Mesoproterozoic suturing of Archean crustal blocks in western peninsular India: Implications for India–Madagascar correlations

    Mesoproterozoic suturing of Archean crustal blocks in western peninsular India: Implications for India-Madagascar correlations C. Ishwar-Kumar, M. Santosh, S.A. Wilde, T. Tsunogae, T. Itaya, B.F. Windley, K. Sajeev PII: DOI: Reference:

S0024-4937(16)00045-1 doi: 10.1016/j.lithos.2016.01.016 LITHOS 3816

To appear in:

LITHOS

Received date: Accepted date:

26 September 2015 22 January 2016

Please cite this article as: Ishwar-Kumar, C., Santosh, M., Wilde, S.A., Tsunogae, T., Itaya, T., Windley, B.F., Sajeev, K., Mesoproterozoic suturing of Archean crustal blocks in western peninsular India: Implications for India-Madagascar correlations, LITHOS (2016), doi: 10.1016/j.lithos.2016.01.016

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ACCEPTED MANUSCRIPT Mesoproterozoic suturing of Archean crustal blocks in

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Madagascar correlations

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western peninsular India: Implications for India-

C. Ishwar-Kumar a, M. Santosh b, c, S.A. Wilde d, T. Tsunogae e, f, T. Itaya g,

a

Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India

School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China

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Curtin University, Bentley, Western Australia 6102, Australia

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d

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c

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Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia

Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan f g

Department of Geology, University of Johannesburg, Auckland Park 2006, South Africa

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b

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B.F. Windley h, K. Sajeev a*

Research Institute of Natural Sciences, Okayama University of Science, Okayama, Japan h

Department of Geology, The University of Leicester, Leicester LE1 7RH, UK

*Corresponding author E-mail: [email protected] (K. Sajeev) Telephone: +91-80-2293-3404

Submitted to Lithos September, 2015 1

ACCEPTED MANUSCRIPT Abstract The Kumta and Mercara suture zones welding together Archean crustal blocks in

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western peninsular India offer critical insights into Precambrian continental juxtapositions

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and the crustal evolution of eastern Gondwana. Here we present the results from an integrated

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study of the structure, geology, petrology, mineral chemistry, metamorphic P-T conditions, zircon U-Pb ages and Lu-Hf isotopes of metasedimentary rocks from the two sutures. The

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dominant rocks in the Kumta suture are greenschist- to amphibolite-facies quartz-phengite schist, garnet-biotite schist, chlorite schist, fuchsite schist and marble. The textural relations,

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mineral chemistry and thermodynamic modeling of garnet-biotite schist from the Kumta suture indicate peak metamorphic P-T conditions of c. 11 kbar at 790C, with detrital

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SHRIMP U-Pb zircon ages ranging from 3420 to 2547 Ma, εHf (t) values from -9.2 to 5.6,

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and TDMc model ages from 3747 to 2792 Ma. The K-Ar age of phengite from quartz-phengite

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schist is ca. 1326 Ma and that of biotite from garnet-biotite schist is ca. 1385 Ma, which are interpreted to broadly constrain the timing of metamorphism related to the suturing event. The Mercara suture contains amphibolite- to granulite-facies mylonitic quartzo-feldspathic

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gneiss, garnet-kyanite-sillimanite gneiss, garnet-biotite-kyanite-gedrite-cordierite gneiss, garnet-biotite-hornblende gneiss, calc-silicate granulite and metagabbro. The textural relations, mineral chemistry and thermodynamic modeling of garnet-biotite-kyanite-gedritecordierite gneiss from the Mercara suture indicates peak metamorphic P-T conditions of c. 13 kbar at 825C, followed by isothermal decompression and cooling. For pelitic gneisses from the Mercara suture, LA-ICPMS U-Pb zircon ages vary from 3249 to 3045 Ma, εHf (t) values range from -18.9 to 4.2, and TDMc model ages vary from 4094 to 3314 Ma. The lower intercept age of detrital zircons in the pelitic gneisses from the Mercara suture range from 1464 to 1106 Ma, indicating the approximate timing of a major lead-loss event, possibly corresponding to metamorphism, and are broadly coeval with events in the Kumta suture. 2

ACCEPTED MANUSCRIPT Synthesis of the above results indicates that the Kumta and Mercara suture zones incorporated sediments from Paleoarchean to Mesoproterozoic sources and underwent high-

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pressure metamorphism in the late Mesoproterozoic. The protolith sediments were derived

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from regions containing juvenile Paleoarchean crust, together with detritus from the recycling

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of older continental crust. Integration of the above results with published data suggests that the Mesoproterozoic (1460-1100 Ma) Kumta and Mercara suture zones separate the Archean (3400-2500 Ma) Karwar-Coorg block and Dharwar Cratons in western peninsular India.

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Based on regional structural and other geological data we interpret the Kumta and Mercara

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suture zones as extensions of the Betsimisaraka suture of eastern Madagascar into western

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India.

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correlation

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Key words: Zircon U-Pb and Lu-Hf isotopes; Kumta suture, Mercara suture, India-Madagascar

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ACCEPTED MANUSCRIPT 1. Introduction Transcrustal shear/suture zones hold prime importance as ‘piercing points’ (e.g., Katz

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and Premoli, 1979) and are among the critical parameters used for paleogeographic

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configurations of supercontinental assemblies. The direct correlation between continental

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fragments through time has often been hindered by the effect of multiple tectonic events within the same terranes, coupled with differential degrees of weathering and alteration, and variable rates of exhumation, uplift and erosion. These paleo-subduction zones/sutures are

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considered to be tectonic boundaries, where two different continents were juxtaposed by the

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subduction of oceanic lithosphere (Dewey, 1977). Paleo-suture zones are characterised by, at least in the recent geological past, the presence of high-pressure rocks, ophiolitic remnants,

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relict continental shelves, accretionary wedges, granitoids related to arc magmatism, thrusts

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and tectonic mélanges (Dewey, 1977). Some suture zones are characterised by mylonitic ductile shears and the crustal blocks on either side of the suture, may have different

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lithologies, structure, age, geochemistry, isotopic characteristics and metamorphic histories and different orientations of paleo-magnetic vectors (Moores and Twiss, 1995).

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The period between the assembly of Rodinia and its break-up to form the Gondwana supercontinent in the Neoproterozoic marks an important stage in the tectonic history of southern peninsular India (Santosh et al., 2009). One of the major factors to be determined for paleo-geographic reconstruction is to delineate the zone of amalgamation or suturing within the present continent, based on the above criteria, to establish correlations with other continental fragments. Katz and Premoli (1979) suggested that crustal-scale tectonic lineaments/shear zones/suture zones across continental fragments are one of the major features that can be used for paleo-geographic reconstruction, based on which they proposed a correlation between India and Madagascar. Following this study, several workers attempted to place India and Madagascar into their Gondwana setting, based on regional lithological,

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ACCEPTED MANUSCRIPT structural, geochronological, geochemical and geophysical evidence (e.g., Agarwal et al., 1992; Windley et al., 1994; Collins and Windley, 2002; Raval and Veerasamy, 2003; Ghosh

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et al., 2004; Collins et al., 2007; Raharimahefa and Kusky, 2006, 2009; Tucker et al., 2011a,

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b; Ishwar-Kumar et al., 2013b, 2015; Rekha et al., 2013, 2014; Rekha and Bhattacharya,

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2014; Ratheesh-Kumar et al., 2015). However, the many and varied models have led to considerable inconsistency, mismatch and disagreements about specific correlations. Some of the reasons for this inconsistency are variation in age, the precise position/extent of the

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shear/suture zones, problems with bathymetry, and the variation or distortion in scale.

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Although some correlations have minimum scale distortion that does not affect the proposed correlation (e.g., Katz and Premoli, 1979; Collins et al., 2007; Tucker et al., 2011a, b, 2014;

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Ishwar-Kumar et al., 2013b, 2015; Ratheesh-Kumar et al., 2015), other correlations have

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large-scale distortions so that, when corrected, the correlation of shear zones proposed is not supported (e.g., Rekha et al., 2013, 2014) (Supplementary Fig S1). To minimise the distortion

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in scale in the present study the Geographic Information System (GIS) platform (Arc GIS 10 software) was used.

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The Betsimisaraka suture in eastern Madagascar separates the ArcheanNeoproterozoic Antananarivo block (2700-2500 Ma gneisses and 824-550 Ma granitoids) to the west from the Archean Antongil-Masora block (3300-2490 Ma gneisses and granitoids) to the east (Supplementary Fig S2). The Betsimisaraka belt contains cataclastic/mylonitic, banded and augen gneisses (Hottin, 1969) and was established as a suture zone by Kröner et al. (2000), Collins et al. (2000), Collins and Windley (2002) and Raharimahefa and Kusky (2006, 2009), which they considered was formed during the amalgamation of East and West Gondwana in the Neoproterozoic. However, recently the Betsimisaraka suture, particularly its age and correlation with other shear/suture zones has become a major controversy (Key et al., 2011; Tucker et al., 5

ACCEPTED MANUSCRIPT 2011a, b, 2014; Ishwar-Kumar et al., 2013b, 2015; Rekha et al., 2013, 2014; Brandt et al., 2014; Plavsa et al., 2014). Recent studies by Tucker et al. (2011a, 2014) have dismissed the

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concept of the Betsimisaraka as a Neoproterozoic suture. They proposed that, the zone was

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occupied by a sedimentary basin (the Manampotsy Group) that was deposited in the period

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840–760 Ma, According to Tucker et al. (2011a) there may have been an ocean on the site of the Manampotsy basin in the Neoarchean, which was destroyed at 2550–2480 Ma when the Antananarivo block was amalgamated with the Dharwar Craton of India and the Antongil–

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Masora Craton of Madagascar. They further correlated the Angavo shear zone of Madagascar

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with the Moyar shear zone of southern India and this correlation is comparable with that of Brandt et al. (2014). Based on structural, geological and geochronological data, along with mineral chemistry and thermodynamic modelling, Ishwar-Kumar et al. (2013b) proposed the

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existence of Mesoproterozoic (ca. 1300 Ma) Kumta and Coorg (“Mercara” hereafter) sutures in western India and interpreted them as the eastern extension of the Betsimisaraka suture and

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this correlation was supported by Ratheesh-Kumar et al. (2015) based on geophysical results. Based on geochemical and geochronological results, Santosh et al. (2015) identified the

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Mesoarchean Coorg block as an exotic micro-continent that amalgamated with the Dharwar Craton after ca. 2500 Ma along the Mercara suture. Rekha et al. (2014) proposed a PaleoMesoproterozoic South Maharashtra Shear Zone (SMSZ) and interpreted it as the northern boundary of the western Dharwar Craton, and consequently it is located in the northern segment of the Kumta suture (Figs. 1, 2a). Rekha et al. (2014) disputed the Mesoproterozoic age of the Kumta suture and correlated the Betsimisaraka suture zone of Madagascar directly to the proposed Manjeshwara-Sullya shear zone, which lies within the northern segment of the Mercara shear zone as proposed by Krishnaraj et al. (1994), Chetty et al. (2012), IshwarKumar et al. (2013a,b) and Santosh et al. (2015) (Figs. 1, 2b). Based on mesoscopic structures and monazite age data, Rekha et al. (2014) suggested that the Mercara suture

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ACCEPTED MANUSCRIPT formed at 2300-2500 Ma, and proposed that if the Betsimisaraka suture extended into western India, it should correlate with the 2300-2500 Ma Mercara suture and hence it should be a

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Neoarchean suture.

