An earlier concept of the Variscan foreland in Poland (Narkiewicz, 2007) is reconsidered in the light of new stratigraphic, tectonic and geophysical evidence, providing new data on Devonian sedimentation, Carboniferous magmatism and the deep crustal structure of SE Poland. Regional comparisons with the tectonic evolution of Central Europe and the Black Sea region show that the subsidence pattern in the foreland was controlled by alternating phases of accelerated convergence and tectonic standstill along the southern margin of Euramerica. In particular, the Bretonian (Devonian/Carboniferous) compressional deformation resulted from intensified orogenic convergence in the West-Central European Variscides leading to closure of the Saxo-Thuringian Basin and East-Sudetic back-arc basin. Another turning point in the regional tectonosedimentary development around the Mississippian-Pennsylvanian boundary was probably related to the termination of terrane collision in the Black Sea region. Late Pennsylvanian basin inversion was associated with a roughly N-S tectonic shortening. This was partly due to displacement along pre-existing basement discontinuities comprising reactivated Caledonian sutures that also pre-determined the Devonian-Carboniferous basin boundaries. Consequently, deeply-rooted tectonic zones, including the Kraków-Lubliniec and Holy Cross faults and the Teisseyre-Tornquist Zone, focussed maximum compressional and transpressional deformation and associated uplift. Such a concept of terminal Variscan tectonism, termed here the “decoupled model”, is discussed with reference to the recently proposed “coupled model”. The latter assumes a wide extent of the Variscan Orogen, reaching as far as the marginal Radom-Kraśnik Fold-and-Thrust Belt linked with the Bohemian Massif through a major basal detachment. It is concluded that the “decoupled model” is more consistent with the documented seismic and structural evidence as well as with the present knowledge of the heterogeneous pre-Devonian basement in southern Poland.
Maturity modelling was carried out using basin and petroleum system modelling (BPSM) software in the lithologic sections of 17 wells of the Upper Silesian Coal Basin (Poland). The best fit between calculated and measured vitrinite reflectance (VR), porosity and density data was obtained by applying a thickness of eroded sedimentary overburden from 1700 m in the east to 4500 m in the west and relatively low to moderate heat flow values during the maximum late Carboniferous burial. These heat flow values were in the range 50-71 mW/m2
Many granitic intrusions display evidence of magma mixing processes. The interaction of melts of contrasting composition may play a significant role during their generation and evolution. The Strzegom-Sobótka massif (SSM), located in the Sudetes (SW Poland) in the north-eastern part of the Bohemian Massif of the Central European Variscides, exhibits significant evidence of magma mingling on the macro- and micro-scales. The massif is a composite intrusion, with four main varieties: hornblende-biotite granite (with negligible amount of hornblende) and biotite granite in the western part, and two-mica granite and biotite granodiorite in the eastern part. Field evidence for magma mingling is easily found in the biotite granodiorite, where dark enclaves with tonalitic composition occur. Enclaves range from a few centimeters to half a meter in size, and from ellipsoidal to rounded in shape. They occur individually and in homogeneous swarms. The mixing textures in the enclaves include fine-grained texture, acicular apatite, rounded plagioclase xenocrysts, ocellar quartz and blade-shaped biotite. The most interesting feature of the enclaves is the presence of numerous monazite-(Ce) crystals, including unusually large crystals (up to 500 μm) which have grown close to the boundaries between granodiorite and enclaves. The crystallization of numerous monazite grains may therefore be another, previously undescribed, form of textural evidence for interaction between two contrasting magmas. The textures and microtextures may indicate that the enclaves represent globules of hybrid magma formed by mingling with a more felsic host melt. Chemical dating of the monazite yielded an age of 297±11 Ma.
