The lithium potential in the Aïr massif is represented by mineral index of spodumene pegmatites and, lepidolite pegmatites. The mineral deposits of lithium occur in cluster or veins that cut the host rock or are ...The lithium potential in the Aïr massif is represented by mineral index of spodumene pegmatites and, lepidolite pegmatites. The mineral deposits of lithium occur in cluster or veins that cut the host rock or are located near the contact between the greenstone belt and granitic massif. The evidence of lithium is in the form of clusters or disseminated and stockwerk. Mineralogical characteristics show similarities between the Air Massif pegmatites and indicate the same homogenous source during the magma-generation process. The pegmatite rocks attracted the attention due to their wide exposure and composition, well appearance, and economically hosting of significant rare earth metals such as Sn and W. The mineralogical and petrographical investigations on the eight pegmatites rocks samples observed have a relative similarity, while a little difference in the shapes attributed to the ratio in the pegmatite rocks of the minerals. The occurrence of the kink band indicates the influence of the tectonic processes which affected the Aïr massif after the emplacement of late magmatic or post-magmatic pegmatites by injection into fractured rocks in the upper part of the crust. The Air Massif pegmatite has higher concentrations Li and of all trace elements except Hf and occasionally Zr, Ti, Sn and Mg of for the economic exploration.展开更多
The hydrochemical characterization and irrigation suitability assessment of the GangesBrahmaputra River System(GBRS)has immense importance for the livelihoods of people and ecosystem sustainability in the region.This ...The hydrochemical characterization and irrigation suitability assessment of the GangesBrahmaputra River System(GBRS)has immense importance for the livelihoods of people and ecosystem sustainability in the region.This study aims to assess the hydrochemical characteristics and evaluate the irrigation suitability of water in the GBRS by reviewing published literature of the major tributaries.The studied rivers were categorized into two groups namely Group-1 and Group-2 considering the similarities of climatic patterns,hydrochemical attributes,and drainage characteristics.The hydrochemistry of the river water was characterized by the Piper diagram,Gibbs plot,mixing plots,and ionic ratios.Furthermore,irrigation water qualities were evaluated by electrical conductivity(EC),sodium percentage(Na%),sodium adsorption ratio(SAR),magnesium hazard(MH),and Wilcox diagram.The results indicated that the hydrochemistry of the GBRS was slightly alkaline to alkaline(7.42-8.78)in nature.The average concentrations of most of the chemical attributes showed higher in Group-1,whereas the average concentrations of K^(+) and NO_(3)^(-) were found higher in Group-2.The average concentration of the major ions followed the dominancy order Ca^(2+)>Mg^(2+)>Na^(+)>K^(+) for cations and HCO_(3)^(-)>SO_(4)^(2-)>Cl^(-)>NO_(3)^(-) for anions in both groups.Gibbs plot and mixing plot indicated that carbonate rock weathering dominates the hydrochemical process,which was further confirmed by the Piper diagram and the ionic ratios.From the analyses of irrigational water quality,almost all the rivers(except Gomti River in terms of MH and Rangit River in terms of Na%)in the GBRS were found to be suitable based on EC,SAR,Na%,MH,and Wilcox diagram.Finally,the majority of river systems in the GBRS were characterized by carbonate dominated lithology and irrigational water quality is mostly suitable for utilization.This study could be useful for water quality management in the glacial-fed Himalayan river under the context of global climate change.展开更多
The basement granite gneisses from the north-central Aravalli Craton in NW India were investigated for geochemistry and geochronology.In a peneplain terrain,the granite gneiss outcrops are scanty and samples were coll...The basement granite gneisses from the north-central Aravalli Craton in NW India were investigated for geochemistry and geochronology.In a peneplain terrain,the granite gneiss outcrops are scanty and samples were collected mainly from two small hills and several ground-level exposures in the Sakhun–Ladera region.Wellfoliated granite gneiss is the dominant lithology that also hosts dark,lenticular enclaves,and is in turn,intruded by mafic dykes.The granite gneiss has silica content ranging from 61.37 wt.%to 68.27 wt.%that marks a slight overlap with the enclaves(54.32wt.%to 62.17wt.