scholarly journals Minerály pegmatitových hnízd z okolí Jablonce nad Nisou (krkonošsko-jizerský pluton) - část I. silikáty

2020 ◽  
Vol 28 (2) ◽  
pp. 466-482
Author(s):  
Jana Ulmanová ◽  
Zdeněk Dolníček
Keyword(s):  
Internal Structure ◽  
Mineral Composition ◽  
Mineral Assemblage ◽  
Central Zone ◽  
Single Sample ◽  
Coarse Grained ◽  
Silicate Minerals ◽  
Host Granite ◽  
Substantial Modification ◽  
Miarolitic Cavity

We have studied silicate minerals in pegmatite nests from the Tanvald Granite (4 sites) and the Liberec Granite (1 site) in the vicinity of Jablonec n. Nisou, situated within the Variscan Krkonoše-Jizera Pluton. They contain major quartz, K-feldspar and plagioclase (An0-11), subordinate biotite, muscovite and locally schorl. Accessory phases include garnet (spessartine-almandine), andalusite, Hf-rich zircon and thorite. In addition, zinnwaldite was found in a single sample. The studied pegmatites show simple internal structure including aplitic, granitic and coarse-grained “blocky” units; the central zone commonly contains miarolitic cavity which is sometimes filled by tourmaline. The mineral composition and fractionation degree largely reflect those of the host granite; the more fractionated are pegmatites hosted by the Tanvald Granite. The pegmatite nest from Nová Ves nad Nisou II exhibits distinct mineral assemblage with zinnwaldite, pure albite and lack of biotite and garnet, therefore we suggest here a substantial modification of mineral assemblage by superimposed processes. Moreover, tourmaline (schorl) composition with local increasing of Mg toward rim indicates a possible contamination derived from adjacent rocks during tourmaline crystallization.

scholarly journals Petrogenesis of a late-stage calc-alkaline granite in a giant S-type batholith: geochronology and Sr–Nd–Pb isotopes from the Nomatsaus granite (Donkerhoek batholith), Namibia

2021 ◽  
Author(s):  
S. Aspiotis ◽  
S. Jung ◽  
F. Hauff ◽  
R. L. Romer
Keyword(s):  
Partial Melting ◽  
Mineral Assemblage ◽  
Central Zone ◽  
Calc Alkaline ◽  
Pb Isotope ◽  
Alkaline Granite ◽  
Ti Oxides ◽  
Eu Anomaly ◽  
Environment Characteristic ◽  
Southern Central

AbstractThe late-tectonic 511.4 ± 0.6 Ma-old Nomatsaus intrusion (Donkerhoek batholith, Damara orogen, Namibia) consists of moderately peraluminous, magnesian, calc-alkalic to calcic granites similar to I-type granites worldwide. Major and trace-element variations and LREE and HREE concentrations in evolved rocks imply that the fractionated mineral assemblage includes biotite, Fe–Ti oxides, zircon, plagioclase and monazite. Increasing K2O abundance with increasing SiO2 suggests accumulation of K-feldspar; compatible with a small positive Eu anomaly in the most evolved rocks. In comparison with experimental data, the Nomatsaus granite was likely generated from meta-igneous sources of possibly dacitic composition that melted under water-undersaturated conditions (X H2O: 0.25–0.50) and at temperatures between 800 and 850 °C, compatible with the zircon and monazite saturation temperatures of 812 and 852 °C, respectively. The Nomatsaus granite has moderately radiogenic initial 87Sr/86Sr ratios (0.7067–0.7082), relatively radiogenic initial εNd values (− 2.9 to − 4.8) and moderately evolved Pb isotope ratios. Although initial Sr and Nd isotopic compositions of the granite do not vary with SiO2 or MgO contents, fSm/Nd and initial εNd values are negatively correlated indicating limited assimilation of crustal components during monazite-dominated fractional crystallization. The preferred petrogenetic model for the generation of the Nomatsaus granite involves a continent–continent collisional setting with stacking of crustal slices that in combination with high radioactive heat production rates heated the thickened crust, leading to the medium-P/high-T environment characteristic of the southern Central Zone of the Damara orogen. Such a setting promoted partial melting of metasedimentary sources during the initial stages of crustal heating, followed by the partial melting of meta-igneous rocks at mid-crustal levels at higher P–T conditions and relatively late in the orogenic evolution.

