Jaromír Leichmann

Cathodoluminescence of silicified trunks from the Permo-Carboniferous basins in eastern Bohemia, Czech Republic

The relationship between the actual anatomy of silicified plants and the nature of their permineralization has yet to be fully understood from a mineralogical point of view. Thin sections of silicified trunks obtained from the extinct Permo-Carboniferous arborescent plant taxa Arthropitys GOEPP., Psaronius COTTA and Dadoxylon ENDL., were studied by transmitted normal light (PPL), polarized-light (XPL), hot or scanning cathodoluminescence (CL), and electron microscopy (SEM) with energy and wavelength dispersive X-ray analysis (EDS and WDS). X-ray diffraction analysis (XRD) indicates that the SiO 2 phase is highly crystalline, probably due to its extreme age (approximately 300 million years). The cathodoluminescence of the silicifed trunks is seen to be unique and related to the petrographical characteristics of SiO 2 matter, which is closely connected to variation in plant anatomy. Microquartz (up to 20 μm) and fine megaquartz crystals (20–50 μm) generally produced red CL. They are present in most of the former plant tissues, especially in parenchyma and sclerenchyma, and also in cell walls and lumina of tracheids and rays of the secondary xylem. They almost completely reflect the original anatomical structures and as polyblastic textures preserve them best. Thick-walled sclerenchyma cells are usually best preserved, tracheids with lignin thickenings to a lesser extent. In contrast, megaquartz (above 50 μm) with brownish-red CL, spherulitic chalcedony with pinkish-purple or light violet CL, and agate-like structures sometimes crystallized as hyperblastic textures irrespective of the original plant tissues. This occurred especially in former thin-walled parenchyma, aerenchyma, voids, and in empty spaces and cracks. Parenchyma is thus well preserved only occasionally but aerenchyma is always transformed to an undifferentiated mineral phase. In the SiO 2 ground-mass, stable red CL prevails and blue CL is less common. CL sometimes allows visualisation of important fine scale anatomical detail that is not obvious under normal transmitted light. Furthermore, in several cases short-lived blue CL was recorded, which revealed a secondary overprint caused by a later silicification phase. CL also revealed traces of earlier calcification (orange CL). Detrital mineral grains, trapped in a compact silicified body (easily exposed by CL and analyzed by SEM/EDS) can serve as a clue to plant taphonomy, as for example black sands in “mineral pockets” probably indicate well-sorted sedimentary units from original riparian environments.

Garnet as a major carrier of the Y and REE in the granitic rocks: An example from the layered anorogenic granite in the Brno Batholith, Czech Republic

Abstract Garnet and other rock-forming minerals from A-type granite dikes in the Pre-Variscan Brno Batholith were analyzed to determine relative contributions of individual minerals to whole-rock Y and REE budget and to assess incorporation mechanisms of these elements in garnet. Minor to accessory garnet (<2 vol%) is the essential reservoir for Y+REE in the Hlína granite accounting ∼84% Y and 61% REE of the total whole-rock budget. Zircon is another important carrier of REE with ∼13% Y and ∼11% REE. At least ∼21% REE and 1% Y were probably hosted by Th- and U-rich monazite that has been completely altered to a mixture of secondary REE-bearing phases. The contribution of major rockforming minerals (quartz and feldspars) is low (∼1% Y; 10% LREE; ∼1% HREE) excluding Eu, which is hosted predominantly by feldspars (∼90%). Minor to accessory muscovite and magnetite incorporate ∼1% Y and ∼2% REE of the whole-rock budget. Magmatic garnet Sps41-46Alm28-44And0-13 Grs6-12Prp0-1 is Y- and HREE-rich (up 1.54 wt% Y; up ∼1 wt% ΣREE), and the Y+REE enter the garnet structure via the menzerite-(Y) substitution. The Y and REE show complex zoning patterns and represent sensitive indicator of garnet evolution, in contrast to a homogeneous distribution of major divalent cations. General outward decrease of Y+REE is a common feature due to the strong partitioning of Y+HREE in the garnet relative to the other phases. REE underwent significant fractionation during growth of early garnet I; the YbN/NdN ratio generally decreases from the core to rim of garnet I. Higher Mn and Al, lower Ca, and Y+REE contents, as well as higher YbN/NdN ratio and more negative Eu anomaly in garnet II overgrowths indicate its crystallization from a more evolved melt. Application of zircon saturation geothermometry provides upper temperature limit of 734 ± 14 °C for the closed-system crystallization. Mineral equilibria reveal that crystallization started at QFM + 1.2, and preferential sequestration of Fe3+ into garnet and magnetite was responsible for progressively reducing conditions. Equilibrium between magnetite, garnet, quartz, and plagioclase, representing the final crystallization stage of the granitic magma, occurred at 658-663 °C and QFM 0 to + 0.8, hence at undercooling of ∼75 °C.

