Axinit a doprovodné minerály z lokality Jezuitský rybník východně od Golčova Jeníkova (moldanubikum, Česká republika)

2020 ◽  
Vol 28 (2) ◽  
pp. 437-453
Author(s):  
Zdeněk Dolníček ◽  
Michal Kovář ◽  
Jana Ulmanová
Keyword(s):  
Bohemian Massif ◽  
Mineral Assemblage ◽  
Chemical Fractionation ◽  
Moldanubian Zone ◽  
Rock Types ◽  
Magmatic Stage ◽  
Host Rocks

A new occurrence of axinite at the locality Jezuitský rybník near Sirákovice (ENE from Golčův Jeníkov), situated in rocks of the Variegated (Drosendorf) Series (Moldanubian Zone of the Bohemian Massif), is a nice example of contaminated pegmatite in a Ca-skarn with intense superimposed hydrothermal overprint. Axinite [axinite-(Fe) to axinite-(Mg)] forms young hydrothermal infill of pocket/fissure in pegmatite cutting a brecciated Ca-skarn. The hydrothermal assemblage includes amphibole II (actinolite to ferro-actinolite), albite, K-feldspar II, chlorite, epidote (locally containing 0.20 - 0.30 apfu REE), muscovite and Al,F-enriched titanite (with up to 2 % SnO2) passing exceptionally to unnamed CaAlFSiO4. Quartz, plagioclase (andesine), K-feldspar I and amphibole I (mostly K-rich or even potassian ferro-pargasite to ferro-tschermakite) originated in magmatic stage associated with intrusion of externally derived pegmatite melt. Sporadic garnet (grossular-rich almandine) represents relics of mineral assemblage of the host skarn. Dominance of Nd among REE in the REE-rich epidote is explained in terms of chemical fractionation of REE, probably caused by the presence of strong REE-complexing ligands (F-, OH- and/or CO32-) in aqueous fluids enriched in MREE/HREE due to alteration of garnet. With regard to the presence of B, Cr and elevated XMg in some hydrothermal phases compared to the older Fe-Mg minerals, we suggest circulation of fluids affecting host rocks as well as additional rock types.

Compositional and Textural Variations of Columbite-Group Minerals from Beryl-Columbite Pegmatites in the Maršíkov District, Bohemian Massif, Czech Republic: Magmatic versus Hydrothermal Evolution

2020 ◽  
Author(s):  
Štěpán Chládek ◽  
Pavel Uher ◽  
Milan Novák
Keyword(s):  
Czech Republic ◽  
Bohemian Massif ◽  
High Mobility ◽  
Oscillatory Zoning ◽  
Hydrothermal Conditions ◽  
Magmatic Stage ◽  
Compositional Variations ◽  
Host Rocks ◽  
Crystal Volume ◽  
Residual Melt

Abstract We studied compositional variations in columbite group minerals (CGM) from several granitic pegmatites of the beryl-columbite subtype in the Maršíkov district, Silesian Domain of the Bohemian Massif, Czech Republic. The CGM are characterized by distinct zoned patterns in BSE images. Primary magmatic homogeneous to oscillatory zoning is preserved in corroded crystal cores, whereas the majority of the crystal volume is replaced by secondary complexly zoned domains formed via post-magmatic processes. The primary domains show relatively uniform evolutionary trends from core to rim, generally with steeply increasing Ta/(Ta + Nb) and negligible to slightly increasing Mn/(Mn + Fe). In contrast, the compositions of secondary CGM domains indicate a reversed evolution, with: (1) steeply decreasing Ta/(Ta + Nb) and relatively constant Mn/(Mn + Fe) characteristics for CGM in the Bienergraben and Scheibengraben pegmatites, and (2) insignificantly decreasing Ta/(Ta + Nb) and strongly decreasing Mn/(Mn + Fe) characteristics for CGM in the Schinderhübel I and Lysá Hora pegmatites. Patchy zoning and secondary evolution in CGM result from metasomatic replacement processes related to fluids. These fluids are probably late-magmatic and exsolved from the residual melt and in later stages locally mixed with external Mg-enriched fluids derived from the host rocks. The presence of volatiles (mainly H2O, F) facilitated high mobility of the elements and replacement of the early CGM. Textural characteristics and compositional variations in CGM show the complex evolution of the pegmatite system from the magmatic stage to subsolidus-hydrothermal conditions.

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.

scholarly journals Eclogite-like rocks from Southern Pirin Mountains – preliminary results about petrology and time of formation

2021 ◽  
Vol 82 (3) ◽  
pp. 61-63
Author(s):  
Lyubomirka Macheva ◽  
Philip Machev ◽  
Rossitsa Vassilevа ◽  
Yulia Plotkina
Keyword(s):  
Mineral Assemblage ◽  
Late Jurassic ◽  
Mineral Chemistry ◽  
Metasomatic Alteration ◽  
Preliminary Results ◽  
Icp Ms ◽  
Geological Map ◽  
Host Rocks ◽  
The Village

North-northeast of the village of Ilinden (Southern Pirin Mnt.) three eclogite boudins were separated on the geological map in scale 1:50 000 (Sarov, 2010). The rocks belong to the Slasten lithotectonic unit. The mineral assemblage and mineral chemistry do not allow these rocks to be classified as eclogites. They can be considered as eclogite-like ones, formed by postmagmatic-metasomatic alteration of the host rocks. Based on LA-ICP-MS sphene U-Pb dating, eclogite-like rocks yield a Late Jurassic age (160±19 Ma).

