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The Chalk hills of Salem complex also called Salem mafic and ultramafic complex (SMUC), occurs in northern part of Cauvery suture zone (CSZ), southern granulite terrane (SGT), India with the lithological sequence of ultramafic cumulates, mafic intrusions of gabbros and amphibolites with quartzo-feldspathic veins and ultrapotassic dykes. Recently the complex has been described as Neoproterozoic Alaskan-type. The Ti- rich gabbros are in association with serpentinized dunites and pyroxenites in the form of several intrusions at various locations of the complex. The petrography of these gabbros shows sub-alkaline to alkaline in nature with mineralogy of two pyroxenes and plagioclases of calcicsodic assemblages along with magnetite-titanomagnetite-ilmenite (Ti-spinels). The whole rock geochemistry indicates that they are tholeiitic in nature with enrichment of LILE (Rb, Ba, Th, Sr) and depletion of HFSE (Nb, Ta, Ti) with reference to N-MORB. The mineral chemistry of clinopyroxenes from these gabbros show slightly higher Mg# (0.68–0.80), TiO2 (0.40–0.73 wt%) with lower Al2O3 (4.4–5.5 wt%), Na2O (0.53–0.94 wt%) and Cr2O3 (0.1–0.17 wt%) contents. The orthopyroxenes also show low Al2O3 (1.4–2.3 wt%), Cr2O3 (up to 0.13 wt%), and relatively higher MgO (17.11–21.79 wt%). The Ti- bearing oxides (ilmenites) of these gabbros are characterized by higher contents of TiO2 (38–51 wt%) and FeO (46–56 wt%), similar to that of Ti-Fe rich Alaskan- type of mafic rocks. On various tectonic discrimination diagrams of whole rock and clinipyroxene mineral chemistry of these gabbros reveal that they are derived from subduction related components of arc magmas of titanium rich, evolved through the process of high degree of crystal fractionation. From the two-pyroxene thermometry, the temperature of formation of these gabbros are determined as 893–1014°C and the clinopyroxene barometry results variable pressures of 8–13 kbars. The tectonic setting with the available age relationships from the complex suggest these intrusions are syntectonic and co-genetic of late emplacements along with the ultramafics during Neoproterozoic subduction events. Such occurrences of high Ti- bearing gabbros are common in many Alaskan- type of complexes like Neoproterozoic Arabian Nubian Shield and other parts of the world.

The Aniyapuram Mafic and Ultramafic Complex (AMUC) is a dismembered ophiolite of Neoarchean to Paleoproterozoic age, exposed in south-central part of the Cauvery Suture Zone (CSZ), Southern Granulite Terrane (SGT), India. The complex comprises ultramafic rocks like serpentinized peridotites of harzburgite variety and pyroxenites of websterite variety along with metagabbros, amphibolites, plagiogranites and metacherts. The pyroxenites in the complex occur in the form of dykes, veins and lenses in association with serpentinized peridotites and metagabbros. The chemical compositions of olivine from the peridotites show a moderate forsterite content (Fo88–87) and spinels are enriched in aluminum (Al2O3 > 60 wt%) with depletion of Cr contents (Cr# < 0.5). The pyroxenites are composed of orthopyroxenes with dominance of clinopyroxene and sulphide occurrences (up to 62 wt% S) along the grain boundaries of pyroxenes. The whole rock geochemistry of these pyoxenites shows enrichment of LILE and depletion of HFSE with negative Nb anomalies on N-MORB and primitive normalization. The mineral chemistry of clinopyroxenes from the pyroxenites shows tholeiitic in nature with high Mg# ratios [Mg/(Mg + Fe) = 0.70–0.88]. These mineral chemistry results together with whole rock chemistry reveal their origin in Island arc setting of supra-subduction zone (SSZ) tectonics possibly evolved by the interaction of subduction derived fluids of host serpentinized peridotites. The estimated two-pyroxene thermobarometry of these pyroxenites represents varied re-equilibrium temperatures of 820–980°C and medium to slightly high pressures of 10–12 kbar. With the available age relationship from the complex, the study supports as a strong evidence for the occurrence of Neoarchean to Paleoproterozoic suprasubduction tectonics and associated lithologies of formation in the terrane.