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The above inconsistencies and disagreements about the existence and correlations of

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different shear/suture zones constitute the major barrier in understanding the tectonic evolution of eastern Gondwana. Defining the actual shear/suture zones and estimating their

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ages are critical factors and require detailed studies of rocks on either side, and within, the proposed sutures; particularly a detailed study of metasedimentary rocks within the suture

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zones that might provide evidence of their provenance prior to ocean closure. In addition, the timing of collision of the surrounding blocks and their metamorphic history are key features

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that need to be established. In the present study, we therefore focus on metasedimentary rocks

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from the Kumta and Mercara suture zones. We discuss the detailed geology, structure and metamorphic conditions of these rocks and present zircon U-Pb geochronological and

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hafnium isotope results. Based on these results, we estimate the time of suturing and establish the metamorphic evolution of rocks within these zones and use this information to constrain

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the possible correlations between India and Madagascar. 2. The Kumta and Mercara suture zones 2.1. The Kumta suture The Kumta suture is located at the western margin of peninsular India (Figs. 1, 2a), and has been interpreted as the eastern extension of the Betsimisaraka suture zone of Madagascar (Ishwar-Kumar et al., 2013b). The suture separates ca. 3200 Ma tonalitetrondhjemite-granodiorite (TTG) and amphibolite of the Karwar block in the west from ca. 2571 Ma quartzo-feldspathic gneisses of the Dharwar Craton in the east. Rekha et al. (2013) reported Th-U-Pb monazite ages from granitoids and gneisses of the Karwar block that show 7

ACCEPTED MANUSCRIPT a range from 2436-2958 Ma. The Sirsi shelf on the eastern side of the suture is a c. 80 kmwide, westerly-dipping sequence of sedimentary/metasedimentary rocks (limestone, phyllite,

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shale, banded iron formation, sandstone and quartzite) that makes up a passive continental

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margin or shelf along the western margin of the Dharwar Craton. The c. 15 km-wide

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curvilinear Kumta suture changes in strike from NW-SE to N-S to NE-SW (progressing southwards) and generally dips to the west at 30°-65°. Rocks in the Kumta suture are at greenschist- to amphibolite-facies, and are highly sheared and deformed schistose lithologies

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that include garnet-biotite schist (Fig. 3a; Supplementary Fig S3a,b), quartz-phengite schist

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(Fig. 3b; Supplementary Fig S3c,d), fuchsite schist, quartz-chlorite schist (Fig. 3c), biotite augen gneiss (Fig. 3d) , carbonate-quartz-chlorite schist (Fig. 3e), marble (Fig. 3f), and iron

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and manganese formations (Geological Survey of India, 2005; Ishwar-Kumar et al., 2013b).

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The quartz-phengite schist contains high-Si phengite and isochemical phase diagram estimations suggest peak metamorphic conditions of c. 18 kbar at c. 550º C (Ishwar-Kumar et

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al., 2013b). SHRIMP U-Pb detrital zircon ages from the quartz-phengite schist define four age populations, ranging from 3280 to 2993 Ma (Ishwar-Kumar et al., 2013b). Phengite from

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the quartz-phengite schist and biotite from garnet-biotite schist have K-Ar metamorphic ages of ca. 1326 and ca. 1385 Ma, respectively (Ishwar-Kumar et al., 2013b). The north-western part of the Kumta suture contains the NW-SE trending, c. 4 km wide and 12 km long Bondla ultramafic-gabbro complex (Fig. 2a). This consists of dolerite, gabbro, troctolite, wehrlite, dunite, peridotite, pyroxenite, chromitite and chromite-bearing serpentinite (Jena et al., 1985; Dessai et al., 2009; Ishwar-Kumar et al., 2013b). 2.2. The Mercara suture The Mercara suture zone is located ~200 km south of the Kumta suture, marking the south-west termination of the Dharwar Craton (Chetty et al., 2012; Ishwar-Kumar et al., 2013a, b; Santosh et al., 2015) (Figs. 1, 2b). The northern part of the Mercara suture zone was

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ACCEPTED MANUSCRIPT defined earlier as the Jalsoor-Mercara shear zone by Krishnaraj et al. (1994) and more recently as the Manjeshwara-Sullya shear zone by Rekha et al. (2014). The Coorg block lies

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west of the suture and is distinct from the Dharwar Craton to the east in terms of its structure,

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lithology, chronology and metamorphic P-T conditions (Chetty et al., 2012; Ishwar-Kumar et

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al., 2013a,b; Santosh et al., 2015). The Coorg block is characterised by sub-rounded structural geometry/ structural lineaments, which are distinct from the Dharwar Craton to the north and the granulite blocks of peninsular India to the south (Fig. 2b). It consists mainly of

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hornblende gabbro, charnockite and layered hornblende anorthosite, interpreted as rocks

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formed in a magmatic arc (Ishwar-Kumar et al., 2013b; Santosh et al., 2015). The c. 20 km wide, curved Mercara suture zone (Figs. 1, 2b) contains highly sheared

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and deformed gneisses that vary in strike from E-W to NW-SE to N-S (progressing

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southwards), and dip to the W with dextral kinematic indicators (Chetty et al., 2012). At its southern end, the NS-trending segment of the Mercara suture terminates against the E-W to

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NW-SE trending Moyar shear zone. The major rock types in the Mercara suture zone are granulite-facies metapelites, including, garnet-kyanite-biotite-gedrite-cordierite gneiss (Fig.

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4a; Supplementary Fig. S4a), garnet-biotite-kyanite gneiss (Fig. 4b; Supplementary Fig. S4b), garnet-biotite hornblende gneiss (Fig. 4c; Supplementary Fig. S4c), garnet-biotite-sillimanitecordierite gneiss (Fig. 4d), mylonitic quartzo-feldspathic gneiss (Fig. 4e; Supplementary Fig. S4d); garnet-biotite-sillimanite gneiss (Fig. 4f,g), garnet-sillimanite-graphite gneiss (Fig. 4h), mafic granulite, amphibolite, and younger granite and syenite (Geological Survey of India, 2005; Chetty et al., 2012; Ishwar-Kumar et al., 2013a,b; Santosh et al., 2015). The southern Coorg block is separated from the Nilgiri block by the western segment of the Moyar shear zone and it mainly consist of garnet-biotite gneiss and hornblende-biotite gneiss with amphibolite enclaves, quartzite (Fig. 4i) and is intruded by younger granite (Geological Survey of India, 2005).

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ACCEPTED MANUSCRIPT Granulites from the Coorg block and Mercara suture have a range of reported P-T conditions. Srikantappa et al. (1994) reported 7.0 to 8.6 kbar at 720-760oC pressure-

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temperature conditions for the granulites of the Coorg block and also identified high-density

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(1.07–1.09 g/cm3) CO2-rich fluid inclusions. Based on the mineral chemistry of hornblende in

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charnockite, Santosh et al. (2015) reported P-T conditions of 6 kbar at 820-870oC from the Coorg block. Based on thermodynamic modelling, Ishwar-Kumar et al. (2013a) reported 1520 kbar at 1000o C peak pressure-temperature conditions for mafic granulites from the

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Mercara suture.

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A gravity study by Sunil et al. (2010) shows unusually high gravity values beneath the Coorg block, interpreted to reflect thrusting or the presence of a high-density intrusive body

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in the lower crust. An electrical resistivity study of the Coorg block by Azeez et al. (2015)

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suggested differences in the geophysical characteristics between the Dharwar Craton and Coorg block and supported the presence of the Mercara suture. The Sm-Nd TDM model ages

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of charnockite, mafic granulite and migmatitic gneiss from the Coorg block range from 2910 to 3700 Ma (Peucat et al., 2013). Granite and syenite in the Mercara suture have Rb-Sr

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whole-rock ages in the range of 638-710 Ma (Ghosh et al., 2004 and references therein). Recently Santosh et al. (2015) reported comprehensive LA-ICPMS

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Pb/206Pb zircon ages

from the western part of the Coorg block, ranging from 3133 ± 12 Ma to 3164 ± 7 Ma for charnockites, 3156 ± 10 Ma to 3158 ± 8 Ma for a mafic enclave, 3161 ± 16 Ma for diorite, 3173 ± 16 Ma for felsic volcanic tuff, 3153 ± 9 Ma to 3184 ± 6 Ma for syenogranite, 3170 ± 7 Ma for biotite granite and 3275 ± 5 Ma for trondhjemite. K-Ar dating of biotite from a mylonitic quartzo-feldspathic gneiss sample from the Mercara suture yielded an age of 933 ± 16 Ma (Ishwar-Kumar et al., 2013b). 3. Petrography and mineral chemistry

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ACCEPTED MANUSCRIPT The textural features of rocks from the Kumta and Mercara suture zones are shown in thin section photomicrographs in Figs. 3 and 4, X-ray elemental maps in Fig. 5, and back-

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scattered electron images (Fig. 6a, b for garnet-biotite schist and Fig. 6c, d for garnet-biotite-

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kyanite-gedrite-cordierite gneiss). Mineral assemblages and their approximate modal

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abundances are listed in Table 1; mineral abbreviations are after Kretz (1983). The petrographic and mineral chemistry of representative samples from the Kumta and Mercara

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sutures are given below.

Chemical analyses of all the minerals were obtained using an electron microprobe

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analyser (JEOL JXA-8900R microprobe) housed at the Okayama University of Science, Japan and by JXA-8530F at the University of Tsukuba, Japan. The analyses were performed

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under conditions of 15-20 kV accelerating voltage, 10-12 nA sample current and a spot size

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of 3 µm. The data were regressed using the oxide-ZAF correction method. Natural and synthetic silicates and oxides were used for calibration. All the major minerals were analysed

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for SiO2, TiO2, Cr2O3, Al2O3, FeO, MgO, MnO, CaO, Na2O, and K2O. Representative compositions of minerals are given in Supplementary Tables S1 and S2. Back-scattered

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electron images were taken and X-ray elemental maps were made during the analyses. X-ray mapping was carried out using the JEOL JX8900 electron probe micro-analyser at Okayama University of Science with an accelerating voltage of 15 kv and a 2.387e-7 Å beam current. 3.1. Garnet-biotite schist (IK-0504) from the Kumta suture Garnet-bearing schists were collected from Dodamarg, in the northern part of the Kumta suture (Fig. 2a). The rocks contain garnet, biotite, plagioclase and K-feldspar, with retrograde amphibole and biotite that is partially altered to chlorite. The garnet porphyroblasts contain inclusions of biotite, plagioclase, K-feldspar, ilmenite, kyanite and staurolite, as well as many inclusions of zircon and apatite. Garnet-biotite schist sample IK11

ACCEPTED MANUSCRIPT 0504 contains garnet porphyroblasts within a fine-grained matrix of biotite, plagioclase and chlorite. The rock shows a weak foliation defined by biotite and is mainly composed of

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garnet (15-20 vol. %), biotite (40-45 vol. %), quartz and feldspar (5-10 vol. %), chlorite (15-

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20 vol. %), and amphibole (5-10 vol. %), with minor kyanite, staurolite and Fe-Te oxides

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(Fig. 3a; 6a,b).