Thermodynamic Modeling and Sensitivity Analysis of Kd Values for Radionuclide Migration in Sedimentary Host Rocks

2003 ◽  
Vol 807 ◽  
Author(s):  
Caterina Talerico ◽  
Michael Ochs ◽  
Shinzo Ueta ◽  
Noriyuki Sasaki
Keyword(s):  
Sensitivity Analysis ◽  
Ion Exchange ◽  
Mineral Assemblage ◽  
Surface Complexation ◽  
Critical Component ◽  
Radionuclide Migration ◽  
Sorption Model ◽  
Geochemical Parameters ◽  
Kd Values ◽  
Host Rocks

ABSTRACTThe effects of key geochemical parameters on Kd values for radionuclides in the host rock (pumice, sandstone) of a LLW repository were elucidated through a sensitivity analysis, using a thermodynamic speciation/sorption model for the elements Sr and Ni. The complex mineral assemblage of the rock was approximated by a component-additivity approach. Using published ion exchange and surface complexation parameters, Kd for both Sr and Ni could be well explained by the same model mineralogy and surface chemistry. Model results suggest that pCO2 can have a significant effect on Kd, and that a correct approximation of groundwater chemistry is a critical component of sorption modeling.

A Discussion on natural strain and geological structure - The control of ductility on the deformation of pebbles and conglomerates

1976 ◽  
Vol 283 (1312) ◽  
pp. 109-128 ◽  
Keyword(s):  
Confining Pressure ◽  
Geological Structure ◽  
Metamorphic Rocks ◽  
Tectonic Deformation ◽  
Low Grade ◽  
Rock Types ◽  
Gravitational Loading ◽  
The Matrix ◽  
Host Rocks

Pebbles are commonly used parameters for the determination of finite strain in deformed rocks. In high grade metamorphic environments, rocks probably behave as viscous fluids and a theory exists which relates the deformation experienced by a pebble to that of the host rocks. However, some deformed conglomerates are found in low grade metamorphic rocks where the assumption of viscous behaviour is unrealistic The deformation of artificial conglomerates made of geological materials, at room temperature and varying confining pressure is described. In these experiments, pebbles deform by cataclasis at surprisingly low applied loads and large finite strains are achieved. The amount of deformation experienced by pebbles of different rock types depends mainly on their yield strengths and ductility contrasts with respect to the matrix. A theoretical analysis assuming that pebble and matrix behave as workhardening Bingham materials during deformation relates the strain experienced by a pebble to that of the host rock. The results suggest that significant pebble deformation can occur during gravitational loading of sediments. An attempt is made to verify this idea by analysing the shape of pebbles in conglomerates of the Upper Witwatersrand System. At some sites the pebbles appear to have deformed during gravitational compaction while at others a tectonic deformation has been superimposed upon the pre-tectomic strain.

Deciphering the petrogenesis of deeply buried granites: whole-rock geochemical constraints on the origin of largely undepleted felsic granulites from the Moldanubian Zone of the Bohemian Massif

2004 ◽  
Vol 95 (1-2) ◽  
pp. 141-159 ◽  
Author(s):  
Vojtěch Janoušek ◽  
Fritz Finger ◽  
Malcolm Roberts ◽  
Jiří Frýda ◽  
Christian Pin ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Granitic Rocks ◽  
Granitic Magma ◽  
Moldanubian Zone ◽  
Trace Element Contents ◽  
High Grade Metamorphism ◽  
Early Palaeozoic ◽  
High Level ◽  
Geochemical Constraints ◽  
Variation Trends

ABSTRACTThe prominent felsic granulites in the southern part of the Bohemian Massif (Gföhl Unit, Moldanubian Zone), with the Variscan (∼340 Ma) high-pressure and high-temperature assemblage garnet+quartz+hypersolvus feldspar ± kyanite, correspond geochemically to slightly peraluminous, fractionated granitic rocks. Compared to the average upper crust and most granites, the U, Th and Cs concentrations are strongly depleted, probably because of the fluid and/or slight melt loss during the high-grade metamorphism (900–1050°C, 1·5–2·0 GPa). However, the rest of the trace-element contents and variation trends, such as decreasing Sr, Ba, Eu, LREE and Zr with increasing SiO2 and Rb, can be explained by fractional crystallisation of a granitic magma. Low Zr and LREE contents yield ∼750°C zircon and monazite saturation temperatures and suggest relatively low-temperature crystallisation. The granulites contain radiogenic Sr (87Sr/86Sr340 = 0·7106–0·7706) and unradiogenic Nd ( = − 4·2 to − 7·5), indicating derivation from an old crustal source. The whole-rock Rb–Sr isotopic system preserves the memory of an earlier, probably Ordovician, isotopic equilibrium.Contrary to previous studies, the bulk of felsic Moldanubian granulites do not appear to represent separated, syn-metamorphic Variscan HP–HT melts. Instead, they are interpreted as metamorphosed (partly anatectic) equivalents of older, probably high-level granites subducted to continental roots during the Variscan collision. Protolith formation may have occurred within an Early Palaeozoic rift setting, which is documented throughout the Variscan Zone in Europe.

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