The dismembered units of the Neoproterozoic Manamedu Ophiolite Complex (MOC) in the Cauvery Suture Zone, southern India comprises a well preserved ophiolitic sequence of ultramafic cumulates of altered dunites, pyroxenites, mafic cumulates of gabbros, gabbro-norites and anorthosites in association with plagiogranites, isotropic gabbros, metadolerites, metabasalts/amphibolites and thin layers of ferruginous chert bands. The isotropic gabbros occur as intrusions in association with gabbroic anorthosites, plagiogranite and metabasalts/amphibolites. The gabbros are medium to fine grained with euhedral to subhedral orthopyroxenes, clinopyroxenes and subhedral plagioclase, together with rare amphiboles. Mineral chemistry of isotropic gabbros reveal that the clinopyroxenes are diopsidic to augitic in composition within the compositional ranges of En(42–59), Fs(5–12), Wo(31–50). They are Ca-rich and Na poor (Na2O

The Cauvery suture zone (CSZ) in southern India has witnessed multiple deformations associated with multiple subduction-collision history, with incorporation of the related accretionary belts sequentially into the southern continental margin of the Archaean Dharwar craton since Neoarchean to Neoproterozoic. The accreted tectonic elements include suprasubduction complexes of arc magmatic sequences, high-grade supracrustals, thrust duplexes, ophiolites, and younger intrusions that are dispersed along the suture. The intra-oceanic Neoarchean-Neoproterozoic arc assemblages are well exposed in the form of tectonic melanges dominantly towards the eastern sector of the CSZ and are typically subjected to complex and multiple deformation events. Multi-scale analysis of structural elements with detailed geological mapping of the sub-regions and their structural cross sections, geochemical and geochronological data and integrated geophysical observations suggest that the CSZ is an important zone that preserves the imprints of multiple cycles of Precambrian plate tectonic regimes.

Thick horizons of iron formations including Banded Iron Formations (BIFs) and Banded Silicate Formations (BSFs) occur as E–W trending bands in the eastern part of Cauvery Suture Zone (CSZ) in the Sothern Granulite Terrane of India. Some of these occur in close association with the Neoarchean-Neoproterozoic suprasubduction zone complexes, where as some others are associated with metamorphosed accretionary sequences including pyroxene granulites and other high grade rocks. The iron formations are highly deformed and metamorphosed under amphibolite to granulite facies conditions and are composed of quartz–magnetite–hematite–goethite–garnet–pyrite together with grunerite and pyroxene. Here we report the geochemical characteristics of twenty representative samples from the iron formations that reveal a widely varying composition with Fe2O3(t) (22–65 wt.% as total iron) total- Fe2O3/TiO2 (205–6532), MnO/TiO2 (0.25–12.66) and SiO2 (33–85 wt.%), broadly representing the two types of iron formations. These formations also show very low Al/(Al + Fe + Mn) ratio (0.001–0.01), Al2O3 (0.07–0.76 wt.%), Al2O3/TiO2 ratio (2.7–21), MgO (0.01–4.41 wt.%), CaO (0.1–1.24 wt.%), Na2O (0.01–0.05 wt.%) and K2O (0.01 wt.%) together with low total REE (3.38–31.63 ppm). The trace and REE elemental distributions show wide variation with high Ni (274 ppm), and Zn contents (up to 87 ppm) when compared to mafic volcanics of the adjoining areas. Tectonic discrimination plots indicate that the iron formations of the Cauvery Suture Zone are of hydrothermal origin. Their chondrite normalized patterns show slight positive Eu anomaly (Eu/Eu* = up to 1.77) and relatively less fractionation of REE with slight LREE enrichment compared to HREE. However, the PAAS (Post Archean Average of Australian Sediments) normalized REE patterns display significant positive Eu anomaly (Eu/Eu* up to 2.32) with well represented negative Ce anomalies (Ce/Ce* = 0.66–1.28). The above results together with petrological characteristics and available geochronology of the associated lithologies suggest that the iron formations can be correlated to Algoma-type. The Fe and Si were largely supplied by medium to high temperature sub-marine hydrothermal systems in Neoarchean and Neoproterozoic convergent margin settings.

