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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Africa
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Southern Africa
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Kaapvaal Craton (1)
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Lesotho (1)
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South Africa
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Bushveld Complex (1)
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Free State South Africa
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Vredefort Dome (1)
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Gauteng South Africa
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Pretoria South Africa (1)
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KwaZulu-Natal South Africa (1)
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Transvaal region (4)
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Asia
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Indian Peninsula
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India
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Andhra Pradesh India
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Cuddapah Basin (6)
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Nellore mica belt (1)
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Bastar Craton (5)
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Bundelkhand (2)
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Cauvery Basin (1)
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Dharwar Craton (7)
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Ghats
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Eastern Ghats (1)
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Jharkhand India (1)
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Karnataka India
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Chitradurga schist belt (1)
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Closepet Granite (1)
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Pranhita-Godavari Valley (1)
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Rajasthan India
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Aravalli Range (1)
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Singhbhum shear zone (6)
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Southern Granulite Terrain (2)
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Trans-Aravalli Vindhyan Basin (3)
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Vindhyan Basin (2)
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Australasia
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Australia (1)
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North America
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Canadian Shield (1)
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South America
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Brazil
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Brazilian Shield (1)
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commodities
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asbestos deposits (1)
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barite deposits (1)
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diamond deposits (1)
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gems (1)
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limestone deposits (1)
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metal ores
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chromite ores (1)
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copper ores (2)
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gold ores (1)
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iron ores (1)
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lead ores (1)
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lead-zinc deposits (1)
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manganese ores (1)
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molybdenum ores (1)
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platinum ores (1)
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uranium ores (2)
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zinc ores (1)
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mineral deposits, genesis (2)
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phosphate deposits (1)
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elements, isotopes
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large-ion lithophile elements (1)
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metals
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platinum group
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platinum ores (1)
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rare earths (2)
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geochronology methods
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Pb/Pb (1)
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U/Pb (2)
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U/Th/Pb (1)
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geologic age
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Cenozoic
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Quaternary
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Holocene
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upper Holocene (1)
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Mesozoic
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Jurassic (1)
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Triassic
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Upper Triassic
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Molteno Formation (1)
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Paleozoic
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Cambrian (1)
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Precambrian
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Archean
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Aravalli System (1)
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Mesoarchean (2)
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Neoarchean
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Dharwar Supergroup (1)
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Sargur Group (1)
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Paleoarchean (2)
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Sausar Series (1)
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Singhbhum Granite (1)
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Bijawar System (1)
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Transvaal Supergroup (4)
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upper Precambrian
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Proterozoic
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Huronian (1)
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Mesoproterozoic (3)
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Neoproterozoic (4)
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Paleoproterozoic
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Rooiberg Group (1)
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Pretoria Group (2)
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Witwatersrand Supergroup (1)
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Vindhyan (3)
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igneous rocks
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igneous rocks
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volcanic rocks
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pyroclastics
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tuff (1)
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ophiolite (1)
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metamorphic rocks
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metamorphic rocks
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gneisses
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tonalite gneiss (1)
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metasedimentary rocks
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metapelite (1)
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migmatites (1)
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quartzites (1)
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schists (1)
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ophiolite (1)
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minerals
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oxides (1)
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phosphates
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monazite (1)
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silicates
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orthosilicates
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nesosilicates
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zircon group
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zircon (2)
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Primary terms
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absolute age (5)
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Africa
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Southern Africa
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Kaapvaal Craton (1)
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Lesotho (1)
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South Africa
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Bushveld Complex (1)
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Free State South Africa
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Vredefort Dome (1)
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Gauteng South Africa
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Pretoria South Africa (1)
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KwaZulu-Natal South Africa (1)
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Transvaal region (4)
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asbestos deposits (1)
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Asia
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Indian Peninsula
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India
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Andhra Pradesh India
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Cuddapah Basin (6)
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Nellore mica belt (1)
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Bastar Craton (5)
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Bundelkhand (2)
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Cauvery Basin (1)
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Dharwar Craton (7)
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Ghats
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Eastern Ghats (1)
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Jharkhand India (1)
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Karnataka India
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Chitradurga schist belt (1)
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Closepet Granite (1)
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Pranhita-Godavari Valley (1)
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Rajasthan India
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Aravalli Range (1)
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Singhbhum shear zone (6)
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Southern Granulite Terrain (2)
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Trans-Aravalli Vindhyan Basin (3)
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Vindhyan Basin (2)
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Australasia
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Australia (1)
