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Alexandra Herg and Kurt Stüwe

Abstract

In order to constrain tectonic models for the nature of the Eoalpine high pressure belt at the eastern end of the Alps, we investigate the formation pressure of metamorphic rocks along a profile between the Koralpe and the well-known UHP rocks of the southern Pohorje mountains. Rocks from three different regions are considered: (i) the rocks of the southernmost Koralpe to the north, (ii) the rocks of the Plankogel Unit between the Plankogel detachment and the Drava valley and (iii) the rocks between the Possruck range and the southern Pohorje mountains. In the Koralpe, pelitic rocks record a formation pressure around 15 – 18 kbar, as reported in the literature. For the Plankogel Unit, we derive pressures between 7.1 ± 1.95 kbar and 11.5 ± 3.42 kbar at 650 °C and recognize only a single Eoalpine metamorphic event. For the high grade rocks of the Pohorje mountains, we derive peak metamorphic pressures (explored with the garnet-muscovite-kyanite-quartz assemblage) that rise from 16.2 ± 3.45 kbar (at 700°C) in the north, to 23.9 ± 2.49 kbar (at 700 °C) in the south. There, we also recognize a later lower pressure event that is derived from pressure calculations with the full equilibrium assemblage. This lower pressure event yields similar conditions around 10 ± 2 kbar at 650 °C for the entire north-south transect within the Pohorje mountains. Peak metamorphic conditions in the Koralpe and Pohorje regions are matched by a continuous field gradient of about 1.3 kbar per 10 kilometers distance corresponding to a depth increase of about 0.5 km per kilometers distance assuming lithostatic conditions. We suggest that this supports that the two units may be interpreted together in terms of a 45° dipping subducting plate. Above this subducting plate, it is inferred that a slab was extracted that was located between the Plankogel Unit and the high pressure rocks, causing a first exhumation stage that is associated with buoyant upwards tilting of the subducted slab to mid crustal levels. Within this model, the Plankogel Unit was located in the hanging wall of the extracted slab and the Plankogel detachment forms the suture of the extracted slab. Exhumation from mid crustal levels to the surface during a 2nd stage occurred due to erosion and normal faulting. This normal faulting is responsible for some 10 km of upward displacement of the Pohorje mountains relative to the Koralpe and ultimately for the current distribution of lithologies on a map scale.

Open access

Pitsanupong Kanjanapayont, Peekamon Ponmanee, Bernhard Grasemann, Urs Klötzli and Prayath Nantasin

Abstract

The NW–trending Three Pagodas shear zone exposes a high–grade metamorphic complex named Thabsila gneiss in the Kanchanaburi region, western Thailand. The quartz mylonites within this strike–slip zone were selected for strain analysis. 2–dimensional strain analysis indicates that the averaged strain ratio (Rs) for the lower greenschist facies increment of XZ–plane is Rs = 1.60–1.97 by using the Fry’s method. Kinematic vorticity analysis of the quartz mylonites in the shear zone showed that the mean kinematic vorticity number of this increment is Wk = 0.75–0.99 with an average at 0.90 ±0.07. The results implied that the quartz mylonites within the Three Pagodas shear zone have a dominant simple shear component of about 72% with a small pure shear component. A sinistral shear sense is indicated by kinematic indicators from macro– to micro–scale. We conclude that the Three Pagodas shear zone deformed in the process of sinstral shear–dominated transpression, which is similar to the Mae Ping shear zone in the north.