Lead–zinc–barite veins of the Dorion Area, Thunder Bay District, Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1963-1979 ◽  
Author(s):  
James M. Franklin ◽  
Roger H. Mitchell
Keyword(s):  
Lead Isotopes ◽  
Central Zone ◽  
Chloride Ion ◽  
Coarse Grained ◽  
Vein Wall ◽  
Sulphur Isotope ◽  
Thunder Bay ◽  
Basement Rocks ◽  
Lake Formation ◽  
Lead Zinc

The lead–zinc–barite deposits of the Dorion region are spatially associated with the unconformity between the Sibley Group (Helikian) and Archean and Aphebian basement rocks. The veins are coarse grained, and mineralogically zoned with galena–calcite in the central zone, sphalerite–quartz surrounding the central zone, and barite (±chalcopyrite) in the vein extremities. Veins occur near the pinch-out of the "Pass Lake formation" (basal Sibley Group), within the dolomite of the overlying "Rossport formation", or in nearby basement fractures. Rossport dolomite, where it forms a vein wall, is highly altered to metal-enriched chert and calcite. Archean wall rocks are not altered.Potassium–argon isotopic determinations on mica in Archean pegmatite immediately adjacent to a vein indicate that the transporting solutions were too cool to cause re-equilibration of the Ar within the mica. Sulphur-isotope data indicate equilibrium between galena and sphalerite yielding a depositional temperature range of 35–135 °C, and disequilibrium between sulphide–sulphate pairs. Lead isotopes are highly anomalous, yielding a secondary isochron which indicates either an Archean, or more probably a mixed Archean–Aphebian, source of lead.The deposits formed from metal leached from either basement rocks or breakdown of Sibley sandstone matrix. Metals and sulphate moved through the permeable sandstone, probably as chloride-ion complexes, and precipitated at the sandstone pinch-out. Reduced sulphur, possibly derived from organic decay, and probably held in a gas trap at the sandstone pinch out, caused precipitation of the sulphides by reaction with metal-bearing brines.

Research on Coarse-Grained Soil Collapsibility in Gobi Region

2012 ◽  
Vol 446-449 ◽  
pp. 1450-1453 ◽  
Author(s):  
Zhi Hong Nie ◽  
Kun Li ◽  
Jian Xia
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Mineral Composition ◽  
Load Test ◽  
Coarse Grained ◽  
Soil Test ◽  
Internal Reasons ◽  
High Degree ◽  
Scanning Electron ◽  
Coarse Grained Soil

This paper has carried out soaking load test, routine soil test, X diffraction, scanning electron microscopy on coarse-grained soil in Gobi region, analyzed the coarse-grained soil collapsibility and explored the mechanism of collapsibility generation. The results showed that: the coarse-grained soil in Gobi region had a high degree of collapsibility; mineral composition, microstructure and salinity constituted the main internal reasons resulting in such phenomenon. In soaking conditions, the cementation strengthen between grains reduces, the structure is damaged under external force and the grain movement leads to greater settlement.

The Mealy dykes, Labrador: petrology, age, and tectonic significance

1984 ◽  
Vol 21 (4) ◽  
pp. 437-446 ◽  
Author(s):  
R. F. Emslie ◽  
W. D. Loveridge ◽  
R. D. Stevens
Keyword(s):  
Chemical Composition ◽  
Coarse Grained ◽  
Bulk Chemical Composition ◽  
Grenville Province ◽  
Silicate Minerals ◽  
Tectonic Significance ◽  
Quartz Monzonite ◽  
Bulk Chemical ◽  
Basic Rocks

