Gemeric Unit Research Articles

Mineralogy and genetic considerations of the metamorphosed As-rich manganese ore mineralisation at the Diely occurrence near Poráč (Northern Gemeric Unit, Western Carpathians, Slovakia)

Mineralogy and genetic considerations of the metamorphosed As-rich manganese ore mineralisation at the Diely occurrence near Poráč (Northern Gemeric Unit, Western Carpathians, Slovakia)

Mineralogy and genetic aspects of the metamorphosed manganese mineralization at the Július ore occurrence near Betliar (Gemeric Unit, Western Carpathians, Slovakia)

Mineralogy and genetic aspects of the metamorphosed manganese mineralization at the Július ore occurrence near Betliar (Gemeric Unit, Western Carpathians, Slovakia)

Maldonite (Au2Bi) from hydrothermal U-As mineralization near Henclová (Spišsko-gemerské rudohorie Mts., Western Carpathians): the first occurrence in Slovakia

In Slovakia, maldonite was identified in the hydrothermal vein with U-sulphidic ore mineralization near Henclová village (Gelnica district) in the Spišsko-gemerské rudohorie Mts. (Vlachovo Formation, Gemeric Unit). It is the first occurrence of this mineral in Slovakia. Mineralization is developed in a hydrothermal quartz-chlorite (± fine grained white mica) vein with abundant arsenopyrite and minor quantities of uraninite, gersdorffite, löllingite, galenobismutite, bismuthinite, maldonite, bismuth and gold. Maldonite forms irregular grains up to 12 μm in size embedded in arsenopyrite, or extremely fine capillary veinlets in it. An intergrowth of maldonite with bismuthinite was rarely also observed. The chemical composition of maldonite is relatively monotonous, its average empirical formula can be expressed as (Au1.79Fe0.15)Σ1.94(Bi0.98As0.02S0.04)Σ1.04. Microstructural relationships of ore minerals suggest that maldonite precipitated in the final stages of ore mineralization, when the temperature of the system decreased (after the crystallization of sulphoarsenides and löllingite).

Oxidation and decomposition of stratiform SedEx sulfidic mineralization in the epidote-amphibolite facies producing cassiterite, V-rich micas, In-Sn-Ag-Sb-Pb-Bi-Zn-Fe-As-Cu-Ni-Co sulfides and Fe-Ca-Pb carbonates in situ (Bystrý potok locality, Gemeric unit, W. Carpathians)

