in the Coorg Block. The D2 and D3 structures (Ntrending upright folds and high strain zones, top-to-the east sense of transport) in the N/NNW-trending segment of the Antananarivo domain are similar to the DM5 structures in the Manjeshwar–Sulya shear zone, MSSZ (WNW-trending folds and high-strain zones, top-to-the-north transport), if the NNE-trending structures in central Madagascar were to be oriented parallel to the WNW-trending transpressional accretion zone (this study). The existing chronologic data across the Neoarchean accretion zone in areas neighboring the coast lines in eastern Madagascar is compiled in Fig. 12a (Mesoproterozoic and younger ages are S. Rekha et al. / Precambrian Research 252 (2014) 191–208 205 Fig. 11. Tectonic cartoons showing accretion stages at >2.5, 2.5 and <2.5 Ga involving the WDC, EDC and the crustal domains fringing the WDC (see text for details). Closepet granite is shown in black. excluded since these dates are not relevant to the topic of discussion). The Antongil and the Masora Blocks are dominated by U–Pb zircon ages of 3.0–3.3 Ga (magmatic emplacement age) from felsic intrusives and tonalite–trondjhemite gneisses of the Nosy Boraha Suite, and a younger age population (2.5–2.6 Ga) corresponding to high-grade metamorphism/anatexis related to tectonic emplacement of disparate belts of mafic gneiss and schist (Tucker et al., 1999, 2011a). By contrast, the dominant dates obtained in the lithodemic groups in the Antananarivo domain lies between 2.5–2.6 Ga, with rare U–Pb zircon ages of ≥3.0 Ga and 2.6–2.7 Ga (Collins et al., 2003a,b,c; Tucker et al., 2011a,b) comparable to those in the Coorg Block. The variation in zircon ages in the crustal domains across the accretion zone is similar to the variation in monazite ages obtained in this study across the MSSZ. It is suggested therefore that the MSSZ continues into Madagascar as the <2.5 Ga accretion zone sandwiched between the Antongil Block and the Antananarivo domain (Fig. 12b). 4.5. The South Maharashtra shear zone: the Madagascar connection The Paleo/Mesoproterozoic South Maharashtra shear zone (SMSZ) is inferred to extend across the facing coastlines (Fig. 12b) into Madagascar north of the Antongil block (≈ WDC) (Rekha and Bhattacharya, 2014). In Madagascar, however, the Antongil Block in the north abuts against the ensemble of Neoproterozoic intrusives and metasediments of the South Bemarivo Belt, which in turn rests on an older basement that outcrops as the Fig. 12. (a) Compilation of available U–Pb zircon ages across the 2.5 Ga accretion zone south of the Antongil Block (eastern Madagascar). 1 Tucker et al. (2011a), 2 De Waele et al. (2011), 3 Tucker et al. (1999), 4 Tucker et al. (2011b), 5 Collins et al. (2003b), 6 Kröner et al. (2000). a U–Pb SHRIMP, b U–Pb LA-ICPMS, c U–Pb TIMS, d Pb–Pb evaporation. (b) Suggested linkage of selected shear zones across east-central Madagascar and South India. SMSZ (north of the WDC; Rekha and Bhattacharya, 2014) possibly extends into Madagascar as a buried suture zone north of the Antongil Block (A). The shear zone (oblique-hatched line) sandwiched between the Coorg granulites and the WDC possibly links with the <2.5 Ga shear zone separating the Antongil Block (A) from the Antananarivo domain (ANT) (the Betsimisaraka suture zone (BS)). AIHSZ (Fig. 2) is linked with the Palghat–Cauvery Shear Zone (cf. Tucker et al., 2011a). Other acronyms are the same as in Figs. 1 and 2. Closepet granite is shown by ‘+’ sign. 206 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Mesoproterozoic Sahantaha Formation. The detrital zircon grains in the Sahantaha Formation quartzites yield