Granitoid intrusions occur widely in the Southern Granulite Terrain (SGT) of India, particularly within the Cauvery Suture Zone (CSZ), which is considered as the trace of the Neoproterozoic Mozambique ocean closure. Here we present the petrological and geochemical features of 19 granite plutons across the three major tectonic blocks of the terrain. Our data show a wide variation in the compositions of these intrusions from alkali feldspathic syenite to granite. The whole rock geochemistry of these intrusions displays higher concentrations of $$\hbox {SiO}_{2}$$ , FeO*, $$\hbox {K}_{2}\hbox {O}$$ , Ba, Zr, Th, LREE and low MgO, $$\hbox {Na}_{2}\hbox {O}$$ , Ti, P, Nb, Y and HREE’s. The granitoids are metaluminous to slightly peraluminous in nature revealing both I-type and A-type origin. In tectonic discrimination plots, the plutons dominantly show volcanic arc and syn-collisional as well as post-collisional affinity. Based on the available age data together with geochemical constrains, we demonstrate that the granitic magmatism in the centre and south of the terrain is mostly associated with the Neoproterozoic subduction–collision–accretion–orogeny, followed by extensional mechanism of Gondwana tectonics events. Similar widespread granitic activity has also been documented in the Arabian Nubian shield, Madagascar, Sri Lanka and Antarctica, providing similarities for the reconstruction of the crustal fragments of Gondwana supercontinent followed by Pan-African orogeny.

Several Precambrian mafic–ultramafic complexes occur along the Cauvery Suture Zone (CSZ) in Southern Granulite Terrain, India. Their origin, magmatic evolution and relationship with the associated high-grade rocks have not been resolved. The Aniyapuram Mafic–Ultramafic Complex (AMUC), the focus of the present study in southern part of the CSZ, is dominantly composed of peridotites, pyroxenites, gabbros, metagabbros/mafic granulites, hornblendites, amphibolites, plagiogranites, felsic granulites and ferruginous cherts. The rock types in the AMUC are structurally emplaced within hornblende gneiss (TTG) basement rocks and are highly deformed. The geochemical signature of the amphibolites indicates tholeiitic affinity for the protolith with magma generation in island arc-setting. N-MORB normalized pattern of the amphibolites show depletion in HFS-elements (P, Zr, Sm, Ti, and Y) and enrichment of LIL-elements (Rb, Ba, Th, Sr) with negative Nb anomalies suggesting involvement of subduction component in the depleted mantle source and formation in a supra-subduction zone tectonic setting. Our new results when correlated with the available age data suggest that the lithological association of AMUC represent the remnants of the Neoarchean oceanic lithosphere.

The Mahadevi hills, located in the axial zone of Cauvery Suture Zone, comprise a sequence of granulite facies rocks represented by garnet-bearing pyroxene granulites and quartzo-feldspathic gneisess interfolded with banded iron formations. Structural mapping with hand held GPS reveals that the Mahadevi hills constitute a mega sheath fold structure exposing well developed easterly plunging extension lineations. Depressional and culmination surfaces are well demarcated in association with elliptical map patterns. The development of the mega sheath fold structure is genetically related to the regional thrust-nappe tectonics, supporting the model of subduction-accretion-collisional history for the evolution of the Cauvery Suture Zone.

A new map of structural architecture has been compiled involving modern mapping techniques at the cratonmobile belt interface in the Western Ghats around the Coorg granulite massif revealing the occurrence of important shear zones. The shear zones are linked to the Moyar-Bhavani Shear Zone in Southern India. The nature, geometry and kinematics of the shear zones in the granulitic crust and the cratonic part are distinctly different.

Ophiolites, the remnants of ancient oceanic lithosphere, have been described from collisional sutures of various ages with only few examples from Archean terranes. Here we report the discovery of a Neoarchean ophiolite suite from the southern margin of the Dharwar Craton in India, tectonically intercalated within a Neoproterozoic suture zone. The metamorphosed and variably dismembered ophiolite suite, exposed around Devanur, comprises altered ultramafic units, websterite, gabbros, mafic dykes, amphibolites, trondhjemites and pegmatites associated with ferruginous metachert. Structural and petrographic studies indicate that the rocks represent a highly sheared and metamorphosed suite emplaced as a thrust sheet. The major and trace element geochemistry of the mafic dykes indicate derivation from basaltic–andesitic magmas with tholeiitic to calc-alkaline characteristics. The rocks display negative Nb anomalies with enrichment of LILE (K, Rb, Ba, Th) and depletion in HFSE (Ti, Nb, Hf, Tb). The tectonic discrimination of these rocks based on various geochemical plots suggests that they were generated in a suprasubduction zone setting. We present new SHRIMP zircon U–Pb data for two trondhjemite samples from this complex, which yield 238U–206Pb ages of 2528 ± 61 and 2545 ± 56 Ma. The Neoarchean age from the trondhjemites obtained in our study is closely comparable to similar ages obtained in recent studies from magmatic zircons in charnockites and orthogneisses in the area. The suprasubduction zone assemblages and arc magmas suggest a Neoarchean ocean closure along the southern margin of the Dharwar Craton.