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barite deposits (1)
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Cenozoic
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Quaternary
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Holocene
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upper Holocene (1)
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crust (3)
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deformation (3)
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diamond deposits (1)
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faults (6)
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folds (1)
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foliation (1)
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gems (1)
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geochemistry (4)
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glacial geology (1)
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igneous rocks
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volcanic rocks
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pyroclastics
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tuff (1)
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inclusions
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fluid inclusions (1)
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intrusions (3)
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limestone deposits (1)
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magmas (2)
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mantle (2)
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Mesozoic
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Jurassic (1)
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Triassic
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Upper Triassic
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Molteno Formation (1)
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metal ores
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chromite ores (1)
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copper ores (2)
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gold ores (1)
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iron ores (1)
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lead ores (1)
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lead-zinc deposits (1)
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manganese ores (1)
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molybdenum ores (1)
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platinum ores (1)
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uranium ores (2)
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zinc ores (1)
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metals
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platinum group
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platinum ores (1)
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rare earths (2)
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metamorphic rocks
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gneisses
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tonalite gneiss (1)
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metasedimentary rocks
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metapelite (1)
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migmatites (1)
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quartzites (1)
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schists (1)
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metamorphism (4)
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mineral deposits, genesis (2)
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North America
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Canadian Shield (1)
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orogeny (3)
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paleogeography (2)
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Paleozoic
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Cambrian (1)
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phosphate deposits (1)
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plate tectonics (3)
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Precambrian
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Archean
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Aravalli System (1)
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Mesoarchean (2)
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Neoarchean
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Dharwar Supergroup (1)
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Sargur Group (1)
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Paleoarchean (2)
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Sausar Series (1)
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Singhbhum Granite (1)
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Bijawar System (1)
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Transvaal Supergroup (4)
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upper Precambrian
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Proterozoic
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Huronian (1)
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Mesoproterozoic (3)
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Neoproterozoic (4)
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Paleoproterozoic
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Rooiberg Group (1)
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Pretoria Group (2)
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Witwatersrand Supergroup (1)
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sea-level changes (3)
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sedimentary petrology (2)
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sedimentary rocks
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carbonate rocks
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limestone (1)
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chemically precipitated rocks
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chert (2)
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iron formations (1)
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clastic rocks
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arenite (1)
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argillite (2)
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arkose (1)
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conglomerate (2)
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mudstone (1)
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orthoquartzite (2)
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porcellanite (1)
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sandstone (7)
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shale (1)
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sedimentary structures
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planar bedding structures
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bedding (1)
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cross-bedding (2)
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sedimentation (13)
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sediments
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clastic sediments
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cobbles (1)
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pebbles (1)
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South America
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Brazil
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Brazilian Shield (1)
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stratigraphy (2)
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tectonics (5)
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weathering (1)
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rock formations
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Beaufort Group (1)
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Elliot Formation (2)
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Karoo Supergroup (1)
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sedimentary rocks
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sedimentary rocks
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carbonate rocks
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limestone (1)
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chemically precipitated rocks
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chert (2)
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iron formations (1)
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clastic rocks
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arenite (1)
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argillite (2)
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arkose (1)
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conglomerate (2)
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mudstone (1)
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orthoquartzite (2)
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porcellanite (1)
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sandstone (7)
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shale (1)
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volcaniclastics (1)
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sedimentary structures
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boudinage (1)
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sedimentary structures
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planar bedding structures
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bedding (1)
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cross-bedding (2)
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sediments
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sediments
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clastic sediments
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cobbles (1)
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pebbles (1)
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volcaniclastics (1)
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Classification of basins, with special reference to Proterozoic examples
Abstract Basin classification rests on a plate tectonic foundation, highlighting lithospheric substrate, proximity to plate margin and relative motion of the nearest plate boundary. Major mechanisms for regional subsidence and uplift are subdivided into isostatic, flexural and dynamic groups. Basin-forming mechanisms and basin types do not exhibit simple cause-and-effect relationships, but rather reflect a matrix-type relationship. Different basin types have different spans of existence, with generally shorter life spans related to more tectonically active settings. Many ‘polyhistory’ basins, composed of two or more megasequences, reflect a long evolution dominated by different basin-forming and basin-modifying mechanisms. The supercontinent cycle is marked by distinct sets of basin types, developed during successive phases of the cycle. Major classification schemes are reviewed briefly, before surveying the range of basin types represented in the Proterozoic of several key cratonic areas. Basins examined encompass almost the entire Neoarchaean–Neoproterozoic period. All of these basins have a relatively long history of preservation, which can be tied to the essentially continental character of their basement rocks and concomitant enhanced ‘survivability’. Their preservation thus underlines the longevity and inherent stability of the continental lithosphere. The distinction between basin occurrence over geological time and preferential preservation is important when viewing the geological record.