multiple ages between 1.9 and 2.5 Ga suggesting that the source rocks from which the zircons were derived are Paleoproterozoic to Neoarchean in age. We suggest that the SMSZ, having similar monazite ages, possibly extends into NE Madagascar (Fig. 12b) underlying the Sahantaha, and the multi-aged detrital zircon grains in the Sahantaha quartzite were possibly derived from the underlying tectonic zone. 5. Conclusions Mesoscopic structures, deformation microstructures and Th–Utotal Pb monazite chemical ages are combined with existing chronology (U–Pb zircon and Th–U-total Pb monazite chemical ages) to reconstruct the tectonic history of the Precambrian crystalline rocks of the WDC and its neighboring crustal domains in a 430 km long corridor (50–60 km wide) along the western coast of India. The large body of structural, mineralogical and chronological data suggests that the WDC is limited in the north and south by two NW-trending Paleoproterozoic ductile shear zones that post-date the accretion between the East and the West Dharwar Cratons (Fig. 12b). The southern craton-limiting shear zone, the Manjeshwar–Sulya shear zone fringing the northern margin of the Coorg Block (metamorphic age: 2.2–2.5 Ga), is the zone of accretion between the greenschist facies supracrustal belts (2.5 and 3.3 Ga), foliated granitoids (2.5 and 2.9 Ga) and amphibolite facies anatectic gneisses (>3.0 Ga) in the WDC and the >2.9 Ga granulite facies ortho/para-gneisses in the Coorg Block. This shear zone extends into east-central Madagascar as the 2.4–2.5 Ga accretion zone, in the general location of the Betsimisaraka suture zone, between the Antongil Block and the Antananarivo Domain (Fig. 12b). The northern shear zone (metamorphic age: 2.3–1.8 Ga) is inferred to extend into Madagascar as a hitherto undiscovered tectonic zone north of the Antongil Block forming the basement for the Mesoproterozoic Sahantaha Formation underlying the supracrustals (Fig. 12b). The monazite chemical ages and U–Pb zircon ages in the WDC, however, fail to show Neoproterozoic/Early Palaeozoic tectonism especially in areas where the Betsimisaraka suture zone are inferred to extend into WDC within western India. We infer that the Betsimisaraka suture, if it were Neoproterozoic/Early Palaeozoic in age, does not extend into India, but the data do not preclude the extension of the suture into western India, if it were Neoarchean in age. Acknowledgments This work forms part of the doctoral dissertation of RS. RS acknowledges the financial support provided by CSIR-UGC (Ref No: 20-6/2008(ii)EU-IV) research fellowship for the work. AB acknowledges the financial support (CPDA funds) provided by the Indian Institute of Technology, Kharagpur (India) for the work. T. A. Viswanath (Goa University) kindly provided critical samples from his own collection. Prof. S. Patel and N. Prabhakar (Indian Institute of Technology, Mumbai) helped with monazite age determination at short notice. The comments of Ingo Braun and an anonymous reviewer greatly improved the styling and presentation of the manuscript. Editorial handling of the ms by R. Parrish is greatly appreciated. References Beckinsale, R.D., Drury, S.A., Holt, R.W., 1980. 