Dissolution of fluorite(CaF2)and/or fluorapatite(FAP)[Cas(PO4)3F],pulled by calcite precipitation,is thought to be the dominant mechanism responsible for groundwater fluoride(F)contamination.Here,one dimensional react...Dissolution of fluorite(CaF2)and/or fluorapatite(FAP)[Cas(PO4)3F],pulled by calcite precipitation,is thought to be the dominant mechanism responsible for groundwater fluoride(F)contamination.Here,one dimensional reactive-transport models are developed to test this mechanism using the published dissolution and precipitation rate kinetics for the mineral pair FAP and calcite.Simulation results correctly show positive correlation between the aqueous concentrations of F and CO_(2)and negative correlation between F-and Ca^2+.Results also show that precipitation of calcite,contrary to the present understanding,slows down the FAP dissolution by 10G orders of magnitude compared to the FAP dissolution by hydrolysis.For appreciable amount of fluoride contamination rock-water interaction time must be long and of order 106 years.展开更多
Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic ...Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence （LHS） of Eastern Himalaya, namely the Daling Group in Sikkim and the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite- slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. Multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic-Mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. Kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here： （1） the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; （2） the older deformation and metamorphism relate to a Pacific type accretionary orogen which affected the northern margin of greater India. Better understanding of geodynamic evolution of the northern margin of India in the Paleoproterozoic has additional bearing on more refined model of reconstruction of Colllrnhia.展开更多
The Palaeoproterozoic-Mesoproterozoic transition （ -1600 Ma） is a significant event in the Earth history as a global thermal perturbation affected the pre-1600 Ma landmasses. Like other cratonic blocks of the world,...The Palaeoproterozoic-Mesoproterozoic transition （ -1600 Ma） is a significant event in the Earth history as a global thermal perturbation affected the pre-1600 Ma landmasses. Like other cratonic blocks of the world, lithospheric thinning, sedimentation, magmatism, metamorphism and crustal melting/anatexis are associated with this significant geological event in the Singhbhum cratonic province of India. This paper is a review of sedimentological, magmatic and tectono-thermal events in the Singhbhum craton at 1600 Ma. The Palaeo-Mesoproterozoic sedimentation and volcanism in the Singhbhum craton took place in a terrestrial intracontinental rift setting. The available geochronological data are indicative of late Palaeoproterozoic to Neoproterozoic tectono-thermal events in the Chhotanagpur Granite Gneissic Complex （CGGC）, an east-west trending arcuate belt of granite gneisses, migmatites and metasedi- mentary rocks. A detailed multidisciplinary geo-scientific investigation of the Dalma volcanic belt and the area to its north （Chandil Formation） and further north in CGGC will enable us to constrain the extant surface processes and crust-mantle interactions, the collision events between the North and South Indian cratonic blocks, and the position of India in the Columbia supercontinent.展开更多
A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave bas...A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave base, have rheomorphie features indicative of viscoplastic flow, and geochem- ical signatures of rhyolitic to rhyodacitic unwelded to welded tufts, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag- matic reactions. The widespread and repeated occurrences of felsic tufts in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.展开更多
Equisetum(Equisetaceae)has long been a focus of attention for botanists and palaeontologists because,given its extensive and well-documented fossil record,it is considered the oldest extant vascular plant and a key el...Equisetum(Equisetaceae)has long been a focus of attention for botanists and palaeontologists because,given its extensive and well-documented fossil record,it is considered the oldest extant vascular plant and a key element in understanding vascular plant evolution.However,to date,no authentic fossil evidence of Equisetum has been found from the Indian Cenozoic.Here,we describe a new fossil species,namely,E.siwalikum sp.nov.,recovered from the middle Siwalik(Late Miocene)sediments of Himachal Pradesh,western Himalaya.We identified fossil specimens based on morphological and epidermal characters.In addition,X-Ray diffraction(XRD)analysis was used to determine the mineral composition of compressed stems of Equisetum.The close affinity of our recovered Siwalik fossils to Equisetum is supported by the presence of both macromorphological and epidermal characters.Because Equisetum generally grows in wet conditions around water reservoirs,our findings indicate that the fossil locality was humid and surrounded by swamp and lowland regions during deposition.Ample fossil evidence indicates that this sphenopsid once existed in the western Himalaya during the Siwalik period.However,at present Equisetum is confined to a particular area of our fossil locality,probably a consequence of severe environmental changes coupled with competition from opportunistic angiosperms.Our discovery of Equisetum fossils in appreciable numbers from the Siwalik sediments of the Himachal Himalayas is unique and constitutes the first reliable recognition of Equisetum from the Indian Cenozoic.展开更多