%).Both groups have a highK2O/Na2O(~2 or higher)ratio.Geochemically,the granite gneiss classify as granite–granodiorite,and enclaves as granodiorite-diorite.The In-situ LA-ICP-MS zircon U–Pb geochronology of granite gneiss has yielded a statistically valid 1721±9 Ma age that we interpret as the emplacement age for the granitic protolith.Geochemical characteristics of granite gneiss underline fractional crystallization of an I-type melt as themain process,and continuity of trends in enclaves underlines their mutual genetic link.The genetic association is further verified by a consistency in the trace element characteristics and REE patterns.The Nd-isotope signatures define a single grouping for both granite gneiss and enclaves,withεNd(t)values ranging from−6.38 to−6.61,further substantiating a common source.The geochemical tectonic discrimination schemes consistently point toward an extensional setting and A-type characteristics for granite gneiss and enclaves.These are analogous to the coeval(1.72–1.75 Ga),A-type granitoids from the Khetri and Alwar basin in the North Delhi Fold Belt,implying a much larger areal extent for the Paleoproterozoic anorogenic magmatism in the northern segment of the Aravalli Craton.The Paleoproterozoic age for the presumed‘Archean’basement in this region offers tacit evidence that the BGC–II is a stratigraphically younger terrane as compared to the Archean age,BGC–I.展开更多
Increased dimensionality of the satellite data proves to be very useful for discriminating features with very close spectral matching. Present study concentrates on the retrieval of reflectance spectra from the level ...Increased dimensionality of the satellite data proves to be very useful for discriminating features with very close spectral matching. Present study concentrates on the retrieval of reflectance spectra from the level one radiometrically corrected data in Koraput district (Orissa) for the Bauxite ore. In the present study, atmospheric correction model FLAASH has been used to retrieve reflectance from the radiance data. Preprocessing of the dataset has been done before applying atmospheric correction on the dataset. Spectral subsetting of noise prone bands has been successfully done. Local destriping of the affected bands has been done using a 3*3 local mean filter. Spectral signatures of samples were derived from the processed data. Spectral signature of each sample and derived features vectors were correlated with the satellite image of the area and distribution of each feature was demarcated. Spatial abundance of each feature was used in preparation of mineral abundance map. Accuracy of the map was assessed using training sets of representative geological units. The mineral abundance mapping using the spectral analysis of the reflectance image involves the endmember collection using the N-Dimensional visualizer tool in ENVI software. Laterite, Bauxite, Iron and silica rich Aluminous laterite soil, Alluvium and Forest were selected as the end members after understanding the geology and analysis of the reflectance image. Various mapping techniques were applied to generate the final classified mineral abundance Map, Linear Spectral Unmixing, Mixture Tune Matched Filtering, Spectral Feature Fitting, Spectral Angle Mapper were the techniques used. Results have revealed the ability of Hyper spectral Remote sensing data for the identification and mapping of Hydrothermal altered products like Bauxite, Aluminous Laterite. This technology can be utilized for targeting minerals in the altered zone.展开更多
The Cameroon hot line is dominated by magmatic rocks. The variations of magma and chemistry are generally due to the difference of physical conditions and chemistry in the magma source region during the ascent of magm...The Cameroon hot line is dominated by magmatic rocks. The variations of magma and chemistry are generally due to the difference of physical conditions and chemistry in the magma source region during the ascent of magma. The Mt Etinde and the Mt Cameroon, both edifices belong to the Cameroon Hot line, have a particularity some rare rocks such as camptonite and nephelinite. The relationship between the silica undersaturated rocks in the both edifices is characterized by the lateral variation appear through the petrography of the different rocks. The concerned geochemical data allow to compare the Mount Etinde nephelinite and Mount Cameroon camptonite where the differentiation process reflects geochemical affinities from a basaltic magma source on the Cameroon hot line. The compatible elements between the Mount Etinde nephelinite and the Mount Cameroon camptonite and basalt correlate with the difference in modal compositions of mineral phases. The lateral variation of major and trace element contents in the Mount Cameroon camptonite and Mount Etinde nephelinite seem to be related to the difference in the fractional crystallization processes of mineral phases, the difference in the partial melting processes and the metasomatism source rich in volatile. The silica-undersaturated character of the camptonite and nephelinite could be attributed to assimilation of carbonate rocks within depth-level magma chambers. Trace element AFC modelling revealed that the parental magmas of both edifice volcanic rocks were mostly affected by fractional crystallisation coupled with metasomatism process in Ca rich source.展开更多