The studied area of Bystrý potok locality (Gemeric unit, W. Carpathians) is built of lenses of lydites and limestones, being a part of the graphite bearing phyllites of Silurian Holec Beds. The Holec Beds represent the bedrock of the albite-quartz bearing keratophyre (trachyte sensu IUGS classif.) sequence with stratiform SedEx (sedimentary-exhalation) sulfidic mineralization in the Gemeric Lower Paleozoic stratigraphy. This SedEx mineralization was contemporaneous with Late Silurian–Devonian keratophyre/basalt magmatism and originated at 280–340 °C from the seafloor exhalates in Lower Paleozoic rift magmatism. The Silurian-Devonian rock sequences were metamorphosed in Permian. The limestone lenses were altered to Permian skarn in the epidote-amphibolite facies (526–546 °C, 3–6 kbar) and in related chlorite-apatite zone (420–540 °C) they consisted of garnet Grs41.4-60.2Sps19.8-32.8Alm16.7-22.2Adr0-8.5, hedenbergite Wo44.5-50.1Fs31.6-38.2En12.7-20.7, epidote, actinolite, fluorapatite, titanite, chlorite, ankerite and siderite. The disseminated original millerite was partially replaced by hauchecornite, hauchecornite-(Sb) and cobaltite was formed in the silicate matrix of the skarn. The Permian metamorphism of the epidote-amphibolite facies and the chlorite-apatite zone has also released a fluid phase rich in O2, H2O, CO2, H3PO4, H2S, HF and V from the organic matter-bearing rock (Holec Beds) into the overlying bed with keratophyres and primary stratiform SedEx sulfidic mineralization where V-rich micas, V-rich chlorite and schreyerite formed. The primary stratiform SedEx sulfidic mineralization composed predominantly of pyrite 1 less pyrrhotite, chalcopyrite, sphalerite 1, galena 1, arsenopyrite, ferrokesterite, stephanite, gudmundite, bismuthinite 1, PbBiSb-rich sulphide (A2B2S5-type) and kobellite has been oxidized and decomposed by this fluid phase to form a new metamorphic minerals in situ. The pyrrhotite decomposed to form szomolnokite, pyrite 2, goethite and siderite. The galena 1 was partly oxidized and decomposed to anglesite and cerussite. The In-rich ferrokesterite, Sn-rich sakuraiite and In-rich sphalerite 1 oxidized, decomposed, and reacted with the fluid phase to form cassiterite, chalcopyrite, In-rich sakuraiite and sphalerite 2. The PbSbBi-rich sulfide (A2B3X6-type), wittite, bismuthinite 2, native Bi and Se-rich galena 2 are new minerals, formed by the decomposition of original PbBiSb-rich sufhide (A2B2X5-type), kobellite and bismuthinite 1. Tetrahedrites 1–3 ranging from tetrahedrite-(Fe), kenoargentotetrahedrite-(Fe) to rozhdestvenskayaite-(Fe) show a gradual ordering in three separate zones controlled by immiscibility gaps in the Cu-Ag substitution of tetrahedrite group. These tetrahedrites were formed by the decomposition of the original SedEx ferrokesterite, stephanite and gudmundite. The gudmundite was also commonly oxidized to form valentinite and the decomposition of ferrokesterite, galena 1 and gudmundite also produced bournonite and plumosite-like. Altogether 22 reactions illustrate the relationship between the source SedEx mineralization and the new metamorphic minerals, which have formed at the expense of the original stratiform SedEx sulfidic mineralization in situ. The metamorphogenic fluid phase, released from the Holec Beds, has been enriched with additional elements from the stratigraphic horizon of the stratiform SedEx sulfidic mineralization and is genetically part of the Permian metamorphic-magmatic-hydrothermal (MMH) cycle (281–256 Ma).

Gadolinium-dominant monazite and xenotime: Selective hydrothermal enrichment of middle REE during low-temperature alteration of uraninite, brannerite, and fluorapatite (the Zimná Voda REE-U-Au quartz vein, Western Carpathians, Slovakia)

AbstractA hydrothermal quartz vein with REE-U-Au mineralization in the Zimná Voda (Gemeric Unit, Western Carpathians, Slovakia) is associated with contact metamorphism between Permian granites and host phyllites and metaquartzites. It contains unique REE minerals of the monazite and xenotime groups. Monazite-(Ce), monazite-(Nd), monazite-(Sm), and Gd-dominant monazite [“monazite-(Gd)”], along with xenotime-(Y) to Gd-dominant xenotime [“xenotime-(Gd)”] and Gd-rich hingganite-(Y) show heterogeneous compositions and reflect a strong fractionation trend toward the enrichment of MREE (Sm to Dy), particularly Gd. Here, the gadolinium abundance reported in “monazite-(Gd)” (≤23.4 wt% Gd2O3) and Gd-rich xenotime-(Y) to “xenotime-(Gd)” (≤28.7 wt% Gd2O3) and accompanied by Gd-rich hingganite-(Y) (≤15.8 wt% Gd2O3), is among the highest Gd concentrations ever reported in natural minerals. The Gd-richest compositions show the following formulas: (Gd0.31Sm0.24 Nd0.15Ce0.10La0.05Dy0.03Y0.03…)0.98PO4 [“monazite-(Gd)”], (Gd0.36Y0.32Dy0.13Sm0.08Tb0.05…)0.98 (P0.96As0.04)1.00O4 [“xenotime-(Gd)”] and (Y0.71Gd0.43Dy0.23Sm0.22Tb0.06Er0.04Nd0.06…Ca0.06)1.96 (☐0.87Fe0.132+)1.00(Be1.82B0.18)2.00(Si1.90As0.10)2.00O8(OH1.70O0.30)2.00 [hingganite-(Y)]. The MREE-rich monazites, xenotimes, and hingganite-(Y) precipitated in response to the alteration of primary uraninite, brannerite, and fluorapatite by low-temperature hydrothermal fluids of heterogeneous compositions on a microscale. These are responsible for the strong enrichment of individual MREE, especially Gd in the secondary minerals. This is accompanied by the advancing development of the W-type tetrad effect on REE through monazite species. The substantial incorporation of Gd into both REE-selective monazite and xenotime structures that are accompanied by LREE vs. HREE segregation indicates the possibility of differently sized REE3+ miscibility in REEPO4 solid solutions, as well as the stabilization of the Gd-rich orthophosphate structure by substitution of the remaining A-site cations with smaller HREE+Y in the xenotime-type, and/or larger LREE in the monazite-type structure.