Abstract The Precambrian geological history of Peninsular India covers nearly 3.0 Ga. The Peninsula is an assembly of five different cratonic nuclei known as the Aravalli–Bundelkhand, Eastern Dharwar, Western Dharwar, Bastar and Singhbhum cratons along with the Southern Granulite Province. Final amalgamation of these elements occurred either by the end of the Archaean (2.5 Ga) or by the end of the Palaeoproterozoic ( c. 1.6 Ga). Each of these nuclei contains one or more sedimentary basins (or metasedimentary basins) of Proterozoic age. This chapter provides an overview of each of the cratons and a brief description of the Precambrian sedimentary basins in India that form the focus of the remainder of this book. In our view, it appears that basin formation and subsequent closure can be grossly constrained to three separate intervals that also broadly correspond to the assembly and disaggregation of the supercontinents Columbia, Rodinia and Gondwana. The oldest Purana-I basins developed during the 2.5–1.6 Ga interval, Purana-II basins formed during the 1.6–1.0 Ga interval and the Purana-III basins formed during the Neoproterozoic–Cambrian interval.
Abstract The Aravalli Mountains and neighbouring areas have well-preserved records of a protracted history of development of Precambrian basins, which spans about 2500 myr of the Earth’s history. The oldest depositional basins are the greenstone belts that occur within the Archaean gneiss–granite terrain. Geochronological data indicate evolution of one such greenstone belt from 3300 to 2850 Ma. The younger Proterozoic cover successions include the Aravalli Supergroup, Delhi Supergroup and Sirohi Group, which evolved during three successive orogenic cycles spanning between c. 2200 and c. 1850 Ma, c. 1700 and c. 1450 Ma, and c. 1000 and c. 850 Ma, respectively. Each of these lithostratigraphic units evolved in separate basins having distinctive tectonic, metallogenic and evolutionary histories. The inversion of the youngest ‘orogenic’ basin marks the final cratonization of the Precambrian Aravalli crust at around 850 Ma. The succeeding depositional episodes include formation of ephemeral basins during the early phase of the plume-related Malani Group from 780 to 730 Ma, and the formation of the Marwar Supergroup deposited in stable platformal basins marks the terminal phase of the Precambrian crust-building history in the region.
Abstract Overlying Archaean Bundelkhand Granite Gneiss Complex, the Gwalior and Bijawar Groups of rocks represent two Palaeoproterozoic basin successions which, despite their common sediment provenance and analogous rift-related tectonic setup, record more dissimilarity in their sedimentation pattern than similarity. Whereas early sedimentation in the Gwalior Basin is clastic, the early Bijawar sedimentation is dominantly chemogenic (limestone and chert) except for an early, restricted volcano-clastic record. Although both of the basins record syn-depositional volcanic/volcaniclastic event(s) in the form of occurrence of basaltic and basaltic–andesite sills encased within their respective basin fills, the occurrence of iron formation in the later part of Gwalior sedimentation history and its absence in the Bijawar succession is related to variable oxidation conditions in the water columns of the two basins. Rising sea-level and upwelling on the continental margins of these two rift-related basins possibly generated different water chemistries; these allowed the deposition of iron formation in the Gwalior Basin and phosphorite in the Bijawar Basin. Effects of post-depositional digenetic re-crystallization are noticed within both iron formation and phosphorite deposits present in the basin successions.
