Ultramafic volcaniclastics of the Precambrian Dalma Volcanic Belt, Singhbhum, Eastern India

1982 ◽  
Vol 119 (5) ◽  
pp. 505-510 ◽  
Author(s):  
A. Gupta ◽  
A. Basu ◽  
P. K. Ghosh
Keyword(s):  
Volcanic Belt ◽  
Mineralogical Composition ◽  
Eastern India ◽  
Indian Shield ◽  
Volcanic Origin ◽  
Glass Shards

SummaryThe Dalma volcanic belt in the Precambrian Eastern Indian shield is composed of a thick sequence of volcani-sedimentary assemblage with a group of predominantly ultramafic volcaniclastics having komatiitic chemistry. A volcanic origin is suggested by textural relationships and mineralogical composition, together with the presence of devitrified glass shards; these rocks are now mostly chlorite-tremolite schist.

scholarly journals Depositional condition, provenance and tectonic framework of the Upper Tertiary sandstones of the Arunachal Himalaya, India

1997 ◽  
Vol 15 ◽  
Author(s):  
I. M. Hazarika ◽  
P. K. Das
Keyword(s):  
Mineralogical Composition ◽  
Climatic Conditions ◽  
Size Analysis ◽  
Eastern India ◽  
Continental Block ◽  
Tectonic Disturbances ◽  
Tectonically Active ◽  
Tectonic Framework ◽  
Arunachal Himalaya ◽  
Compositional Study

The Upper Tertiary sandstones of the foothills of the Arunachal Himalaya, eastern India were studied to determine the depositional condition, provenance and tectonic framework of deposition of the sandstones. For this purpose, size analysis and mineralogical and basin configuration studies were carried out. The mineralogical composition of the sandstones indicates that the sandstones were mainly derived from the metamorphic and igneous rocks. The compositional study indicates that these immature sandstones were developed in the continental block provenance under humid climatic conditions affected by major tectonic disturbances. The sedimentological study shows that the sediments of the sandstones were waterlaid and deposited rapidly in the Arunachal basin, which was a shallow and fresh water basin and tectonically active at the time of sedimentation.

Mineralogical and morphological characterization of a suspected lunar silicic construct: The Wolf crater

2020 ◽  
Author(s):  
Himela Moitra ◽  
Sumit Pathak ◽  
Mamta Chauhan ◽  
Saibal Gupta ◽  
Satadru Bhattacharya
Keyword(s):  
Outer Part ◽  
Mineralogical Composition ◽  
Holistic Approach ◽  
Morphological Characterization ◽  
Volcanic Origin ◽  
Mare Basalt ◽  
Multispectral Data ◽  
Rock Fragments ◽  
Narrow Angle ◽  
Lunar Reconnaissance Orbiter

<p>The Wolf crater is an irregularly shaped crater situated within the central part of Mare Nubium in the southern hemisphere on the lunar near side (16.573°W, 22.904°S). With an approximate diameter of about 25 km, this crater has been recently suspected to be a lunar silicic construct, hinting at a felsic composition that is more silicic than pure, immature anorthite. These suspicions have mainly been triggered by the high thorium anomaly in this region, and Christiansen Feature (CF) and Concavity Index (CI) mapping using Diviner multispectral data from the Lunar Reconnaissance Orbiter (LRO) mission. Many areas in the Wolf crater show CF values lower than 7.84 µm (CF for pure, immature anorthite). This study adopts a more holistic approach by studying the mineralogical composition and morphology of this crater complex using Moon Mineralogy Mapper (M<sup>3</sup>) data for mineralogical analysis and LROC WAC (wide angle camera) and NAC (narrow angle camera) data for morphological analysis. The whole complex can be divided into two parts- highland massif and mare basalt regions. CSFD analyses show that the outer part of the massif is older than the mare basalt, whereas the inner part have relatively younger surfaces. Analysis of the M<sup>3</sup> data reveals the presence of pyroxene exposures on the massif as well as the mare basalt. However, their compositions are distinctly different, the massif pyroxenes being low-Ca pyroxene while the mare pyroxenes are High-Ca pyroxenes in composition. It can be inferred that the pyroxene exposures on the massif are not related to any ejecta deposits from the mare basalts. The highly silicic compositions implied by the CF and CI maps are limited to only certain parts of the massif, indicating a compositional heterogeneity in the massif region as well. Morphologically, the highland massif shows an extremely knobby structure which surrounds the mare basalt in a topographically depressed central part. The massif is discontinuous and the mare-highland boundary is very irregular, suggesting that the central depression is not of an impact-related origin. Extensional deformation features near the mare-highland boundaries also support this. In some parts, dome like features can be identified, with fresh rock fragments being visible on the surface. The rock fragments seem to be of two different tones- one very bright tone, and another comparatively darker tone. These rock fragments cannot be related to any nearby cratering activity, and they seem to be embedded in their locations. Pyroclastic deposits can also be identified around some of these domes, by their characteristic low albedo and smooth appearance. Overall, the Wolf crater complex shows signatures of non-mare volcanic activity and can be of non-impact related volcanic origin.</p>