Dve nové lokality pyromorfitu v Slovenskej republike: Chvojnica a Hnilčík

Two new localities of pyromophite were recently discovered at the Chvojnica base metals occurrence in the Strážovské vrchy Mts. (Tatric Unit), and at the supergene zone of the Piata siderite-type hydrothermal vein near Hnilčík (Spišsko-gemerské rudohorie Mts., Gemeric Unit), Slovak Republic. At the Chvojnica occurrence pyromorphite occurs as bright green crystalline crusts and radial aggregates up to 3 mm developed in cavities and fractures in the porous quartz gangue with relicts of primary galena. It is associated with minor crystalline coatings of cerussite. The refined unit-cell parameters of pyromorphite from Chvojnica (for the hexagonal space group P63/m) are a 9.9750(2) Å, c 7.3569(2) Å and V 633.93(2) Å3. Except of dominant contents of Pb, P and Cl, only minor amounts of Ca (up to 0.10 apfu), Al (up to 0.05 apfu), Fe (up to 0.04 apfu), As (up to 0.05 apfu) and S (up to 0.02 apfu) were detected in studied pyromorphite. At the Hnilčík, pyromorphite occurs rarely in the cavities of the cavernous quartz-limonite gangue in the supergene zone of the Piata vein. It forms colourless to very light green prismatic crystals up to 2 mm in size, or crystalline aggregates associated with goethite, Mn oxides and malachite. The refined unit-cell parameters of pyromorphite from Hnilčík (for the hexagonal space group P63/m) are a 9.9484(15) Å, c 7.315(2) Å, V 627.0(2) Å3 (Ca-poor) and a 9.8983(6) Å, c 7.2589(8) Å, V 615.92(9) Å3 (Ca-rich). Pyromorphite from Hnilčík shows strong chemical zoning caused by variation of Pb and Ca contents, with outer parts of the crystals enriched in Ca. Contents of Ca are ranging between 0.09 to 0.96 apfu, with the atomic Pb/(Pb+Ca) ratio ranging from 0.98 to 0.81, which is close to the compositional boundary with phosphohedyphane. Interesting are also elevated concentrations of Cu reaching up to 0.07 apfu. Other minor elements detected in pyromorphite from Hnilčík are As (up to 0.12 apfu), Al, V and S (all up to 0.02 apfu).

Carboniferous mafic metavolcanic rocks in the Northern Gemeric Unit: Petrogenesis, geochemistry, isotope composition and tectonic implication

Carboniferous mafic metavolcanic rocks in the Northern Gemeric Unit: Petrogenesis, geochemistry, isotope composition and tectonic implication

Permian A-type granites of the Western Carpathians and Transdanubian regions: products of the Pangea supercontinent breakup