A rhyolite porphyry in the Radzimowice deposit at Bukowinka Hill has a SHRIMP zircon U-Pb age of 314.9 ± 3.1 Ma. This is consistent with previous zircon dating of a monzogranite and a rhyodacite (ca. 315 Ma) in the Żeleźniak sub-volcanic intrusion (ZI), considered to be the igneous rocks, representing the oldest magmatic pulses in the region. First-stage mesothermal auriferous sulphide mineralization in the deposit was connected to hydrothermal processes, associated with the rhyodacite intrusions. This was followed by tectonic activity and younger alkaline magmatism in a post-collisional geotectonic setting. The first-stage Au-bearing sulphide mineralization was cataclased and overprinted by younger epithermal base-metal sulphides with microscopic Au, associated with Bi-Te-Ag minerals. The younger magmatic pulses are represented by porphyritic andesites and lamprophyric dykes, which cut the ZI. Zircon from these dykes yielded ages of 312.8 ± 2.8 Ma for an andesite porphyry and 312.4 ± 4 Ma for a lamprophyre. All these magmatic pulses, evidenced in the Radzimowice deposit, are considered to be the oldest post-orogenic sub-volcanic magmatism cutting the basement of the intramontane basins in the Sudetes, on the NE margin of the Bohemian Massif. A rhyolite porphyry in the famous 'Organy' exposure at Wielisław Złotoryjski (WZ) on the SE margin of the North-Sudetic Basin is younger, 297.5 ± 2.8 Ma. Vein-type auriferous ore mineralization, hosted by Early Palaeozoic graphitic schists in intimate contact with rhyolite porphyry in WZ, is also correlated with this magmatism. The auriferous ore mineralization at Radzimowice and Wielisław Złotoryjski formed at different times, during different magmatic pulses and successive hydrothermal stages, despite several similarities in geologic setting and country- and host-rock compositions. There was a transition from a post-collisional to a within-plate setting over about 20 Ma in Late Carboniferous-Early Permian times, with the older Żeleźniak and Bukowinka sub-volcanic intrusions in the uplifted part of the Kaczawa Metamorphic Complex (ZI) and the younger Wielisław Złotoryjski sub-volcanic intrusion in the metamorphic basement of an intramontane basin.
W artykule przedstawiono wyniki datowań metodą Re–Os wieku molibdenitów związanych z waryscyjskimi intruzjami granitoidowymi w Polsce. W masywie karkonoskim oraz w jego wschodniej osłonie metamorficznej stwierdzono dwa etapy krystalizacji molibdenitów (od 326 ±1 do 310 ±1 mln lat), które odzwierciedlają aktywność pneumatolityczną i hydrotermalną w okresie karbońskim od wizenu/ serpuchowu do moskowu. W masywie Strzegom–Sobótka zarówno molibdenity rozetkowe występujące w formie impregnacji w granitach, jak i molibdenity w przecinających je żyłkach kwarcowych wykazują zbliżony wiek (od 309 ±1 do 296 ±2 mln lat). Krystalizacja molibdenitów w tym masywie była pochodną procesów pomagmowych związanych z powolnym stygnięciem magm odpowiedzialnych za powstanie monzogranitów hornblendowo-biotytowych. Zakres wiekowy krystalizacji molibdenitów ze strefy kontaktu bloku małopolskiego z blokiem górnośląskim mieści się w czasie od 301 ±2 do 296,3 ±1,4 mln lat. Najstarszy wiek izotopowy Re–Os krystalizacji wśród zbadanych dotychczas molibdenitów uzyskano dla próbki molibdenitu pochodzącej z Tatr – 350,5 ±1,2 mln lat. Z kolei najmłodsze wieki krystalizacji molibdenitów stwierdzono w próbkach z kamieniołomu w Siedlimowicach (257 ±1 mln lat) oraz w Miedziance (213 ±1 mln lat). Wieki te wskazują na procesy kataklazy i remobilizacji roztworów hydrotermalnych w młodszych okresach, tj. w późnym permie i triasie. Wyniki badań izotopowych molibdenitów pozwoliły określić relacje czasowe pomiędzy poszczególnymi hydrotermalnymi etapami krystalizacji kruszców i procesami magmowo-tektonicznymi w czasie ok. 140 mln lat, tj. od missisipu (karbon) do noryku (późny trias) w różnych obszarach wystąpień waryscyjskich intruzji granitoidowych w Polsce.
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The paper presents the results of molybdenites that closely correlate with the Variscan granite intrusions in Poland. In the Karkonosze Massif and its eastern metamorphic cover, there are two separate stages of Re-Os ages of molybdenite crystallization (326 ±1 to 310 ±1 Ma), which reflect pneumatolitic and hydrothermal activity in the Carboniferous (from the Visean/Serpukhovian to the Moscovian). In the Strzegom–Sobótka Massif, both rosette-like molybdenites disseminated in granitoids and those from the quartz veinlets reveal similar Re-Os ages that range from 309 ±1 to 296 ±2 Ma. Molybdenite crystallization in the Strzegom–Sobótka Massif was related to the post-magmatic processes associated with a slow cooling of magma responsible for the formation of hornblende-biotite monzogranites. The time range of molybdenites crystallization form the contact zone between the Małopolska and Upper Silesian blocks is from 301 ±2 to 296.3 ±1.4 Ma. The oldest Re-Os isotopic age of molybdenite (350.5 ±1.2 Ma) was received for a molybdenite sample from the Polish part of the Tatra Mountains. The molybdenites from the eastern part of the Strzegom–Sobótka Massif (Siedlimowice quarry, 257 ±1 Ma) and from the Miedzianka abandoned Cu (-U) mine (213 ±1 Ma) yielded the youngest Re-Os ages. These ages indicate tectonic reactivation and remobilization of hydrothermal fluids in the Late Permian and Late Triassic. The Re-Os isotopic studies of molybdenites allowed defining the time relation between successive hydrothermal stages of ore precipitation and tectonic-magmatic processes during ca. 140 million years e.g. from the Mississippian (Carboniferous) to the Norian (Late Triassic) in different areas of the occurrence of Variscan granitoid intrusions in Poland.