Abstract This chapter attempts an understanding of the Proterozoic Vindhyan Basin history in the broad framework of central India. Although the entire Vindhyan Supergroup is within the scope of this work, particular attention is paid to the little-known northwestern fringe exposures. Distinctive facies assemblages and diverse palaeocurrents in these exposures of the Lower Vindhyan play a pivotal role in the interpretation. Analysis of outcrop and subsurface data that extend under the Gangetic alluvium to the north of the Vindhyan outcrops further supports the hypothesis that an east–west-elongated basement ridge initially separated the master Vindhyan Basin from smaller contemporary basins to the north. Deposition took place in isolated lacustrine and fluvial basins north of the divide and largely in a marine realm south. Dextral shear accompanying rifting generated ridges that criss-crossed the Lower Vindhyan seafloor to the south. The uniform character of the Upper Vindhyan throughout, nevertheless, testifies to later drowning of the divide and unification of all of the basins as a consequence of regional tilt northward. However, the extended Vindhyan Sea was restricted by a second east–west-elongated ridge from merger with the contemporary Proterozoic sea further north, disparate sediments of which have been encountered in a few drill cores only.
Abstract The Older Metamorphic Group and the Older Metamorphic Tonalite Gneiss are classic examples of Palaeaoarchaean high-grade metamorphic rocks of the Singhbhum Craton of India. The Older Metamorphic Group is a supracrustal assemblage that was probably deposited as a greenstone belt-type succession before c. 3.32 Ga, the low-grade equivalents of which are found in parts of the Iron Ore Group. The Older Metamorphic Tonalite Gneiss represents a suite of granitoids that are tectonically interleaved with the supracrustal gneisses and that formed over an extended period of time, 3.53–3.45 Ga and possibly later, by processes of Archaean crustal growth.
Archaean sedimentation on the Singhbhum Craton: depositional environments of conglomerates in Jharkhand (east India)
Abstract Archaean to Palaeoproterozoic metasediments overlie the Archaean granitoid pluton of the Singhbhum Craton in east India. Relatively little is known about the Archaean metasediments, but they comprise several conglomerates in the state of Jharkhand. Their age is most probably Mesoarchaean, possibly earliest Neoarchaean. They occur at separate localities and their exposures commonly consist of scattered patches with a limited extent. Their interrelationships are consequently poorly known. Sedimentological analysis of their structure, architecture and clast composition suggests that most of them represent individual occurrences that partly have been largely eroded away. Other occurrences must have had a limited extent from the very beginning. The various conglomerates were deposited in different environments. Some represent braided or meandering fluvial environments, whereas others seem to have been deposited by mass flows with different degrees of viscosity, possibly mainly on alluvial fans.
Abstract The Singhbhum Craton preserves large low-grade tracts of an extensive stratigraphic period in the Precambrian and therefore is of prime importance for studying the Earth’s early evolutionary processes. An early ( c. 3.1 Ga) crustal stabilization followed by a long period ( c. 500 Ma) of high freeboard conditions has been postulated from the terrane in recent times. Tectonostratigraphic analyses of the supracrustal successions, carried out in the present study, from the west-northwestern margin of the Singhbhum Granite body in the craton identify a hitherto undetected Mesoarchaean shelf sequence among these supracrustal successions. In contrast to current thinking, the observations imply immediate development of a passive margin setting following the craton’s early stabilization. The cratonic margin later succumbed to a major compression, resulting in successive emplacement of thrust sheets from the northern hinterland side that produced an intermingling of thrust slices of basement rocks and the deformed shelf and rift sequences. This later compressive episode not only involved a part of the Mesoproterozoic Kolhan Basin, but its effects are also manifest as a second deformation throughout the western Iron Ore Group belt. Involvement of the Kolhan Group in the deformation milieu constrains the timing of this orogeny to the Grenvillian ( c. 1.0 Ga).
Abstract The Singhbhum Craton in eastern India preserves a depositional record from the Palaeo-Mesoarchaean to the Mesoproterozoic. Herein, we have summarized the Palaeo-Mesoproterozoic supracrustal record of the Singhbhum Craton, discussed tectonosedimentary processes and discriminated Palaeo-Mesoproterozoic global and craton-specific events. The late Palaeo-Mesoproterozoic supracrustal record of the Singhbhum Craton is limited. It includes evidence for high continental freeboard conditions during 2.6–2.1 Ga in the form of terrestrial deposits (alluvial fan–fluvial) of the Dhanjori Formation. This was followed by a major transgression and a transition to the relatively deeper-water shelf to shallow intertidal environments recorded by the Chaibasa Formation. A long hiatus ensued before deposition of the Dhalbhum Formation and conformably overlying Dalma and Chandil formations, suggesting continued high continental freeboard during 2.2–1.6 Ga. In significant contrast to the craton-specific Dhanjori Formation volcanism, the 1.7–1.6 Ga plume-related Dalma volcanism was probably part of a global tectonothermal event.