3360 m-yr. old gneisses from the south Indian Craton. Nature 283, 469–470. BGS (British Geological Survey), USGS (US. Geological Survey), GLW (GLW Conseil), 2008. Revision de la cartographiege ologique et miniere des zones Nord et Centre de Madagascar (Zones A, B et D). Ministere de L’Energie et des Mines (MEM/SG/DG/UCP/PGRM), Republique de Madagascar, pp. 1049. Bhaskar Rao, Y.J., Naha, K., Srinivasan, R., Gopalan, K., 1991. Geology, geochemistry and geochronology of the Archaean Peninsular Gneiss around Gorur, Hassan District, Karnataka, India. Proc. Indian Acad. Sci. (Earth Planet. Sci.) 100, 399–412. Bhaskar Rao, Y.J., Sivaraman, T.V., Pantulu, G.V.C., Gopalan, K., Naqvi, S.M., 1992. RbSr ages of late Archean metavolcanics and granites, Dharwar Craton, South India and evidence for early Proterozoic thermotectonic events. Precambrian Res. 59, 145–170. Bhaskar Rao, Y.J., Chetty, T.R.K., Janardhan, A.S., Gopalan, K., 1996. Sm–Nd and Rb–Sr ages and P–T history of the Archaean Sittampundi and Bhavani layered complexes in the Cauvery shear zone, South India: evidence for Neoproterozoic reworking of Archaean crust. Contrib. Mineral. Petrol. 125, 237–250. Bhaskar Rao, Y.J., Janardhan, A.S., Vijaya Kumar, T., Narayana, B.L., Dayal, A.M., Taylor, P.N., Chetty, T.R.K., 2003. Sm–Nd Model Ages and Rb–Sr isotopic systematics of charnockites and gneisses across the Cauvery shear zone, Southern India: implications for the Archaean–Neoproterozoic terrane boundary in the Southern Granulite Terrain. In: Ramakrishnan, M. (Ed.), Tectonics of Southern Granulite Terrain – Kuppam–Palani Geotransect. Geol. Soc. India Mem. 50, 297–317. Bingen, B., van Breemen, O., 1998. U–Pb monazite ages in amphibolite- to granulite-facies orthogneiss reflect hydrous mineral breakdown reactions: Sveconorwegian Province of SW Norway. Contrib. Mineral. Petrol. 132, 336–353. Blasband, B., White, S.H., Brooijmans, P., Visser, W., De Boorder, H., 2000. Late Proterozoic extensional collapse in the Arabian–Nubian Shield. J. Geol. Soc. Lond. 157, 615–628. Brandt, S., Schenk, V., Raith, M.M., Appel, P., Gerdes, A., Srikantappa, C., 2011. Late Neoproterozoic P–T evolution of HP-UHT granulites from the Palni Hills (south India): new constraints from phase diagram modeling, LA–ICP–MS zircon dating and in-situ EMP monazite dating. J. Petrol. 52, 1813–1856. 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. Chem. Geol. 146, 65–85. Budzyn, B., Hetherington, C.J., Williams, M.L., Jercinovic, M.J., Michalik, M., 2010. Fluid–mineral interactions and constraints on monazite alteration during metamorphism. Mineral. Mag. 74, 659–681. Cabella, R., Lucchetti, G., Marescotti, P., 2001. Authigenic monazite and xenotime from pelitic metacherts in pumpellyite actinolite-facies conditions. SestriVoltaggio zone, Central Liguria, Italy. Can. Mineral. 39, 717–727. Chadwick, B., Vasudev, V.N., Hedge, G.V., 2000. The Dharwar Craton, southern India, interpreted as the result of Late Archaean oblique convergence. Precambrian Res. 99, 91–101. Chardon, D., Jayananda, M., 2008. Three-dimensional field perspective on deformation, flow, and growth of the lower continental crust (Dharwar Craton, India). Tectonics 27, TC1014. Chatterjee, N., Banerjee, M., Bhattacharya, A., Maji, A.K., 2011. Monazite chronology, metamorphism-anatexis and tectonic relevance of the mid-Neoproterozoic eastern Indian Tectonic Zone. Precambrian Res. 179, 99–120. Cherniak, D.J., Watson, E.B., Grove, M., Harrison, T.M., 2004. Pb diffusion in monazite: a combined RBS/SIMS study. Geochim. Cosmochim. Acta 68, 829–840. Chetty, T.R.K., Mohanty, D.P., Yellappa, T., 2012. Mapping of shear zones in the Western Ghats, Southwestern part of Dharwar Craton. J. Geol. Soc. India 79, 151–154. Collins, A.S., 2000. The tectonic evolution of Madagascar: its place in the East African Orogen. Gondwana Res. 3, 549–552. Collins, A.S., 2006. Madagascar and the amalgamation of central Gondwana. Gondwana Res. 9, 3–16. Collins, A.S., Pisarevsky, S.A., 2005. Amalgamating eastern Gondwana: the evolution of the Circum-Indian Orogens. Earth Sci. Rev. 71, 