The Central-Sudetic ophiolites comprise mafic-ultramafic complexes around the E and S edges of the Góry Sowie Massif in SW Poland and are recognized as fragments of Devonian (~400 Ma old) oceanic crust. They contain small rodingite bodies and tectonized granite dykes that potentially can highlight the igneous, metamorphic and structural development of the ophiolitic suites. The granite dykes have been tentatively correlated with the Variscan granitoids of the Strzegom-Sobótka Massif to the north. However, new U-Pb SHRIMP zircon data for granites from the serpentinite quarry at Jordanów show a concordia age of 337 š4 Ma for the main zircon population, and of 386 š10 Ma for minor inheritance. Thus, the age of the granite is considerably older than the ages of the Strzegom-Sobótka granitoids, dated at ~310-294 Ma. The granite dyke has a similar age as some other granitoids found near the ophiolitic fragments, e.g., the Niemcza granitoids to the south, dated at 338 +2/-3 Ma; these older granitoids all represents a relatively early stage of granitoid magmatism recorded in that part of the Variscan Orogen. The age of the granitoid dyke within serpentinites confirms that the Paleozoic ophiolites were incorporated into the continental crust already in early Visean times.
U-Pb SHRIMP ages of one granodiorite and two tonalite samples from the Strzelin Massif, northern part of Brunovistulicum, reveal three distinct stages of Carboniferrous-early Permian granitoid magmatism: tonalitic I - 324 Ma, granodioritic - 305 Ma and tonalitic II/granitic - 295 Ma. The first stage of magmatism coincided with the first migmatization event which took place shortly after the first deformation. The second stage of granitoid plutonism was coeval with the second migmatization event which produced abundant pegmatites. It took place after compressional phases of the second deformation and was related to decompression at the beginning of tectonic denudation. The third, most abundant stage of magmatism was connected with late extension in that part of the Variscan Orogen.
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Many basement units of the Variscan orogen that are exposed in the Sudetes, SW Poland, comprise widespread ~500 Ma orthogneisses and associated mica schists, the latter often of unknown age and derivation. Our new U-Pb sensitive high resolution ion microprobe (SHRIMP) zircon ages from two samples of the Izera metagranites, both around 503 Ma, are in a good agreement with the well established late Cambrian-early Ordovician magmatism in the West Sudetes. An Archean inherited zircon age of ~ 3.4 Ga is one of the oldest zircon ages reported so far from the Bohemian Massif. The orthogneisses of the Karkonosze-Izera Massif (KIM) have calculated TDM ages of between 1.50 and 1.93 Ga, but these ages are not necessarily evidence for a Mid-Proterozoic crustal derivation: more probably, they reflect the average of several detrital components mixed into the granitoid magma sources. In spite of likely age differences, the Lusatian greywackes, which outcrop to the west, and the mica schists of the KIM display similar geochemical characteristics, suggesting that both could have been derived from similar sources. However, the presence of lower Ordovician products of within-plate volcanism - intercalations of quartzofeldspathic rocks and amphibolites within the mica schists - supports an idea that the mica schist protoliths, derived mainly from crustal rocks, could have also contained an admixture of contemporaneous volcanic materials. The age spectra of inherited zircons from the KIM orthogneisses and their Nd-isotopic signatures are comparable to the Lusatian greywackes: this suggests that the Lusatian greywackes, or very similar rocks, could have been the source material for the granitic protoliths of the KIM orthogneisses.