The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is ...The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.展开更多
This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma...This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma:The Himalayan crust thickened to~40 km through Barrovian-type metamorphism(15–25°C/km),and the Himalaya rose from<0 to~1000 m.Stage 40–16 Ma:The crust gradually thickened to 60–70 km,resulting in abundant high-grade metamorphism and anatexis(peak-P,15–25°C/km;peak-T,>30°C/km).The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust,High Himalayan thrust,and Main Central thrust,and the Himalaya rose to≥5,000 m.Stage 16–0 Ma:the mountain roots underwent localized delamination,causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism(30–50°C/km),and the Himalaya reached the present elevation of~6,000 m.Underplating and imbricate thrusting dominated the Himalaya’growth and topographic rise,conforming to the critical taper wedge model.Localized delamination of mountain roots facilitated further topographic rise.Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events,contact metamorphism and rare metal mineralization,metamorphic decarbonation and the carbon cycle in collisional belts.展开更多
文摘The lithium potential in the Aïr massif is represented by mineral index of spodumene pegmatites and, lepidolite pegmatites. The mineral deposits of lithium occur in cluster or veins that cut the host rock or are located near the contact between the greenstone belt and granitic massif. The evidence of lithium is in the form of clusters or disseminated and stockwerk. Mineralogical characteristics show similarities between the Air Massif pegmatites and indicate the same homogenous source during the magma-generation process. The pegmatite rocks attracted the attention due to their wide exposure and composition, well appearance, and economically hosting of significant rare earth metals such as Sn and W. The mineralogical and petrographical investigations on the eight pegmatites rocks samples observed have a relative similarity, while a little difference in the shapes attributed to the ratio in the pegmatite rocks of the minerals. The occurrence of the kink band indicates the influence of the tectonic processes which affected the Aïr massif after the emplacement of late magmatic or post-magmatic pegmatites by injection into fractured rocks in the upper part of the crust. The Air Massif pegmatite has higher concentrations Li and of all trace elements except Hf and occasionally Zr, Ti, Sn and Mg of for the economic exploration.
基金financially supported by National Natural Science Foundation of China(Grant No.41761144078)Kathmandu Center for Research and Education,CAS-TU,Kathmandu,44618,Nepal。
文摘The hydrochemical characterization and irrigation suitability assessment of the GangesBrahmaputra River System(GBRS)has immense importance for the livelihoods of people and ecosystem sustainability in the region.This study aims to assess the hydrochemical characteristics and evaluate the irrigation suitability of water in the GBRS by reviewing published literature of the major tributaries.The studied rivers were categorized into two groups namely Group-1 and Group-2 considering the similarities of climatic patterns,hydrochemical attributes,and drainage characteristics.The hydrochemistry of the river water was characterized by the Piper diagram,Gibbs plot,mixing plots,and ionic ratios.Furthermore,irrigation water qualities were evaluated by electrical conductivity(EC),sodium percentage(Na%),sodium adsorption ratio(SAR),magnesium hazard(MH),and Wilcox diagram.The results indicated that the hydrochemistry of the GBRS was slightly alkaline to alkaline(7.42-8.78)in nature.The average concentrations of most of the chemical attributes showed higher in Group-1,whereas the average concentrations of K^(+) and NO_(3)^(-) were found higher in Group-2.The average concentration of the major ions followed the dominancy order Ca^(2+)>Mg^(2+)>Na^(+)>K^(+) for cations and HCO_(3)^(-)>SO_(4)^(2-)>Cl^(-)>NO_(3)^(-) for anions in both groups.Gibbs plot and mixing plot indicated that carbonate rock weathering dominates the hydrochemical process,which was further confirmed by the Piper diagram and the ionic ratios.From the analyses of irrigational water quality,almost all the rivers(except Gomti River in terms of MH and Rangit River in terms of Na%)in the GBRS were found to be suitable based on EC,SAR,Na%,MH,and Wilcox diagram.Finally,the majority of river systems in the GBRS were characterized by carbonate dominated lithology and irrigational water quality is mostly suitable for utilization.This study could be useful for water quality management in the glacial-fed Himalayan river under the context of global climate change.
