Moldanubian granite
198996008
Calcic tourmalines from eastern part of metamorphic envelope of the Karkonosze Granite Massif (NE part of Moldanubian Zone, Lower Silesia, Poland)
The crystallochemical evolution of tourmalines from a quartz vein cutting an amphibolitic insert within mica schists in the eastern part of metamorphic envelope of the Karkonosze Granite massif close to the Kowary town in Lower Silesia, Poland (NE part of Moldanubian) was studied in detail. The amphibolite was formed from a mixed magmatic sedimentary protoliths (connected with pre Variscian bimodal volcanism products like basic lavas and basic tuffs) which underwent regional Variscan metamorphism under MP MT conditions, and then were modified by contact metamorphism induced by the intrusion of the Karkonosze Granite pluton [1]
Mateusz Sek Adam Pieczka
150168969
Radioactivity and zoning in granite plutons of Weinsberg type: indicator of differentiation of the Vydra and Prasily plutons (Moldanubian Batholith, Czech Republic)
Vladimir Zacek
129009867
Mechanisms of myrmekite formation: case study from the Weinsberg granite, Moldanubian zone, Upper Austria
Myrmekites have attracted the attention of petrographers over more than a century, and several genetic models have been proposed. We report on myrmekites from the Weinsberg granite of the Moldanubian zone of Upper Austria. Based on petrographic evidence, fluid mediated replacement of alkali feldspar by myrmekite during the sub solidus evolution of the granite is inferred. The replacement was metasomatic on the scale of the myrmekite domains requiring addition of sodium and calcium and removal of potassium from the reaction site. In contrast, silica and aluminum were conserved across the reaction front. Myrmekite formation appears to have been synchronous with and related to the hydration of orthopyroxene and concomitant replacement of primary magmatic plagioclase by biotite at around 500 degC. The evolution of the myrmekite microstructure and a peculiar composition zoning of the plagioclase constituting the myrmekite matrix is qualitatively explained by a model for discontinuous precipitation, which accounts for chemical segregation by diffusion within the reaction front and the propagation of the reaction front with finite mobility as potentially rate limiting processes. Constraints on the underlying reaction rates are derived from the preserved microstructure and chemical pattern. Crystal orientation imaging by electron backscatter diffraction reveals grain internal deformation, which is primarily concentrated in the quartz and less pronounced in the plagioclase matrix of the myrmekite. This is interpreted as a growth feature related to different transformation strain at the segments of the myrmekite reaction front, where quartz and plagioclase are formed.
Contributions to Mineralogy and Petrology
Rainer Abart David Heuser Gerlinde Habler
199832607
Titanite from Titanite Spots Granodiorites of the Moldanubian Batholith (Central European Variscan Belt)
Titanite rich granodiorites occurring in the Austrian Muhlviertel are intimately associated with the I/S granites of the Mauthausen/Freistadt granite suite. These rocks form small irregular bodies in granites of this granitic suite of the Moldanubian batholith that are represented by usually fine grained and dark granodiorites, which contain a large amount of titanite hell "spots" formed by aggregates of plagioclases and quartz. Titanite as a relative plentiful accessory mineral exists in the center of these "spots" as idiomorphic and sphenoidal grains. The composition of titanite ranges from 89 to 92 mol. titanite end member. According to its Al concentration, the analyzed titanites could be considered as low Al titanites (Al 0.05 0.08 atoms per formula unit) Titanite contains low concentrations of both (Al Fe) OH (2 9 mol. and (Al Fe) F (0 8 mol. Titanite together with Na enriched plagioclase and quartz is originated during late magmatic evolution of titanite spots granodiorites.