The Palghat-Cauvery Suture Zone (PCSZ) in southern India defines the trace of the collisional suture developed during the assembly of the Gondwana supercontinent through the closure of the Mozambique Ocean in the Late Neoproterozoic–Cambrian. Here we report Secondary Ion Mass Spectrometry (SIMS) U–Pb ages from zircons in plagiogranites and gabbros from a suprasubduction zone ophiolitic complex at Manamedu, located along the southern periphery of the PCSZ. The morphology and internal structures, together with the high Th/U values of the zircons from the plagiogranite suggest a magmatic crystallization history. The dominant population of zircons in the two plagiogranite samples analyzed in this study yield 206Pb/238U ages of 737 ± 23 Ma and 782 ± 24 Ma corresponding to the timing of emplacement of these rocks. The plagiogranite from Manamedu also contains two other zircon populations: the first group shows a discordant population with 207Pb/206Pb ages between 2278 and 2527 Ma with an upper intercept age of 2418 ± 65 Ma. Similar Neoarchean–early Paleoproterozoic ages have been widely reported from the surrounding rocks within the PCSZ and also from the Salem Block to the north. We interpret these older zircons as xenocrysts entrained in the plagiogranite during magma ascent and consolidation. The third group of zircons in the plagiogranite yield 206Pb/238U age of 513 ± 4.6 Ma, comparing well with the Cambrian ages reported in several recent studies from magmatic and metamorphic rocks in the PCSZ and the crustal blocks to the south, correlating with the tectono-thermal events associated with the collision and post-collisional extension associated with the assembly of the Gondwana supercontinent. Zircons in the two gabbro samples from the Manamedu complex analyzed in this study yield well-defined clusters on the concordia and show weighted mean 206Pb/238U ages of 744 ± 11 Ma and 786 ± 7.1 Ma. The internal structure of the zircons from these gabbro samples and their high Th/U values also suggest a magmatic crystallization history. The zircon ages that we obtained from the Manamedu forearc complex also compare with the recently reported zircon age of 825 ± 17 from the gabbro–anorthosite complex and the 766 ± 8 Ma age from oscillatory-zoned euhedral crystals of magmatic zircons in felsic volcanic suite of the Kadavur Dome, to the south of Manamedu. The ages also compare with the 819 ± 26 Ma 206Pb/238U age reported from zircons in arc-related rapakivi granite from an adjacent locality within the PCSZ. All these data suggest a prominent mid Cryogenian subduction system along the southern periphery of the PCSZ prior to the destruction of the Mozambique Ocean lithosphere and the final amalgamation of the Gondwana supercontinent.

We present here a regional tectonic fabric analysis of the southern margin of the Bastar Craton, Central India, obtained from different spatial data sets that include Shuttle Radar Topographic Mission (SRTM), Landsat ETM+ (Enhanced Thematic Mapper) and IRS (Indian Remote sensing Satellite) P6-LISS3, integrated with available geological information, as well as field and microscopic observations. The southern margin of the Bastar Craton exhibits large-scale structures, such as regional-scale folds, major shear zones and associated tectonic fabric affected by strong brittle–ductile deformation. The deformational features are related to large-scale thrusting, regional compression, and episodic igneous activity during the Precambrian, and display a major tectonic control on magmatism and the evolution of a shear zone system. The NW–SE to E–W and NE–SW trending brittle to ductile shear zones traversing the craton display both dextral as well as sinistral displacements. Well-developed kinematic indicators include, sheared quartz veins, tension gashes, rotated porphyroblasts, S–C fabrics, pinch-and-swell structures, sigmoidal foliations and riedel fractures that are well preserved in the basement Sukma–Bengpal supracrustals, as well as in the younger granitoids of the Dongargarh Supergroup. Large-scale well-developed NW–SE trending isoclinal folding in the basement gneisses and major folding in mafic intrusions in the south-western margin and tight, upright doubly-plunging large-scale folds in the eastern margins of the craton represent two major tectonic events. These events can be correlated to large-scale thrusts and suggest an initial N–S compression of the craton followed by E–W thrusting at different intervals during the tectonic evolution of the craton. The occurrence of several NW–SE trending mafic dykes parallel to the shear zones indicate that regional-scale tensile stresses were operating during the Proterozoic, associated with a possible continental rift environment in the centre of the craton. The structural pattern obtained, together with the structures mapped with the coherence of remote sensing images, give significant information and an opportunity to reconstruct the timing, style of deformation and its kinematics in the southern part of the Bastar Craton and provide important constraints on the kinematics of the shear zone system and evolution of the craton. Copyright © 2011 John Wiley & Sons, Ltd.