文摘The basement granite gneisses from the north-central Aravalli Craton in NW India were investigated for geochemistry and geochronology.In a peneplain terrain,the granite gneiss outcrops are scanty and samples were collected mainly from two small hills and several ground-level exposures in the Sakhun–Ladera region.Wellfoliated granite gneiss is the dominant lithology that also hosts dark,lenticular enclaves,and is in turn,intruded by mafic dykes.The granite gneiss has silica content ranging from 61.37 wt.%to 68.27 wt.%that marks a slight overlap with the enclaves(54.32wt.%to 62.17wt.%).Both groups have a highK2O/Na2O(~2 or higher)ratio.Geochemically,the granite gneiss classify as granite–granodiorite,and enclaves as granodiorite-diorite.The In-situ LA-ICP-MS zircon U–Pb geochronology of granite gneiss has yielded a statistically valid 1721±9 Ma age that we interpret as the emplacement age for the granitic protolith.Geochemical characteristics of granite gneiss underline fractional crystallization of an I-type melt as themain process,and continuity of trends in enclaves underlines their mutual genetic link.The genetic association is further verified by a consistency in the trace element characteristics and REE patterns.The Nd-isotope signatures define a single grouping for both granite gneiss and enclaves,withεNd(t)values ranging from−6.38 to−6.61,further substantiating a common source.The geochemical tectonic discrimination schemes consistently point toward an extensional setting and A-type characteristics for granite gneiss and enclaves.These are analogous to the coeval(1.72–1.75 Ga),A-type granitoids from the Khetri and Alwar basin in the North Delhi Fold Belt,implying a much larger areal extent for the Paleoproterozoic anorogenic magmatism in the northern segment of the Aravalli Craton.The Paleoproterozoic age for the presumed‘Archean’basement in this region offers tacit evidence that the BGC–II is a stratigraphically younger terrane as compared to the Archean age,BGC–I.
文摘Increased dimensionality of the satellite data proves to be very useful for discriminating features with very close spectral matching. Present study concentrates on the retrieval of reflectance spectra from the level one radiometrically corrected data in Koraput district (Orissa) for the Bauxite ore. In the present study, atmospheric correction model FLAASH has been used to retrieve reflectance from the radiance data. Preprocessing of the dataset has been done before applying atmospheric correction on the dataset. Spectral subsetting of noise prone bands has been successfully done. Local destriping of the affected bands has been done using a 3*3 local mean filter. Spectral signatures of samples were derived from the processed data. Spectral signature of each sample and derived features vectors were correlated with the satellite image of the area and distribution of each feature was demarcated. Spatial abundance of each feature was used in preparation of mineral abundance map. Accuracy of the map was assessed using training sets of representative geological units. The mineral abundance mapping using the spectral analysis of the reflectance image involves the endmember collection using the N-Dimensional visualizer tool in ENVI software. Laterite, Bauxite, Iron and silica rich Aluminous laterite soil, Alluvium and Forest were selected as the end members after understanding the geology and analysis of the reflectance image. Various mapping techniques were applied to generate the final classified mineral abundance Map, Linear Spectral Unmixing, Mixture Tune Matched Filtering, Spectral Feature Fitting, Spectral Angle Mapper were the techniques used. Results have revealed the ability of Hyper spectral Remote sensing data for the identification and mapping of Hydrothermal altered products like Bauxite, Aluminous Laterite. This technology can be utilized for targeting minerals in the altered zone.
