Petrology and Geochemistry of Layered Ultramafic to Mafic Complexes from the Archaean Craton of Karnataka, Southern India

Srikantappa, C.; Hörmann, P. K.; Raith, M.

doi:10.1007/978-3-642-70001-9_7

Cited by 4 publications

(7 citation statements)

References 36 publications

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“…They are, however, not readily distinguishable from gabbroic amphibolites of the associated layered complexes, although the gabbroic amphibolites are intimately associated in the field with some members of layered suite. The layered complexes form semi-coherent units of serpentinised peridotites and meta-pyroxenites (tremoliteactinolite-anthophyllite-cummingtonite-chlorite schists) with discontinuous chromitite reefs, gabbroic amphibolites (±garnet) with seams of titaniferous and vanadiferous magnetite, and anorthosites Srikantappa et al 1984). The layered complexes show a dominant tholeiitic trend.…”

Section: Sargur Groupmentioning

confidence: 99%

Precambrian mafic magmatism in the Western Dharwar Craton, southern India

Ramakrishnan¹

2009

J Geol Soc India

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Mafic rocks of Western Dharwar Craton (WDC) belong to two greenstone cycles of Sargur Group (3.1-3.3 Ga) and Dharwar Supergroup (2.6-2.8 Ga), belonging to different depositional environments. Proterozoic mafic dyke swarms (2.4, 2.0-2.2 and 1.6 Ga) constitute the third important cycle. Mafic rocks of Sargur Group mainly constitute a komatiitic-tholeiite suite, closely associated with layered basic-ultrabasic complexes. They form linear ultramaficmafic belts, and scattered enclaves associated with orthoquartzite-carbonate-pelite-BIF suite. Since the country rocks of Peninsular Gneiss intrude these rocks and dismember them, stratigraphy of Sargur Group is largely conceptual and its tectonic environment speculative. It is believed that the Sargur tholeiites are not fractionated from komatiites, but might have been generated and evolved from a similar mantle source at shallower depths. The layered basic-ultrabasic complexes are believed to be products of fractionation from tholeiitic parent magma. The Dharwar mafic rocks are essentially a bimodal basalt-rhyolite association that is dominated by Fe-rich and normal tholeiites. Calc-alkaline basalts and andesites are nearly absent, but reference to their presence in literature pertains mainly to carbonated, spilitized and altered tholeiitic suites. Geochemical discrimination diagrams of Dharwar lavas favour island arc settings that include fore-, intra-and back-arcs. The Dharwar mafic rocks are possibly derived by partial melting of a lherzolite mantle source and involved in fractionation of olivine and pyroxene followed by plagioclase. Distinctive differences in the petrography and geochemistry of mafic rocks across regional unconformities between Sargur Group and Dharwar Supergroup provide clinching evidences in favour of distinguishing two greenstone cycles in the craton. This has also negated the earlier preliminary attempts to lump together all mafic volcanics into a single contemporaneous suite, leading to erroneous interpretations. After giving allowances for differences in depositional and tectonic settings, the chemical distinction between Sargur and Dharwar mafic suites throws light on secular variations and crustal evolution. Proterozoic mafic dyke swarms of three major periods (2.4, 2.0-2.2 and 1.6 Ga) occur around Tiptur and Hunsur. The dykes also conform to the regional metamorphic gradient, with greenschist facies in the north and granulite facies in the south, resulting from the tilt of the craton towards north, exposing progressively deeper crustal levels towards the south. The low-grade terrain in the north does not have recognizable swarms, but the Tiptur swarm consists essentially of amphibolites and Hunsur swarm mainly of basic granulites, all of them preserving cross-cutting relations with host rocks, chilled margins and relict igneous textures. There are also younger dolerite dykes scattered throughout the craton that are unaffected by this metamorphic zonation. Large-scale geochemical, geochronological and palaeomagnetic data acquisition through s...