Quaternary tectonics at the eastern border of the Bohemian Massif: new outcrop evidence

Recently, an outcrop with clear evidence for Quaternary faulting has been discovered in the eastern part of Bohemian Massif, 25 km southwest of Brno (Moravia, Czech Republic). Basement serpentinite, fluvial gravels, loess and young scree are affected by a steep NNW–SSE trending fault. The geological situation of the outcrop is described for the first time in this article.

Element mobility and fluid path ways during feldspar alteration: textural evidence from cathodoluminescence and electron microprobe study of an example from tonalites (High Tatra, Poland-Slowakia)

Infiltration of aqueous or CO2 rich fluids into plutonic rocks cause strong redistribution of the major elements within individual feldspar grains. This paper documents these features, using cathodoluminescence and electron microprobe analyses, on an example from a tonalite (High Tatra). An-rich plagioclase with small inclusions of K-feldspar decomposed under the influence of H2O fluids into albite, white mica, prehnite and quartz . This reaction leads to separation of alkalies from Ca and migration of alkalies and Ca over a distance of around 200 micrometers within the grain. Redistribution of Al is less affected by this reaction. Infiltration of H2O + CO2 -rich fluids through the An-rich plagioclase with minor orthoclase component produces calcite together with prehnite, albite and white mica. Reactions preferably affect the An-rich domains in plagioclase, Ab-rich domains remain unaffected, and the presence of K-feldspar in plagioclase either as inclusion or as a solid solution component facilitates the reactions.

Zeletice Group: Very low-grade Palaeozoic sequence at the base of Moravicum, Czech Republic

Definice a charakteristika nově objevene, velmi nizce metamorfovane metasedimentarni jednotky na bazi moravniho přikrovu.

Volcanism on Anafi island: short living, extensional, hydromagmatic volcanism in the central part of the South Aegean volcanic chain (Greece)

Aegean, volcanism,alteration,stable isotopes,strontium isotopes, implication for the evolution of Aegean arc, hydromagmatic volcanism, petrology, geochemistry, Anafi island, tectonic interpretation

Microstructural analysis of a urinary stone as evidence of experimentally observed processes of their formation

Careful and detailed comparative morphology analysis of individual crystals and crystal aggregates forming real urinary stone and its comparison with experimental results provides evidence of the processes that were previously identified in laboratory experiments. This study is based on electron microprobe observations of a polished thin-section of a surgically removed stone formed by oxalates and apatite. The original concrement was surgically removed from upper part of the left ureter. The patient was 72-yearold man with normal laboratory values. The nidus of the stone was not distinguished.

Granátické páskované anorogenní granity a pegmatity suity Hlína v brunovistuliku – textury a plošné rozšíření

The SW part of the Brno Batholith as well as NE part of the Thaya batholith have undergone recent mapping focused on layered granite dykes belong to the Hlina A-type granite suite. Dykes cropping out throughout the both other granitic suites in the region (Rena I-type and Tetcice S-type) widespread more than 60 km in N–S direction. Structures of the Hlina granites are easily distinguishable by their layering parallel to the contact, alternating of major aplite-like zones and minor pegmatite-like zones with oriented UST comb-like Qtz, Pland Kfs. The lamination of the rock is pronounced by parallel stripe-like arrangement of the garnet. The purpose of text below is highlighted the volumetrically scarce but genetically very important part of the Brunovistulian unit.