229–270. Collins, A.S., Windley, B.F., 2002. The tectonic evolution of central and northern Madagascar and its place in the final assembly of Gondwana. J. Geol. 110, 325–339. Collins, A.S., Fitzsimons, I.C.W., Hulscher, B., Razakamanana, T.S., 2003a. Structure of the eastern margin of the East African Orogen in central Madagascar. Precambrian Res. 123, 111–133. Collins, A.S., Johnson, S., Fitzsimons, I.C.W., Powell, C.M., Hulscher, B., Abello, J., Razakamanana, T., 2003b. Neoproterozoic deformation in central Madagascar: a structural section through part of the East African Orogen. In: Yoshida, M., Windley, B., Dasgupta, S. (Eds.), Proterozoic East Gondwana: Supercontinent Assembly and Breakup. Geol. Soc. Lond. Spec. Pub. 206, 363–379. Collins, A.S., Kröner, A., Fitzsimons, I.C.W., Razakamanana, T., 2003c. Detrital footprint of the Mozambique ocean: U/Pb SHRIMP and Pb evaporation zircon geochronology of metasedimentary gneisses in eastern Madagascar. Tectonophysics 375, 77–99. Cox, R., Coleman, D.S., Chokel, C.B., DeOreo, S.B., Wooden, J.L., Collins, A.S., Kröner, A., DeWaele, B., 2004. Proterozoic tectonostratigraphy and paleogeography of central Madagascar derived from detrital zircon U–Pb age populations. J. Geol. 112, 379–399. De Waele, B., Horstwood, M.S.A., Pitfield, P.E.J., Thomas, R.J., Key, R.M., Rabarimana, M., 2009. The architecture of the “Betsimisaraka Suture Zone”, a record of oceanic arcs and associated metasedimentary successions between the “Indian” and “African” parts of Madagascar. In: The Macquarie Arc Conference. International Conference on Island Arc, Continent Collisions, pp. 56–57. De Waele, B., Thomas, R.J., Macey, P.H., Horstwood, M.S.A., Tucker, R.D., Pitfield, D.P.E.J., Schofield, I., Goodenough, K.M., Bauer, W., Key, R.M., Potter, C.J., Armstrong, R.A., Miller, J.A., Randramananjara, T., Ralison, V., Rafahatelo, J.M., Rabarimanana, M.H., Bejoma, M., 2011. Provenance and tectonic significance of the Palaeoproterozoic metasedimentary successions of central and northern Madagascar. Precambrian Res. 189, 18–42. S. Rekha et al. / Precambrian Research 252 (2014) 191–208 De Wit, M.J., 2003. Madagascar: heads it’s a continent, tails it’s an island. Annu. Rev. Earth Planet. Sci. 31, 213–248. Friend, C.R.L., Nutman, A.P., 1991. Shrimp U–Pb geochronology of the Closepet Granite and Peninsular Gneiss, Karnataka, South-India. J. Geol. Soc. India 38, 357–368. Gardès, E., Jaoul, O., Montel, J.M., Seydoux-Guillaume, A.M., Wirth, R., 2006. Pb diffusion in monazite: an experimental study of Pb + Th = 2Nd inter diffusion. Geochim. Cosmochim. Acta 70, 2325–2336. Gardès, E., Montel, J.M., Seydoux-Guillaume, A.M., Wirth, R., 2007. Pb diffusion in monazite: new constraints from the experimental study of Pb2+ = Ca2+ inter diffusion. Geochim. Cosmochim. Acta 71, 4036–4043. Ghosh, S.K., Sen, G., Sengupta, S., 2003. Rotation of long tectonic clasts in transpressional shear zones. J. Struct. Geol. 25, 1083–1096. Ghosh, J.G., de Wit, M.J., Zartman, R.E., 2004. Age and tectonic evolution of Neoproterozoic ductile shear zones in the Southern Granulite Terrain of India, with implications for Gondwana studies. Tectonics 23, http://dx.doi.org/10.1029/2002TC001444. Gordon, S.M., Grove, M., Whitney, D.L., Schmitt, A.K., Teyssier, C., 2009. Time–temperature–fluid evolution of migmatite dome crystallization: coupled U–Pb age, Ti thermometry, and O isotopic ion microprobe depth profiling of zircon and monazite. Chem. Geol. 262, 186–201. Harlov, D.E., Wirth, R., Hetherington, C.J., 2007. The relative stability of monazite and huttonite at 300–900 ◦ C and 200–1000 MPa: metasomatism and the propagation of metastable mineral phases. Am. Mineral. 