scholarly journals O GRUPO IBIÁ (FAIXA BRASÍLIA MERIDIONAL): EVIDÊNCIAS ISOTÓPICAS SM-ND E U-PB DE BACIA COLISIONAL TIPO FLYSCH

2013 ◽  
Author(s):  
Paulo Henrique Amorim Dias ◽  
Carlos Mauricio Noce ◽  
Antônio Carlos Pedrosa-Soares ◽  
Hildor José Seer ◽  
Ivo Antônio Dussin ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Mineralogical Composition ◽  
Isotopic Data ◽  
Volcanic Origin ◽  
Zircon Population

O Grupo Ibiá inclui as formações Cubatão e Rio Verde. A primeira, composta por metaconglomerado suportado pela matriz, com intercalações de metapelito e quartzito, ocorre em lentes esparsas sobre discordância erosiva no topo do Grupo Canastra. Datações U-Pb em grãos detríticos de zircão deste conglomerado indicam idade máxima de sedimentação em ca. 1190 Ma, e mostram o mesmo amplo espectro de valores dados pelo Grupo Canastra. A Formação Rio Verde, composta de clorita-muscovita xisto com lentes de quartzito, repousa sobre as unidades antes referidas. Grãos de zircão do xisto Rio Verde fornecem idades dominantemente menores que 1000 Ma, com a média da moda dos menores valores em ca. 639 Ma. Esta população de zircão consiste de grãos mal arredondados a euédricos. Os dados analíticos, incluindo Sm-Nd (Nd(640 Ma) de -0,1 a 0,5 Ma e idades-modelo em 1,2 Ga) e a composição mineralógica do xisto Rio Verde sugerem protólitos provenientes de fontes ricas em rochas ígneas intermediárias a máficas, tais como arcos magmáticos e ofiolitos. Em conclusão, o Grupo Ibiá representaria bacia colisional (flysch), relacionada a frentes de empurrão da Faixa Brasília Meridional.Palavras-chave: geocronologia U-Pb, bacia orogênica, Grupo Ibiá, Faixa BrasíliaABSTRACT: THE IBIÁ GROUP (SOUTHERN BRASÍLIA BELT): ISOTOPIC SM-ND AND U-PB EVIDENCE FOR A COLLISIONAL FLYSCH-TYPE BASIN. The Ibiá Group includes the Cubatão and Rio Verde formations. The first consists of matrix-supported metaconglomerate with intercalations of metapelite and quartzite, occurring in sparse lenses on the top of the Canastra Group. U-Pb ages of detrital zircon grains from the Cubatão conglomerate and Canastra quartzite show similar wide age spectra and youngest values around 1190 Ma. The Rio Verde Formation, consisting of chlorite-muscovite schist and quartzite lenses, overlies the Cubatão Formation and Canastra Group. U-Pb data from zircon grains of the Rio Verde schist show a great dominance of ages younger than 1000 Ma, with a mean age of the youngest values around 639 Ma. The younger zircon population shows poorly rounded to euhedral zircon crystals, some of them of volcanic origin. Lithochemical data, including Sm-Nd isotopic data (Nd(640 Ma) from -0.1 to 0.5 and Tdm model ages around 1.2 Ga), together with the mineralogical composition suggest provenance from intermediate to mafic igneous sources for the Rio Verde sediments. In conclusion, the Ibiá Group is related to a collisional (flysch) basin associated with thrust fronts along the Southern Brasília Belt.Keywords: U-Pb geochronology, orogenic basin, flysch, Ibiá Group, Brasília Belt