The Mealy dykes constitute a major olivine diabase swarm in the Mealy Mountains, Grenville Province, Labrador. The dykes intrude anorthosites and monzonites of the Mealy Mountains complex and outcrop over an area of at least 4000 km2. The swarm strikes east-northeast and may constitute the largest group of unmetamorphosed diabase dykes in the Grenville Province.The Mealy dykes are moderately iron-rich olivine tholeiites, typically nonporphyritic. Thick dykes have coarse-grained interiors that show some fractionation but variations in bulk chemical composition are relatively modest. Olivine (Fo47–Fo27), plagioclase (cores An63–An47, rims An47–An30), and low-Ca augite are the principal silicate minerals. Coexisting magnetite and ilmenite suggest that solidus temperatures were about 980 °C and that subsolidus oxide re-equilibration continued to near 530 °C or perhaps lower.A whole-rock Rb–Sr (errorchron) age for the Mealy dykes yielded 1380 ± 54 Ma, Sr1 = 0.7028 ± 0.0002, which, within precision estimates, is the same as published ages for other basic rocks in the region including Shabogamo gabbros, Seal Lake basalts and diabases, Harp dykes, and Michael gabbros. Together, these rocks signify a major episode of crustal dilation in central and southern Labrador that succeeded widespread anorthosite–monzonite–quartz monzonite intrusion. K–Ar ages on hornblendes, biotites, and whole rocks imply that if prograde heating of the Mealy Mountains terrane occurred at all during the Grenvillian event it was restricted to greenschist grade or lower.

scholarly journals TEM analysis of the internal structures and mineralogy of Asian dust particles and the implications for optical modeling

2014 ◽  
Vol 14 (5) ◽  
pp. 6619-6661 ◽  
Author(s):  
G. Y. Jeong ◽  
T. Nousiainen
Keyword(s):  
Remote Sensing ◽  
Internal Structure ◽  
Mineral Composition ◽  
Radiation Effects ◽  
Mineral Dust ◽  
Ion Beam ◽  
Single Scattering ◽  
Asian Dust ◽  
Dust Particles ◽  
Internal Structures

Abstract. Mineral dust interacts with incoming/outgoing electromagnetic radiation in the atmosphere. This interaction depends on the microphysical properties of the dust particles, including size, mineral composition, external morphology, and internal structure. Ideally all these properties should be accounted for in dust remote sensing, the modeling of single-scattering properties, and radiative effect assessment. There have been many reports on the microphysical characterizations of mineral dust, but no investigations of the internal structures or mineral composition of individual dust particles. We explored the interiors of Asian dust particles using the combined application of focused ion beam thin-slice preparation and high-resolution transmission electron microscopy. The results showed that individual dust particles consisted of numerous mineral grains, which were organized into several types of internal structure: single and polycrystalline cores of quartz, feldspars, calcite, and amphibole often with oriented clay coatings; individual clay agglomerates of nano-thin clay platelets showing preferred to random orientations commonly with coarser mineral inclusions; and platy coarse phyllosilicates (muscovite, biotite, and chlorite). Micron to submicron pores were scattered throughout the interior of particles. Clays in the coatings and agglomerates were dominated by nano-thin platelets of the clay minerals of illite-smectite series including illite, smectite, and their mixed layers with subordinate kaolinite and clay-size chlorite. Submicron iron oxide grains, dominantly goethite, were distributed throughout the clay agglomerates and coatings. Unlike the common assumptions and simplifications, we found that the analyzed dust particles were irregularly shaped with birefringent, polycrystalline, and polymineralic heterogeneous compositions. Accounting for this structural and mineralogical makeup may improve the remote sensing retrieval of dust and the evaluation of radiation effects, but will also require sophisticated single-scattering modeling. In particular, the observed internal structures of dust particles such as clay coatings, preferred orientation, embedded grains in clays, and pores, likely have a great impact on the light scattering of dust particles. The distribution and size of structural components with contrasting dielectric properties, such as iron oxides, should also be explicitly accounted for.

scholarly journals Plasticity and deformation resistance of the alloyed rail steels in rolling temperature interval

2019 ◽  
Vol 62 (6) ◽  
pp. 452-460 ◽  
Author(s):  
A. A. Umanskii ◽  
A. V. Golovatenko ◽  
A. S. Simachev ◽  
V. V. Dorofeev ◽  
T. N. Oskolkova
Keyword(s):  
Deformation Rate ◽  
Deformation Temperature ◽  
Rail Steel ◽  
Central Zone ◽  
Deformation Resistance ◽  
Coarse Grained ◽  
Regression Equations ◽  
Surface Layers ◽  
Metallic Inclusions ◽  
Continuously Cast