Permian biotite leucogranites to granite porphyries and rhyolites form small intrusions in several Alpine tectonic units in the Western Carpathians and the Pannonian region (Slovakia and Hungary). Their A-type signature is inferred from main- and trace-element geochemistry, with high K, Rb, Y, REE, Zr, Th, Nb, Fe/Mg and Ga/Al, low Al, Mg, Ca, P, Sr, V and strong negative Eu-anomaly. This geochemical signature is further supported by the mineralogy comprising local hypersolvus alkali feldspars, annitic biotite and the presence and composition of HFSE accessory minerals. The δ18O values measured for zircon (mean value 8.3 ‰ ± 0.36) may be explained by the melting of igneous material of crustal origin and/or mantle basalts which interacted with low-temperature fluids. The in-situ SHRIMP U–Pb isotope dating of zircon from the granites highlights two different periods of magmatic crystallisation and pluton emplacement: the older 281 ± 3 Ma Cisuralian age in the southern part, Velence Hills in the Pannonian region (Transdanubian Unit) and younger Guadalupian ages in the northern part, the West-Carpathian area: 262 ± 4 Ma (Turčok, Gemeric Unit), 267 ± 2 Ma (Hrončok, Veporic Unit) and 264 ± 3 Ma (Upohlav, granitic pebbles in Cretaceous conglomerates of the Pieniny Klippen Belt). The ~ 280 to 260-Ma interval is simultaneous with post-orogenic or anorogenic, rift-related and mainly alkaline (A-type) magmatism on the broader European scale. Our study documents a close relationship between the Permian continental rifting and the Neotethyan Meliatic oceanic basin opening in the Middle Triassic. The A-type granites originated from the partial melting of the ancient lower crustal quartzo-feldspatic rocks with the possible contribution of meta-basic material from the mantle in an extensional tectonic regime consistent with disintegration of the Pangea supercontinent during the Permian–Triassic period.

Primary Minerals and Age of The Hydrothermal Quartz Veins Containing U-Mo-(Pb, Bi, Te) Mineralization in the Majerská Valley near Čučma (Gemeric Unit, Spišsko-Gemerské Rudohorie Mts., Slovak Republic)

An occurrence of vein U-Mo mineralization is located in the Majerská valley near Čučma, about 7 km to the NNE of the district town of Rožňava (Eastern Slovakia). Mineralization is hosted in the acidic metapyroclastics of the Silurian Bystrý Potok Fm. (Gemeric Unit), and originated in the following stages: (I.) quartz I, fluorapatite I; (II.) quartz II, fluorapatite II, zircon, rutile chlorite, tourmaline; (III.) uraninite, molybdenite, U-Ti oxides; (IV.) pyrite I, ullmannite, gersdorffite, cobaltite; (Va.) galena, bismuth, tetradymite, joséite A and B, Bi3(TeS)2 mineral phase, (BiPb)(TeS) mineral phase, ikunolite; (Vb.) minerals of the kobellite–tintinaite series, cosalite; (VI.) pyrite II; (VII.) titanite, chlorite; and (VIII.) supergene mineral phases. The chemical in-situ electron-microprobe U-Pb dating of uraninite from a studied vein yielded an average age of around 265 Ma, corresponding to the Guadalupian Epoch of Permian; the obtained data corresponds with the age of Gemeric S-type granites. The age correlation of uraninite with the Gemeric S-type granites and the spatial connection of the studied mineralization with the Čučma granite allows us to assume that it is a Hercynian, granite-related (perigranitic) mineralization.

Mineralogická charakteristika granátického skarnu z lokality Trohanka pri Prakovciach (gemerikum, Slovenská republika)

Garnet skarn mineralization was recently studied at the Trohanka locality near Prakovce (Gemeric Unit, Eastern Slovakia). Ca-skarn forms lenticular bodies in green schist environment. It mainly consists of zonal garnets, pyroxenes, amphiboles and magnetite accumulations. Studied garnets are rich in andradite component (up to 89.95 mol. %) with minor grossular component (6.83 - 39.67 mol. %). Strong oscillatory zoning in andradite is caused by substitution of Fe3+ and Al3+. Most pyroxenes are rich in the hedenbergite component. In some cases, euhedral diopside crystals with marginal transition zones (composed of diopside with lower content of Mg2+ and higher content of Fe2+) were found in hedenbergite matrix. Amphiboles are dominantly represented by ferro-actinolite and ferro-hornblende in association with isolated euhedral crystals of ferro-tschermakite and ferro-pargasite. Indistinct chemical zonality of amphibole euhedral crystals is caused by presence of ferro-pargasite in the central parts and ferro-tschermakite in the peripheral parts of crystals.