The Pranhita-Godavari Basin in central eastern India is one of the Proterozoic ＂Purana＂ basins of cratonic India. New geochronology demonstrates that it has a vast depositional history of repeated basin reactivation...The Pranhita-Godavari Basin in central eastern India is one of the Proterozoic ＂Purana＂ basins of cratonic India. New geochronology demonstrates that it has a vast depositional history of repeated basin reactivation from the Palaeoproterozoic to the Mesozoic. U-Pb laser ablation inductively coupled plasma mass spectrometry dating of detrital zircons from two samples of the Somanpalli Group--a member of the oldest sedimentary cycle in the valley--constrains its depositional age to - 1620 Ma and demonstrates a tripartite age provenance with peaks at - 3500 Ma, - 2480 Ma and - 1620 Ma, with minor age peaks in the Eoarchaean （ - 3.8 Ga） and at - 2750 Ma. These ages are consistent with palaeocurrent data suggesting a southerly source from the Krishna Province and Enderby Land in East Antarctica. The similarity in the maximum depositional age with previously published autbigenic glauconite ages suggest that the origin of the Pranhita-Godvari Graben originated as a rift that formed at a high angle to the coeval evolving late Meosproterozoic Krishna Province as Enderby Land collided with the Dharwar craton of India. In contrast, detrital zircons from the Cycle III Sullavai Group red sandstones yielded a maximum depositional age of 970 - 20 Ma and had age peaks of -2550 Ma, -1600 Ma and then a number of Mesoproterozoic detrital zircons terminating in three analyses at - 970 Ma. The provenance of these is again consistent with a southerly source from the Eastern Ghats Orogen and Antarctica. Later cycles of deposition include the overlying Albaka/Usur Formations and finally the late Palaeozoic to Mesozoic Gondwana Supergroup.展开更多
The Southern Granulite Terrane(Dharwar Craton),South India,is a key unit for understanding the origin of charnockite.New U-Pb and Lu-Hf analyses in zircon crys-tals from 16 samples representing a wide variety of litho...The Southern Granulite Terrane(Dharwar Craton),South India,is a key unit for understanding the origin of charnockite.New U-Pb and Lu-Hf analyses in zircon crys-tals from 16 samples representing a wide variety of litho-types from the quarries in Kabbaldurga reveal a complex geological history in the Archean and early Paleoprotero-zoic.Magmatic protoliths predominantly record Paleoar-chean ages between 3.4 and 3.2 Ga.Combined U-Pb and Lu-Hf signatures indicate a history of recurrent crustal anatexis,juvenile magmatic input,and felsic injections.Mesoarchaean magmatic charnockites were generated mainly from hornblende-dehydration melting of Paleoar-chaean mafic rocks.In addition,Peninsular Gneissic Com-plex of the Dharwar Craton,commonly described as TTG suites,are likely generated by melting of hydrated basalt.The new data are consistent with the idea of a convecting magmatic cycle and also support the proposal that the southern Dharwar Craton comprises a tilted cross-sec-tion through the Archaean crust.Paleoproterozoic high-temperature event is documented here as a complex unit involving juvenile mafic magmatism,granulite facies imprints and crustal anatexis as well as felsic injections,occurring within a short time period around 2.5 Ga.展开更多
26-28 August,2011,Hyderabad,India As part of its Golden Jubilee Celebrations,the National Geophysical Research Institute(NGRI)and the Council of Scientific and Industrial Research(CSIR),India,organized the 2011 annual...26-28 August,2011,Hyderabad,India As part of its Golden Jubilee Celebrations,the National Geophysical Research Institute(NGRI)and the Council of Scientific and Industrial Research(CSIR),India,organized the 2011 annual convention of the International Association of Gondwana Research(IAGR),and the 8^(th) International Symposium on Gondwana to Asia at Hyderabad under the major theme“Super Continent Dynamics:India and Gondwana”during August 26-28,2011.展开更多
The twelve Gondwanan stratigraphic horizons of India have yielded varied vertebrate fossils.The oldest fossil record is the Endothiodon-dominated multitaxic Kundaram fauna,which correlates the Kundaram Formation with ...The twelve Gondwanan stratigraphic horizons of India have yielded varied vertebrate fossils.The oldest fossil record is the Endothiodon-dominated multitaxic Kundaram fauna,which correlates the Kundaram Formation with several other coeval Late Permian horizons of South Africa,Zambia,Tanzania,Mozambique,Malawi,Madagascar and Brazil.The Permian-Triassic transition in India is marked by distinct taxonomic shift and faunal characteristics and represented by small-sized holdover fauna of the Early Triassic Panchet and Kamthi fauna.展开更多
文摘Dissolution of fluorite(CaF2)and/or fluorapatite(FAP)[Cas(PO4)3F],pulled by calcite precipitation,is thought to be the dominant mechanism responsible for groundwater fluoride(F)contamination.Here,one dimensional reactive-transport models are developed to test this mechanism using the published dissolution and precipitation rate kinetics for the mineral pair FAP and calcite.Simulation results correctly show positive correlation between the aqueous concentrations of F and CO_(2)and negative correlation between F-and Ca^2+.Results also show that precipitation of calcite,contrary to the present understanding,slows down the FAP dissolution by 10G orders of magnitude compared to the FAP dissolution by hydrolysis.For appreciable amount of fluoride contamination rock-water interaction time must be long and of order 106 years.