92, 1652–1664. Hawkins, D.P., Bowring, S.A., 1999. U–Pb monazite, xenotime, and titanite geochronological constraints on the prograde to post-peak metamorphic thermal history of Paleoproterozoic migmatites from the Grand Canyon, Arizona. Contrib. Mineral. Petrol. 134, 150–169. Hoisch, T.D., Wells, M.L., Grove, M., 2008. Age trends in garnet-hosted monazite inclusions from upper amphibolite facies schist in the northern Grouse Creek Mountains, Utah. Geochim. Cosmochim. Acta 72, 5505–5520. Ishwar-Kumar, C., Windley, B.F., Horie, K., Kato, T., Hokada, T., Itaya, K., Yagi, T., Gouzu, C., Sajeev, K., 2013. A Rodinian suture in western India: new insights on India–Madagascar correlations. Precambrian Res. 236, 227–251. Janots, E., Engi, M., Rubatto, D., Berger, A., Gregory, C., Rahn, M., 2009. Metamorphic rates in collisional orogeny from in situ allanite and monazite dating. Geology 37, 11–14. Janots, E., Berger, A., Engi, M., 2011. Physico-chemical control on the REE minerals in chloritoid-grade metasediments from a single outcrop (Central Alps, Switzerland). Lithos 121, 1–11. Jayananda, M., Moyen, J.-F., Martin, H., Peucat, J.-J., Auvray, B., Mahabaleshwar, B., 2000. Late Archaean (2550–2520 Ma) juvenile magmatism in the eastern Dharwar Craton, southern India: constraints from geochronology, Nd–Sr isotopes and whole rock geochemistry. Precambrian Res. 99, 225–254. Kapp, J.L.D., Harrison, T.M., Kapp, P.A., Grove, M., Lovera, O.M., Lin, D., 2005. The Nyaingentanglha Shan: a window into the tectonic, thermal, and geochemical evolution of the Lhasa block, southern Tibet. J. Geophys. Res. 110, B08413. Kempe, U., Lehmann, B., Wolf, D., Rodionov, N., Bombach, K., Schwengfelder, U., Dietrich, A., 2008. U–Pb SHRIMP geochronology of Th-poor, hydrothermal monazite: an example from the Llallagua tin-porphyry deposit, Bolivia. Geochim. Cosmochim. Acta 72, 4352–4366. Kretz, R., 1983. Symbols for rock-forming minerals. Am. Mineral. 68, 277–279. Kröner, A., Hegner, E., Collins, A.S., Windley, B.F., Brewer, T.S., Razakamanana, T., Pidgeon, R.T., 2000. Age and magmatic history of the Antananarivo Block, central Madagascar, as derived from zircon geochronology and Nd isotopic systematics. Am. J. Sci. 300, 251–288. Lawver, L.A., Scotese, C.R., 1987. A revised reconstruction of Gondwanaland. In: McKenzie, G.W. (Ed.), Gondwana Six: Structure, Tectonics and Geophysics. Washington, DC, American Geophysical Union, pp. 17–23. Ludwig, K.R., 2003. User’s Manual for ISOPLOT/3.00: A Geochronological Toolkit for Microsoft Excel. Berkeley Geochron Centre Special Publication 4, pp. 71. McWilliams, M.O., 1981. Paleomagnetism and Precambrian tectonic evolution of Gondwana. In: Kröner, A. (Ed.), Precambrian Plate Tectonics. Elsevier, Amsterdam, pp. 649–687. Meen, J.K., Rogers, J.J.W., Fullagar, P.D., 1992. Lead isotopic compositions of the Western Dharwar Craton, Southern India: evidence for distinct Middle Archean terranes in a Late Archean Craton. Geochim. Cosmochim. Acta 56, 2455– 2470. Meert, J.G., Lieberman, B.S., 2004. A palaeomagnetic and palaeobiogeographical perspective on latest Neoproterozoic and early Cambrian tectonic events. J. Geol. Soc. Lond. 161, 477–487. Meert, J.G., Van der Voo, R., Ayub, S., 1995. Paleomagnetic investigation of the Late Proterozoic Gagwe lavas and Mbozi complex, Tanzania and the assembly of Gondwana. Precambrian Res. 69, 113–131. Meißner, B., Deters, P., Srikantappa, C., Köhler, H., 2002. Geochronological evolution of the Moyar, Bhavani and Palghat shear zones of southern India: implications for east Gondwana correlations. Precambrian Res. 114, 149–175. Montel, J.M., Foret, S., Veschambre, M., Nicollet, C., Provost, A., 1996. Electron microprobe dating of monazite. Chem. Geol. 131, 37–53. Moyen, J.F., Martin, H., Jayananda, M., Auvray, B., 2003a. Late Archaean granites: a typology based on the Dharwar Craton (India). Precambrian Res. 127, 103–123. Moyen, J.