K-cymrite pseudomorphs in high-ultrahigh- pressure rocks

The Orlica-Snieznik Dome (OSD) is located in the northeastern part of the Bohemian Massif and is interpreted as a fragment of the Moldanubian zone within the Variscan orogen, representing part of the Variscan orogenic root. The dome is composed primarily of orthogneisses interspersed with metamorphosed volcano-sedimentary sequences. In the Snieznik Massif, which forms the eastern segment of the OSD, lenses of high- and ultrahigh-pressure (UHP) rocks, including granulites and eclogites, are embedded within the orthogneisses. This study investigates the metamorphic evolution of eclogites exposed in two specific areas of the Snieznik Massif: Nowa Wies and Bielice.We distinguish two varieties among the examined eclogites: Ph-bearing and Ph-free eclogite. Both exhibit a typical metamorphic trajectory for UHP rocks, encompassing a UHP metamorphic event followed by isothermal decompression and subsequent retrogression under amphibolite-facies conditions. The samples are characterized by steeply dipping, subvertical foliation, defined by alternating garnet- and omphacite-rich layers and the parallel alignment of elongated grains of kyanite, rutile ± phengite. Evidence of isothermal decompression is observed in the form of small amphibole grains and diopside-amphibole-plagioclase symplectite, which occur locally along grain boundaries. The final metamorphic stage is marked by amphibole+plagioclase+zoisite/clinozoisite±margarite±tytanite, found within fractures that crosscut the primary foliation. This stage is associated with retrogression under amphibolite-facies conditions.The UHP metamorphic event in the studied samples is reconstructed based on the results of thermodynamic modelling and the presence of coesite, identified as tiny (~10–20 µm) inclusions within omphacite and garnet. The well-preserved mineral assemblage indicative of UHP conditions includes garnet + omphacite + kyanite + rutile + coesite ± phengite. Phase diagram modeling combined with isopleth geothermobarometry indicates peak metamorphic conditions of approximately 3.0 GPa and 750°C. These findings are consistent with results from conventional geothermobarometry (Grt-Cpx-Ph-Ky-Coe geothermobarometer) and Zr-in-rutile thermometry. The onset of isothermal decompression is marked by the formation of small amphibole grains, indicating conditions of around 2.3 GPa at 750°C, within the stability field of amphibole.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101005611 for Transnational Access conducted at Earth Sciences Department, University of Cambridge. The project was also supported by the Polish National Science Centre (UMO-2022/47/I/ST10/02504) and the Deutsche Forschunggemeinschaft (project Nr. 535198529).

SUMMARY The Variscan orogeny is the major Middle to Late Palaeozoic tectonometamorphic event in central Europe, and the Bohemian Massif is the largest exposure of rocks deformed during this orogeny. The Bohemian Massif consists of the Saxothuringian, Barrandian and Moldanubian units. Adjacent to this massif in the southeast, the Western Carpathians form an arc-shaped mountain range related to the Alpine orogeny during the Cretaceous to Tertiary. The complex crustal-scale geological structure of the Variscan Bohemian Massif and the Western Carpathians, and especially their contact, were analysed in this study employing the data of the SUDETES 2003 international seismic refraction experiment. The analysed seismic data were acquired along the 740 km long, NW–SE oriented S04 profile that crossed the Bohemian Massif and the Western Carpathians before terminating in the Pannonian Basin. The data were interpreted by 2-D trial-and-error forward modelling of P waves, and additional constraints on crustal structure were provided by gravity modelling. The complex velocity structure derived in our analysis included low velocities of 5.85 km s−1 at the contact of the Saxothuringian and Barrandian units that reflect the presence of low-density granites. There are distinct lateral variations in deep crustal structure in the transition between the Bohemian Massif and the Western Carpathians. The abrupt change of the crustal thickness in this transition zone may be associated with the Pieniny Klippen Belt, a deep-seated boundary between the colliding Palaeozoic lithospheric plate to the north and the ALCAPA microplate to the south. In the upper crust of this transition, low velocities of 4 km s−1 extend to 6 km and represent the sedimentary fill of the Carpathian Flysch and Foredeep that thins towards the foreland. This basin is also expressed as a pronounced gravity low. The Moho in the Carpathians reaches a depth of 32–33 km. In contrast, in the Pannonian Basin the Moho rises to a depth of 25 km, which corresponds to the Pannonian gravity high.