Initial replacement stage of primary uranium (UIV) minerals by supergene alteration: association of uranyl-oxide hydroxy-hydrates and “calciolepersonnite” from the Krátka Dolina Valley (Gemerská Poloma, Gemeric Unit, Western Carpathians, Slovakia)

Initial replacement stage of primary uranium (UIV) minerals by supergene alteration: association of uranyl-oxide hydroxy-hydrates and “calciolepersonnite” from the Krátka Dolina Valley (Gemerská Poloma, Gemeric Unit, Western Carpathians, Slovakia)

Accessory minerals and evolution of tin-bearing S-type granites in the western segment of the Gemeric Unit (Western Carpathians)

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.

Magnetic fabric overprints in multi-deformed polymetamorphic rocks of the Gemeric Unit (Western Carpathians) and its tectonic implications

In the Gemeric Unit of the Central West Carpathians, the magnetic fabric was investigated in Early Palaeozoic metasediments and metavolcanics, Permian to Early Triassic granites, and Late Palaeozoic (molasse) metasediments. In addition to Variscan greenschist facies metamorphism in the Early Palaeozoic basement, all rocks underwent Cretaceous (Alpine) low-grade metamorphism, which significantly modified their mineral composition and fabric; original magnetic minerals were destroyed at least partially and new, mostly paramagnetic, minerals were created.In the Early Palaeozoic metasediments, the magnetic fabric is entirely metamorphic/deformational in origin. In metavolcanics, the magnetic foliations are partly parallel to the Alpine metamorphic foliations developed in relatively incompetent lithologies such as tuffs and tuffites and partly to disjunctive foliations developed in competent rhyolites and its subvolcanic members. Their magnetic fabrics probably represent gradual transition from Variscan to Alpine fabrics. In the Permian granites, the magnetic foliations are near the Alpine mesoscopic disjunctive foliations crosscutting metamorphic schistosity in contact aureoles of granite. In the Late Palaeozoic (molasse) metasediments, the magnetic foliations are near the Alpine metamorphic foliations that are mostly parallel to the original bedding. On regional scale, the magnetic fabrics show curved pattern indicating complex interactions between the Gemeric and underlain Veporic units in the final stages of intendation and collision.The magnetic fabric pattern in the Gemeric Unit roughly resembles that in the Veporic Unit. This results from similar tectonic movements operating at least during Cretaceous collision in both the units. This tectonic process occurred subsequent to the closure of the Meliata ocean and was responsible for creation of the final structure of the Central Western Carpathians. Nevertheless, in contrast to the Veporic unit, where dominantly Alpine type of magnetic fabrics is present, in the Gemeric Unit the Alpine overprint had variable degrees of modification of AMS fabrics ranging from relatively weak to totally obliterated.

3D density modelling of Gemeric granites of the Western Carpathians

Abstract The position of the Gemeric Superunit within the Western Carpathians is unique due to the occurrence of the Lower Palaeozoic basement rocks together with the autochthonous Upper Palaeozoic cover. The Gemeric granites play one of the most important roles in the framework of the tectonic evolution of this mountain range. They can be observed in several small intrusions outcropping in the western and south-eastern parts of the Gemeric Superunit. Moreover, these granites are particularly interesting in terms of their mineralogy, petrology and ages. The comprehensive geological and geophysical research of the Gemeric granites can help us to better understand structures and tectonic evolution of the Western Carpathians. Therefore, a new and original 3D density model of the Gemeric granites was created by using the interactive geophysical program IGMAS. The results show clearly that the Gemeric granites represent the most significant upper crustal anomalous low-density body in the structure of the Gemeric Superunit. Their average thickness varies in the range of 5–8 km. The upper boundary of the Gemeric granites is much more rugged in comparison with the lower boundary. There are areas, where the granite body outcrops and/or is very close to the surface and places in which its upper boundary is deeper (on average 1 km in the north and 4–5 km in the south). While the depth of the lower boundary varies from 5–7 km in the north to 9–10 km in the south. The northern boundary of the Gemeric granites along the tectonic contact with the Rakovec and Klátov Groups (North Gemeric Units) was interpreted as very steep (almost vertical). The results of the 3D modelling show that the whole structure of the Gemeric Unit, not only the Gemeric granite itself, has an Alpine north-vergent nappe structure. Also, the model suggests that the Silicicum–Turnaicum and Meliaticum nappe units have been overthrusted onto the Golčatov Group.