Open access

Ján Spišiak, Lucia Vetráková, David Chew, Štefan Ferenc, Tomáš Mikuš, Viera Šimonová and Peter Bačík

Abstract

Calc–alkaline lamprophyres are known from several localities in the Malá Fatra Mountains. They form dykes (0.5–3 m) of varying degree of alteration that have intruded the surrounding granitoid rocks which are often incorporated xenoliths. Clinopyroxenes (diopside to augite), amphiboles (kaersutitic), biotites (annite) and plagioclases are major primary minerals of the dykes, accessory minerals include apatite, ilmenite, rutile, pyrite, chalcopyrite, and pyrrhotite. Apatite has a relatively low F, but increased Cl content compared to typical apatite from lamprophyres or magmatic apatite from granitic rocks in the Western Carpathians. The chemical composition of the lamprophyres indicates their calc–alkaline character, but affinity to alkaline lamprophyres is suggested by the Ti enrichment in clinopyroxene, amphibole and biotite. According to modal classification of the minerals, the studied rocks correspond to spessartite. The differences in the chemical composition of the rocks (including Sr and Nd isotopes) probably result from the contamination of primary magma by crustal material during magma ascent. The age of the lamprophyres, based on U/Pb dating in apatite, is 263.4 ± 2.6 Ma.

Open access

Tamás Csibri, Samuel Rybár, Katarína Šarinová, Michal Jamrich, Ľubomír Sliva and Michal Kováč

Abstract

The Blatné Depression located in the NW part of the Danube Basin represents the northernmost sub-basins of the Pannonian Basin System. Its subsidence is associated with oblique collision of the Central Western Carpathians with the European platform, followed by the back-arc basin rifting stage in the Pannonian domain. The conglomerates recognized in the Cífer-2 well document the latest Burdigalian–early Langhian deposition in fan delta lobes situated above the footwall and hanging wall of a WSW–ENE trending fault system, the activity of which preceded the opening of the late Langhian–Serravallian accommodation space with a NE–SW direction. The provenance area of the “Cífer conglomerate” was linked to the Tatric Super-unit complexes. Similar rocks crop out in the southern part of the Malé Karpaty Mts. and are also present in the pre-Cenozoic basement of the Danube Basin. Documented extensive erosion of the crystalline basement and its sedimentary cover lasted until the early/middle Miocene boundary. The “Cífer conglomerate” has distinct clast composition. The basal part consists of poorly sorted conglomerate with sub-angular clasts of metamorphic rocks. Toward the overlying strata, the clasts consist of poorly sorted conglomerates with sub-rounded to well-rounded carbonates and granitoids. The uppermost part consists of poorly sorted conglomerates with sub-rounded to rounded clasts of carbonate, granitoid and metamorphic rock. Within the studied samples a transition from clast to matrix supported conglomerates was observed.

Open access

Maria S. Karpuk, Ekaterina A. Shcherbinina, Ekaterina A. Brovina, Galina N. Aleksandrova, Andrey Yu. Guzhikov, Elena V. Shchepetova and Ekaterina M. Tesakova

Abstract

Previous studies made in different parts of the world have shown that Barremian–Aptian times imply many difficulties in deciphering the biostratigraphy, microfossil evolution and correlation of bioevents. In an attempt to improve our knowledge of this period in a particular area of the Tethyan realm, we present the first integrated study of microbiota (including planktonic foraminifera, calcareous nannofossils, ostracods and palynomorphs) and magnetostratigraphy of the upper Barremian–Aptian sediments from south-eastern Crimea. The nannofossils display the classical Tethyan chain of bioevents in this interval, while the planktonic foraminifera demonstrate an incomplete succession of stratigraphically important taxa. Our study enabled the recognition of a series of biostratigraphic units by means of four groups of microfossils correlated to polarity chrons. The detailed analysis of the microfossil distribution led to a biostratigraphic characterization of the Barremian/Aptian transition and brought to light an interval, which may correspond to the OAE1a.