On the basis of conducted experimental studies, regularities of the influence of temperature-speed rolling conditions on the plasticity and deformation resistance in the zones of continuously cast billets of alloy rail steels of E76KhF, E76KhSF grades are determined and scientifically substantiated. The results indicate the complex nature of dependence of rail steel E76KhF plasticity on deformation temperature. In particular, for near-surface layers of continuously cast billets, a noticeable decrease in plasticity in the temperature range of 1025 – 1075 °Cwas recorded, which is absent for the layers located in central zone of that billets. Generalization of the results of plasticity studies of various layers of continuously cast rail E76KhF steel billets has shown that absolute values of the plasticity criterion are significantly reduced with the distance from the surface to the central zone. This fact can be explained by a coarse-grained structure and increased concentration of non-metallic inclusions in the central zone of continuously cast billets relative to their surface layers; it was confirmed by the results of metallographic studies. In particular, it was found that the average grains diameter in the surface layer of deformed continuously cast billets is in 1.3 – 2.1 times less compared to the central zone. There was confirmed the presence of significant concentrations of non-deformable inclusions of the silicate type (Al2O3· SiO2 ; FeO·SiO2 ; MnO·SiO2 ), which have most negative influence on steel plasticity while in the surface area such inclusions are absent. On the basis of conducted researches it was established that with increase in deformation temperature of rail steel E76KhSF there is a decrease in resistance to plastic deformation according to the exponential law. In this case, absolute values of the steel deformation resistance are reduced with the distance from the surface to the central zone of continuously cast billets, which is associated with the above illustrated increase in grain size and localization of non-metallic inclusions. The revealed tendency to reduce the deformation resistance from the surface layers to the center of continuously cast billets is maintained regardless to deformation rate, while the absolute values of the deformation resistance increase significantly with the growth of deformation rate from 1 to 10 s–1. Mathematical processing of the obtained experimental data allowed to obtain regression equations that help to predict plastic and deformation properties of alloyed rail steels of E76KhF and E76KhSF grades with a sufficient degree of reliability under the specified rolling conditions and are complex theoretical basis for the development and improvement of new heating modes of billets for rolling and rail rolling schemes. Adequacy of the obtained experimental dependences is confirmed by results of pilot industrial testing of the new mode of railway rails production on the universal rail mill of “EVRAZ ZSMK”.

Cumulate mush hybridization by melt invasion: Evidence from compositionally-diverse amphiboles in ultramafic-mafic arc cumulates within the eastern Gangdese Batholith, southern Tibet

2021 ◽  
Author(s):  
Wei Xu ◽  
Di-Cheng Zhu ◽  
Qing Wang ◽  
Roberto F Weinberg ◽  
Rui Wang ◽  
...  
Keyword(s):  
Mineral Assemblage ◽  
Large Body ◽  
The Body ◽  
Coarse Grained ◽  
Southern Tibet ◽  
Fine Grained ◽  
Arc Magmas ◽  
Rock Types ◽  
Geochemical Study ◽  
Host Rocks