The garnet grain-size varies from 100µm to about 2mm and most crystals are

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idioblastic and show distinct compositional zoning of Ca, Fe, Mg and Al in X-ray elemental maps (Fig. 5). The garnets have almandine contents of [Fe/(Fe+Mn+Mg+Ca), XAlm, = 0.556

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in cores and 0.582 in rims] and grossular contents of [XGrs, Ca/(Fe+Mn+Mg+Ca) = 0.130 in cores and 0.207 in rims], with variable pyrope contents [XPrp, Mg/(Fe+Mn+Mg+Ca) = 0.066

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in cores and 0.051 in rims]. The spessartite content [XSp, Mn/(Fe+Mn+Mg+Ca)] decreases

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from 0.216 in the cores to 0.147 in the rims. The Fe and Ca contents increase, and Mg and

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Mn decrease, from core to rim (Supplementary Table S1). 3.2. Quartz-phengite schist (IK-2302L) from the Kumta suture

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Sample IK-2302L from Kathagal, in the southern part of the Kumta suture (Fig. 2a), is mainly composed of quartz (40-45 vol. %) and phengite (40-50 vol. %), with minor amounts of rutile, chloritoid and chlorite (Fig. 3b); chlorite is present as a retrograde phase replacing chloritoid. Accessory minerals include zircon, monazite and tourmaline. The rock is highly sheared and contains augen-shaped quartz porphyroclasts within a fine-grained phengite matrix. The X-ray elemental maps indicate the presence of fine-grained alumino-silicate (kyanite) inclusions within phengite (Ishwar-Kumar et al., 2013b). Phengite is comparatively silica-rich (Si ranges from 3.13 to 3.30 afu), with XMg [Mg/(Mg+Fe)] ranging from 0.37 to 0.73 and XNa [Na/(Na+Ca)] content ranging from 0.02 to 0.08. The phengite composition is

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ACCEPTED MANUSCRIPT comparable with compositions from paleo-subduction zones world-wide (Ishwar-Kumar et al., 2013b).

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3.3. Garnet-biotite-kyanite-cordierite-gedrite gneiss (KR23-20C) from the Mercara suture

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Sample KR23-20C is a quartz-rich rock possibly derived from a semi-pelite and is composed of garnet-, biotite- and kyanite-rich layers, with the foliation defined by aligned biotite. It is composed of quartz (35-45 vol. %), biotite (15-20 vol. %), plagioclase (10-15

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vol. %), garnet (5-10 vol. %), cordierite (2-5 vol. %), kyanite (2-5 vol. %), and gedrite (~1 vol. %), with minor rutile, zircon and apatite (Fig. 4a; Fig. 6c,d). Garnet occurs as fine-

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grained (0.2-0.7 mm) idioblastic to sub-idioblastic crystals that form aggregates in the garnetrich domains. Grain boundaries of the garnet are filled by xenoblastic cordierite (0.1-0.6

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FMASH reaction:

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mm), which also occurs as aggregates surrounding the garnet, suggesting the following

(1)

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Grt + Ky1 + Qtz + H2O= Crd

This is a common reaction observed in many high-grade terranes and is evidence of decompression after peak metamorphism, suggesting a clockwise P-T path for this rock.

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Cordierite is partly replaced by fine-grained (<0.1 mm) aggregates of kyanite (Ky2) + gedrite + quartz (Fig. 4a), suggesting further retrogression: Crd + H2O = Ky2 + Ged + Qtz

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This hydration reaction is common in granulite terranes and is indicative of rock interaction with H2O-bearing fluid during retrograde metamorphism. The occurrence of biotite associated with garnet rims also suggests the presence of H2O-bearing fluids during retrograde metamorphism. The biotite is associated with fine-grained kyanite (Ky2) and quartz, forming Ky2 + biotite + quartz aggregates possibly formed by the following hydration reaction: Grt + Kfs + H2O = Ky2 + Bt + Qtz ± St 13

ACCEPTED MANUSCRIPT The rare occurrence of fine-grained staurolite associated with the aggregates implies its retrograde origin.

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Garnet in the kyanite-bearing layer is poikiloblastic and contains numerous inclusions

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of quartz, biotite, kyanite, and rutile. Its grain-size is coarser (~4.3 mm) than that which

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forms the aggregates. The garnet here is surrounded by aggregates of cordierite. Quartz is xenoblastic (~3.5 mm), plagioclase is sub-idioblastic (~0.8 mm) and occurs around the ferromagnesian minerals, together with aligned biotite flakes. The occurrence of prograde

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and retrograde kyanite (Ky1 and Ky2, respectively) has been confirmed by laser Raman

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spectroscopy analysis, and no sillimanite was detected during the Raman analysis. The representative mineral chemistry is given in Supplementary Table S2.

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3.4. Garnet-biotite-kyanite gneiss (KR23-20K) from the Mercara suture

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Sample KR23-20K is composed of quartz (40-50 vol. %), biotite (10-20 vol. %), kyanite (10-15 vol. %), garnet (10-15 vol. %), and plagioclase (2-5 vol. %), with accessory

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rutile (Fig. 4b). The foliation is the result of compositional layering defined by garnet-, kyanite-, and quartz-rich layers. The sample is characterised by coarse-grained (~7 mm)

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porphyroblastic kyanite surrounded by ferromagnesian minerals, including garnet and biotite; the kyanite is blue in hand specimen, although it is colourless under the microscope. Garnet occurs as aggregates of medium-grained idioblasts or as coarse-grained porphyroblasts, similar to those in sample KR23-20C. 3.5. Garnet-biotite-hornblende gneiss (KR23-20F) from the Mercara suture Sample KR23-20F is composed of garnet (2-5 vol. %), biotite (25-35 vol. %), quartz (30-40 vol. %), plagioclase (15-25 vol. %), hornblende (1-2 vol. %), and rutile (< 1 vol. %) (Fig. 4c). Garnet occurs as coarse-grained poikiloblasts that contain fine-grained inclusions of quartz, plagioclase, and kyanite. The rock matrix is composed mainly of quartz, plagioclase

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ACCEPTED MANUSCRIPT and biotite. Greenish xenoblastic hornblende is intergrown with the rims of biotite at the contact with garnet.

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4. Metamorphic evolution

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4.1. Geothermobarometry

metamorphic conditions of the pelitic paragneisses. 4.1.1. Grt-Bt geothermometer

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Conventional geothermobarometers were used to determine peak and retrograde

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The Fe-Mg exchange between garnet and biotite is probably the most widely used

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thermometer for estimating temperatures of medium-grade pelitic metamorphic rocks. Among the numerous published thermometers based on experimental studies and empirical

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calibrations of ideal (e.g., Thompson, 1976) and non-ideal (e.g., Ganguly and Saxena, 1984;

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Indares and Martignole, 1985) behaviour of garnet and biotite, we adopted the method of Kaneko and Miyano (2004) that considers the effect of Fe3+ and AlIV in biotite.

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The garnet-biotite thermometer gave a wide range of temperatures for the garnetbiotite schist sample from the Kumta suture, all at a reference pressure of 8 kbar [XMg (Grt) =

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0.11, XGrs (Grt) = 0.13, XSps (Grt) = 0.21, XMg (Bt) = 0.45], as follows: Ferry and Spear (1978) = 506° C, Perchuk and Lavrenteva (1983) = 616° C, Pigage and Greenwood (1982) = 685° C and Thompson (1976) = 492o C. The difference in temperature between these thermometers results from the difference in experimental conditions, as the distribution coefficient [KD= XMg (Grt)/XMg (Bt)] of the Grt-Bt pair remains the same. The geothermometry results are compared with the results from phase diagram estimation in a later section. Application of the thermometer to the porphyroblastic garnet and the matrix biotite in garnet-biotite-kyanite-cordierite-gedrite gneiss (KR23-20C) from the Mercara suture yielded a temperature range of 700-710°C at 7 kbar. Application of other methods (e.g., Indares and Martignole, 1985) also gave consistent temperatures of 650-750°C.

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ACCEPTED MANUSCRIPT 4.1.2. Grt-Ky-Pl-Qtz (GASP) geobarometer The GASP geobarometer, which is applicable for garnet + sillimanite/kyanite +

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plagioclase + quartz assemblages, has been widely applied to pelitic and psammitic

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metamorphic rocks. Newton and Haselton (1981) formulated the geobarometer based on the

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experiments of Goldsmith (1980) and the activity model of garnet (Newton et al., 1977) and plagioclase (Newton et al., 1980). Koziol and Newton (1988) re-evaluated the experimental

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data of Newton and Haselton (1981) and revised the geobarometer. We thus applied the method of Koziol and Newton (1988) to sample KR23-20C, which yielded a pressure range

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of 9.1-9.2 kbar at 700°C. Applying the methods of Newton and Haselton (1981) and Ganguly and Saxena (1984) to the sample gave slightly lower values, but consistent pressure

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4.2.1. Calculation methods

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4.2. Thermodynamic modelling

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conditions of 8.1-8.4 kbar.

The peak and retrograde P-T conditions of the rocks were constrained using Perple_X

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version 6.7.0. This software is useful for calculating the stable mineral assemblage and phase compositions based on Gibbs Free Energy minimization for a given bulk composition at specified P-T conditions. The computations enable construction of rock-specific equilibrium assemblage diagrams (also called pseudosections). In the present study, the phase diagrams were constructed by using free energy minimization (Connolly, 2005), with end-member thermodynamic data given by Holland and Powell (1998) and revised by these authors in 2002 and 2011 (Figs. 7, 8). The solution models used and references are given in Supplementary Table S3. The calculation was made in the system Na2O-CaO-K2O-FeOMgO-Al2O3-SiO2-TiO2-H2O. Bulk composition of the rocks was determined by X-ray fluorescence spectroscopy at Activation Laboratories, Canada (Table 2). The composition (in 16

ACCEPTED MANUSCRIPT wt.%) of sample IK-0504 is SiO2 = 45.46, Al2O3 = 21.75, FeO = 17.07, MgO = 6.10, CaO = 3.13, Na2O = 1.48, K2O = 3.31, TiO2 = 0.92 and H2O = 0.78 (Fig. 7) and for sample KR23-

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20C is SiO2 = 60.05, Al2O3 = 20.74, FeO = 8.70, MgO = 6.66, CaO = 0.27, Na2O = 0.31,

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K2O = 1.60, TiO2 = 1.04 and H2O = 0.64 (Fig. 8). Minor amounts of Cr and Mn were ignored

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for simplification of the system. Fe2O3 was not considered because magnetite and hematite were not observed in the samples, suggesting that peak metamorphism was under relatively reduced conditions. For the calculations, excess water was added because the samples contain

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biotite as a stable phase.

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4.2.2. Results

4.2.2.1. Garnet-biotite schist (IK-0504) from the Kumta suture

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Biotite and garnet are stable in all fields within the P-T range of the pseudosection.

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Rutile is present in all high-pressure fields; jadeite is stable only on the high-pressure, lowtemperature side, whereas corundum appears only in the high-pressure, high-temperature

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corner of the pseudosection. Retrograde phases chlorite and amphibole are absent within the P-T window of the pseudosection. The stability field of the peak assemblage

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(Grt+Bt+Pl+Ky+Qtz) ranges from 9-13 kbar and 750-825C. The isopleths calculated for the grossular content of garnet [XGrs (Grt) = 0.13, XGrs = Ca/ (Fe+Mn+Mg+Ca)] and the anorthite content of plagioclase [XAn (Pl) = 0.33, XAn = Ca/ (Ca+Na+K)] suggest a peak metamorphic P-T condition of c. 11 kbar at 790C. The earlier temperature estimate obtained by Pigage and Greenwood (1982) is comparable with these results. Thus, the phase-diagram estimations suggest that the Grt+Bt+Pl+Ky+Qtz assemblage must have equilibrated at a minimum pressure of c. 11 kbar at 790 C (Fig. 7). 4.2.2.2. Garnet-biotite-kyanite-cordierite-gedrite gneiss (KR23-20C) from the Mercara suture

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ACCEPTED MANUSCRIPT The mineral pair biotite and gedrite is stable at low-temperature, whereas cordierite is stable only in the low-pressure and high-temperature corner of the pseudosection, where

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kyanite is absent. The peak mineral assemblage of the rock (Bt + Grt + Ky + Pl + Rt+ Qtz) is

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stable above 9 kbar and 700-1000C. The compositional isopleths based on the XMg [Mg/

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(Fe+Mg)] content of biotite and XAb [Na/ (Ca+Na+K)] content of plagioclase provides a peak metamorphic condition of c. 13 kbar at 825 C. The retrograde cordierite and sillimanite

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appear at c. 8 kbar pressure after near-isothermal decompression. Gedrite appears during later-stage retrogression after isobaric cooling, at temperatures lower than 750C. Thus, the

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thermodynamic modeling suggests the Grt+Bt+Pl+Ky+Qtz+Rt assemblage must have been

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5. Timing of metamorphism

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exhumed from a P-T condition of c. 13 kbar and 825 C (Fig. 8).