Open access

Noemi Mészárosová, Roman Skála, Šárka Matoušková, Petr Mikysek, Jakub Plášil and Ivana Císařová

Abstract

The apatite assemblage from Maglovec hill (Slanské vrchy Mountains near the city of Prešov) from fissures of hydrothermally altered neovolcanic rocks (andesites and related lithologies) was studied. The assemblage consists of two different morphological apatite types (apatite in cores of prismatic crystals and fibrous apatite mantling these cores). The assemblage was investigated by a multi-analytical approach to reveal its unique chemical composition and structure. Both types of apatite display zoning visible in back-scattered electron (BSE) images. Core apatite is relatively homogenous with porous rims appearing darker in the BSE images at the contact with fibrous apatite, and occasionally with darker regions along fractures. These parts are depleted in trace elements, mostly in LREE. Fibrous apatites display concentric and/or patchy zoning. Dark regions in fibrous apatite occasionally display a porous structure. In part of fibrous crystals, substitution of (CO3)2− for phosphorus is confirmed by Raman spectroscopy by the presence of a band at ~ 1071 cm−1. This method also confirmed the presence of OH in different populations in the structure of all apatite types. The three most important observed peaks are caused by vibrations of hydroxyls influenced by different adjacent anions: hydroxyl (band at ~ 3575 cm−1); fluorine (band at ~ 3535–3540 cm−1); chlorine (band at ~ 3494 cm−1). In REE-depleted parts of both apatite types, fine inclusions of monazite and rarely Th-rich silicate are observed. The acquired data suggest a hydrothermal origin of this assemblage and indicate a formation sequence of distinct apatite types. Moreover, minerals from the epidote group were identified, which have not been described from this locality before as well as vanadium-rich magnetites that form exsolution lamellae in ilmenite grains.

Open access

Igor Broska and Michal Kubiš

Abstract

The S-type accessory mineral assemblage of zircon, monazite-(Ce), fluorapatite and tourmaline in the cupolas of Permian granites of the Gemeric Unit underwent compositional changes and increased variability and volume due to intensive volatile flux. The extended S-type accessory mineral assemblage in the apical parts of the granite resulted in the formation of rare-metal granites from in-situ differentiation and includes abundant tourmaline, zircon, fluorapatite, monazite-(Ce), Nb–Ta–W minerals (Nb–Ta rutile, ferrocolumbite, manganocolumbite, ixiolite, Nb–Ta ferberite, hübnerite), cassiterite, topaz, molybdenite, arsenopyrite and aluminophosphates. The rare-metal granites from cupolas in the western segment of the Gemeric Unit represent the topaz–zinnwaldite granites, albitites and greisens. Zircon in these evolved rare-metal Li–F granite cupolas shows a larger xenotime-(Y) component and heterogeneous morphology compared to zircons from deeper porphyritic biotite granites. The zircon Zr/Hfwt ratio in deeper rooted porphyritic granite varies from 29 to 45, where in the differentiated upper granites an increase in Hf content results in a Zr/Hfwt ratio of 5. The cheralite component in monazite from porphyritic granites usually does not exceed 12 mol. %, however, highly evolved upper rare-metal granites have monazites with 14 to 20 mol. % and sometimes > 40 mol. % of cheralite. In granite cupolas, pure secondary fluorapatite is generated by exsolution of P from P-rich alkali feldspar and high P and F contents may stabilize aluminophosphates. The biotite granites contain scattered schorlitic tourmaline, while textural late-magmatic tourmaline is more alkali deficient with lower Ca content. The differentiated granites contain also nodular and dendritic tourmaline aggregations. The product of crystallization of volatile-enriched granite cupolas are not only variable in their accessory mineral assemblage that captures high field strength elements, but also in numerous veins in country rocks that often contain cassiterite and tourmaline. Volatile flux is documented by the tetrad effect via patterns of chondrite normalized REEs (T1,3 value 1.46). In situ differentiation and tectonic activity caused multiple intrusive events of fluid-rich magmas rich in incompatible elements, resulting in the formation of rare-metal phases in granite roofs. The emplacement of volatile-enriched magmas into upper crustal conditions was followed by deeper rooted porphyritic magma portion undergoing second boiling and re-melting to form porphyritic granite or granite-porphyry during its ascent.