Mineralogy [Working Title]
Milos Rene
126687834
Reply to the comments on "Magmatic history and geophysical signature of a post collisional intrusive center emplaced near a crustal scale shear zone: the Plechy granite pluton (Moldanubian batholith, Bohemian Massif)"
Krystof Verner Jiri Zak Jaroslava Pertoldova Jakub Trubac Patricie Tycova
129590279
Magmatic history and geophysical signature of a post collisional intrusive center emplaced near a crustal scale shear zone: the Plechy granite pluton (Moldanubian batholith, Bohemian Massif)
The Plechy pluton, southwestern Bohemian Massif, represents a late Variscan, complexly zoned intrusive center emplaced near the crustal scale Pfahl shear zone; the pluton thus provides an opportunity to examine the interplay among successive emplacement of large magma batches, magmatic fabric acquisition, and the late Variscan stress field associated with strike slip shearing. The magmatic history of the pluton started with the emplacement of the porphyritic Plechy and Haidmuhler granites. Based on gravity and structural data, we interpret that the Plechy and Haidmuhler granites were emplaced as a deeply rooted, ~NE SW elongated body; its gross shape and internal fabric (steep ~NE SW magmatic foliation) may have been controlled by the late Variscan stress field. The steep magmatic foliation changes into flat lying foliation (particularly recorded by AMS) presumably as a result of divergent flow. Magnetic lineations correspond to a sub horizontal ~NE SW finite stretch associated with the divergent flow. Subsequently, the Tristolicnik granite, characterized by steep margin parallel magmatic foliation, was emplaced as a crescent shaped body in the central part of the pluton. The otherwise inward younging intrusive sequence was completed by the emplacement of the outermost and the most evolved garnet bearing granite (the Marginal granite) along the southeastern margin of the pluton.
Krystof Verner Jiri Zak Jaroslava Pertoldova Joseph Sramek Jiri Sedlak Jakub Trubac Patricie Tycova
134125127
Model ages of fracture fillings and mineralogical and geochemical evidence for water rock interaction in fractures in granite: The Melechov Massif, Czech Republic
Abstract The mineral, chemical and Pb isotope composition were investigated in the host granite and low temperature open fracture fillings from the 100 m deep borehole PDM 1 located in the Melechov Massif of the Moldanubian Batholith. The fillings are dominated by limonite and clay mineral (illite, kaolinite, montmorillonite, nontronite, chlorite) mixtures, accompanied by minor amounts of residual minerals from the parent rock (quartz, feldspars, zircon, monazite) Chemically contrasting fracture assemblages occur mainly at lesser depths
Vaclav Prochazka Jiri Zacharias Ladislav Strnad
56107154
Source compositions and melting temperatures of the main granitic suites from the Moldanubian Batholith
The granitoids of the Moldanubian Batholith (Moldanubian Zone of the Bohemian Massif) are represented by three main suites: Ito I/S type Weinsberg biotite granites granodiorites, S type Eisgarn two mica granites and I/S type Freistadt biotite granites granodiorites. As shown by major element data and zircon with monazite saturation thermometry, partial melting of metapelites likely produced most of the Eisgarn suite (Mrakotin/Cimer varieties) at c. 775 825 oC. Parental melts of the Weinsberg and Freistadt suites could have been generated by partial melting of a metagreywackes metabasalts mixture at c. 740 940 oC. This study confirms that the CaO/Na2O ratio could be used for source assignment of S type granite melts, whereas the CaO/(FeO MgO TiO2) ratio is more suitable for I/S type granites. The observed systematic positive shift of Al2O3/ TiO2 temperatures compared with zircon and monazite saturation temperatures in all granitoids of the Moldanubian Batholith (up to 118 oC) may be explained by accumulation of ilmenite in the S type Eisgarn suite. In the Iand I/S granite types of the Weinsberg and Freistadt suites the Al2O3/TiO2 ratio is controlled by the accumulation of ilmenite and/or titanite. Consequently, the Al2O3/TiO2 ratio may be used as a thermometer only with caution.