Tourmalines from the siderite-quartz-sulphide hydrothermal veins, Gemeric unit, western Carpathians, Slovakia: crystal chemistry and evolution

Tourmaline is an important gangue mineral in a large number of Cretaceous siderite-quartz-sulphide hydrothermal veins in the Gemeric Unit, Slovak Ore Mountains, Slovakia, such as Dobsina, Vlachovo, Rožňavske Bystre, Hnilcik, Rakovnica, Novoveska Huta, Gretla, Rudňany, and Bindt. In this study we combine by electron microprobe analysis, powder X-ray diffraction, Mossbauer and optical emission spectroscopy to determine the range of tourmaline compositions in the deposits and constrain the mechanisms of its precipitation. Selected samples from the mentioned deposits belong mostly to the alkali group, schorl to dravite series, rarely dominant X-site vacant foititic tourmaline (Vlachovo and Bindt) and oxy-dravite compositions (Hnilcik) were detected. Rim zones of some schorlitic tourmalines show high concentrations of Ti (up to 2.35 wt.% TiO2, 0.30 apfu; Rožňavske Bystre). The chemical composition is mostly controlled by alkali-deficient X □AlNa−1(Mg,Fe2+)−1 and proton-deficient AlO(Mg,Fe2+)−1(OH)−1 substitutions. Titanium is incorporated into the structure by Y Ti Y (Mg,Fe) Y Al−2, Y Ti Z Mg Y Al−1 Z Al−1, Y TiO( Y AlOH), and X Ca Y Ti Z MgO2 X □−1 Y,Z Al−2(OH)−2 substitutions. Along trace elements, Sr and V attain concentrations of ~80–450 and ~70–320 ppm, respectively. The unit-cell parameter a varies between 15.960 and 15.985 A; variations in c are larger, between 7.177 and 7.236 A indicating the presence of Fe3+ and Mg2+ at Z site. Mossbauer spectroscopy has shown variable Fe3+ proportions (0.17–0.55 apfu) in all samples. The gathered dataset suggests some qualitative considerations on the mechanisms controlling tourmaline compositions at the regional scale. The highest Fe3+ concentrations occur in samples from Rudňany and Gretla in the external part of Gemeric unit, suggesting higher oxidation during longer transport of fluids. We propose that the determined XFe in the samples are correlated with the compositions of the host rocks, as schorlitic to foititic tourmalines occur in veins located in the meta-rhyolites host, and tourmalines with the highest Mg contents occur in metabasalts.

Low-temperature constraints on the Alpine thermal evolution of the Western Carpathian basement rock complexes

The Cretaceous to Palaeogene Alpine exhumation of previously buried Variscan basements is recorded in the southern portion of the Western Carpathians in the Gemeric and Veporic units. The Meso-Cenozoic collisional processes resulted in basement exhumation of the Tatric Unit from Palaeogene to Neogene times. According to zircon and apatite fission track data, the Gemeric Unit, an uppermost thick-skinned thrust sheet, cooled from depth levels of ∼10 up to 2.5 km (temperature interval of ∼250–60 °C) about 88–64 Ma ago, after the collapse of overlying Meliata-Turňa-Silica Mesozoic accretionary prism. The middle and lower thick-skinned thrust sheets, Veporic and Tatric units, cooled from the depths of ∼10 up to 2.5 km ∼110–40 Ma ago. The process was controlled by unroofing of footwall from beneath the Gemeric Unit. About 50–20 Ma ago, the internal zone of Tatric Unit gradually exhumed to depth of <2 km and some parts of the unit appeared at the surface level. However, the external zone of Tatric Unit was buried beneath the Eocene to Lower Miocene sedimentary successions and exhumed to the subsurface level at ∼21–8 Ma ago, as a result of oblique collision of the Western Carpathians with the European Platform.