Partial melting, fluid supercriticality and element mobility in ultrahigh-pressure metamorphic rocks during continental collision

The Western Carpathians are traditionally recognized as one of the hotspots of temperate European biodiversity. The polyploid and apomictic group of Cotoneaster integerrimus s.l. is supposed to be particularly variable there, and this is also mirrored by taxonomy. We therefore examined the ploidal and reproductive pattern of C. integerrimus s.l. and its close relative Cotoneaster tomentosus in the Western Carpathians and compared it to that in the Bohemian Massif. Using flow cytometry, we detected tetraploid (468 individuals, 100 populations) and pentaploid (35 individuals, 11 populations) cytotypes, and eight additional mixed populations. The pentaploid cytotype was found exclusively in C. tomentosus, which only occurs in the Western Carpathians. A further flow cytometric seed screen (1114 seeds) revealed facultative apomixis (10.1% of sexual progeny) of tetraploid C. integerrimus s.l., whereas the pentaploid C. tomentosus was almost obligately apomictic. In addition, 3.8% of sexual progeny was formed with the contribution of an unreduced female gamete. Moreover, apomixis in tetraploids was further structured into distinct subtypes: pseudogamy (77.2%), autonomous apomixis (3.7%) and haploid parthenogenesis (0.3%). There were no significant differences in the proportions of sexual and asexual seeds between both species and geographic regions. Our comparative dataset from the Western Alps also included sexual diploids. For this reason, greater ploidal and reproductive variation may be expected in that region. The Western Carpathians therefore do not represent a centre of cytotype and reproductive variation of C. integerrimus s.l., and facultative apomixis is a reproductive strategy that predominates in both the Western Carpathians and the Bohemian Massif.

The Meliata Unit (Meliaticum) is a tectonic superunit of the Western Carpathians that incorporates the blueschists-facies Bôrka Nappe and the low-grade metasediments and polygenetic mélange, Meliata Unit s.s., both occurring as scattered tectonic slices overlying the Gemeric Superunit. Calcitic marbles were sampled in a wide area within the Bôrka Nappe and blocks embedded in Jurassic oceanic sediments (Meliata Unit s.s.). Based on the microstructural evaluation and electron backscatter diffraction analysis (EBSD), the carbonates of the Bôrka Nappe experienced differential post-subduction P–T–D paths related to a collisional/exhumation setting following closure of the Neotethys-related “Meliata Ocean”. Variations in the calcite deformation microstructures were used to distinguish three principal microstructural groups. The first group (G1) contains large columnar and lobate calcite grains (≥ 1 mm) reflecting peak P–T conditions during subduction of the Meliata oceanic lithosphere. The second group (G2) exhibits dynamic recrystallization of the original G1 grains resulting in grain size reduction (< 0.5 mm) and shape-preferred orientation related to exhumation and formation of the accretionary complex. The third group (G3) shows a ‘foam’ microstructure with a uniform grain size (0.4–1 mm), sharp grain boundaries and triple junctions. The G3 microstructure may have been caused by a static recrystallization at elevated temperatures postdating the main deformation, and it is restricted to peripheries of the underlying Veporic metamorphic dome and probably is not associated with the Meliata sequences nor its tectono-metamorphic evolution. The corrected kinematic sections indicate dominantly ESE–WNW-trending lineations suggesting top-to-WNW kinematics of the Meliata subduction–exhumation process for G1 and G2 microstructures, and Gemeric–Veporic E–W orogen-parallel stretching for G3.

Metabasites related to the Triassic Meliata oceanic basin occur along three tectonic zones in the Western Carpathians: (1) the Folkmar Zone, (2) the Roz?n?ava Zone (Meliata Unit, s.s.) and the (3) Bodva valley - Darno Hill Zone. The first two zones form the northern and southern boundary of the Paleozoic of the Gemericum (south-eastern Slovakia), respectively, and the latter is located south of the Meliata Unit, NE Hungary. All three zones contain metabasites. The serpentinites, radiolarian shales and cherts are considered to be complementary members of an ancient oceanic crust. Geochemical characteristics of metabasites from the Folkmar Zone indicate a MORB affinity. Metabasites from the Roz?n?ava Zone have affinity between MORB and within plate basalts, but metagabbros comparable with alkaline basalts are also present. The Darno Hill metabasites have MORB compositions and those from the Bodva valley are similar to the metabasites from the Roz?n?ava Zone. The geochemical and petrographic features of these metabasites suggest a continental rift volcanism, followed by spreading of the Triassic Meliata oceanic basin. During the Middle Jurassic, part of the oceanic crust and adjacent passive continental margin underwent a subduction-related blueschist facies metamorphism afterwards they were exhumed within a melange complex of the Meliata Unit in the southern part of Gemericum.

