The Ďumbier – Prašivá high K calc-alkaline granite suite (Low Tatra Mts., Western Carpathians): Insights into their evolution from geochemistry and geochronology
Abstract: The geochemistry of major Low Tatra granitic types, namely Prašivá porphyritic Bt (biotite)-granodiorite and Ďumbier Bt-tonalite, indicate their derivation from initial hybrid magmas and represent a mixture among several magma pulses formed via melting of the heterogeneous lower crust. The high K calc-alkaline peraluminous character, along with high Ba, Sr + LREE contents correspond to the partial melting of K-rich mafic and the intermediate hydrated lower crustal source in equilibrium with amphibole or possibly garnet with variable involvement of metasedimentary and/or felsic metaigneous sources. The zircon isotopic age of 360.4 ± 2.7 Ma recorded from diatexite reflects the timing of high-temperature metamorphism of subducted continental crust, and thus corresponds in age to other anatectic zones within the present Tatric Unit. The magmatic ages are in the largely overlapping sequence of 353 ± 2 Ma for the Ďumbier tonalite and 352 ± 3 Ma and 351.9 ± 2.9 Ma for Prašivá Aln (allanite bearing)-subtype and Mnz (monazite bearing)-subtypes, which indicate successive multiple emplacement of magma batches and natural evolution towards their more crustal character. Magmatism in the Low Tatra Mts. represents a post-collisional plutonic system related to the slab break-off mechanism described in the close Malá Fatra crystalline basement as well. Heat from mantle upwelling and volatiles from previous subduction forced the melting of the lower crust towards K-rich mafic or intermediate lithologies, as well as during the emplacement of long-lasting melting of felsic metasedimentary crustal sources. The crystalline core of the Low Tatra Mts. is another example of composite granite pluton in the Western Carpathians, which represents a product of the multiphase Late-Variscan post-collisional setting.
The Orava segment of the Pieniny Klippen Belt: Lithology, structure and stratigraphy based on the organic-walled dinoflagellate cysts
Abstract: The Pieniny Klippen Belt of the Western Carpathians is built up by Jurassic to Eocene Oravic units, with the Šariš, Subpieniny, and Pieniny Unit on the top. Major emphasis was placed on the dark fine-grained clastic deposits exposed in the vicinity of the villages of Beňova Lehota and Revišné (Orava sector of the Pieniny Klippen Belt). Through investigation of palynological material, the age of dark flysch strata was determined as predominantly uppermost Toarcian to Middle Aalenian and affiliated with the Szlachtowa and/or Skrzypny formations, belonging to the Šariš Unit. The results from the dinoflagellate cysts were supplemented by a structural investigation of the Šariš Unit. The complicated tectonic evolution of the Pieniny Klippen Belt is documented by intermixing of the soft shale deposits of Jurassic and Cretaceous age and by the presence of folds and cleavages. Based on the acquired data, the D1 event records a compression with a NE–SW direction and is represented by folds with axial-plane cleavage. The younger D2 phase is marked by the presence of south-vergent backthrusts, resulting from the ongoing compression and subsequent tilting of the originally north-vergent nappe stack of the Oravic units.
Evolution of the lower Badenian depositional system in the East Slovakian Basin: Implications for reservoir rock potential
Abstract: The Transcarpathian Basin, consisting of the Prešov and Trebišov sub-basins, is situated at the border of the Western and Eastern Carpathians. Hydrocarbon exploration in this basin has been ongoing for more than 60 years and reserves of economic importance are located in the E to NE part of the basin. The Trebišov sub-basin was analysed to characterize and predict lower Badenian (Langhian) reservoir rocks. To achieve this aim, new sedimentary facies, seismic facies, petrographic and paleontological analyses were performed, combined with original total porosity and permeability measurements. Based on the planktic foraminifera and calcareous nannoplankton zonation, the lower Badenian sequence in the Trebišov sub-basin was divided into a lower and an upper interval. The presence of very well sorted sandstone layers, glauconite grains, albitization, selective alteration of tuffs into zeolites as well as the fossil assemblages reinforce the volcanic influenced marine environments. Documented sedimentary structures indicate subaqueous density flows preceded by the newly observed fluvial and deltaic facies. The total sandstone porosity measurements indicate a gradual porosity decrease with depth marked by a value of 13.21 % at the surface decreasing down to 6.41 % at ~3 km below the surface. These numbers correspond to reservoirs with low to reduced porosity. Diagenetic products such as illite, chlorite and feldspar cement together with compaction effects, and variations in the crystallinity in siliceous cement led to the modification of initial porosity. The potential lower Badenian reservoir sandstones are frequently deformed by strike-slip faults responsible for the large pull-apart basin complex (seen as horsetail structures on reflection seismic sections) forming various fault-bounded structural traps. The lower Badenian sandstones present at the top of two anticlinal structures in the central part of the basin, display very strong reflection amplitudes on newly merged 3D reflection seismic data underlining the additional exploration potential in the basin.