In order to determine the timing of peak metamorphism which in turn marks the

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timing of suturing, U-Pb dating was carried out on zircons from the metasedimentary rocks of the Kumta and Mercara suture zones. The SHRIMP U-Pb zircon dating and in situ zircon

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hafnium isotopic analysis were determined for a garnet-biotite schist sample from the Kumta suture. LA-ICPMS U-Pb zircon dating and in situ zircon hafnium isotopic analyses were carried out for garnet-biotite-kyanite-cordierite-gedrite gneiss (KR23-20C), a garnet-biotitekyanite gneiss (KR23-20K), and a garnet-biotite-hornblende gneiss (KR23-20F) from the Mercara suture. 5.1. SHRIMP U-Pb zircon geochronology and zircon Lu-Hf isotopic analysis The zircons from garnet-biotite schist sample (IK-0504) are colourless to pale brown and mostly 50-200µm in size. Cathodoluminescene (CL) imaging shows that the zircons have variable internal structures and morphology. The zircon grains are euhedral to sub-rounded, commonly with unzoned grey interiors surrounded by fine-scale oscillatory zones (Fig. 9a). A 18

ACCEPTED MANUSCRIPT total of 20 zircons were analysed (Supplementary Table S4) and gave a wide range of 207

Pb/206Pb ages from 2208 to 3420 Ma, with concordant age populations at ca. 2547 Ma,

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2736 Ma, 3088 Ma and 3420 Ma. Because the zircons either lack metamorphic rims or have

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rims too thin to analyse, no direct estimation of metamorphic age can be made for the garnet-

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biotite schist sample (Fig. 10a).

The twenty zircon sites were analysed for Lu-Hf compositions of which 19 spots were used. The ɛHf (t) value varies from -9.2 to 5.6 and TDMc model age ranges from 3747 to 2792

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Ma (Supplementary Table S6). The ɛHf (t) vs. U-Pb zircon age (207Pb/206Pb age) plot shows

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that pattern follows the 2.8 to 3.8 Ga Archean crustal growth line (Fig. 11). The wide range in model ages and ɛHf (t) values suggests that the protolith sediments were derived from

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different regions, including both recycled continental crust and more juvenile material.

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5.2. LA-ICPMS U-Pb zircon geochronology and zircon Lu-Hf isotopic analysis Zircons from garnet-biotite-kyanite-cordierite-gedrite gneiss (KR23-20C) are brown

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to brownish-orange and mostly 50-200µm in size. Cathodoluminescence (CL) images show that the zircons have a variety of internal structures, with some preserving well-developed

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oscillatory zoning, whereas others lack zoning. Some grains also possess a thin recrystallized rim (Fig. 9b). The zircon grains range from elongate to sub-rounded and rounded in shape. A total of 35 sites were analysed on 35 grains (Supplementary Table S5). The Th/U ratios range from 0.03 to 0.40 and, although a few grains have Th/U values <0.1, the dominant population is magmatic. The U-Pb data yield an upper intercept age of 3249 ± 27 Ma and a lower intercept age of 1464 ± 94 Ma (n=21, MSWD=2.9) (Fig. 10b). Unfortunately, the rims were too narrow for LA-ICPMS analysis. However, the common lower intercept age of 1464 ± 94 Ma, suggests a major lead-loss event and we interpret the rock underwent metamorphism at ca. 1400-1500 Ma. A total of six zircon sites were analysed for Lu-Hf composition. The ɛHf (t) values vary from -13.5 to 4.2 and TDMc model ages range from 4094 to 3314 Ma

19

ACCEPTED MANUSCRIPT (Supplementary Table S6). In the ɛHf (t) vs. U-Pb zircon age (207Pb/206Pb age) plot, the zircons mostly fall along the 3.3 to 4.0 Ga Archean crustal growth line (Fig. 11).

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Zircons from garnet-biotite-kyanite gneiss (KR23-20K) are light brownish and mostly

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50-200µm in length. Cathodoluminescence (CL) images indicate that most crystals are dark

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and have oscillatory zoning, with several grains having thin rims. Morphologically, the zircons are elongate to rounded (Fig. 9c). A total of 35 sites were analysed from 35 zircon grains (Supplementary Table S5). The Th/U ratios range from 0.09 to 1.0, and the CL images

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show that the zircons are mostly magmatic. The zircons yield an upper intercept age of 3158

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± 25 Ma and a lower intercept age of 1106 ± 64 Ma (n=27, MSWD=1.5) (Fig. 10c). The lower intercept is taken to indicate the timing of a major lead-loss event, possibly corresponding to metamorphism. A total of six zircon sites were analysed for Lu-Hf

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composition. The ɛHf (t) values show a wide range from -18.9 to 3.8 and the TDMc model ages range from 4061 to 3326 Ma (Supplementary Table S6). The data indicate provenances

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involving both recycled continental crust and juvenile crustal sources (Fig. 11). Zircons from garnet-biotite-hornblende gneiss (KR23-20F) are light pink and mostly

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50-200µm in diameter. Cathodoluminescence (CL) images show weak oscillatory zoning and most zircons are sub-rounded (Fig. 9d). A total of 33 sites were analysed on 33 grains (Supplementary Table S5). The Th/U ratios range from 0.37 to 0.56, suggesting a magmatic origin. The zircons yield an upper intercept age of 3064 ± 28 Ma and a lower intercept age of 1278 ± 66 Ma (n=26, MSWD=0.88) (Fig. 10d). The lower intercept age may be equated with a metamorphic event at ca. 1250-1300 Ma. A total of six zircon sites were analysed for Lu-Hf composition and the ɛHf (t) shows a wide range of negative values from -4.5 to -10.7 and TDMc model ages from 3890 to 3708 Ma (Supplementary Table S6). The data show the sediments were sourced from Meso- and Paleo-archean recycled continental crust (Fig. 11).

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ACCEPTED MANUSCRIPT In summary, the metasedimentary rocks from the Mercara suture show prominent Paleoarchean to Mesoproterozoic sources. The lower intercept of U-Pb data in all rocks

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suggests a metamorphic event during the mid- to late Mesoproterozoic (Fig. 10).

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Surprisingly, all the zircons from samples KR23-20C, KR23-20K and KR23-20F fall on a

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common discordia line, suggesting source rocks of a similar age. However the spread in ɛHf (t) values indicates a range from juvenile to ancient protolith materials, suggesting either magma mixing or a variety of rock-types. The hafnium isotopic compositions suggest that the

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sediments were derived from mixed sources including both juvenile and recycled continental

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crust. The ɛHf (t) vs. U-Pb zircon age (207Pb/206Pb age) plot defines a major distribution along the 3.0 to 4.0 Ga Archean crustal growth lines (Fig. 11).

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6. Discussion: Implications for tectonic evolution

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6.1. Evolution of the Kumta and Mercara suture zones

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Geological sutures represent zones along which an ocean has closed and these zones may contain relicts of former oceanic crust, supra-subduction arc, shelf or continental

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material (Dewey, 1977). The identification and precise delineation of suture zones is sometimes difficult, because the rocks have undergone different degrees of metamorphism and alteration after amalgamation, or overprinting by multiple tectonic events. The age of the Kumta suture zone was interpreted by Rekha et al. (2014) as ca. 2500 Ma and they also suggested this was a high-strain internal zone within the Antongil-Western Dharwar Craton (WDC). The arguments presented by Rekha et al. (2014) suggest that the similarity in lithology and structure across the proposed Kumta suture (Ishwar-Kumar et al., 2013b) would be unexpected if it was a zone of accretion of two crustal blocks. They also determined identical U-Pb zircon and U-Th-total Pb monazite chemical ages across the Kumta suture.

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ACCEPTED MANUSCRIPT Below we summarize some of the key lines of evidence why we take an alternative view and consider that the Kumta shear zone does represent a paleo-subduction zone.

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6.1.1. Lithology

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Lithologically, the Kumta shear zone preserves evidence for a paleo-suture. The diagnostic rocks within the Kumta suture (high-pressure schists), and the rock sequence from the Sirsi shelf across the Kumta suture (Ishwar-Kumar et al., 2013b) are comparable with the

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well-established sequences in present and paleo-subduction zones worldwide, so that a comparable tectonic environment is extremely likely. The occurrence of high-pressure

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metasedimentary rocks, including quartz-phengite schist and garnet-biotite schist, within this high-strain zone indicates that the sediments were subducted to considerable depths and were

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later exhumed. Rocks with garnet-bearing assemblages are uncommon in the Dharwar

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Craton, except in a few areas such as the Chitradurga-Gadag shear zone (Swami Nath and

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Ramakrishnan, 1981; Chadwick et al., 2000), the Holenarsipur schist belt (Ramakrishnan and Vishwanatha, 1981; Kunugiza et al., 1996) and the Sargur schist belt (Swami Nath and Ramakrishnan, 1981; Rollinson et al., 1981; Ramakrishnan and Vaidyanadhan, 2010), all of

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which have been proposed as suture zones that preserve remnants of oceanic crust. However, it is not possible to rely solely on rock type for delineating suture zones. For example similar rock types in the Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC) occur on either side of the Chitradurga-Gadag suture zone (Swami Nath and Ramakrishnan, 1981; Chadwick et al., 2000; Jayananda et al., 2013). The Nilgiri and Madurai blocks in the Southern Granulite Terrane (SGT) occur on either side of the Palghat-Cauvery suture zone (Drury and Holt, 1980; Ghosh et al., 2004; Chetty and Bhaskar Rao, 2006; Santosh et al., 2009) but also have identical lithologies, with charnockites and gneisses occurring in both blocks.