Open access

Reihaneh Roshanak, Farid Moore, Alireza Zarasvandi, Behnam Keshavarzi and Reinhard Gratzer

Abstract

The Qorveh-Takab travertines, which are connected to thermal springs, are situated in the northwest of the Sanandaj- Sirjan metamorphic zone in Iran. In this study, the travertines were investigated applying petrography, mineralogy and isotope geochemistry. Oxygen and carbon isotope geochemistry, petrography, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis were used to determine the source of the CO2 and the lithofacies and to classify the travertines. Isotope studies, morphological and mineralogical observations and distribution of travertines revealed that the travertines of the Qorveh-Takab could be of thermal water origin and, therefore, belong to the thermogene travertine category. These travertines are usually massive with mound-type morphology and are essentially found in regions with recent volcanic or high tectonic activity. The measured δ13C values of the travertines indicate that the δ13C of the CO2 released from the water during travertine deposition, while the source of the CO2 in the water springs seems to have been of crustal magmatic affinity. These travertines are divided into two lithofacies: (1) crystalline crust travertine and (2) pebbly (phytoclastic travertine with pebble- size extraclasts) travertine. δ18O and δ13C values of travertines are -0.6 to -11.9 (‰VPDB) and +6.08 to +9.84 (‰VPDB), respectively. A probable reason for the heavy carbon isotope content observed in these deposits is the presence of algae microorganisms, which was verified by SEM images. Fissure ridges, fluvial crusts with oncoids, and mound morphological features are observed in the study area. Based on the petrographic and SEM criteria, Qorveh-Takab travertines are classified into four groups: (1) compacted, (2) laminated, (3) iron-rich spring deposit and (4) aragonite-bearing travertines. Stable isotope compositions of Turkish travertines are largely similar to the travertines in the study area.

Open access

Petra Lukeneder and Alexander Lukeneder

Abstract

Lower Jurassic ammonites were collected from deep-water limestones of the Tannscharten section, southwest of Reichraming (Northern Calcareous Alps, Upper Austria). The outcrop provides a rich Upper Sinemurian (Lower Jurassic) ammonite fauna of the Allgäu Formation. The area is situated in the westernmost part of the Schneeberg Syncline in the north of the Reichraming Nappe (High Bajuvaric Unit). The ammonite fauna consists of seven different genera, each apparently represented by 1-2 species. Echioceratids are the most frequent components (Echioceras, Leptechioceras, Paltechioceras), followed by the phylloceratids (Juraphyllites, Partschiceras) and oxynoticeratids (Gleviceras, Paroxynoticeras). Juraphyllites libertus, Partschiceras striatocostatum, Gleviceras paniceum, Echioceras quenstedti, Echioceras raricostatoides, Paltechioceras boehmi, Leptechioceras meigeni, Leptechioceras macdonnelli and Paltechioceras oosteri are new for the Schneeberg Syncline and allow for the first time a detailed biostratigraphy of the Echioceras raricostatum zone. The assemblage is correlated with other faunae from Austria, Germany, United Kingdom, France, Switzerland and Romania. The cephalopod fauna consists of a mix of elements from the Northwest European Province and the Mediterranean Province. The detailed biostratigraphy based on ammonites is presented here.

Open access

Mathias Harzhauser, Oleg Mandic, Matthias Kranner, Petra Lukeneder, Andrea K. Kern, Martin Gross, Giorgio Carnevale and Christine Jawecki

Abstract

Sarmatian and Pannonian cores, drilled at the western margin of the Vienna Basin in the City of Vienna, reveal a complex succession of marine and lacustrine depositional environments during the middle to late Miocene transition. Two Sarmatian and two Pannonian transgressive-regressive sequences were studied in detail. Identical successions of benthic faunal assemblages and similar patterns in magnetic susceptibility logs characterise these sequences. This allows a correlation of the boreholes over a distance of ~3.5 km across one of the major marginal faults of the Vienna Basin. Biostratigraphic data, combined with rough estimates of sedimentation rates, reveal large gaps between these sequences, suggesting that only major transgressions reached this marginal area. In particular, during the Sarmatian-Pannonian transition, the basin margin completely emerged and turned into a terrestrial setting for at least 600 ka.