文摘The Cameroon hot line is dominated by magmatic rocks. The variations of magma and chemistry are generally due to the difference of physical conditions and chemistry in the magma source region during the ascent of magma. The Mt Etinde and the Mt Cameroon, both edifices belong to the Cameroon Hot line, have a particularity some rare rocks such as camptonite and nephelinite. The relationship between the silica undersaturated rocks in the both edifices is characterized by the lateral variation appear through the petrography of the different rocks. The concerned geochemical data allow to compare the Mount Etinde nephelinite and Mount Cameroon camptonite where the differentiation process reflects geochemical affinities from a basaltic magma source on the Cameroon hot line. The compatible elements between the Mount Etinde nephelinite and the Mount Cameroon camptonite and basalt correlate with the difference in modal compositions of mineral phases. The lateral variation of major and trace element contents in the Mount Cameroon camptonite and Mount Etinde nephelinite seem to be related to the difference in the fractional crystallization processes of mineral phases, the difference in the partial melting processes and the metasomatism source rich in volatile. The silica-undersaturated character of the camptonite and nephelinite could be attributed to assimilation of carbonate rocks within depth-level magma chambers. Trace element AFC modelling revealed that the parental magmas of both edifice volcanic rocks were mostly affected by fractional crystallisation coupled with metasomatism process in Ca rich source.
文摘The Baïbokoum-Touboro-Ngaoundaye area is located in the Adamoua-Yade domain of the Pan-African Fold Belt in Central Africa. The present work concerns the petrographic and geochemical study. The study area is made up of plutonic rocks including two amphibole granites, four biotite and muscovite granites, two syenites and one monzonite sample. These rocks have a granular porphyroid texture, with a mylonitic tendency. The primary paragenesis consists of Opx + Cpx + Amp + Bt + Pl + Or + Mic + Qtz + Ap + Sph + Zr and the secondary paragenesis consisting of Ch + Op. Plutonic rocks are shoshonitic to calc-alkaline with a strong potassic affinity. The REE profiles of these rocks show a negative anomaly of Eu in the granites and no Eu anomaly in syenites and monzonite (syeno-diorite). Multielement spectra of plutonic rocks present a negative anomaly in Nb-Ta and Ti. Fractional crystallization is the process that made these rocks of study area. These rocks are placed in a subduction to syn-collisional (VAG + Syn-COLG) and of intraplate granitoids (WPG) environment.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research program(Grant No.2019QZKK0703)the National Natural Science Foundation of China(Grant Nos.41972065 and 41888101)+1 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences(Grant No.2022065)the State Key Laboratory of Lithospheric Evolution(Grant No.E152510201).
文摘This paper introduces how crustal thickening controls the growth of the Himalaya by summarizing the P-T-t evolution of the Himalayan metamorphic core.The Himalayan orogeny was divided into three stages.Stage 60–40 Ma:The Himalayan crust thickened to~40 km through Barrovian-type metamorphism(15–25°C/km),and the Himalaya rose from<0 to~1000 m.Stage 40–16 Ma:The crust gradually thickened to 60–70 km,resulting in abundant high-grade metamorphism and anatexis(peak-P,15–25°C/km;peak-T,>30°C/km).The three sub-sheets in the Himalayan metamorphic core extruded southward sequentially through imbricate thrusts of the Eo-Himalayan thrust,High Himalayan thrust,and Main Central thrust,and the Himalaya rose to≥5,000 m.Stage 16–0 Ma:the mountain roots underwent localized delamination,causing asthenospheric upwelling and overprinting of the lower crust by ultra-high-temperature metamorphism(30–50°C/km),and the Himalaya reached the present elevation of~6,000 m.Underplating and imbricate thrusting dominated the Himalaya’growth and topographic rise,conforming to the critical taper wedge model.Localized delamination of mountain roots facilitated further topographic rise.Future Himalayan metamorphic studies should focus on extreme metamorphism and major collisional events,contact metamorphism and rare metal mineralization,metamorphic decarbonation and the carbon cycle in collisional belts.