Petrochemistry of the lavas from proterozoic dalma volcanic belt, Singhbhum, eastern India

1989 ◽  
Vol 78 (2) ◽  
pp. 633-648 ◽  
Author(s):  
Mihir K. Bose ◽  
Manas K. Chakrabarti ◽  
A. D. Saunders
Keyword(s):  
Volcanic Belt ◽  
Eastern India

The Proterozoic ultramafic and mafic lavas and tuffs of the Dalma greenstone belt, Singhbhum, eastern India

1980 ◽  
Vol 17 (2) ◽  
pp. 210-231 ◽  
Author(s):  
Anupendu Gupta ◽  
Aniruddha Basu ◽  
Protip K. Ghosh
Keyword(s):  
Greenstone Belt ◽  
Evolutionary Model ◽  
Volcanic Belt ◽  
Thermal Conditions ◽  
Eastern India ◽  
Low Potassium ◽  
Igneous Activity ◽  
New Interpretation ◽  
Mafic Lavas ◽  
High Degree

A detailed petrochemical study of the Proterozoic "Dalma Epidiorites" of Singhbhum leads to a completely new interpretation of this dominantly volcanic belt. The initial igneous activity is represented by mafic and ultramafic intrusives and lavas of tholeiitic. alkaline, and komatiitic affinities. Interlayered are lithic tuffs and tuffaceous sediments. Also present is an analcite basalt heretofore unreported from the Dalma. This suite is overlain by a high-magnesian vitric tuff horizon, which along with its comagmatic intrusives shows quench textures and its chemistry is closely comparable to peridotitic-pyroxenitic komatiites of Archean greenstone terrains. It is noteworthy that the komatiitic magma in this belt is dominantly pyroclastic. The vitric tuff horizon is followed upwards by a thick sequence of high-iron, low-potassium, pillowed tholeiites with ocean-floor affinities.The proposed evolutionary model of the Dalma belt suggests that stretching of Archean proto-continental crust gave rise to the Dalma graben within the Proterozoic (Chaibasa) basin and unique thermal conditions coupled with a disrupted crust led to a high degree of melting and direct tapping of the mantle producing the komatiitic extrusives at a particular stage of the development of the belt.

Microbialites as bioindicators of lake hydric dynamics: the evolution of microbial populations and mineralogy of Mexican lacustrine microbialites along an alkaline-saline gradient

2021 ◽  
Author(s):  
Miguel Iniesto ◽  
Karim Benzerara ◽  
David Moreira ◽  
Nina Zeyen ◽  
Rosaluz Tavera ◽  
...  
Keyword(s):  
Microbial Community ◽  
Microbial Communities ◽  
Salinity Gradient ◽  
Volcanic Belt ◽  
Mineralogical Composition ◽  
Orthosilicic Acid ◽  
Microbial Composition ◽  
Crater Lakes ◽  
Salinity Gradients ◽  
Planktonic Communities