-F., Nedelec, A., Martin, H., Jayananda, M., 2003b. Syntectonic granite emplacement at different structural levels: the Closepet granite, South India. J. Struct. Geol. 25, 611–631. Mukhopadhyay, D., 1986. Structural patterns in the Dharwar Craton. J. Geol. 94, 167–186. 207 Naha, K., Srinivasan, R., Naqvi, S.M., 1986. Structural unity in the early Precambrian Dharwar tectonic province, Peninsular India. Q. J. Geol. Min. Metallurg. Soc. India 58, 219–243. Naha, K., Srinivasan, R., Jayaram, S., 1990. Structural evolution of the Peninsular Gneiss – an early Precambrian migmatitic complex from South India. Geol. Runds. 79, 99–109. Naha, K., Srinivasan, R., Jayaram, S., 1991. Sedimentational, structural, and migmatitic history of the Archean Dharwar tectonic province, southern India. Proc. Indian Acad. Sci. (Earth Planet. Sci.) 100, 413–433. Naha, K., Srinivasan, R., Gopalan, K., Pantulu, G.V.C., Subba Rao, M.V., Vrevsky, A.B., Bogomolov, Y.E.S., 1993. The nature of the basement in the Archaean Dharwar Craton of southern India and the age of the Peninsular Gneiss. Proc. Indian Acad. Sci. (Earth Planet. Sci.) 102, 547–565. Naha, K., Mukhopadhyay, D., Dastidar, S., Mukhopadhyay, R.P., 1995. Basementcover relations between a granite gneiss body and its metasedimentary envelope: a structural study from the Early Precambrian Dharwar tectonic province, southern India. Precambrian Res. 72, 283–299. Naha, K., Srinivasan, R., Mukhopadhyay, D., 1996. Structural studies and their bearing on the Early Precambrian history of the Dharwar tectonic province, southern India. Proc. Indian Acad. Sci. (Earth Planet. Sci.) 105, 379–412. Nutman, A.P., Chadwick, B., Krishna Rao, B., Vasudev, V.N., 1996. SHRIMP U–Pb zircon ages of acid volcanic rocks in the Chitradurga and Sandur Groups and granites adjacent to Sandur schist belt. J. Geol. Soc. India 47, 153–161. Paquette, J.L., Moine, B., Rakotondrazafy, M.A.F., 2003. ID-TIMS using the stepwise dissolution technique versus ion microprobe U–Pb dating of metamict Archean zircons from NE Madagascar. Precambrian Res. 121, 73–84. Paterson, S.R., Vernon, R.H., Tobisch, T.H., 1989. A review of criteria for the identification magmatic and tectonic foliations in granitoids. J. Struct. Geol. 11, 349–363. Peucat, J.J., Bouhallier, H., Fanning, C.M., Jayananda, M., 1995. Age of the Holenarsipur Greenstone-Belt: relationships with the surrounding gneisses (Karnataka, South India). J. Geo. 103, 701–710. Peucat, J.-J., Jayananda, M., Chardon, D., Capdevila, R., Fanning, C.M., Paquette, J.L., 2013. The lower crust of the Dharwar Craton, Southern India: patchwork of Archean granulitic domains. Precambrian Res. 227, 4–28. Peucat, J.J., Mahabaleshwar, B., Jayananda, M., 2007. Age of younger tonalitic magmatism and granulitic metamorphism in the South Indian transition zone (Krishnagiri area); comparison with older Peninsular gneisses from the Gorur–Hassan area. J. Metamorph. Geol. 11, 879–888. Poitrasson, F., Chenery, S., Shepherd, T.J., 2000. Electron microprobe and LA–ICP–MS study of monazite hydrothermal alteration: implications for U–Th–Pb geochronology and nuclear ceramics. Geochim. Cosmochim. Acta 64, 3283–3297. Prabhakar, N., 2013. Resolving poly-metamorphic Paleoarchean ages by chemical dating of monazites using multi-spectrometer U, Pb and Th analyses and subcounting methodology. Chem. Geol. 347, 255–270. Pyle, J.M., Spear, F.S., 2003. Four generations of accessory phase growth in lowpressure migmatites from SW New Hampshire. Am. Mineral. 