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ACCEPTED MANUSCRIPT The Bondla ultramafic-gabbro complex west of the Kumta suture zone contains a sequence of rock types including black shale, dolerite dykes, basalt, gabbro, serpentinite,

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chromitite, dunite and peridotite (Jena et al., 1985; Dessai et al., 2009; Ishwar-Kumar et al.,

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2013b). The chromite from the chromitites and serpentinites indicates evolution in a supra-

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subduction arc setting (Ishwar-Kumar et al., under review). Iyer et al. (2010) suggested that the chromian spinel in the Sindhudurg district (Kankavalli, c. 25 km north of the Bondla complex), is of podiform type, similar to those in ophiolites or arc-related settings. Based on

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the above evidence, we suggest that the Kumta high-strain zone is a suture zone formed as a

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result of accretion of the Karwar block and Dharwar Craton. Rekha and Bhattacharya (2014) have proposed a Mesoproterozoic/Paleoproterozoic shear zone [Northern Shear Zone (NSZ)

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and South Maharashtra Shear Zone (SMSZ) (Fig. 2a)], which lies within the northern

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segment of the Kumta suture as proposed by Ishwar-Kumar et al. (2013b); the NSZ-SMSZ shear zones contain, high-pressure garnet-biotite schists and an ultramafic-gabbro complex

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with an ophiolitic signature. We suggest that the proposed NSZ and SMSZ (Rekha and Bhattacharya, 2014; Rekha et al., 2014) are segments of the northern part of the Kumta suture

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and with comparable ages to the Mesoproterozoic Kumta suture. We do not consider this suture as the northern boundary of the WDC. In this study, we have presented evidence for Mesoproterozoic ages from this suture, and therefore it cannot be correlated with the Chitradurga shear zone which has been established as Archean in age (ca. 2500 Ma) (Swami Nath and Ramakrishnan, 1981; Chadwick et al., 2000; Chardon et al., 2008; Jayananda et al., 2013; Hokada et al., 2013). Based on U-Pb zircon geochronological study of tonalitic basement xenoliths hosted in Deccan trap dykes, Upadhyay et al. (2015) proposed that the WDC extends to form the basement of the Deccan volcanic province and South Maharashtra Shear Zone (SMSZ) cannot be considered as northern limit of the western Dharwar Craton. 6.1.2. Structures 23

ACCEPTED MANUSCRIPT The regional structural lineament patterns derived from satellite images show that the NW-SE, N-S, and NE-SW trending segments of the Kumta high strain zone separates two

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distinct terranes. The western part (Karwar block) is dominated by randomly-oriented

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structural features, whereas the eastern part (Dharwar Craton) is dominated by NW-SE to

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NNW-SSE trending structures (Chardon et al., 2008). These NNW-SSE trending structures are related to a major Archean deformation event (at ca. 2500 Ma) and NE-SW crustal shortening (Chadwick et al., 2000). However, these structures are absent within the Karwar

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and Coorg blocks, indicating that they were not part of the WDC at ca. 2500 Ma or that the

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deformation was heterogeneous. By implication, the accretion of these blocks with the Dharwar Craton must have occurred after ca. 2500 Ma.

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6.1.3. Metamorphic conditions

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The textural evidence and thermodynamic modelling of quartz-phengite schist and

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garnet-biotite schist from the Kumta suture suggest peak metamorphic P-T conditions of c. 18 kbar at 550 C and c. 11 kbar at 790 C, respectively. The P-T estimation of garnet-biotite-

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kyanite-gedrite-cordierite gneiss from the Mercara suture indicates that it reached c. 13 kbar at 825 C. The peak metamorphic P-T conditions (high-pressure, low- to mediumtemperature) of the metasedimentary rocks in the two shear zones indicate that the sediments would have been subducted to a depth of about 40-50 km and were later exhumed. The possible scenario where such subduction events can occur is at a convergent margin, followed by exhumation following ocean closure and collision of crustal blocks on either side of the former ocean. Late hydration, probably during exhumation, led to the retrograde assemblages of chlorite, amphibole and cordierite. 6.1.4. Geochronology

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ACCEPTED MANUSCRIPT Interpreting the isotopic ages of crustal blocks on either side of a suture zone is not straightforward. The isotopic ages can be similar across suture zones, or they may vary within

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a block. The ages of the gneisses are not coeval either within the WDC and EDC, and show a

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range from 2500 to 3400 Ma (Beckinsale et al., 1980; Radhakrishna and Naqvi, 1986;

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Bhaskar Rao et al., 1992; Jayananda et al., 2000; 2015; Ishwar-Kumar et al., 2013b; Rekha et al., 2013, 2014). These data suggest that the blocks are composed of several terranes, as is

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also attested by the presence of greenstone belts.

The timing of suturing of continental blocks requires a precise understanding of the

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metamorphic history of the rocks within a suture. In high-grade metamorphic rocks, zircon may be the ideal mineral for geochronology, as its closure temperature is high, but in low- to

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medium-grade metamorphic rocks, phengite and biotite can give better age constraints,

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because associated zircons seldom recrystallise or develop metamorphic rims under low P-T conditions. The timing of suturing can also be estimated by dating the specific syn-collisional

2011).

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igneous events and tectonic/metamorphic fabrics of rocks within the suture zones (Key et al.,

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Rekha et al. (2014) interpreted the deformation related to the Kumta suture as Archean in age (ca. 2500 Ma), formed during the accretion of the WDC and EDC. However, K-Ar dating of phengite from quartz-phengite schist from the southern part of the Kumta suture and biotite from the garnet-biotite schist from the northern part of the Kumta suture gave consistent metamorphic ages of 1326 Ma and 1385 Ma respectively (Ishwar-Kumar et al., 2013b). The SHRIMP U-Pb zircon geochronological data from garnet-biotite and quartzphengite schists in our study also supports the above interpretation. We therefore interpret this as a regional event and not a result of local deformation or metamorphism.

25

ACCEPTED MANUSCRIPT The garnet-biotite schist from the northern Kumta suture contains detrital zircons with a wide age range (2547 Ma to 3420 Ma). This suggests that the sediments were sourced from

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crustal blocks of Neoarchean and Mesoarchean age, which we interpret as the Karwar block

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in the west (ca. 3200 Ma) and the Dharwar Craton in the east (ca. 2571 Ma). The zircons in

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samples from the Mercara suture (samples KR20-20K, KR23-20C and KR-23-20F) show a small age range from ca. 3045-3249 Ma and each sample defines a common discordia line. The zircons from metasedimentary rocks can have a common discordia if they are derived

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from a similar age magmatic provenance (e.g., Yang and Santosh, 2014). The range of ages

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for detrital zircons in this suture is less than for the metasedimentary rocks in the Kumta suture, possibly because the crustal blocks on either side of the Mercara suture (i.e. Coorg

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block and southern part of the Dharwar Craton) have largely similar ages (3200-3400 Ma)

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compared to the variation between the Karwar block (ca. 3200 Ma) and the northern part of the Dharwar Craton (ca. 2571 Ma). The lower intercept ages of ca. 1106-1464 Ma defined by

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zircons from pelitic gneisses in the Mercara suture are broadly consistent with K-Ar phengite and biotite ages from the metasedimentary rocks in the Kumta suture (1326 Ma and 1385

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Ma) and possibly indicate a common metamorphic event. Rekha et al. (2014) suggested that the Coorg block amalgamated with the Dharwar Craton at 2300-2500 Ma based on Th-U-Pb monazite ages. However, results of the present study indicate that the Mercara suture is a Mesoproterozoic that can be correlated with the Kumta suture of similar age. LA-ICPMS UPb detrital zircon age data from a quartz-mica schist from the Mercara suture range from 3400 to 1350 Ma (Santosh et al., 2014). This suggests that sedimentation within the Mercara suture continued into the Mesoproterozoic and excludes the possibility of suturing at 23002500 Ma. K-Ar phengite and biotite ages can be used to broadly constrain the age of metamorphism in greenschist to amphibolite facies rocks, if zircons do not recrystallise or

26

ACCEPTED MANUSCRIPT have metamorphic overgrowths, or if the latter are too thin to measure. In the Kumta suture (greenschist to amphibolite facies) the SHRIMP U-Pb dating of zircons from quartz-phengite

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schist (Ishwar-Kumar et al., 2013b) and garnet-biotite schist (present study) was unable to

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date the metamorphic rims. However, phengite from quartz-phengite schist and biotite from

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the garnet-biotite schist gave K-Ar ages of ca. 1326 Ma and ca. 1385 Ma, respectively (Ishwar-Kumar et al., 2013b). In the Mercara suture zone, which is a higher grade terrane (granulite facies) compared to the Kumta suture, biotite from a mylonitic quartzo-feldspathic

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gneiss gave a K-Ar age of ca. 933 Ma (Ishwar-Kumar et al., 2013b). However, the LA-

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ICPMS U-Pb dating of zircons gave lower intercept ages ranging from 1106-1464 Ma, older than the K-Ar age. In the Betsimisaraka suture of NE Madagascar (amphibolite facies), LA-

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ICPMS U-Pb dating of zircons from biotite-kyanite-sillimanite gneiss gave a lower intercept

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age of ca. 497 Ma and biotite gave a K-Ar age of ca. 486 Ma which is very close to the zircon lower intercept age (Ishwar-Kumar et al., 2015). So, we infer that the consistent

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Mesoproterozoic K-Ar ages from the Kumta suture relate to the age of crustal amalgamation and can be compared with the Mesoproterozoic zircon lower intercept ages from the Mercara

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suture.

6.2. Comparison of the Kumta and Mercara suture zones The Kumta suture contains amphibolite- to greenschist-facies schistose rocks that include quartz-phengite schist, chlorite schist, fuchsite schist, garnet-biotite schist, and marble. The Mercara suture contains amphibolite- to granulite-facies garnet-kyanitesillimanite gneiss, mylonitic quartzo-feldspathic gneiss, garnet-biotite-kyanite-gedritecordierite gneiss, garnet-biotite-hornblende gneiss, and calc-silicate granulite, which possibly represent the high-grade equivalents of the schistose rocks in the Kumta suture. Isochemical phase diagrams indicate the quartz-phengite schist and garnet-biotite schist attained peak metamorphic P-T conditions of ca. 18 kbar at 550° C and c. 11 kbar at 790° C, respectively.

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ACCEPTED MANUSCRIPT Thermodynamic modelling of garnet-biotite-kyanite-gedrite-cordierite gneiss yields peak P-T conditions of 13 kbar at 825° C. Phengite from quartz-phengite schist and biotite from garnet-

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biotite schist in the Kumta suture record K-Ar ages of ca. 1326 Ma and ca. 1385 Ma,

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respectively (Ishwar-Kumar et al., 2013b) . Biotite from mylonitic quartzo-feldspathic gneiss

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in the Mercara suture yield a K-Ar age of ca. 933 Ma (Ishwar-Kumar et al., 2013b). Detrital SHRIMP U-Pb zircon populations from quartz-phengite schist and garnetbiotite schist from the Kumta suture range in age from 2993-3280 Ma (Ishwar-Kumar et al.,

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2013b) and 2547-3420 Ma (present study), respectively. Detrital zircons in metasedimentary

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gneisses from the Mercara suture range in age from 3045 to 3249 Ma. The lower intercept ages for metasedimentary rocks from the Mercara suture are in the range of 1106-1464 Ma. The garnet-biotite schist from the Kumta suture has ɛHf (t) values ranging from -9.2 to 5.6

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and TDMc model ages ranging from 3747 to 2792 Ma, whereas those from the Mercara suture have ɛHf (t) values ranges from -18.9 to 4.2 and TDMc model ages of 4094 to 3314 Ma. In the

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Kumta suture, the wide range in model ages and ɛHf (t) values suggests that the protolith sediments were derived from both recycled continental crust and juvenile crust. In the

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Mercara suture, the TDMc model ages and ɛHf (t) values indicate the detritus was derived mostly from recycled older crust. The Karwar block on the western side of the Kumta suture contains ca. 3200 Ma TTG gneisses with enclaves of amphibolite (Ishwar-Kumar et al., 2013b). The Coorg block on the western side of the Mercara suture consists of ca. 3200 Ma gneisses and ca. 3200 charnockites with enclaves of amphibolite and mafic granulite (Santosh et al., 2015). The Coorg block can be considered as a high-grade equivalent of the Karwar block, and the Mercara suture as the high-grade equivalent of the Kumta suture, with deeper crust exposed in the Coorg area. The Kumta suture is characterised by a sedimentary shelf sequence to the east, but the shelf is absent to the east of the high-grade Mercara suture, as it was likely 28

ACCEPTED MANUSCRIPT eroded away and the underlying lower crust is now exposed. However, the occurrence of patches of calc-silicate rocks and quartzites possibly represent remnants of the shelf.