文摘Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence （LHS） of Eastern Himalaya, namely the Daling Group in Sikkim and the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite- slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. Multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic-Mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. Kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here： （1） the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; （2） the older deformation and metamorphism relate to a Pacific type accretionary orogen which affected the northern margin of greater India. Better understanding of geodynamic evolution of the northern margin of India in the Paleoproterozoic has additional bearing on more refined model of reconstruction of Colllrnhia.
基金Financial support for this research came from the Department of Science and Technology,Government oF India(to RM,SD and PC)the Yokohama National University,Japan(to MR and MA)the School of Biology,Earth and Environmental Sciences.the University of New South Wales,Australia(to RM)
文摘The Palaeoproterozoic-Mesoproterozoic transition （ -1600 Ma） is a significant event in the Earth history as a global thermal perturbation affected the pre-1600 Ma landmasses. Like other cratonic blocks of the world, lithospheric thinning, sedimentation, magmatism, metamorphism and crustal melting/anatexis are associated with this significant geological event in the Singhbhum cratonic province of India. This paper is a review of sedimentological, magmatic and tectono-thermal events in the Singhbhum craton at 1600 Ma. The Palaeo-Mesoproterozoic sedimentation and volcanism in the Singhbhum craton took place in a terrestrial intracontinental rift setting. The available geochronological data are indicative of late Palaeoproterozoic to Neoproterozoic tectono-thermal events in the Chhotanagpur Granite Gneissic Complex （CGGC）, an east-west trending arcuate belt of granite gneisses, migmatites and metasedi- mentary rocks. A detailed multidisciplinary geo-scientific investigation of the Dalma volcanic belt and the area to its north （Chandil Formation） and further north in CGGC will enable us to constrain the extant surface processes and crust-mantle interactions, the collision events between the North and South Indian cratonic blocks, and the position of India in the Columbia supercontinent.
基金supported by the Indian Statistical Institute(ISI), Kolkata in the form of several research grants to DS during the past decadeVT acknowledges a senior research fellowship granted by ISI during the initial stage of the worka DST grant(SR/S4/ES-307/2007) which partly supported this work
文摘A first report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented. The rhyolitic to rhodacitic tufts, overlying shelfal limestones formed at depths below storm wave base, have rheomorphie features indicative of viscoplastic flow, and geochem- ical signatures of rhyolitic to rhyodacitic unwelded to welded tufts, similar to those described from other Proterozoic intracratonic basins like Vindhyan and Chhattisgarh basins in India. Fragmentary nature of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomag- matic reactions. The widespread and repeated occurrences of felsic tufts in these basins, possibly derived from low degree melting of continental crust, suggest intermittent tectonothermal instability which likely influenced basinal topography and cyclic development of the carbonate platforms.
基金DST-SERB,GOI,New Delhi,India(File no.CRG/2020/001303)for their financial assistance。
文摘Equisetum(Equisetaceae)has long been a focus of attention for botanists and palaeontologists because,given its extensive and well-documented fossil record,it is considered the oldest extant vascular plant and a key element in understanding vascular plant evolution.However,to date,no authentic fossil evidence of Equisetum has been found from the Indian Cenozoic.Here,we describe a new fossil species,namely,E.siwalikum sp.nov.,recovered from the middle Siwalik(Late Miocene)sediments of Himachal Pradesh,western Himalaya.We identified fossil specimens based on morphological and epidermal characters.In addition,X-Ray diffraction(XRD)analysis was used to determine the mineral composition of compressed stems of Equisetum.The close affinity of our recovered Siwalik fossils to Equisetum is supported by the presence of both macromorphological and epidermal characters.Because Equisetum generally grows in wet conditions around water reservoirs,our findings indicate that the fossil locality was humid and surrounded by swamp and lowland regions during deposition.Ample fossil evidence indicates that this sphenopsid once existed in the western Himalaya during the Siwalik period.However,at present Equisetum is confined to a particular area of our fossil locality,probably a consequence of severe environmental changes coupled with competition from opportunistic angiosperms.Our discovery of Equisetum fossils in appreciable numbers from the Siwalik sediments of the Himachal Himalayas is unique and constitutes the first reliable recognition of Equisetum from the Indian Cenozoic.