88, 338–351. Raharimahefa, T., Kusky, T.M., 2006. Structural and remote sensing studies of the southern Betsimisaraka Suture, Madagascar. Gondwana Res. 10, 186–197. Raharimahefa, T., Kusky, T.M., 2009. Structural and remote sensing analysis of the Betsimisaraka Suture in northeastern Madagascar. Gondwana Res. 15, 14–27. Raharimahefa, T., Kusky, T.M., 2010. Temporal evolution of the Angavo and related shear zones in Gondwana: constraints from LA-MC-ICP-MS U–Pb zircon ages of granitoids and gneiss from central Madagascar. Precambrian Res. 182, 30–42. Raith, M., Srikantappa, C., Buhl, D., Koehler, H., 1999. Niligiri enderbites, South India: nature and age constraints on protolith formation, high-grade metamorphism and cooling history. Precambrian Res. 98, 129–150. Ramakrishnan, M., Vaidyanadhan, R., 2008. Geology of India, vol. 1. Bangalore, Geological Society of India. Rasmussen, B., Muhling, J.R., 2007. Monazite begets monazite: evidence for dissolution of detrital monazite and reprecipitation of syntectonic monazite during low-grade regional metamorphism. Contrib. Mineral. Petrol. 154, 675–689. Rasmussen, B., Fletcher, I.R., McNaughton, N.J., 2001. Dating low-grade metamorphic events by SHRIMP U–Pb analysis of monazite in shales. Geology 29, 963–966. Rasmussen, B., Fletcher, I.R., Sheppard, S., 2005. Isotopic dating of the migration of a low-grade metamorphic front during orogenesis. Geology 33, 773–776. Raval, U., Veeraswamy, K., 2003. India-Madagascar separation: breakup along a preexisting mobile belt and chipping of the craton. Gondwana Res. 6, 467–485. Rekha, S., Bhattacharya, A., 2013. Growth, preservation of Paleoproterozoicshear-zone-hosted monazite, north of the Western Dharwar Craton (India), and implications for Gondwanaland assembly. Contrib. Mineral. Petrol. 166, 1203–1222. Rekha, S., Bhattacharya, A., 2014. Paleoproterozoic/Mesoproterozoic tectonism in the northern fringe of the Western Dharwar Craton (India): its relevance to Gondwanaland and Columbia supercontinent reconstructions. Tectonics 33, 552–580. Rekha, S., Bhattacharya, A., Viswanath, T.A., 2013a. Microporosity linked fluid focusing and monazite instability in greenschist facies para-conglomerates, western India. Geochim. Cosmochim. Acta 105, 187–205. Rekha, S., Viswanath, T.A., Bhattacharya, A., Prabhakar, N., 2013b. Meso/Neoarchean crustal domains along the north Konkan coast, western India: the Western Dharwar Craton and the Antongil-Masora Block (NE Madagascar) connection. Precambrian Res. 233, 316–336. Santosh, M., Xiao, W.J., Tsunogae, T., Chetty, T.R.K., Yellappa, T., 2012. The Neoproterozoic subduction complex in southern India: SIMS zircon U–Pb ages and implications for Gondwana assembly. Precambrian Res. 192, 190–208. 208 S. Rekha et al. / Precambrian Research 252 (2014) 191–208 Santosh, M., Yang, Q.-Y., Shaji, E., Tsunogae, T., Mohan, M., Ram Satyanarayanan, M., 2013. An exotic Mesoarchean microcontinent: the Coorg Block, southern India. Gondwana Res., http://dx.doi.org/10.1016/j.gr.2013.10.005. Schärer, U., de Parseval, P., Polve, M., de Saint Blanquat, M., 1999. Formation of the Trimouns talc–chlorite deposits (Pyrenees) from persistent hydrothermal activity between 112 Ma and 97 Ma. Terra Nova 11, 30–37. Schofield, D.I., Thomas, R.J., Goodenough, K.M., De Waele, B., Pitfield, P.E.J., Key, R.M., Bauer, W., Walsh, G., Lidke, D., Ralison, A.V., Rabarimanana, M., Rafahatelo, J.M., Randriamananjara, T., 2010. Geological evolution of the Antongil Craton, NE Madagascar. Precambrian Res. 182, 