This study tests experimentally the hypothesis that calculated bulk compositions of multiphase solid inclusions present in minerals of ultrahigh pressure rocks, can be equated to the composition of the former trapped fluids. We investigated samples from the ultrahigh pressure garnet peridotites of the Bohemian Massif, spatially associated with ultrahigh pressure crustal rocks and representing a former subduction interface environment. Inclusions present in garnets, composed of amphibole + Ba-mica kinoshitalite + carbonates (dolomite + magnesite + norsethite), were taken to their entrapment conditions of c. 4.5 GPa and 1075 ºC. They (re)crystallized into a garnet fringe at the boundary between inclusion and host garnet, kinoshitalite ± olivine, carbonatite melt, and a hydrous fluid. Although the latter may have exsolved from the carbonatite melt upon quenching, microstructures suggest it was present at trapped conditions, and mass balance indicates that it corresponds to a Na-K-Cl-F-rich saline aqueous fluid (brine). Experiments demonstrate the stability of kinoshitalite at 4.5 GPa and 1075 ºC, and suggest that Ba-rich mica + carbonatite melt + brine coexisted at near-peak conditions. Barium is compatible in the carbonatite melt and mica with respect to the brine, with a partition coefficient between carbonatite melt and mica of ≈ 2.5–3. The garnet fringe formed from incongruent reaction of the former inclusion assemblage due to reversing the fluid(s)-host garnet reaction that occurred upon natural cooling/decompression. Loss of H2 or H2O from the inclusions due to volume diffusion through garnet and/or decrepitation, during geological timeframes upon decompression/cooling, may have prevented rehomogenization to a single homogeneous fluid. Our study shows that great care is needed in the interpretation of multiphase solid inclusions present in ultrahigh pressure rocks.

&amp;lt;p&amp;gt;We studied monazite behaviour in UHP diamond-bearing gneiss from Saxn&amp;amp;#228;s in the Seve Nappe Complex of the Scandinavian Caledonides (Petr&amp;amp;#237;k et al., 2019). Although the rock has been re-equilibrated under&amp;amp;#160; granulite facies and partial melting conditions, the UHP stage is recorded by the presence of diamond. Microdiamonds occur in situ as inclusions in garnet, kyanite and zircon, either as single-crystal or polyphase inclusions with Fe-Mg carbonates, rutile and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;. Two garnet types have been recognised: dominant Grt I &amp;amp;#160;with inclusions of diamond found mostly in the garnet rims, which suggests that originally the bulk of Grt I grew at UHP conditions. Grt II, forming small crystals, overgrowths on, or domains within Grt I originated by dehydration melting reactions involving breakdown of phengite and clinopyroxene during decompression. Monazite occurs in the rims of Grt I close to microdiamond, where garnet shows the highest pyrope content and a secondary peak of yttrium. Such a position indicates thermally activated diffusion under high temperature at the end of prograde metamorphism. Based on such textural relations, we argue that monazite formed at UHP conditions.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Monazite composition shows negative Eu anomalies and moderate Y contents, which is not in agreement with common interpretation that UHP conditions necessarily lead to the absence of Eu anomaly and low Y content due to absence of plagioclase and high garnet content. We explain this by the effect of whole-rock composition. LA ICP MS analyses show that whole-rock budget is controlled by monazite, apatite and garnet, all having negative Eu anomalies. Whole rock composition is successfully modelled by (wt. %) garnet 16, apatite 3, monazite 0.06. We conclude that the Eu anomaly is inherited from the source rock, not reflecting the coexistence with plagioclase and/or K-feldspar, which are unstable at UHP conditions. Uniform garnet abundance (16 vol. %) above 20 kbars predicted by pseudo-section modelling explains the lack of Y decrease due to the increase of garnet content at UHP conditions. Our results suggest that the effect of the whole-rock composition may be more important than that of coexisting phases.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;U-Th-Pb chemical age dating of monazites yields an isochron centroid age of 472 &amp;amp;#177;3 Ma. We interpret this age as monazite growth under UHP conditions related to subduction of the Baltican continental margin in Early Ordovician time.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This work was supported by the projects APVV-14-0278 and APVV-18-0107, National Science Center &amp;amp;#8220;CALSUB&amp;amp;#8221; 2014/14/E/ST1/00321&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Reference: Petr&amp;amp;#237;k, I., Jan&amp;amp;#225;k, M., Klonowska, I., Majka, J., Froitzheim, N., Yoshida, K., Sasinkov&amp;amp;#225;, V., Kone&amp;amp;#269;n&amp;amp;#253;, P., Vaculovi&amp;amp;#269;, T. 2019. Journal of Petrology doi: 10.1093/petrology/egz051&amp;lt;/p&amp;gt;