Palaeoproterozoic supracrustals of the Bastar Craton: Dongargarh Supergroup and Sausar Group
Abstract The Bastar Craton of India is composed of Archaean nuclei of tonalite–trondhjemite–granodiorite gneisses, enveloped by an older granite–greenstone belt (>3000 Ma) with banded iron formation (BIF), and an auriferous younger granite–greenstone belt with BIF. Available geological, geochemical and geochronological data indicate multiple episodes of orogeny with high-grade metamorphism at 3200–3300, 2600–2700, 2100–2200, 1900–2000, 1800–1850, 1500–1600 and 1400–1450 Ma, and continental rifting and basin development marked by emplacement of mafic dyke swarms at c. 2900 (subalkaline mafic dykes; BD-1A), 2480 (high-Mg mafic dykes; BD-1B), 2100 (Fe–tholeiite dykes; BD-2A), 1880 (Fe–tholeiites dykes; BD-2B), 1776 and 1422 Ma. Associations of extensive bimodal volcanics and riftogenic sediments are found in the Neoarchaean and Palaeoproterozoic basins of the craton. Evidence of Palaeoproterozoic (Huronian) glaciation and associated ‘cap carbonate’ followed by deposition of fine clastics with manganese ore is found in the Palaeoproterozoic Sausar Group. The lithological association of the Sausar Group is comparable to the carbonate–tillite association of the Huronian Supergroup, Snowy Pass Supergroup, Transvaal Supergroup and Turee Creek Group. The geological evolution of the Bastar Craton matches that of Western Australia and South Africa. Such similarities can be analysed to develop a unified Palaeoproterozoic assembly for these provinces.
Abstract Understanding of the incompatibility of King’s three-fold classification of the Proterozoic (‘Purana’) rocks of the Pranhita–Godavari Valley, south India, and renewed mapping and stratigraphic studies, reveal that syn-depositional basin dynamics, with differential uplift and subsidence, was the major control on basin evolution and the development of multiple unconformity-bound successions. The unconformities demarcate six major successions, the Mallampalli/Devalmari, Somanpalli, Mulug, Penganga, Albaka and Sullavai groups, each with a very distinctive set of sedimentological attributes. There are at least five different conflicting classification schemes so far. The major problems in the classification of the succession appear to lie in the recognition of unconformities and unconformity-bound successions, and in stratigraphic nomenclature. Based on field geology, available age data and the concept of the megasequence, the Mallampali, Devalmari, Mulug and Somanpalli groups have been grouped into the Pakhal Supergroup. The question of combining the rest of the groups has been deferred until the resolution of the Albaka–Penganga relationship is achieved beyond doubt. The relationships between different stratigraphic units have been critically examined to reconstruct the stratigraphic history, events of sea-level change and palaeogeographical evolution.
Geology of Mesoproterozoic Chhattisgarh Basin, central India: current status and future goals
Abstract In the last two decades multiproxy studies involving process-based sedimentology, geochronology of interbedded tuff units from different stratigraphic levels, sediment geochemistry including stable isotope signatures and documentation of structural grains within selective stratigraphic intervals from the Chhattisgarh Basin, central India have resulted in a perception change on various aspects of the basin fill including its time frame, stratigraphic framework and depositional architecture in the space–time domain. In addition to establishing a Mesoproterozoic ( c. 1450–1000 Ma) time frame for the basin on a strong foothold, these studies also proposed revision of its stratigraphy by introducing new stratigraphic units at ‘formation’ and ‘group’ level. From collation of available data, their critical evaluation and presentation of new data, the present work proposes a four-tier lithostratigraphy for the Chhattisgarh Supergroup, namely, Singhora Group, Chadarpur Group, Raipur Group and Kharsiya Group. Further, application of sequence stratigraphic rationale allowed the basin succession to be subdivided into four and three nonconformity/unconformity-bound depositional sequences in its eastern and western parts, respectively. The present chapter also highlights the potential of the basin for carrying out studies related to Mesoproterozoic ocean oxygenation and outlines the necessity of well-planned geophysical transects to resolve issues related to tectonic setup of the basin.