<p>Modern microbialites are frequently studied as analogues of ancient microbialites, the oldest of which date back to ~3.5 Ga. These organo-sedimentary structures are generated by complex microbial communities developing under specific physicochemical conditions, such that fossil microbialites attest for past microbial ecosystems. Lacustrine microbialites, in contrast with marine ones, show a large range of morphologies and mineralogical compositions, including various carbonate and non-carbonate (e.g. Mg-silicates) phases. Major dominant prokaryotic groups (e.g. Cyanobacteria, Planctomycetes or Alphaproteobacteria) and taxa‐associated functions (e.g. oxygenic and anoxygenic photosynthesis) appear conserved across microbialite ecosystems. However, the evolution of the microbial community and/or the chemical and mineralogical composition of lacustrine microbialites with the hydrogeochemistry of lakes remains undescribed. In the present work, we analysed the mineralogical and chemical composition, including major and trace element composition of microbialites as well as their microbial community using samples from ten crater lakes of the Trans‐Mexican volcanic belt along an alkalinity-salinity gradient. We also characterized lake hydrochemistry and planktonic communities to compare them with those of microbialites. We found a large diversity of microbialites in terms of mineralogical composition which was primarily controlled by orthosilicic acid (H<sub>4</sub>SiO<sub>4</sub>) concentrations and Mg/Ca ratios of the solutions. In addition, microbialite size correlated positively with salinity, (Mg/Ca)aq ratio and alkalinity. Our observations suggest that alkalinity values above 1.23 mM and salinity above 0.08 g.L<sup>-1</sup> constitute potential chemical threshold above which lacustrine microbialites can occur. The composition of both prokaryotic and the eukaryotic microbialite-associated communities varied significantly across lakes, correlating with the alkalinity and salinity gradient. Moreover, microbialite-associated communities were clearly distinguishable from their surrounding planktonic communities, being more similar to those of microbialites from distant and chemically different lakes than to planktonic communities present in the same lake. In fact, we identified a microbial core of 247 operational taxonomic units shared by all lake microbialites. This core, mainly dominated by Cyanobacteria, Bacteroidetes, Planctomycetes, Chloroflexi, Alphaproteobacteria and Gammaproteobacteria, represented up to 40% of the relative abundance of the community in lakes displaying the highest alkalinity and most conspicuous microbialites (Alchichica and Atexcac). This suggests a prominent ecological role for those organisms in microbialite formation. We could also show that, in Lake Alchichica, microbialites formed very rapidly on inert surfaces (e.g. plastic) with rates of ~0.6 (and up to 1) mm/year and that nascent hydromagnesite and aragonite-rich microbialites harboured communities   similar to the mature ones in native microbialites. Our study establishes a connection between the chemical, mineralogical and microbial composition of microbialites and the hydrogeochemical evolution of lakes. Alkalinity and salinity gradients reflect lake hydrological balance and status along an evaporation progress trend and/or weathering intensity of the surrounding bedrocks. In this context, microbial communities associated with modern lacustrine microbialites may possibly be used as indicators for management/prediction of limnologic states along alkalinity-salinity gradients.</p><p> </p>

The recognition of volcanic clays and the significance of heavy minerals

Clay Minerals ◽  
1982 ◽  
Vol 17 (3) ◽  
pp. 373-375 ◽  
Author(s):  
D. A. Spears
Keyword(s):  
Volcanic Rocks ◽  
Chemical Properties ◽  
Heavy Minerals ◽  
Volcanic Origin ◽  
Crystal Forms ◽  
Lateral Extent ◽  
Absolute Age ◽  
Early Carbonate ◽  
Diagenetic Environment ◽  
Glass Shards

The explosive ejection of material from a volcanic vent produces pyroclastics. These are stratigraphically important because of their isochronous nature, lateral extent and potential for absolute age determinations. The pyroclastics also provide information on the nature of the volcanic activity, which is possibly the only record because of non-preservation in other areas. The recognition of pyroclastics is therefore important, but often difficult,because the high-temperature igneous material is susceptible to alteration in the diagenetic environment. In Quaternary sediments the composition of glass shards is an important aspect of tephrochronology (Westgate & Briggs, 1980) but in older sediments glass shards are usually altered to clay minerals. Exceptionally, shards are preserved unaltered, as in the case of early carbonate and silica cementation (Francis et al., 1968; Jeans et al., 1977). According to Ross (1928), features that are diagnostic for the recognition of a volcanic clay (bentonite is the term used by Ross) are, in order of apparent reliability: (i) presence of glass relict structure; (ii) presence of minerals and crystal forms characteristic of volcanic rocks, including biotite, feldspar, pyroxenes and hornblende; (iii) absence of minerals that do not have a volcanic origin, including microcline, garnet, muscovite, kyanite and andalusite; (iv) waxy lustre; (v) reaction to water; (vi) optical properties; (vii) chemical properties.

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