Geochronological evidence for the Alpine tectono-thermal evolution of the Veporic Unit (Western Carpathians, Slovakia)

Tectono-thermal evolution of the Veporic Unit was revealed by multiple geochronological methods, including 87Rb/86Sr on muscovite and biotite, zircon and apatite fission-track, and apatite (U–Th)/He analysis. Based on the new data, the following Alpine tectono-thermal stages can be distinguished: The Eo-Alpine Cretaceous nappe stacking (~135–95Ma) resulted in burial of the Veporic Unit beneath the northward overthrusting Gemeric Unit and overlying Jurassic Meliata accretionary wedge. During this process the Veporic Unit reached metamorphic peak of greenschist- to amphibolite facies accompanied by orogen-parallel flow in its lower and middle crust. The subsequent evolution of this crust is associated with two distinct exhumation mechanisms related to collision with the northerly Tatric–Fatric basement. The first mechanism (~90–80Ma) is associated with internal subhorizontal shortening of the Veporic Unit reflected by large-scale upright folding and heterogeneous exhumation of the Veporic lower crust in the cores of crustal-scale antiforms. This led to juxtaposition of the higher and lower grade parts of basement, all cooled down to ~350°C by ~80Ma. The second mechanism is associated with the overthrusting of the Veporic Unit over the attenuated Fatric crust. This led to a passive en-block exhumation of the Veporic crust from ~350°C to 60°C between ~80 and 55Ma followed by erosion (~55–35Ma). The erosion processes resulted in formation of planation surface before the Late Eocene transgression. After erosion and planation, a new sedimentary cycle of the Central Carpathian Palaeogene Basin was deposited with the sedimentary strata thickness of ~1.5–2.0km (~21–17Ma). The early to middle Miocene is characterised by destruction tectonic disintegration and erosion of this basin (~20–13Ma) and formation of the Neogene Vepor Stratovolcano (~13Ma). The final shaping of the area has been linked to erosional processes of the volcanic structure since the Late Sarmatian with accelerated processes during the Plio-Quaternary.

First evidence for Permian-Triassic boundary volcanism in the Northern Gemericum: geochemistry and U-Pb zircon geochronology

AbstractSeveral magmatic events based on U-Pb zircon geochronology were recognized in the Permian sedimentary succession of the Northern Gemeric Unit (NGU). The Kungurian magmatic event is dominant. The later magmatism stage was documented at the Permian-Triassic boundary. The detrital zircon assemblages from surrounding sediments documented the Sakmarian magmatic age. The post-orogenic extensional/transtensional faulting controlled the magma ascent and its emplacement. The magmatic products are represented by the calc-alkaline volcanic rocks, ranging from basaltic metaandesite to metarhyolite, associated with subordinate metabasalt. The whole group of the studied NGU Permian metavolcanics has values for the Nb/La ratio at (0.44–0.27) and for the Nb/U ratio at (9.55–4.18), which suggests that they represent mainly crustal melts. Magma derivation from continental crust or underplated crust is also indicated by high values of Y/Nb ratios, ranging from 1.63 to 4.01. The new206U–238Pb zircon ages (concordia age at 269 ± 7 Ma) confirm the dominant Kungurian volcanic event in the NGU Permian sedimentary basin. Simultaneously, the Permian-Triassic boundary volcanism at 251 ± 4 Ma has been found for the first time. The NGU Permian volcanic activity was related to a polyphase extensional tectonic regime. Based on the new and previous U-Pb zircon ages, the bulk of the NGU Permian magmatic activity occurred during the Sakmarian and Kungurian. It was linked to the post-orogenic transpression/transtension tectonic movements that reflected the consolidation of the Variscan orogenic belt. The Permian-Triassic boundary magmatism was accompanied by extension, connected with the beginning of the Alpine Wilson cycle.