Abstract New geochronological and geochemical data from bedded porcellanitic tuffs present within two sedimentary basins at the eastern fringe of the Archaean Bastar Craton, eastern India (the Ampani and Khariar basins) are presented and compared with data available from tuffaceous beds present within adjoining basins. U–Th–total Pb electron probe microanalysis data of monazite grains from the Ampani tuff revealed several age data clusters: c. 2400, c. 2130, c. 1600, c. 1450 and c. 1000 Ma. An age of 1446±21 Ma is proposed as the depositional/crystallization age for the Ampani tuff, considering its maximum probability. Comparable ages for the tuffaceous units from the Khariar (1455±47 Ma) and Singhora ( c. 1500 Ma) basins allow us to infer a major felsic volcanic event during c. 1450 Ma at the eastern margin of the Indian Craton. Detailed geochemical data suggest rhyolite to andesite character for the siliceous tuff units from three geographically separated basins and point towards the presence of an active volcanic arc in a subduction-related setting in the region. The geochronological and geochemical data prompted us to search for other contemporaneous events in the Indian continent and beyond, that is, within its erstwhile neighbours in the Precambrian supercontinent ‘Columbia’.
Abstract The geology and basin evolutionary history of the Dharwar Craton is discussed. The Dharwar Craton comprises western (WDC) and eastern (EDC) subdivisions (possibly separated by the Closepet granite), predicated on lithological contrasts and inferred metamorphic and magmatic evolution. A postulated genesis of the WDC comprises early, c. 3.5 Ga protocrust, which possibly formed as basement to the c. 3.35–3.2 Ga Sargur Group greenstone belts. The latter are thought to have formed through accretion of plume-related ocean plateaux. The approximately coeval Peninsular Gneiss Complex possibly originated from beneath plateau remnants, leading to metamorphism of Sargur Group belts at c. 3.13–2.96 Ga. At c. 2.9–2.6 Ga, the Dharwar Supergroup, comprising lower Bababudan (mainly braided fluvial, glaciomarine and subaerial volcanic strata) and upper Chitradurga (marine clastic, chemical sedimentary and subaqueous volcanic rocks) groups developed. This supergroup formed younger greenstone belts characterized by two distinct magmatic events, at 2.7–2.6 and 2.58–2.54 Ga; the latter was approximately coeval with c. 2.6–2.5 Ga granitic magmatism, which marked final cratonization of the WDC. The EDC consists of 2.7–2.55 Ga tonalite–trondhjemite–granodiorite gneisses and migmatites, essentially coeval greenstone belts (mainly volcanic lithologies), with minor inferred remnants of an older, c. 3.38–3.0 Ga crust, and voluminous 2.56–2.5 Ga granitoids (including the Closepet). An east–west accretion of EDC island arcs (or possibly of an assembled arc-granitic terrane) on to the WDC is postulated, and the Closepet granite perhaps accreted earlier on to the WDC to form a ‘central Dharwar’ terrane. A final voluminous granitic cratonization event affected the assembled Dharwar Craton at c. 2.5 Ga.
Tectonics of the Cuddapah Basin and a model of its evolution: a review
Abstract The Proterozoic Cuddapah Basin of south India is one of the most important Purana basins of Peninsular India. It hosts the Cuddapah Supergroup and the Kurnool Group of rocks. The structure of the Cuddapah Basin reveals that it forms the frontal part of a larger fold–thrust belt, named the Cuddapah fold–thrust belt (CFTB). The CFTB formed in response to the amalgamation of the Prince Charles Mountains–Rayner Complex of Antarctica with the Krishna province of India during the formation of the Rodinia Supercontinent. The CFTB, bounded by the Nellore–Khammam schist belt and Eastern Ghats terrane in the east and Peninsular Gneissic complex of the Dharwar Craton to the west, includes two frontal thrusts and foreland of an orogen. The frontal Nallamalai thrust structurally separates the basin into two blocks – the eastern Nallamalai fold belt and the western foreland. A model of evolution of the CFTB has been proposed. The CFTB, forming the front-most segment of a larger orogen associated with the intercratonic deformation related to the formation of the Rodinia Supercontinent, is the result of fault-propagation folding, forming an overturned anticline–syncline pair at the tip of the propagating Velikonda thrust which later cuts through the common limb of the fold pair.