基金initiated with the financial support of the Indian Statistical Institute,Kolkata,and was developed to completion with the financial support extended to AKC by the Council of Scientific and Industrial Research,Government of India to work as an Emeritus Scientist (Grant No.21(0578)/03/EMR-Ⅱ)Department of Science and Technology,Government of India under the research project on a DST-funded project(Grant No.SR/S4/ES-210/2006)+1 种基金funded by Australian Research Council grant #FT120100340Australia-India Strategic Research Fund project #ST030046.ASC and UA's contributions form TRaX Record #289
文摘The Pranhita-Godavari Basin in central eastern India is one of the Proterozoic ＂Purana＂ basins of cratonic India. New geochronology demonstrates that it has a vast depositional history of repeated basin reactivation from the Palaeoproterozoic to the Mesozoic. U-Pb laser ablation inductively coupled plasma mass spectrometry dating of detrital zircons from two samples of the Somanpalli Group--a member of the oldest sedimentary cycle in the valley--constrains its depositional age to - 1620 Ma and demonstrates a tripartite age provenance with peaks at - 3500 Ma, - 2480 Ma and - 1620 Ma, with minor age peaks in the Eoarchaean （ - 3.8 Ga） and at - 2750 Ma. These ages are consistent with palaeocurrent data suggesting a southerly source from the Krishna Province and Enderby Land in East Antarctica. The similarity in the maximum depositional age with previously published autbigenic glauconite ages suggest that the origin of the Pranhita-Godvari Graben originated as a rift that formed at a high angle to the coeval evolving late Meosproterozoic Krishna Province as Enderby Land collided with the Dharwar craton of India. In contrast, detrital zircons from the Cycle III Sullavai Group red sandstones yielded a maximum depositional age of 970 - 20 Ma and had age peaks of -2550 Ma, -1600 Ma and then a number of Mesoproterozoic detrital zircons terminating in three analyses at - 970 Ma. The provenance of these is again consistent with a southerly source from the Eastern Ghats Orogen and Antarctica. Later cycles of deposition include the overlying Albaka/Usur Formations and finally the late Palaeozoic to Mesozoic Gondwana Supergroup.
基金funded by the India-Brazil bilateral co-operation Project:INT/BRAZIL/P-02/2013by Indian Statistical Institute,Geoscience Institute of São Paulo University,Brazil and Department of Geology,University of Calcutta.M.Hueck thanks FAPESP for a post-doctoral fellowship(grant 2019/06838-2).
文摘The Southern Granulite Terrane(Dharwar Craton),South India,is a key unit for understanding the origin of charnockite.New U-Pb and Lu-Hf analyses in zircon crys-tals from 16 samples representing a wide variety of litho-types from the quarries in Kabbaldurga reveal a complex geological history in the Archean and early Paleoprotero-zoic.Magmatic protoliths predominantly record Paleoar-chean ages between 3.4 and 3.2 Ga.Combined U-Pb and Lu-Hf signatures indicate a history of recurrent crustal anatexis,juvenile magmatic input,and felsic injections.Mesoarchaean magmatic charnockites were generated mainly from hornblende-dehydration melting of Paleoar-chaean mafic rocks.In addition,Peninsular Gneissic Com-plex of the Dharwar Craton,commonly described as TTG suites,are likely generated by melting of hydrated basalt.The new data are consistent with the idea of a convecting magmatic cycle and also support the proposal that the southern Dharwar Craton comprises a tilted cross-sec-tion through the Archaean crust.Paleoproterozoic high-temperature event is documented here as a complex unit involving juvenile mafic magmatism,granulite facies imprints and crustal anatexis as well as felsic injections,occurring within a short time period around 2.5 Ga.
文摘26-28 August,2011,Hyderabad,India As part of its Golden Jubilee Celebrations,the National Geophysical Research Institute(NGRI)and the Council of Scientific and Industrial Research(CSIR),India,organized the 2011 annual convention of the International Association of Gondwana Research(IAGR),and the 8^(th) International Symposium on Gondwana to Asia at Hyderabad under the major theme“Super Continent Dynamics:India and Gondwana”during August 26-28,2011.
文摘The twelve Gondwanan stratigraphic horizons of India have yielded varied vertebrate fossils.The oldest fossil record is the Endothiodon-dominated multitaxic Kundaram fauna,which correlates the Kundaram Formation with several other coeval Late Permian horizons of South Africa,Zambia,Tanzania,Mozambique,Malawi,Madagascar and Brazil.The Permian-Triassic transition in India is marked by distinct taxonomic shift and faunal characteristics and represented by small-sized holdover fauna of the Early Triassic Panchet and Kamthi fauna.