Using the 2D integrated modelling method, we calculated the temperature model of the lithosphere along transect I passing through theWestern Carpathians. Based on the extrapolation of failure criteria, lithology and calculated temperature distribution, we derived the rheology model of the lithosphere in the area. Our results indicate clearly that the strength decreases from the Bohemian Massif via the Western Carpathians to the Pannonian Basin. The largest strength can be observed within the upper crust on the boundary between the upper and lower crust. This phenomenon is typical for all studied tectonic units: the Bohemian Massif, the Western Carpathians and the Pannonian Basin. These results suggest mostly rigid deformation in the upper crust of the units. By contrast, the lower crust in the Bohemian Massif and the Western Carpathians reflects significantly lower strength, while in the Pannonian Basin the strength is the smallest. In all tectonic units the strength within the uppermost mantle (lower lithosphere) disappears. It can be suggested that the ductile deformation dominates in this part of the lithosphere.

We studied speleothem-fracturing styles and their tectonic context in three cave systems situated in the eastern Bohemian Massif, close to the Western Carpathians orogenic front: the Za hajovnou, Javořicko, and Mladec caves. The morphology of the speleothems in particularly thin stalactites, and supporting evidence from the cave interior, indicates a tectonic origin of the breakage. U/Th series dating of the stalactites, supported by Optically Stimulated Luminiscence (OSL) and 14 C dating of soft sediments indicate that most of the fracturing occurred in the Upper Pleistocene, with the last fracturing events corresponding to MIS6 and MIS5 stages. OSL dating of faulted soft-sediment infill may even indicate that latest Pleistocene to Early Holocene tectonic events occurred in the Mladec Cave. The speleothem fracturing is discussed in the regional context of the seismically active Nysa-Morava Zone situated at the junction between the Bohemian Massif (Elbe Fault Zone) and the Western Carpathians. This study provides the first evidence of palaeoseismicity from the subsurface and the oldest dated palaeoseismicity from the contact between the Western Carpathians and the Bohemian Massif.

This volume of 30 chapters authored by 107 geologists and geophysicists from Austria, Czech Republic, Hungary, Poland, Romania, Slovakia, Ukraine, United Kingdom, and the USA provides a comprehensive and understandable account of geology and hydrocarbon resources of the entire Carpathian system from northeastern Austria to southern Romania, including the Neogene foredeep, the foreland platform both in front and beneath the thrust belt, the Carpathian thrust belt, and the late and post orogenic intermontane basins. Principal chapters on regional geology are supplemented by thematic contributions on geodynamic reconstructions, regional geophysical investigations, hydrocarbon systems, and case studies of major oil and gas fields. To date, close to 7 billion barrels of oil and more than 53 trillion cubic feet of natural gas have been produced from the entire Carpathian system. Additional new reserves may be found, especially at deeper structural levels below the Neogene foredeep and the thin-skinned Carpathian thrust belt. Seventeen chapters of Memoir 84 have been printed in full. The remaining chapters have been printed as abstracts only, with the full paper for all 30 chapters as .pdf files on the CD-ROM in the back of this publication. The publication is intended as a source of information to schools, governmental and private institutions, oil companies, and potential investors.

Even if the Czech Republic occupies a small area in Central Europe, it is unique by the very interesting and varied geological and tectonic development that is recorded in the structure of the present-day Earth’s crust, especially in the case of the Bohemian Massif. The Bohemian Massif can be interpreted as a heterogeneous unit composed of four separate regional domains. Each of them is defined especially by a specific stratigraphic content, tectomagmatic development and tectonic limitation in relation to its surroundings. The history of its development involves a long time period from the Paleoproterozoic to the recent period, i.e. about 2.1 × 109 years. Basic features of the Earth’s crust structure, reflecting in geological maps, were however impressed on the area of the country only by relatively younger phases of Variscan orogeny and, to a lesser extent, Alpine orogeny that affected the eastern part of the country—the Western Carpathians. At the beginning of the Westphalian, the Bohemian Massif became part of the stabilised Variscan crust of the West European Platform, which in consequence meant that it began to act as a single unit, in which any mutual lateral displacement of units, metamorphosis and associated ductile deformation took place no longer. The Western Carpathians are one of partial branches of the vast orogenic belt of the Alpides created from the former Tethys Ocean. The development of the Western Carpathians already begins shortly after terminating the Variscan orogeny. At present, the Carpathians are divided from south to north into the Inner, Central and Outer Western Carpathians. The Central as well as the Inner Carpathians do not occur in the territory of the Czech Republic. The younger accretionary complex in the area of Moravia and Silesia is composed of the Pouzdřany, Ždanice, Subsilesian, Silesian and Fore-Magura Units.