Phosphate minerals from the hydrothermal quartz veins in specialized S-type granites, Gemerská Poloma (Western Carpathians, Slovakia)

An interesting association of phosphate minerals (fluorapatite, triplite, arrojadite-group minerals and viitaniemiite) was studied from intra-granitic hydrothermal quartz veins with minor amounts of albite, orthoclase, muscovite, fluorite, rhodochrosite, arsenopyrite, pyrite, bismuthinite and kobellite. The veins occur in highly evolved, Permian topaz-zinnwaldite leucogranite at the Elisabeth adit near Gemerska Poloma, Gemeric Unit, Western Carpathians (eastern Slovakia). Fluorapatite is enriched in Mn (similar to 4 wt. % MnO, 0.3 apfu Mn) and frequently replaced by triplite, representing the first known triplite occurrence in Western Carpathians. This mineral forms irregular aggregates (<= 7 cm across), Mn/(Mn + Fe) atomic ratio of which attains 0.68 to 0.78 and F/(F + OH) = 0.89-0.92. Fluorarrojadite-(BaNa) to its Mn-dominant analogue fluordickinsonite-(BaNa) (both minerals still not approved by IMA-CNMNC) occurs as aggregates up to 2 cm across, showing Sr-rich (similar to 1.7 wt. % SrO, similar to 0.36 apfu Sr) and Sr-poor (<= 0.6 wt. % SrO, <= 0.13 apfu Sr) compositions with W site F/(F + OH) = 0.74-0.80 and M site Mn/(Mn + Fe) = 0.39-0.52. Rare viitaniemiite is Mn-rich (10 to 11 wt. % MnO, 0.34-0.38 apfu Mn). The phosphate mineralization in quartz represents a high-temperature hydrothermal assemblage. The F-rich Mn, Fe, Ca-bearing phosphates, fluorite, and muscovite precipitated most likely in presence of alkali-and fluorine-bearing post-magmatic fluids which altered primary magmatic minerals (especially Li-rich micas and alkali feldspars) and liberated some elements (Fe, Mn, Al, Ba, Sr, Na, K) from the adjacent granite.

Constraining exhumation pathway in an accretionary wedge by (U-Th)/He thermochronology—Case study on Meliatic nappes in the Western Carpathians

This study reconstructs the late stages in the exhumation history of a nappe derived from the Meliatic accretionary wedge in the Western Carpathians by means of zircon and apatite (U-Th)/He dating. The Meliatic accretionary wedge formed due to the closure of the Neotethyan Triassic–Jurassic Meliata–Hallstatt Ocean in the Late Jurassic. The studied fragments of the blueschist-bearing Meliatic Bôrka Nappe were metamorphosed at low-temperature and high- to medium-pressure conditions at ca. 160–150Ma and included into the accretionary wedge. The time of the accretionary wedge formation constrains the beginning of the Bôrka Nappe northward thrusting over the Gemeric Unit of the evolving Central Western Carpathians (CWC) orogenic wedge. The zircon (U-Th)/He data on four samples recorded three evolutionary stages: (i) cooling through the ∼180°C isotherm at 130–120Ma related to starting collapse of the accretionary wedge, following exhumation of the high-pressure slices in the Meliatic accretionary wedge; (ii) postponed exhumation and cooling of some fragments through the ∼180°C isotherm from 115 to 95Ma due to ongoing collapse of this wedge; and (iii) cooling from 80 to 65Ma, postdating the thrusting (∼100–80Ma) of the Bôrka Nappe slices during the Late Cretaceous compression related to formation of the CWC orogenic wedge. The third stage already documents cooling of the Meliatic Bôrka Nappe slices in the CWC orogenic wedge. The apatite (U-Th)/He data may indicate cooling of a Bôrka Nappe slice to near-surface temperatures at ∼65Ma. The younger AHe age clusters indicate that at least one, or possibly two, reheating events could have occurred in the longer interval from ∼40 to ∼10Ma during the Oligocene–Miocene. These were related to sedimentary burial and/or the magmatism as documented in other parts of the CWC.