Metamorphism of the westernmost Triassic metasedimentary rocks in the Sakar Unit, Sakar–Strandja Zone, Bulgaria
Abstract: Metasedimentary sequence from the westernmost Sakar Unit (Klokotnitsa Village area), Sakar–Strandja Zone, comprises a variety of lithologies with Triassic protolith age. In the study area, the Sakar Unit is affected by low-grade metamorphism in the frame of the Maritsa dextral strike-slip shear zone and separates two first-order units of the Balkan orogenic system – the Rhodope massif and the Srednogorie Zone. We present the petrography, mineral chemical data, and thermodynamic modelling of metasediments for a better understanding of the protoliths origin and metamorphic evolution. The mineral assemblages in Triassic metasediments suggest sedimentary protoliths containing quartz, clay, and carbonate minerals (sandstones, clays, and limestones). The detrital minerals (quartz, albite, orthoclase and accessory phases – zircon, monazite, apatite) reveal potential granite source provenance. The dominance of phengite–chlorite association correlates with low temperature and water-saturated conditions. The Perple_X pseudosection, combined with modelled mineral assemblages and mineral chemistry isopleths of muscovite and chlorite, correspond to metamorphism in the range 275–330 °C and 3–4 kbar. The results correspond with a chlorite geothermometer. The thermodynamic modelling corroborates the petrographic observations and proves greenschist metamorphic conditions that affected the Triassic sedimentary cover of the westernmost Sakar Unit.
Major and trace element signature of epidote-group minerals in altered pegmatites from the Petrovitsa Pb–Zn deposit of the Madan ore region, Central Rhodopes, Bulgaria: Evidence of allanite/epidote transformation
Abstract: The geochemical behaviour of major, rare, and trace elements in members of epidote-group minerals formed at different stages of magmatic and hydrothermal activity in pegmatites from the Madan ore district was studied.
Accessory allanite-(Ce) and two generations of hydrothermal clinozoisite–epidote occur in hydrothermally-altered pegmatite bodies at the 820 mine level in the Petrovitsa Pb–Zn deposit. Abundant large concordant and crosscutting pegmatites (age 49.63 ± 0.94 Ma) with a thickness of more than 2 m are embedded in a high-grade metamorphic complex composed of various gneisses, amphibolites, and marbles in the area of the Petrovitsa deposit. The pegmatites consist mainly of feldspars and quartz, with plagioclases (albite–oligoclase, oligoclase–andesine, anorthite) predominating over K-feldspars. The main accessory minerals are allanite-(Ce), zircon, apatite, and an abundance of titanite. The overprinted hydrothermal mineral association is characterised by the formation of clinozoisite–epidote, adularia, chlorite, Ca-garnet, titanite, leucoxene, carbonates, hematite, and quartz. Based on petrographic observations, mineral relationships, and chemical properties, two generations of epidotes (sensu lato) were recognised: early epidote (Ep1) and late epidote (Ep2). Chemically, allanite-(Ce) contains high amounts of La and Th. The mineral suffered alteration due to several multiphase hydrothermal events and is partly or entirely transformed into REE-rich clinozoisite, causing depletion in REE and Th as well as enrichment of Si, Al, and Ca. The epidote 1 generation is defined chemically as clinozoisite to clinozoisite–epidote, whereas the late epidote 2 generation is clinozoisite–epidote, reaching epidote members. The REE contents in the studied epidotes from both generations are equally low with minor exceptions. The influx of later fluids percolated through and probably extracted REE from allanite and thereafter concentrated them in late-generation epidotes. This is also evidenced by some high REE contents in epidotes from both generations, formed in close proximity to allanite or titanite and/or overgrowing them, which is a sign of restricted REE transport.
Tephrochronology of a distal tonstein layer within the Maritsa East lignite basin, Bulgaria: Potential sources of the Miocene large explosive eruption
Abstract: This contribution presents the age of the detrital zircons from the coal bearing Miocene succession of the Maritsa East lignite basin. We report a new finding of thin kaolinized pyroclastic beds (tonstein) in the coal bearing succession. The analysis of the detrital age component shows sedimentary input from the basement of the proximal area. The most abundant age cluster 290–315 Ma shows that the predominant sources are the Early Permian–Late Carboniferous intrusions in the area. The newly-recognized tonstein beds represent the products of large, distal pyroclastic eruptions and are an important element of the sedimentary succession. They are dated at 14.31±0.30 Ma, which corresponds to the absolute age of the organic matter deposition of the productive middle lignite seam. Their source could most likely be related to the Miocene acid paroxysm ignimbrite eruptions in the Pannonian basin.