Milos Rene
140573920
The generation of voluminous S type granites in the Moldanubian unit, Bohemian Massif, by rapid isothermal exhumation of the metapelitic middle crust
This paper presents new structural, anisotropy of magnetic susceptibility (AMS) petrological, and geochronological data to examine the link between LP HT metamorphism and S type granite formation in the Moldanubian unit, Bohemian Massif. We first describe the intrusive relationships of an S type granite to its host cordierite bearing migmatites, superbly exposed in the Racov locality, northeastern Moldanubian batholith. The knife sharp contacts and rectangular stoped blocks establish that the migmatites cooled and were exhumed above the brittle ductile transition prior to the granite emplacement. The U Pb monazite geochronology combined with P T estimations constrain the age and depth of migmatization at 329 Ma and 21 km (T 730 degC) The migmatite complex was then exhumed at a rate of 6 7 mm y 1 to a depth of 9 km where it was intruded by the granite at 327 Ma. These data indicate that the hot fertile metapelitic middle crust in this part of the Moldanubian unit, newly defined as the Pelhrimov complex, underwent rapid isothermal decompression at 329 327 Ma, giving rise to biotite melting and generation of large volumes of S type granite magma. We propose that the rapid 329 327 Ma exhumation of the Pelhrimov complex may have been partly assisted by the crustal scale Pribyslav mylonite zone, which delineates the underlying western edge of the Brunia microplate underthrust beneath the eastern half of the Moldanubian unit during the early Carboniferous. The front edge of Brunia thus acted as a rigid backstop at depth, localizing the exhumation of the Pelhrimov complex and separating the hot fertile middle crust to the west from the already cooled overthrust complexes to the east. The magnetic fabric of the granite around the migmatite blocks further reveals that the Pelhrimov complex was shortened vertically and extended in the WNW ESE direction during and after its exhumation, implying that the SSE directed underthrusting of Brunia along the eastern margin of the Bohemian Massif was replaced by vertical thinning and WNW ESE stretching of the Moldanubian crust. As a general conclusion, we suggest that even for extremely rapid crustal exhumation, S type granite magmas can be formed at greater depths by isothermal decompression of the metapelitic host, and then ascend almost instantaneously to the already exhumed (and cooled) shallow parts of the same metamorphic core complex. This model may explain the short time spans for the extensive migmatization and associated S type granite formation, crustal exhumation, and granite emplacement, as well as the presence of "cold" discordant granite migmatite contacts in once "hot" migmatite terrains.
Jiri Zak Krystof Verner Fritz Finger Shah Wali Faryad Marta Chlupacova Frantisek Veselovsky
130517185
Contrasting Origins of the Mixed (NYF LCT) Signature in Granitic Pegmatites, with Examples from the Moldanubian Zone, Czech Republic
Two granitic pegmatites with mixed (NYF LCT) signatures from the Moldanubian Zone, Czech Republic, were examined to determine their origin. On the basis of geological setting, paragenesis, geochemical modeling and chemical composition of rocks and minerals, two contrasting modes of origin were discerned. The Li bearing (lithium micas elbaite) Kracovice pegmatite, with "amazonite" samarskite and fergusonite, is the product of the strong fractionation of pegmatite forming melt derived from the orogenic I type Trebic pluton. Geological, petrological, compositional and isotopic data from this ultrapotassic melasyenite melagranite point to mixing of a mantle derived magma with (leuco) granitic melt from crustal rocks. The granite pegmatite system of the Trebic pluton and the mainly Li bearing Kracovice pegmatite are typical examples of the mixed (NYF LCT) petrogenetic family. The contaminated elbaite subtype pegmatite Blizna I, Cesky Krumlov Unit, with lithium tourmalines (elbaite, liddicoatite, uvite) primary REE minerals [bastnasite (Ce) parisite (Ce) allanite (Ce) and Ca(Mg) rich minerals (diopside, uvite, titanite) gained its mixed signature through a unique pre emplacement process involving the external contamination with Ca, Mg and REE of an evolved (LCT) pegmatite forming melt by distal carbonatite like marbles with an NYF signature. Despite the clearly mixed signature mineralogy and geochemistry, the Blizna I pegmatite represents a special type of contaminated LCT pegmatite rather than a member of the mixed family.
Milan Novak Radek Skoda Petr Gadas Lukas Krmicek Petr Cerny