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We now address the ambiguity in the variation of metamorphic grade in the different

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rock types of the Karwar and Coorg blocks. The granulite-facies metamorphic rocks exposed

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in southern and eastern India and parts of Madagascar, Antarctica and Sri Lanka are mostly related to the Pan-African metamorphic event at 550-600 Ma related to the assembly of east

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and west Gondwana (e.g. Collins et al., 2014). The Karwar block in the north was not affected by this event, whereas the Coorg block in the south was affected, maybe because it

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was close to the boundary of amalgamation (the Angavo and Palghat-Cauvery shear zones). Another possibility is that in the north, the Karwar block was once covered by

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Cretaceous Deccan basalt, whereas farther south, the Coorg block was not covered by these

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volcanics. The weathering and erosion of continents is more intense in the equatorial regions, as compared with mid-latitudes. At the time when India passed across the equator after rifting

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from Madagascar, the Karwar block was possibly covered by Deccan volcanics, and erosion has now exposed the basement, although the north-eastern part is still covered by Deccan

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basalt. However, in the south, the Coorg block lacks the Deccan volcanic cover, and therefore, the upper crust was intensely eroded to expose lower crustal rocks. Another possibility is the northward tilting of the Dharwar Craton (Ramakrishnan and Vaidyanadhan, 2010). Because of this, the upper crust of the southern part of Dharwar Craton was eroded and deeper crust exposed. 6.3. Correlation with north-eastern Madagascar Based on the results of the present study, and integrated with published data, we propose a close-fit correlation between India and Madagascar. Figure 12 summarises the key geochronological data from the Betsimisaraka-Kumta-Mercara sutures and surrounding regions. The Mesoproterozoic Kumta and Mercara suture zones can be correlated with the 29

ACCEPTED MANUSCRIPT northern and southern sections of the Betsimisaraka suture of Madagascar, respectively (Fig. 12). The Palghat-Cauvery shear zone of southern India can be correlated with the

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Neoproterozoic Angavo shear zone of Madagascar, and the Achankovil shear zone of

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southern India can be correlated with the Tranomaro shear zone of southern Madagascar. The

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proposed correlation is consistent with the results of Ishwar-Kumar et al. (2013b, 2015) and Ratheesh-Kumar et al. (2015). The correlation is also supported by the available geophysical data, including effective elastic thickness, crustal thickness and bathymetric data (Ratheesh-

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Kumar et al., 2015). Based on mesoscopic structures and Th-U-Pb monazite ages, Rekha et

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al. (2013, 2014) proposed a correlation between crustal blocks in western India and northeastern Madagascar. Although their correlation is in agreement with lithological units and

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ages, the reconstructed position of India and Madagascar is inconsistent with the present

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results.

The Betsimisaraka suture zone is mainly composed of paragneisses (with common

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augen, cataclastic and mylonitic fabrics) associated with pelitic mica schists containing garnet, staurolite, kyanite, sillimanite and graphite) (Hottin, 1969; Collins and Windley,

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2002). The metasedimentary rocks contain abundant mafic-ultramafic lenses. Such features can be correlated with those of the Kumta and Mercara suture zones, which include quartzphengite schist, chlorite schist, garnet-biotite schist, marble and amphibolite- to granulitefacies garnet-, kyanite-, sillimanite- and quartz-, feldspar-bearing paragneisses with metagabbro and calc-silicate granulites. The Betsimisaraka suture records a wide range of detrital zircon ages (2950-1740 Ma) (Kröner et al., 2000; Tucker et al., 2011a, b, 2014). However, Collins et al., (2003) has reported detrital zircon ages in the Betsimisaraka suture as young as ca. 600 Ma. The Kumta and Mercara suture zones have a wide range of detrital zircon ages ranging from 3420 to 1350 Ma. The Antongil and Masora blocks of Madagascar contain 3320-3150 Ma TTG gneisses and the 2700-2490 Ma Masaola suite (De Waele et al., 30

ACCEPTED MANUSCRIPT 2008; Tucker et al., 1999, 2011a, b, 2014), which can be correlated with the 3400-3200 Ma TTG gneisses and 2700-2500 Ma younger gneisses from the Dharwar Craton (Beckinsale et

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al., 1980; Nutman et al., 1992; Peucat et al., 1995; Jayananda et al., 2000, 2015; Ishwar-

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Kumar et al., 2013b, 2015). However, in contrast, the Karwar and Coorg blocks are

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composed of ca. 3200 Ma TTG and charnockites intercalated with amphibolite and mafic granulite (Ishwar-Kumar et al., 2013b; Santosh et al., 2015) and the Antananarivo block contains 2700-2500 Ma gneisses intruded by younger granites (820-520 Ma) with >3000 Ma

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inherited zircon ages (Kröner et al., 2000; Collins et al., 2003; Tucker et al., 2011a, b). The

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Antananarivo block west of the Angavo shear zone contains 2500-2700 Ma gneisses with 820-520 Ma granitoids and can be correlated with the Madurai block in southern India, which

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also contains 800-500 Ma granitoids. The structural, lithological and geochronological results

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from the present study, when integrated with published data, suggest closure of the Mesoproterozoic ocean occurred along the Kumta and Mercara suture zones in western India.

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Based on the regional structural and geological data we propose that these sutures represent the eastern extension of the northern and southern parts of the Betsimisaraka suture of north-

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eastern Madagascar. 7. Conclusions

Structural and regional geological evidence indicates the presence of high-strain zones (Kumta and Mercara shear zones) at the western margin of peninsular India. Textural evidence and metamorphic P-T estimations for the metasedimentary rocks (11-18 kbar at 790-550oC for the Kumta suture and 13 kbar at 825oC for the Mercara suture) indicate that the sediments were subducted to depths of about 40-50 km, and were later exhumed.

31

ACCEPTED MANUSCRIPT A detailed study of the field relations within the suture zones and in the crustal blocks on either side, combined with the metamorphic P-T conditions of metasedimentary rocks

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from the suture zones, indicates that the Kumta and Mercara shear zones represent zones of

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paleo-oceanic closure. The zircon SHRIMP and LA-ICPMS U-Pb geochronology of

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metasedimentary rocks from the Kumta and Mercara suture zones suggest a common metamorphic event in the Mesoproterozoic at 1464-1100 Ma.

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Integration of results with published data indicates that the Archean blocks in western peninsular India were sutured during the Mesoproterozoic. The regional structural and

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geological data suggest that the Kumta and Mercara sutures are the eastern extension of the northern and southern parts of the Betsimisaraka suture of north-eastern Madagascar.

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Acknowledgements

We utilized laboratory facilities developed through the Ministry of Earth Sciences,

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Government of India project MoES/ATMOS/PP-IX/09. This study is a contribution to ISROIISc Space Technology Cell projects ISTC/MES/SK/232 and ISTC/CEAS/SJK/291 and is

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The Institute for Geoscience Research (TIGeR) publication number 602. This study also contributes to the Talent Award to M. Santosh under the 1000 Plan from the Chinese Government and to the Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (JSPS) to Tsunogae (No. 26302009). We thank Q.Y. Yang and Q. Li at the China University of Geosciences, Beijing for help with the LA-ICPMS U-Pb zircon geochronology and Jinhui Yang for access to the Lu-Hf facility at the Chinese Academy of Sciences. References

32

ACCEPTED MANUSCRIPT Agarwal, P.K., Pandey, O.P., Negi, J.G., 1992. Madagascar: A continental fragment of the paleo-super Dharwar Craton of India. Geology 20, 543-546.

T

Azeez, K.K.A., Veeraswamy, K., Gupta, A.K., Babu, N., Chandrapuri, S., Harinarayana, T.,

IP

2015. The electrical resistivity structure of lithosphere across the Dharwar Craton

SC R

nucleus and Coorg block of South Indian shield: Evidence of collision and modified and preserved lithosphere. Journal of Geophysical Research: Solid Earth 120, DOI: 10.1002/2014JB011854.

NU

Beckinsale, R.D., Drury, S.A., Holt, R.W., 1980. 3360 Ma old gneisses from south Indian

MA

Craton. Nature 283, 469-470.

Bhaskar Rao, Y.J., Sivaraman, T.V., Pantulu, G.V.C., Gopalan, K., 1992. Rb-Sr ages of late

D

Archean metavolcanics and granites, Dharwar Craton, South India and evidence for

TE

early Proterozoic thermotectonic events. Precambrian Research 59, 145-170. Brandt, S., Raith, M.M., Schenk, V., Sengupta, P., Srikantappa, C., Gerdes, A., 2014. Crustal

CE P

evolution of the Southern Granulite Terrane, south India: New geochronological and geochemical data for felsic orthogneisses and granites. Precambrian Research 246, 91-

AC

122.

Chadwick, B., Vasudev, V.N., Hegde, H.V., 2000. The Dharwar Craton, southern India, interpreted as the result of Late Archean oblique convergence, Precambrian Research 99, 91-111. Chardon, D., Jayananda, M., Chetty, T.R.K., Peucat, J.-J., 2008. Precambrian continental strain and shear zone patterns: South Indian case. Journal of Geophysical Research 113, B08402, DOI: 10.1029/2007JB005299. Chetty, T.R.K., Bhaskar Rao, Y.J., 2006. The Cauvery shear zone, southern granulite terrain, India: A crustal-scale flower structure. Gondwana Research 10, 77-85.

33

ACCEPTED MANUSCRIPT Chetty, T.R.K., Mohanty, D.P., Yellappa, T., 2012. Mapping of Shear Zones in the Western Ghats, South-western Part of Dharwar Craton. Journal of the Geological Society of

T

India 79, 151-154.

IP

.Collins, A.S., Windley, B.F., 2002. The tectonic evolution of central and northern

SC R

Madagascar and its place in the final assembly of Gondwana. Journal of Geology 110, 325-340.

Collins, A.S., Razakamanana, T., Windley, B.F., 2000. Neoproterozoic extensional

NU

detachment in central Madagascar: implications for the collapse of the East African

MA

Orogen. Geological Magazine 137, 39-51.

Collins, A.S., Kröner, A., Fitzsimons, I.C.W., Razakamanana, T. 2003. Detrital footprint of

D

the Mozambique ocean: U/Pb SHRIMP and Pb evaporation zircon geochronology of

TE

metasedimentary gneisses in eastern Madagascar. Tectonophysics 375, 77-99. Collins, A.S., Clark, C., Sajeev, K., Santosh, M., Kelsey, D.E., Hand, M., 2007. Passage

CE P

through India: the Mozambique Ocean suture, high-pressure granulites and the PalghatCauvery shear zone system. Terra Nova 19, 141-147.

AC

Collins, A.S., Clark, C., Plavsa, D., 2014. Peninsula India in Gondwana: The tectonothermal evolution of the Southern Granulite Terrane and its Gondwanan counterparts. Gondwana Research 25, 190-203. Connolly, J.A.D., 2005. Computation of phase equilibria by linear programming: a tool for geodynamic modeling and its application to subduction zone decarbonation. Earth and Planetary Science Letters 236, 524-541. Dessai, A.G., Arolkar, D.B., French, D., Viegas, A., Viswanath, T.A., 2009. Petrogenesis of the Bondla layered mafic-ultramafic complex, Usgaon, Goa. Journal of the Geological Society of India 73, 697-714.

34

ACCEPTED MANUSCRIPT De Waele, B., Horstwood, M.S.A., Bauer, W., Key, R.M., Pitfield, P.E.J., Potter, C.J., Rabarimana, M., Rafahatelo, J.M., Ralison, V., Randriamananjara, T., Smith, R.A.,

T

Thomas, R.J., Tucker, R.D., 2008. U–Pb Detrital Zircon Geochronological Provenance

SC R

of African Geology, Hammamat, Tunisia, p. 3.