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Recent geochronological studies, including sensitive high mass-resolution ion microprobe (SHRIMP) zircon dating, have helped to differentiate into specific age groups the various gneisses that occur within the basement units of the central-European Variscides. The Fore-Sudetic Block basement unit, for example, has been divided into two major gneiss groups of Neoproterozoic and Cambrian/Ordovician age, respectively. These two gneiss groups have been assigned to different tectonic units, themselves separated by a major tectonic boundary that is interpreted to be the northern continuation of the Moldanubian (Lugodanubian) Thrust. This thrust divides the main tectonostratigraphic units of the Bohemian Massif: the Moldanubian and Saxo-Thuringian units to the west, and the Moravo-Silesian unit to the east. This paper interprets new SHRIMP zircon data from the Nowolesie gneiss at Skalice (sample S6) and integrates the results with data from the Strzelin gneiss at Dębniki (sample S3), which is within the Strzelin Massif (E part of the Fore-Sudetic Block). Both the Nowolesie and Strzelin gneisses contain numerous inherited zircons within the age range of 1.5-2.0 Ga, indicating Meso- and Palaeoproterozoic sources for the zircons and suggesting that these zircons were recycled into younger units that subsequently underwent partial melting. The ages derived from samples S6 and S3, together with the absence of the Grenvillian ages (~1.3-0.9 Ga), suggest a West-African and/or Amazonian cratonic crust as the source for both the Nowolesie and Strzelin gneiss protoliths. The main zircon populations from both gneisses fall into two similar age groups: 602 +-7 Ma and 587 +- 4 Ma for the Nowolesie gneiss; 600 +-7 Ma and 568 +- 7 Ma for the Strzelin gneiss. These sets of Ediacaran (late Neoproterozoic) dates possibly reflect anatexis of the gneiss protoliths during the Cadomian orogeny.
The Polish part of the Central European Variscan foreland includes several regional units that differ in crustal structure and are characteried by distinct Devonian to Carboniferous subsidence and depositional histories. These units responded differently to palaeostress changes along the south ernmargin of the Old Red Continent. During the Devonian to Namurian A, areas located to the south-west of the Teisseyre-Tornquist Zone (TTZ), including the Upper Silesian Coal Basin, Małopolska and Łysogóry-Radom blocks, were influ nced by stress fields similar to those in the west ward adjacent Rheno-Hercynian Zone, whilst the Lublin Basin, located to the north-east of the TTZ, shows a similar development to the Pripyat-Dniepr-Donets rift system. After the Namurian A, the entire southern Pol ish foreland started to respond in a more consistent way to the build-up of synorogenic compressional stresses, implying a more uniform development of the stress field. During the Namurian B to early Westphalian D, the Polish foreland was dominated by north-directed compressional stresses emanating from the Southeastern Variscan Belt. During the late Westphalian and early Stephanian, the entire foreland under went compressional deformation and concomitant basin in version under the influence of stresses propagating from the Moravian-Silesian Foldand-Thrust Belt. In the Polish foreland, the development of Devonian-Carbon if erous basins, as well as the architecture of Variscan structures, clearly reflect the reactivation of preexisting crustal discontinuities, including specifically the TTZ, but also other major geophysically defined crustal bound aries. In general, thick-skinned tectonics controlled by the inherited structural grain of the basement prevailed, whereas structural decoup ling, resulting in the development of minor thrusts and reverse faulting, was of local significance only. The distinct structural-depositional development of the Pomerania region reflects its distal location with respect to the evolving orogen. Orogenic compression influenced this area only indirectly, with the TTZ acting as a guide for the transmission of transtensional and transpressional stresses.
The Early Devonian metasandstones of the Jegłowa Beds (Strzelin Massif, NE Bohemian Massif) are low- to medium-grade metamorphosed siliciclastic deposits showing differences in modal composition, especially in the amount of micas and feld spars. Despite the similarity in relative concentrations of trace elements, three chemical groups can be distinguished among the metasandstones that differin the total amounts of major and trace ele ments. The negative Ta and Nb anomalies visible on a spider plot normalised to the average upper continental crust and spe cific ratios of e.g. Th, Zr, Hf, La/Th and Ti/Sc characterize the majority of the metasandstones, indicating the provenance of their sedimentary precursors from a subduction-related tectonic setting. However, few of the samples analysed show strongly differentiated geochemical characteristics with high Zr and Hf contents. This suggests input of relatively strongly reworked mate rial. Thus, it seems that a back-arc setting can account for the mixed nature of the inferred source ar eas with old basement and arcrelated detritus respectively as the end-members of the mix tures. The composition of the metasandstones indicates deposition of the siliciclastic material near an Early to Middle Devonian volcanic arc that was super imposed on rocks originally forming a part of the pre-De vo nian continental margin of the Brunovistulicum microplate. A plausible tectonic scenario in volves formation of the Devonian arc due to east-directed subduction of an oceanic domain between the Brunovistulian microcontinent in the east and the Central Sudetic terrain located fur ther west.