Abstract Amphibole plays an important role in the petrogenesis and evolution of arc magmas, but its role is not completely understood yet. Here, a field, petrological, geochronological and geochemical study is carried out on ultramafic-mafic arc cumulates with textural and chemical heterogeneities and on associated host diorites from the eastern Gangdese Batholith, southern Tibet to explore the problem. The cumulates occur as a large body in diorite host-rocks. The core of the body consists of coarse-grained Cpx hornblendite with a porphyritic texture. Towards the contact with the host diorite, the coarse-grained Cpx hornblendite grades to relatively homogeneous fine-grained melagabbro. Zircon U–Pb dating indicates they all crystallized at 200 ± 1 Ma. Textural features and whole-rock and mineral chemical data reveal that both the Cpx hornblendite and the melagabbro are mixtures of two different mineral assemblages that are not in equilibrium: (1) brown amphibole and its clinopyroxene inclusions; (2) matrix clinopyroxene + green amphibole + plagioclase + quartz + accessory phases. Clinopyroxene and brown amphibole from the first assemblage are enriched in middle rare earth elements (MREE) relative to light REE (LREE) and heavy REE (HREE), and are weakly depleted in Ti, whereas clinopyroxene and green amphibole from the second assemblage are characterized by LREE enrichment over MREE-HREE and more marked Sr and Ti depletion. The higher Mg#, MgO and Cr of the late-formed green amphibole than the early-formed brown amphibole suggest that the two assemblages are not on the same liquid line of descent. Given the close relations of the three rock types in the exposed crustal section, the cumulates are interpreted to have formed in an open system, in which an ultramafic cumulate body consisting of the first assemblage reacted with the host dioritic melt to form new clinopyroxene and amphibole of the second assemblage. The melt calculated to be in equilibrium with the first mineral assemblage resembles an average continental arc basalt, that is less evolved than the host dioritic melt, responsible for the second mineral assemblage. On the basis of whole-rock Sr–Nd–Hf isotopic similarity of the cumulates and a host diorite sample, we argue that the host diorites were formed through crystal fractionation from the parent melt of the first assemblage. Results of least-squares mass-balance calculations suggest the quantities of the host dioritic melts, involved in the generation of these modified cumulates, vary from ~25% to ~44%. The presence of magmatic epidote in the host diorites and Al-in-Hb geobarometry indicate the reaction that occurred when the dioritic melts percolated through the cumulate body was at ~6 kbar. Both the brown and green amphiboles are enriched in MREE relative to HREE, and can impart residual melts with a strong geochemical signature of amphibole fractionation (low Dy/Yb). Thus, we conclude that fractional crystallization and melt-rock reaction are two mechanisms by which amphibole controls arc magma petrogenesis and evolution.

Lithostratigraphy of the Naros Granite (Komsberg Suite), South Africa and Namibia

2021 ◽  
Author(s):  
P.H. Macey ◽  
R.J. Thomas ◽  
H.P. Smith ◽  
D. Frei ◽  
PJ. le Roux
Keyword(s):  
South Africa ◽  
Partial Melting ◽  
Mineral Assemblage ◽  
Chemical Weathering ◽  
Biotite Granite ◽  
Igneous Rocks ◽  
Coarse Grained ◽  
Southern Margin ◽  
A Minor ◽  
Significant Chemical

Abstract The Naros Granite occurs as a large, northwest-trending ovoid batholith roughly 30 km long and 15 km wide straddling the Orange River border between South Africa and Namibia, 25 km northeast of Onseepkans. It consists mainly of a leucocratic to mesocratic grey, coarse-grained equigranular hornblende-biotite granite-granodiorite that is locally mildly feldspar porphyritic. Small, ovoid mafic autoliths are common and characteristic of the Naros Granite. The composition of the unit varies from granite to granodiorite with a minor leucogranitic phase observed along the southern margin of the batholith. Hornblende and biotite are ubiquitous mafic minerals but small amounts of orthopyroxene occur locally. The Naros Granite has yielded tightly-constrained U-Pb zircon ages between 1 114 Ma and 1 101 Ma. The Naros Granite is generally unfoliated to weakly deformed with only localised shearing along contacts with the surrounding country rocks giving rise to orthogneissic fabrics. It has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic autoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant chemical weathering. The Naros Granite is the youngest and most evolved member of the ~1.11 Ga Komsberg Suite, a collection of late- to post-tectonic I-type metaluminous, intermediate to felsic, biotite ± hornblende granitoids and their charnockitic equivalents that have intruded the older pre-tectonic gneisses of the Kakamas Domain of the Namaqua Metamorphic Sector.

scholarly journals Morphological and geochemical features of zircon from intrusive rocks of El Sela area, Eastern Desert, Egypt

2020 ◽  
Vol 59 (3) ◽  
pp. 7-18
Author(s):  
Mohamed Mahmoud Fathy GHONEIM ◽  
◽  
Elena Gennad’evna PANOVA ◽  
Ahmed El Sayed ABDEL GAWAD ◽  
Svetlana Yur’evna YANSON ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Internal Structure ◽  
Detection Limits ◽  
Eastern Desert ◽  
Coarse Grained ◽  
Accessory Mineral ◽  
The Core ◽  
Intrusive Rocks ◽  
The Difference ◽  
Zircon Morphology

The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks

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