Sedimentation in the Papaghni Group of rocks in the Papaghni sub-basin of the Proterozoic Cuddapah Basin, India
Abstract The Gulcheru Quartzite (30–200 m thick) overlies Archaean basement rocks, and comprises an impersistent conglomerate at the base of more widespread quartzites, with shale and ferruginous interbeds. The overlying Vempalle Formation (≤1500 m) comprises mainly stromatolitic carbonates, lesser cherts and mudrocks. Together, these two units make up the Palaeoproterozoic Papaghni Group, which displays an arcuate outcrop belt in the SW Cuddapah Basin, bearing no obvious relationship to the tectonic grain in the basement lithologies. Facies defined in the Gulcheru Quartzite are ascribed to initial alluvial fans, which transitioned into a shallow-marine coastline and shelf, as transgression occurred under overall thermal subsidence, possibly related to post-plume thermal relaxation. The shallow siliciclastic Gulcheru shelf is inferred to have evolved to a stromatolitic ramp that accommodated deposition of the Vempalle chemical sediments. The abrupt vertical transition from clastic to carbonate deposits is ascribed to rapid sea-level rise. Late-stage shoreline progradation during uppermost Vempalle times and concomitant clastic inflows terminated the carbonate factory.
Tectonostratigraphic evolution of the Nellore schist belt, southern India, since the Neoarchaean
Abstract Tectonostratigraphic development of the c. 300 km-long Nellore schist belt (NSB) of southern India is described in relation to the post-Neoarchaean growth of the Dharwar cratonic nucleus. Lying along the eastern margin of the Dharwar cratonic nucleus, the NSB comprises several geologically and geochemically distinct tracts of deformed Palaeoproterozoic to Mesoproterozoic volcanosedimentary successions: the Vinjamuru Group, the Kandra ophiolite complex (KOC), the Kanigiri ophiolitic melange (KOM) and the Udaigiri Group, arranged in relative order of younging. The high-grade Eastern Ghats belt occurs further to the east of the NSB with a tectonic contact. Thrust-transported oceanic crust remnants occur in the 1.9 Ga KOC, 1.34 Ga KOM, and the Vinjamuru Group, which show multiple deformation, amphibolite facies metamorphism and granitic intrusions. The available geological, geochemical and geochronological data have been examined to tentatively constrain the relative age of the different tectonostratigraphic units of the NSB, tectonic juxtaposition and implications in relation to global events in the Proterozoic. Subduction-related ocean closures outboard and east of the Dharwar Craton, evidenced by the KOC and KOM, possibly had links with the assembly of Columbia and its final dispersal, respectively.
Geological history of the Kaladgi–Badami and Bhima basins, south India: sedimentation in a Proterozoic intracratonic setup
Abstract The Proterozoic Kaladgi–Badami and Bhima basins are intracratonic basins occurring over the Archaean Dharwar craton. The Kaladgi–Badami Basin contains arenites, shales and carbonates with minor cherts and conglomerates deposited in continental, transitional and shallow-marine environments presumably during the late Palaeoproterozoic/Mesoproterozoic to Neoproterozoic. The lower part of the succession (Bagalkot Group) is deformed into east–west-trending elongated doubly plunging synclines and anticlines. The upper part of the succession (Badami Group) is undeformed and unconformably overlies the lower part. The evolution of the Kaladgi–Badami Basin was controlled by movements along east–west-trending normal faults under an extensional stress regime. The Bhima Basin hosts mainly limestones with subordinate arenites and shales deposited in fluvial, deltaic and tidal flat environments possibly during the Neoproterozoic. These sediments are undeformed except along faults with significant strike-slip components. The basin is exposed in narrow strips arranged in an en echelon pattern and appears to be a pull-apart basin. Inadequate data exist on the age of the basin fills, the deep basinal architecture, subsidence history and tectonic controls for both of the basins. Future research may be directed towards these aspects which will have wide implications for understanding intracratonic basin formation, reconstructing Proterozoic supercontinents and studying the evolution of the atmosphere and primitive life forms.