Exsolution microstructures have recently been identified in ultrahigh-pressure (UHP) ultramafic and eclogitic minerals from several orogenic belts, including the Western Gneiss Region, Norway; Alpe Arami, Switzerland; the Bohemian massif, central Europe; the Kokchetav massif, Kazakhstan; the Dabie-Sulu UHP terrane, east-central China; and in central Sulawesi, Indonesia. They include ilmenite rods and magnetite lamellae in olivine; K-feldspar, Mg-Al-Cr titanomagnetite and/or ilmenite, quartz, and garnet rods in clinopyroxene; pyroxene and rutile lamellae in garnet; and lamellae of monazite and an unknown phase in apatite. Although the mechanisms for exsolution in some UHP minerals are poorly known, most exsolution microstructures, such as K-feldspar and quartz in clinopyroxene and pyroxene in garnet, may have resulted from nearly isothermal decomposition of very high pressure precursor phases at mantle depths. Detailed characterization and experimental investigations regarding exsolution microstructures of these and other minerals in UHP rocks will improve our understanding of mantle processes and continental subduction.

A detailed petrographic and mineral-chemical study on metapelites from the Meliatic accretionary wedge complex (Borka Nappe, Western Carpathians, Slovak Republic) reveals the HP character of the samples using quantitative phase diagrams contoured with mineral composition, H2O mode isopleths and garnet-phengite thermometry. The presented PT pseudosections prove that small-scale differences in bulk rock composition are responsible for the variations in the mineral assemblages formed at the same PT conditions. The peak conditions indicate blueschist facies metamorphism (520–620 °C, 11–14 kbar) and are correlated with the 150–165 Ma subduction of the Mesozoic Meliata Oceanic branch of the Neotethys. Continuous decrease of P and T from peak conditions enabled the metapelitic rocks to preserve their HP assemblages. The presented HP conditions and retrograde PT path with decreasing P and T are characteristic of subduction zone tectonic settings which are in agreement with most of the geodynamic and tect...

QuestionMosses are important ecosystem engineers in mires. Their pH optima and tolerances presented in the literature differ between regions, even though the high dispersal ability of mosses should prevent local adaptations. Nutrient availability is sometimes suggested as a reason for local niche differentiation. Are patterns in moss niche diversification, optima and tolerance with respect to pH consistent between regions differing in nutrient availability and abundance of calcareous bedrock?LocationWestern Carpathians (Slovakia, a predominantly calcareous P‐ and K‐poor region), Bohemian Massif (Czech Republic, a predominantly crystalline, P‐ and K‐rich region).MethodsAnalyses of an original stratified data set and a large database using species response curves.ResultsAlthough the above two regions differ in abundance of calcareous fens, species pH optima (either original or adjusted according to calcium level) were consistent between the regions and data sets. Calcium‐tolerant peat mosses (Sphagnum warnstorfii, S. contortum, S. teres) showed an optimum at pH 6 and rather narrow niches. Sphagnum fallax was the most acidophilous, and both S. palustre and S. flexuosum had rather wide intermediate niches. The pH amplitudes were largely consistent between the regions (especially when adjusted pH was used), but S. fallax and Aulacomnium palustre exhibited wider niches in the Bohemian Massif. Despite no significant difference in niche optimum and width, some more nutrient demanding and more generalist species occurred at higher frequency in specific parts of the pH gradient in the Bohemian Massif, while some fen specialists showed the opposite pattern.ConclusionsThe small stratified data set and the database data set yielded rather consistent results regarding fen moss niches in the Bohemian Massif and the Western Carpathians. The consistency in pH niches corresponds to the lack of large‐scale genetic differentiation in moss species. The observed inter‐regional differences in species response curves may thus reflect an increased frequency of competitively strong species in certain parts of the pH/Ca gradient in the nutrient‐richer Bohemian Massif rather than genetically conditioned niche shifts. Expansion of these species was probably triggered by potassium enrichment that took place in the 1970s–1980s. Inter‐regional differences in species response curves were observed in both data sets, but in the large database data set they were more frequently statistically significant.