187–203. Sommer, H., Kröner, A., Hauzenberger, C., Muhongo, S., Wingate, M.T.D., 2003. Metamorphic petrology and zircon geochronology of high-grade rocks from the central Mozambique Belt of Tanzania: crustal recycling of Archean and Palaeoproterozoic material during the Pan-African orogeny. J. Metamorph. Geol. 21, 915–934. Stern, R.J., 1994. Arc assembly and continental collision in the Neoproterozoic East Africa Orogen: implications for the consolidation of Gondwanaland. Annu. Rev. Earth Planet. Sci. 22, 319–351. Taylor, P.N., Chadwick, B., Moorbath, S., Ramakrishnan, M., Viswanatha, M.N., 1984. Petrography, chemistry and isotopic ages of Peninsular gneiss, Dharwar acid volcanic rocks and the Chitradurga granite with special reference to the late Archaean evolution of the Karnataka Craton. Precambrian Res. 23, 349–375. Taylor, P.N., Chadwick, B., Friend, C.R.L., Ramakrishnan, M., Moorbath, S., Viswanatha, M.N., 1988. New age data on the geological evolution of southern India. J. Geol. Soc. India 31, 155–157. Tomson, J.K., Bhaskar Rao, Y.J., Vijaya Kumar, T., Choudhury, A.K., 2013. Geochemistry and neodymium model ages of Precambrian charnockites, Southern Granulite Terrain, India: constraints on terrain assembly. Precambrian Res. 227, 295–315. Thomas, R.J., De Waele, B., Schofield, D.I., Goodenough, K.M., Horstwood, M., Tucker, R.D., Bauer, W., Annells, R.A., Howard, K.B., Walsh, G., Rabarimanana, M., Rafahatelo, J.M., Ralison, A.V., Randriamananjara, T., 2009. Geological evolution of the Neoproterozoic Bemarivo Belt, Northern Madagascar. Precambrian Res. 172, 279–300. Torsvik, T.H., Tucker, R.D., Ashwal, L.D., Carter, L.M., Jamtveit, V., Vidyadharan, K.T., Venkataramana, P., 2000. Late Cretaceous India–Madagascar fit and timing of breakup related magmatism. Terra Nova 12, 220–224. Tucker, R.D., Ashwal, L.D., Handke, M.J., Hamilton, M.A., Le Grange, M., Rambelo-son, R.A., 1999. U–Pb geochronology and isotope geochemistry of the Archean and Proterozoic rocks of north-central Madagascar. J. Geol. 107, 135–153. Tucker, R.D., Roig, J.-Y., Delor, C., Amelin, Y., Goncalves, P., Rabarimanana, M.H., Ralison, A.V., Belcher, R.W., 2011a. Neoproterozoic extension in the Greater Dharwar Craton: a reevaluation of the Betsimisaraka Suture in Madagascar. Can. J. Earth Sci. 48, 389–417. Tucker, R.D., Roig, J.-Y., Macey, P.H., Delor, C., Amelin, Y., Armstrong, R.A., Rabarimanana, M.H., Ralison, A.V., 2011b. A new geological framework for south-central Madagascar, and its relevance to the out-of-Africa hypothesis. Precambrian Res. 185, 109–130. Unrug, R. (Ed.), 1996. Geodynamic Map of Gondwana Supercontinent Assembly, Scale 1:10 Million. Bureau de Recherches Geologiques et Minieres, Orleans, France. Veevers, J.J., 2004. Gondwanaland from 650–500 Ma assembly through 320 Ma merger in Pangea to 185–100 Ma breakup: supercontinental tectonics via stratigraphy and radiometric dating. Earth-Sci. Rev. 68, 1–132. Vernon, R.H., Johnson, S.E., Melis, E.A., 2004. Emplacement-related microstructures in the margin of a deformed tonalite pluton: the San Jose pluton, Baja California, Mexico. J. Struct. Geol. 26, 1884–1887. Whitney, D.L., Teyssier, C., Fayon, A.K., Hamilton, M.A., Heizler, M., 2003. Tectonic controls on metamorphism, partial melting, and intrusion: timing and duration of regional metamorphism and magmatism in the Nigde Massif, Turkey. Tectonophysics 376, 37–60. Windley, B.F., Razafiniparany, A., Razakamanana, T., Ackermand, D., 1994. Tectonic framework of the Precambrian of Madagascar and its Gondwana connections: a review and reappraisal. Geol. Runds. 83, 642–659.

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