IP

Patterns of Supracrustal Successions in Central and Northern Madagascar. Colloquium

Dewey, J.F. 1977. Suture zone complexities: a review. Tectonophysics 140, 53-67. Drury, S.A., Holt, R.W., 1980, The tectonic framework of the South Indian Craton: A recon-

NU

naissance involving Landsat imagery. Tectonophysics 65, T1-T15.

MA

Ferry, J.M., Spear, F.S., 1978. Experimental calibration of the partitioning of Fe and Mg between biotite and garnet. Contributions to Mineralogy and Petrology 66, 113-117.

D

Ganguly, J., Saxena, S.K., 1984. Mixing properties of alumina-silicate garnets: constraints

TE

from natural and experimental data, and applications to geothermometry, American Mineralogist 69, 88-97.

CE P

Geological Survey of India, 2005. Geological Map of India, 1: 500000, Hyderabad. Geological Survey of India, 1995. Geological and Mineral Map of Kerala, 1:500000.

AC

Hyderabad.

Ghosh, J.G., de Wit, M.J., Zartman, R.E., 2004. Age and tectonic evolution of Neoproterozoic ductile shear zones in the Southern Granulite terrane of India, with implications for Gondwana studies. Tectonics 23: TC3006, DOI: 1029/2002TC001444. Goldsmith, J.R., 1980. The melting and breakdown reactions of anorthite at high pressures and temperatures. American Mineralogist 65, 272-284. Hokada, T., Horie, K., Satish-Kumar, M., Ueno, Y., Nasheeth, A., Mishima, K., Shiraishi, K., 2013. An appraisal of Archaean supracrustal sequences in Chitradurga Schist Belt, Western Dharwar Craton, Southern India. Precambrian Research 227, 99-119.

35

ACCEPTED MANUSCRIPT Holland, T.J.B., Powell, R., 1998. An internally consistent thermodynamic dataset for phases of petrological interest. Journal of Metamorphic Geology 16, 309-343.

T

Hottin, G., 1969. Les terrains cristallins du centre-nord et du nord-est de Madagascar.

IP

Documentation du Bureau Géologique de Madagascar 178 (2 vols.), 1-192, 193-381.

SC R

Indares, A., Martignole, J., 1985. Biotite-garnet geothermometry in granulite-facies rocks: evaluation of equilibrium criteria. Canadian Mineralogist 23, 187-193. Ishwar-Kumar, C., George, P.M., Adachi, T., Nakano, N., Osanai, Y., Itaya, T., Sajeev, K.,

NU

2013a. Evolution of mafic and calc granulites from Coorg, southern India. In:

MA

Fitzsimons, I., Clark, C. (Editors), Granulites & Granulites, Hyderabad, p. 34. Ishwar-Kumar, C., Windley, B.F., Horie, K., Kato, T., Hokada, T., Itaya, T., Yagi, K.,

D

Gouzu, C., Sajeev, K., 2013b. A Rodinian suture in western India: New insights on

TE

India-Madagascar correlations. Precambrian Research 236, 227-251. Ishwar-Kumar, C., Sajeev, K., Windley, B.F., Kusky, T.M., Feng, P., Ratheesh-Kumar, R.T.,

CE P

Huang, Y., Zhang, Y., Jiang, X., Razakamanana, T., Yagi, K. and Itaya, T., 2015. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar:

AC

Tectonic implications. Tectonophysics 662, 219-242. Iyer, S.D., Babu, E.V.S.S.K., Mislankar, P.G., Gujar, A.R., Ambre, N.V., Loveson, V.J., 2010. Occurrence and emplacement of chromite ores in Sindhudurg district, Maharashtra, India. Acta Geologica Sinica 84, 515-527. Jayananda, M., Moyen J.F., Martin, H, Peucat, J.-J., Auvray, 2000. Late Archean (2550-2520 Ma) juvenile magmatism in the Eastern Dharwar Craton, southern India: constraints from geochronology, Nd-Sr isotopes and whole-rock geochemistry. Precambrian Research 99, 225-254. Jayananada, M., Peucat, J.-J., Chardon, D., Krishna Rao, B., Fanning, C.M., Corfu, F., 2013. Neoarchean greenstone volcanism and continental growth, Dharwar Craton, southern

36

ACCEPTED MANUSCRIPT India: Constraints from SIMS U–Pb zircon geochronology and Nd isotopes. Precambrian Research DOI: http://dx.doi.org/10.1016/j.precamres.2012.05.002

T

Jayananda, M., Chardon, D., Peucat, J.-J., Tushipokla, Fanning, C.M., 2015. Paleo- to

IP

Mesoarchean TTG accretion and continental growth in the western Dharwar Craton,

geochemistry

and

Nd-Sr

isotopes.

SC R

Southern India: Constraints from SHRIMP U-Pb zircon geochronology, whole-rock Precambrian

Research,

DOI:

http://dx.doi.org/doi:10.1016/j.precamres.2015.07.015

NU

Jena, B.K., 1985. Usgaon ultramafic-gabbro complex, Goa. Journal of the Geological Society

MA

of India 26, 492-495.

Kaneko, Y. and Miyano, T., 2004. Recalibration of mutually consistent garnet-biotite and

D

garnet-cordierite geothermometers. Lithos 73, 255-269.

TE

Katz, M.B., Premoli, C., 1979. India and Madagascar in Gondwanaland based on matching Precambrian lineaments. Nature 279, 312-315.

CE P

Key, R.M., Pitfield, P.E.J., Thomas, R.J. et al. (20 authors), 2011. Polyphase Neoproterozoic orogenesis within the East Africa-Antarctica orogenic belt in central and northern

AC

Madagascar. In: van Hinsbergen, D.J.J., Buiter, S.J.H., Torsvik, T.H., Gaina, C., Webb, S.J. (Editors), The Formation and Evolution of Africa: a Synopsis of 3.8 Ga of Earth History. Geological Society of London, Special Publications 357, 49-68. Koziol, A.M., Newton, R.C., 1988. Redetermination of the anorthite breakdown reaction and improvement

of

the

plagioclase-garnet-Al2SiO5-quartz

barometer.

American

Mineralogist 73, 216-223. Kretz, R., 1983. Symbols for rock-forming minerals. American Mineralogist 68, 277-279. Krishnaraj, N.S., Janardhan, A.S., Basavalingu, B., 1994. Garnet-kyanite bearing pelitic and associated mafic-granulites along Jalsoor-Mercara shear zone: Evidence for deep burial and later uplift. Journal of Geological Society of India 44, 617-625.

37

ACCEPTED MANUSCRIPT 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

T

Madagascar, as derived from zircon geochronology and Nd isotopic systematics.

IP

American Journal of Science 300, 251-288.

SC R

Kunugiza, K., Kato, Y., Kano, T., Takaba, Y., Kuruma, I., Sohma, T., 1996. An Archaean tectonic model of the Dharwar Craton, southern India: the origin of the Holenarasipur greenstone belt (Hussan district, Karnataka) and reinterpretation of the Sargur-Dharwar

NU

relationship. Journal of Southeast Asian Earth Sciences 14, 149-160.

MA

Moores, E..M., Twiss, R.J., 1995. Tectonics. W.H. Freeman and Company, New York, pp241-249.

clinopyroxenes

in

the

system

CaO-MgO-Al2O3-SiO2.

Geochimica

et

TE

and

D

Newton, R.C., Charlu, T.V., Kleppa, O.J., 1977. Thermochemistry of high-pressure garnets

Cosmochimica Acta 41, 369-377.

CE P

Newton, R.C., Haselton, M.T. 1981. Thermodynamics of the garnet-plagioclase-Al2SiO5quartz geobarometer. In: Newton, R.C., Navrotsky, A., Wood, B.J. (Editors),

AC

Thermodynamics of minerals and melts. Springer-Verlag, 131-147. Newton, R.C., Smith, J.V., Windley, B.F., 1980. Carbonic metamorphism, granulites, and crustal growth. Nature 288, 45-50. Nutman, A.P., Chadwick, B., Ramakrishnan, M., Viswanatha, M.N., 1992. SHRIMP U-Pb ages of detrital zircon in Sargur supracrustal rocks in western Karnataka, southern India. Journal of the Geological Society of India 39, 367-374. Perchuk, L.L., Lavrenteva, I.V., 1983. Experimental investigation of exchange equilibria in the system cordierite-garnet-biotite. In: Saxena, S.K. (Editor) Kinetics and Equilibrium in mineral reactions. Springer, Berlin, pp. 199 239.

38

ACCEPTED MANUSCRIPT Peucat, J.-J., Bouhallier, H., Fanning, C.M., Jayananda, M., 1995. Age of Holenarsipur schist belt, relationships with the surrounding gneisses (Karnataka, south India). Journal of

T

Geology 103, 701-710.

IP

Peucat, J, -J., Jayananda, M., Chardon, D., Capdevila, R., Fanning, C.M., Paquette, J,-L.,

SC R

2013. The lower crust of the Dharwar Craton, Southern India: Patchwork of Archean granulitic domains. Precambrian Research 227, 4-28.

Pigage L.C., Greenwood, H.J., 1982. Internally consistent estimates of pressure and

NU

temperature: the staurolite problem. American Journal of Science 282, 943-969.

MA

Plavsa, D., Collins, A.S., Payne, J.L., Foden, J.D., Clark, C., Santosh, M., 2014. Detrital zircons in basement metasedimentary protoliths unveil the origins of southern India.

D

Geological Society of America Bulletin DOI: 10.1130/B30977.1

TE

Radhakrishna, B.P., Naqvi, S.M., 1986. Precambrian continental crust of India and its evolution. Journal of Geology 94, 145-166.

CE P

Raharimahefa, T., Kusky, T.M., 2006. Structural and remote sensing studies of the southern Betsimisaraka Suture, Madagascar. Gondwana Research 10, 186-197.

AC

Raharimahefa, T., Kusky, T.M., 2009. Structural and remote sensing analysis of the Betsimisaraka Suture in northeastern Madagascar. Gondwana Research 15, 14-27. Ramakrishnan, M., Vaidyanadhan, R., 2010. Geology of India, Geological society of India, V.1 Ramakrishnan, M., Viswanatha, M.N., 1981. Holenarsipur belt, Memoirs of the Geological Survey of India 112, 115-141. Ratheesh-Kumar R.T., Ishwar-Kumar, C., Windley, B.F., Razakamanana, T., Nair, R. R., Sajeev, K., 2015. India-Madagascar paleo-fit based on the flextural isostasy of their rifted margins. Gondwana Research 28, 581-600.

39

ACCEPTED MANUSCRIPT Raval, U., Veeraswamy, K., 2003. India-Madagascar separation: Breakup along a preexisting mobile belt and chipping of the Craton. Gondwana Research 6, 467-485.

T

Rekha, S., Bhattacharya A., 2014. Paleoproterozoic/Mesoproterozoic tectonism in the

IP

northern fringe of the Western Dharwar Craton (India): Its relevance to Gondwanaland

SC R

and Columbia supercontinent reconstructions. Tectonics 33, 552-580. Rekha, S., Viswanath, T.A., Bhattacharya, A., Prabhakar, N., 2013. Meso/Neoarchean crustal domains along the north Konkan coast, western India: The Western Dharwar Craton

NU

and the Antongil-Masora Block (NE Madagascar) connection. Precambrian Research

MA

233, 316-336.