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Section: Sargur Groupmentioning

confidence: 99%

Precambrian mafic magmatism in the Western Dharwar Craton, southern India

Ramakrishnan¹

2009

J Geol Soc India

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“…The Sargur schist belt has been metamorphosed under conditions of regional upper amphibolite to lower granulite facies metamorplism at 700 o C under 8 to 9 Kb pressure during 2.6 Ga (Srikantappa et al 1984). In the Kurihundi area which forms the part of Sargur schist belt, it is also observed that the intensity of metamorphism is high as indicated by the development of garnet through recrystallization of plagioclase in the associated gabbroanorthositic rocks.…”

Section: Effects Of Metamorphismmentioning

confidence: 99%

“…These anorthosites have been classified into two tectonic associations namely (1) non-layered and extensively deformed anorthosites of mafic-ultrmafic complexes and (2) layered anorthosites with cumulus textures in the Archaean high-grade terrain . In the transition zone from the low to high grade terrain in Karnataka, for example at Sinduvalli belt, these rocks show cumulus textures indicating a genetic connection between anorthosites of these two tectonic milieu Srikantappa et al 1984). Ranganathan et al (1991) reported the occurrence of V-Ti magnetite layers (lodestone) in the layered anorthosites of high-grade Archeaen Sargur supracrustals of the Kurihundi area.…”

Section: Introductionmentioning

confidence: 99%

Ore petrology of the V-Ti magnetite (lodestone) layers of the Kurihundi area of Sargur schist belt, Dharwar craton

Vidyashankar

Govindaiah

2009

J Geol Soc India

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The V-Ti magnetite layers (lodestone) occur within the layered gabbro-anorthosites-ultramafic rocks emplaced into the migmatitic gneisses close to the high grade Archeaen Sargur supracrustal rocks in the Kurihundi area. The ore petrographic studies of the lodestone reveal the presence of primary Ti-magnetite, ilmenite, ulvospinel, pleonaste, hematite and pyrite, chalcopyrite, pyrrhotite and secondary Ti-maghemite, martite and goethite as well as secondary covellite. These layers contain Ti-magnetite (60%) and ilmenite (30%) with silicates (<5%) exhibiting granular mosaic texture with well-defined triple junctions and are classified as adcumulus rocks. The grain-boundary relationships in the ores indicate considerable postcumulus growth and readjustment due to combined effects of sintering and adcumulus growth. Intergrowth textures (ulvospinel, ilmenite and pleonaste in Ti-magnetite and hematite in ilmenite) reflects exsolution features crystallized from solid-solutions compositions under different conditions of oxygen fugacities. Larger bodies of pleonaste and ilmenite in Ti-magnetite become lensoid or rounded in outline and these morphological modifications took place during the regional upper amphibolite to lower granulite facies metamorphism at 2.6 Ga ago. The lodestone contains high TiO 2 (20 to 22.59 wt%), with V 2 O 5 (0.85 to 1.15%) and Fe 2 O 3 t (72.03 to 74.25%). Ti-magnetite shows alteration to Ti-maghemite, martite and goethite due to low temperature oxidation and hydration during weathering.

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“…In Archaean high-grade metamorphic terranes, the complexes are layered and can be grouped into a maficultramafic type and a gabbro-anorthosite type . The geotectonic environment of formation of these ancient complexes is uncertain, but various authors have suggested similarity with island-arc , ocean floor (Weaver et al 1981(Weaver et al , 1982 or continental margin (Srikantappa et al 1984) environments.…”

Section: Mineralogic Comparisons With Other Mafic-ultramafic Complexesmentioning

confidence: 99%

Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

Oliveira¹,

Tarney

1995

Mineral. Deposita

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Abstract. Caraiba, the largest Brazilian copper deposit under exploitation, consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early Proterozoic norite and hypersthenite. The mafic igneous complex comprises multiple intrusions of dykes, veins and breccias of norites and hypersthenites, with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere. The country rocks are high-grade gneisses, granulites and metasediments. Compositions of plagioclase (An6o-40) and orthopyroxene (EnTo-6o) fall in a narrow range similar to the Koperberg Suite from the Okiep copper district, South Africa, and to that in many massif-type anorthosites. Whole-rock major and trace element geochemistry indicate a parental magma enriched in Fe, LREE, P, K, and Cu. Negative Nb anomalies on multi-element plots and fractionated REE patterns, along with sulphide sulphur isotopes in the range 634S = -1.495 to + 0.643%o, suggest a primary mantle lithosphere source, although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded. Geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent (partly transpressional) shearing event associated with the waning stage of evolution of the early Proterozoic Salvador-Curag~ orogen.

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Petrology and Geochemistry of Layered Ultramafic to Mafic Complexes from the Archaean Craton of Karnataka, Southern India

Cited by 4 publications

References 36 publications

Precambrian mafic magmatism in the Western Dharwar Craton, southern India

Precambrian mafic magmatism in the Western Dharwar Craton, southern India

Ore petrology of the V-Ti magnetite (lodestone) layers of the Kurihundi area of Sargur schist belt, Dharwar craton

Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

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