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The metamorphic rocks of the Strzelin Massif, in the Fore-Sudetic Block, underwent polyphase tectonothermal evolution terminating with late orogenic gravitational collapse. These rocks recorded Early Permian cooling ages in the range of 279-285 Ma, obtained on white mica concentrates derived from metasediments of the Jegłowa Beds. The obtained results correspond to the youngest group of ages presented by Maluski et al. (1995) from the northern part of the Jeseník Mts, the Moravo-Silesian Zone of the East Sudetes. They suggest very low exhumation rate.
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Low- to medium-grade metabasites are the most abundant metaigneous rocks in the Early Palaeozoic metavolcanic (ąmetasedimentary) East Krkonoše (Karkonosze) Complex located at the Czech/Polish border in the central West Sudetes (NE Bohemian Massif). These mafic rocks are interpreted as metamorphosed equivalents of basic magmatites - both volcanics (lavas and pyroclastics) and subvolcanic intrusives. The correlation of lithostratigraphic units defined in the Czech (southern) and Polish (central and northern) parts of the East Krkonoše Complex is based on a comparison of the geochemical characteristics and petrography of the (1) The greenschists to greenstones (associated with abundant felsic metavolcanics) of the Czech East Krkonoše Complex, which are finely interfingered with low-grade metasediments, are correlated with the amphibolites forming small- to medium-sized bodies in medium-grade metasediments of the Polish East Karkonosze Complex. Both the low- and medium-grade metabasites are interpreted as comprising a range of metamorphosed tholeiitic, transitional and alkaline WPBs. (2) The largest mafic rock suite, which dominates the Polish part of the East Krkonoše Complex, has a dismembered promontory along the eastern margin of the East Krkonoše Complex Czech component. Most of these mafic rocks (blueschists, greenschists, greenstones and amphibolites) correspond to N- and E-MORBs. The above groups of rocks are broadly coeval and geochronologically overlap the Cambrian/Ordovician boundary. The similarity in magmatic ages and the diversity in geochemical features suggest that the East Krkonoše Complex metabasites are evidence for intracontinental rift development and the subsequent generation of incipient oceanic basin lithosphere in the NE Bohemian Massif during the Early Palaeozoic. Provided that the East Krkonoše Complex metabasites can be matched with similar rock suites in the West and Central European Variscides, their magmatic origin may be related to the rifting of northern Gondwana and large-scale break-up at the beginning of the Palaeozoic.
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The Upper Devonian highly polymict conglomerates (site 26) and sandstones with clasts (site 27) of the Pogorzała Formation in the synorogenic Świebodzice Depression, West Sudetes, are hydrothermally altered and show signs of penetration by mineralized fluids. Nearly all the magnetic minerals present (mainly Fe-oxides and pyrrhotite accompanied by Fe-hydroxides) are of secondary origin. Rocks from each site carry multicomponent natural remanence composed of Mesozoic/post-Mesozoic and Palaeozoic components. In the conglomerates (site 26) two Palaeozoic components, labelled P and C, occur in the matrix and pebbles, whereas in the sandstones with large clasts (site 27) only one Palaeozoic component labeled C1 occurs. This means that the results of the conglomerate test for both sites are negative and the studied rocks were remagnetized during several remagnetization episodes. The overprints present in site 26 closely fit the reference data for the Baltica Plate for the Early Permian component (P) and Viséan component (C). The overprint present in site 27 is slightly shifted from the Westphalian (C1) segment of the reference path. The P component is also close to the path of polar wander for Variscan Europe.
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W pracy przedstawiono wyniki interpretacji badań geofizycznych w południowej części monokliny przedsudeckiej. Interpretacja objęła oszacowanie wpływu grawitacyjnego utworów permomezozoiku na obraz anomalii siły ciężkości Delta/g. Zastosowano metody wyznaczania uskoków i ich parametrów z rozkładów anomalii grawimetrycznych i magnetycznych oraz metodę stripingu. Wykorzystane zostały także wyniki badań sejsmicznych. W wyniku badań potwierdzono istnienie uskoku śląsko-lubuskiego, podano jego lokalizację oraz koncepcję budowy geologicznej podłoża monokliny przedsudeckiej w jego sąsiedztwie
EN
In the study results of interpretation of geophysical investigations in S part of Foresudetic Monocline (SW part of Poland) were presented. The interpretation has enclosed an estimation of Permomesosoic's influence in Delta/g anomaly. Methods to determine faults and their parameters from gravity and magnetic anomalies distributions were applied along with the stripping method. Also results of seismic investigations were used. As a result the presence of Silesia-Lubusz fault has been confirmed and its localisation along with a concept of geological structure of Foresudetic Monocline's basement in its neighbourhood has been given
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