Detailed geological and structural mapping of the Manamedu ophiolite complex (MOC), from the south-eastern part of the Cauvery suture zone (CSZ) within the Gondwana collisional suture in southern India reveals the anatomy of a dismembered ophiolite succession comprising pyroxenite actinolite–hornblendite, hornblendite, gabbro–norite, gabbro, anorthosite, amphibolite, plagiogranite, mafic dykes, and associated pelagic sediments such as chert–magnetite bands and carbonate horizons. The magmatic foliation trajectory map shows inward dipping foliations and a variety of fold structures. Structural cross-sections of the MOC reveal gentle inward dips with repetition and omission of different lithologies often marked by curvilinear hinge lines. The succession displays imbricate thrust sheets and slices of dismembered ophiolite suites distributed along several localities within the CSZ. The MOC can be interpreted as a deformed large duplex structure associated with south-verging back thrust system, consistent with crustal-scale ‘flower structure’. The nature and distribution of ophiolitic rocks in the CSZ suggest supra-subduction zone setting associated with the lithospheric subduction of the Neoproterozoic Mozambique Ocean, followed by collision and obduction during the final stage of amalgamation of the Gondwana supercontinent in the end Precambrian.

Ophiolites provide important clues on the role of subduction and have been widely investigated to reconstruct the history of development and closure of ocean basins in the geological past. The Manamedu Complex within the Palghat-Cauvery Suture Zone in southern India comprises metamorphosed equivalents of the following lithological units: (1) an ultramafic group comprising dominantly of pyroxenite and highly altered dunite, locally preserving cumulate textures; (2) a gabbroic suite consisting of gabbro, gabbro norite, and anorthosite; (3) sheeted mafic dykes of amphibolite to meta-andesite categories, (4) plagiogranite veins and pools; and (5) a thin layer of ferruginous cherts. Cr vs. Y, V vs. Cr, Ti vs. Zr, TiO 2 –MnO–P 2 O 5 and Fe 2 O 3 –Na 2 O + K 2 O–MgO plots of the gabbros and mafic dyke assemblages show that these are related to island arc tholeiite (IAT) group with tholeiitic to calcalkaline signatures. Chondrite normalized REE patterns of mafic dykes do not show any pronounced fractionation and display slight positive Eu anomalies. The normalized MORB plots of the mafic dykes show depletion of HFSE (negative Nb, Ti, Ta, Hf anomalies) and enrichment of LFSE (positive K, Ba, Rb, Th). The petrological and geochemical characteristics of the major lithological units in Manamedu Complex suggest that these rocks represent the remnants of an oceanic crust, developed from mantle-derived arc magmas probably within a suprasubduction zone tectonic setting. From the geological set up and our field observations, we infer that these rocks were obducted on to the continental margin with the closure of an ocean basin during the Neoproterozoic. The Manamedu Complex may represent the remnants of the Mozambique Ocean crust developed during Rodinia breakup and which was destroyed during the amalgamation of the Gondwana supercontinent in the Latest Neoproterozoic-Cambrian.

Occurrence of two lamproitic dykes intruding the basement granite near Khadka village at the northern margin of the Indravati Basin, Bastar craton is reported. Combined field, microscopy, XRD, EPMA and whole-rock geochemical investigations reveal that these lamproites were subjected to high degree of hydrothermal alteration as well as possible metamorphism. However, relicts of their original textures are well-preserved thereby providing important clues as to the nature of the protolith. Quartz, carbonate, chlorite and phlogopite constitute the bulk mineralogy whereas spinel, apatite and iron oxides are the accessory phases. Chemical composition of the groundmass spinels are strikingly similar to those from the lamproites. The Khadka lamproite dykes display high abundances of compatible elements such as Ni (238-396 ppm), Cr (484-892 ppm), and V (160-200 ppm) as well as high-field strength elements such as Zr (719-2057 ppm) and Nb (92-126 ppm) that resemble those in lamproites. Khadka lamproites also have high whole-rock REE abundances (ΣREE up to 1260 ppm) and display fractionated chondrite-normalized REE patterns (La/Yb= 113-237) which together with their average compatible and incompatible trace elemental ratios (e.g. Nb/Zr, Nb/La, Ba/Rb) are strikingly similar to those of the Mesoproterozoic Krishna lamproites of the Eastern Dharwar craton. Available field evidences suggest the Khadka lamproites to be of at least Palaeoproterzoic age (1.88 Ga) which makes them some of the oldest such rocks as yet documented from the Indian shield.