Rekha, S., Bhattacharya, A., Prabhakar, N., 2014. Tectonic restoration of the Precambrian

D

crystalline rocks along the west coast of India: correlation with eastern Madagascar in

TE

East Gondwana. Precambrian Research 252, 191–208. Rollinson, H.R., Windley, B.F., Ramakrishnan, M., 1981. Contrasting high and intermediate

CE P

pressures of metamorphism in the Archaean Sargur Schists of southern India. Contributions to Mineralogy and Petrology 76, 420-429.

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Santosh, M., Maruyama, S., Sato, K., 2009. Anatomy of a Cambrian suture in Gondwana: Pacific-type orogeny in southern India? Gondwana Research 16, 321-341. Santosh, M., Yang, Q.Y., Shaji, E., Tsunogae, T., Ram Mohan, M., Satyanarayanan, M. 2014. Oldest rocks from Peninsular India: Evidence for Hadean to Neoarchean crustal evolution. Gondwana Research (In press). DOI: 10.1016/j.gr.2014.11.003 Santosh, M., Yang, Q.Y., Shaji, E., Tsunogae, T., Ram Mohan, M., Satyanarayanan, M. 2015. An exotic Mesoarchean microcontinent: The Coorg Block, southern India. Gondwana Research. DOI: 10.1016/j.gr.2013.10.005

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ACCEPTED MANUSCRIPT Srikantappa, C., Venugopal, L., Devaraju, J., Basavalingu, B., 1994. P–T conditions of metamorphism and fluid inclusion characteristics of the Coorg granulites, Karnataka.

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Journal of the Geological Society of India 44, 495-504.

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Sunil, P.S., Radhakrishna, M., Kurian, P.J., Murty, B.V.S., Subrahmanyam, C., Nambiar,

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C.G., Arts, K.P., Arun, S.K., Mohan, S.K. 2010. Crustal structure of the western part of the Southern Granulite Terrain of Indian Peninsular Shield derived from gravity data. Journal of Asian Earth Sciences 39, 551-564.

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Swami Nath, J., Ramakrishnan, M., 1981. Present classification and correlation. In: Swami

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Nath, J., Ramakrishnan, M. (Editors), Early Precambrian Supracrustals of Southern Karnataka, Memoirs of the Geological Survey of India 112, 23-38.

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Thompson, A. B., 1976. Mineral reactions in pelitic rocks: II Calculation of some P-T-X (Fe-

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Mg) phase relations. American Journal of Science 276, 425-454. Tucker, R.D., Ashwal, L.D., Handke, M.J., Hamilton, M.A., Le Grange, M., Rambeloson,

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R.A., 1999. U-Pb geochronology and isotope geochemistry of the Archean and Proterozoic rocks of north-central Madagascar. Journal of Geology 107, 135-153.

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Tucker, R.D., Roig, J.Y., Delor, C., Amerlin, Y., Goncalves, P., Rabarimanana, M.H., Ralison, A.V., Belcvher, R.W., 2011a. Neoproterozoic extension in the Greater Dharwar Craton: a reevaluation of the “Betsimisaraka suture’ in Madagascar. Canadian Journal of Earth Sciences 48, 389-417. Tucker, R.D., Roig, J.Y., Macey, P.H., Delor, C., Amelin, Y., Armstrong, R.A. Rabarimanana, M.H., Ralisone, A.V., 2011b. A new geological framework for southcentral Madagascar, and its relevance to the “out-of-Africa” hypothesis. Precambrian Research 185, 109-130. Tucker, R.D., Roig, J.Y., Moine, B., Delor, C., Peters, S.G., 2014. A geological synthesis of the Precambrian shield in Madagascar. Journal of African Earth Sciences 94, 9-30.

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ACCEPTED MANUSCRIPT Windley, B.F., Razafiniparany, A., Razakamanana, T., Ackermand, D. 1994. Tectonic framework of the Precambrian of Madagascar and its Gondwana connections: a review

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and reappraisal. Geologische Rundschau 83, 642-659.

global

plate

tectonic

shutdown.

Gondwana

Research,

(in

press)

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Siderian

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Yang, Q., Santosh, M., 2014. Paleoproterozoic arc magmatism in the North China Craton: No

doi:10.1016/j.gr.2014.08.005

Upadhyay, D., Koojiman, E., Singh, A.K., Mezger, K., Berndt, J., 2015. The Basement of the

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Deccan Traps and Its Madagascar Connection: Constraints from Xenoliths. Journal of

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Geology 123, 295-307.

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Figure captions

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Fig. 1. Regional geology and tectonic framework of southern India (geology from Geological Survey of India, 2005). The shear zones are modified after Ishwar-Kumar et al. (2013b). The

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rectangles show location of the study areas, the Kumta suture (Fig. 2a) and the Mercara suture (Fig. 2b). Acronyms: TTG-tonalite-trondhjemite-granodiorite, KSZ- Kumta Shear

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Zone, ChSZ- Chitradurga Shear Zone, MeSZ- Mettur Shear Zone, KolSZ- Kolar Shear Zone; NSZ- Nallamalai Shear Zone, MSZ- Moyar Shear Zone, McSZ- Mercara Shear Zone, BSZBhavani Shear Zone, SASZ- Salem Attur Shear Zone, CaSZ- Cauvery Shear Zone, PCSZPalghat Cauvery Shear Zone, ASZ- Achankovil Shear Zone. Fig. 2. a. Sample locations and regional structures in and adjacent to the Kumta suture overlain on the geological map (modified after Geological Survey of India, 2005 and IshwarKumar et al., 2013b). b. Sample locations and regional structures of the Mercara suture and surrounding regions overlain on the geological map (modified after Geological Survey of India, 1995, 2005; Chetty et al., 2012 and Ishwar-Kumar et al., 2013b.) Structural lineaments were extracted from Landsat ETM+ satellite imagery and ASTER digital elevation model. 42

ACCEPTED MANUSCRIPT Fig. 3. Plane-polarised light photomicrographs of metasedimentary rocks from the Kumta suture. (a) Garnet-biotite schist showing an idioblastic garnet surrounded by foliated biotite-

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plagioclase matrix (IK-0504). (b) Quartz-phengite schist showing alternating bands rich in

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quartz and fine-grained phengite (IK-2302L). (c) Chlorite schist showing a sheared fabric and

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augen-shaped quartz grains. (d) Sheared biotite-augen gneiss with quartz augen within a biotite-rich matrix. (e) Carbonate-chlorite-biotite schist illustrating typical deformation microstructures. (f) Marble from the Kumta suture. Qtz-quartz, Pl- plagioclase, Grt-garnet,

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Bt-biotite, Phe-phengite, Chl-chlorite, Cal- calcite.

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Fig. 4. Plane-polarised photomicrographs illustrating representative textures of pelitic gneisses from the Mercara suture. (a) Fine-grained intergrowth of kyanite and gedrite

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and biotite in sample KR23-20K. (c) Idioblastic to sub-idioblastic garnet surrounded by biotite and minor hornblende in sample KR23-20F. (d) Coarse-grained aggregates of garnet

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in a matrix of quartz, biotite, sillimanite, rutile, and plagioclase in sample KR23-20C. Cordierite occurs at garnet rims as a retrograde product after garnet + sillimanite + quartz. (e)

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Mylonitic quartzo-feldspathic gneiss with deformed and elongated quartz porphyroclasts in a biotite-chlorite matrix. (f) Garnet-biotite-sillimanite gneiss showing biotite wrapping around garnet grains. (g) Garnet-biotite sillimanite gneiss, showing sillimanite within garnet grains. (h) Garnet-sillimanite-graphite gneiss. (i) Quartzite from the western part of Moyar shear zone. Qtz-quartz, Pl- plagioclase, Grt-garnet, Bt-biotite, Ky-kyanite, Hbl-hornblende, Gedgedrite, Crd-cordierite, Sil-sillimanite, Gr-graphite, Rt-rutile. Fig. 5. X-ray elemental maps (Mg, Ca, Mn, Fe) of a garnet from garnet-biotite schist sample (IK-0504) from the Kumta suture. The images emphasize the prominent Ca and Mn zoning in garnets.

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ACCEPTED MANUSCRIPT Fig. 6. Back-scattered electron images illustrating the mineral assemblages. (a, b) Garnetbiotite schist sample (IK-0504) from the Kumta suture. (c, d) Garnet-biotite-kyanite-gedrite-

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cordierite gneiss sample (KR23-20C) from the Mercara suture. Bt-biotite, Chl-chlorite, Pl-

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Fig. 7. A P-T phase diagram modeled using the bulk composition of garnet-biotite schist (IK0504) in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-TiO2-H2O system. SiO2 = 45.46, Al2O3

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= 21.75, FeO = 17.07, MgO = 6.10, CaO = 3.13, Na2O = 1.48, K2O = 3.31, TiO2 = 0.92 and H2O = 0.78.

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Fig. 8. A P-T phase diagram modeled using the bulk composition of garnet-biotite-kyanitegedrite-cordierite gneiss (KR23-20C) in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-TiO2-

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H2O system. SiO2 = 60.05, Al2O3 = 20.74, FeO = 8.70, MgO = 6.66, CaO = 0.27, Na2O =

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0.31, K2O = 1.60, TiO2 = 1.04 and H2O = 0.64.

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Fig. 9. Representative cathodoluminescence images illustrating zircon structures. Yellow circles are U-Pb analysis spots and red circles are Lu/Hf isotope analysis spots. U-Pb age and

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ɛHf (t) values are marked on the figure. Fig. 10. U-Pb concordia plots of zircons analysed by (a) SHRIMP and (b, c, d) LA-ICPMS. (a) IK-0504- Garnet-biotite schist from the Kumta suture. (b) KR23-20C- Garnet-biotitekyanite-gedrite-cordierite gneiss from the Mercara suture. (c) KR23-20K- Garnet-Biotitekyanite gneiss from the Mercara suture. (d) KR23-20F- Garnet-biotite-hornblende gneiss from the Mercara suture. Fig. 11. A ɛHf (t) vs. U-Pb zircon age (207Pb/206Pb age) plot for the metasedimentary samples from the Kumta and Mercara suture zones.

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ACCEPTED MANUSCRIPT Fig. 12. Compilation of geochronological data from the Betsimisaraka-Kumta-Mercara sutures and surrounding regions (from Kröner et al., 2000; Tucker et al., 2014 and references

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Table 1. Details of samples with location and mineral assemblages

Latitude N 14° 29' 41.7'' N 15° 43' 46.8'' N 12° 03' 40.5'' N 12° 03' 40.5'' N 12° 03' 40.5''

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Mineral assemblage Qtz, Phe, Ky, Rt, Chl, Cld, Tur Grt, Bt, Ky, St, Chl, Am, Qtz, Pl Qtz, Pl, Grt, Bt, Ky,Ged, Crd, St, Rt

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Longitude E 74° 33' Quartz-phengite schist 36.0'' E 73° 55' IK-0504 Garnet-biotite schist 51.6'' KR23- Garnet-biotite-kyanite-gedrite- E 75° 45' 20C cordierite gneiss 42.9'' KR23E 75° 45' 20K Garnet-biotite-kyanite gneiss 42.9'' KR23- Garnet-biotite-hornblende E 75° 45' 20F gneiss 42.9''

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Sample No. IK2302L

Qtz, Pl, Grt, Bt, Ky Qtz, Pl, Grt, Bt, Hbl, Rt

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0.89

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Cr2O3 FeO MnO MgO CaO

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V2O5 NA LOI 1.37 Total 100.00

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Research highlights

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 Kumta and Mercara sutures weld Archean Karwar and Coorg blocks with the Dharwar Craton  Peak metamorphism of 11-18 k bar, at 825-550oC during collision at 14601100 Ma  Kumta and Mercara sutures are correlated with Betsimisaraka suture of E Madagascar

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