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The eastern part of the Saxothuringian Terrane characterized by zircon and monazite data from the Doboszowice Metamorphic Complex in the Sudetes (SW Poland)

Jastrzębski Mirosław, Żelaźniewicz Andrzej, Stawikowski Wojciech, Budzyń Bartosz, Krzemińska Ewa, Machowiak Katarzyna, Madej Stanisław, Białek Dawid, Sláma Jiří, Czupyt Zbigniew, Jaźwa Aleksandra

Annales Societatis Geologorum Poloniae

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2023

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Vol. 93, No. 3

229--249

EN

In the Variscan Bohemian Massif, orthogneiss complexes of different sizes, derived from early Palaeozoic granitoids, are accompanied by metavolcano-sedimentary successions. They are common in the Sudetes, SW Poland, and belong mainly to the Saxothuringian Terrane. In order to better characterize the evolution of the latter, new U-Pb and O isotopic zircon analyses, combined with zircon typology and new U-Th-Pb isotopic monazite analyses, were performed. The present data show that the S-type granitic precursors of the Doboszowice orthogneisses (Fore-Sudetic Block) and the Śnieżnik gneisses (Sudetes) were formed at ca. 495 Ma from differently evolved magmas. Protoliths of the Doboszowice orthogneisses developed entirely in the crust, whereas the precursors to the Śnieżnik gneisses received some mantle input. Metasediments that accompany the Doboszowice orthogneisses reveal zircon spectra, which point to a late Cambrian-Early Ordovician sedimentary age. These spectra, in addition to predominant grains with Ediacaran ages, contain up to 10% of zircons dated at ca. 1.0 Ga. Therefore, it is suggested that the parent basin was supplied with detritus coming from areas, located in the Libyan-Nubian part of North Africa. Using also earlier published data, such a provenance is assigned to the units that now occur in the eastern part of the Fore-Sudetic Block. Late Cambrian-Early Ordovician granite intrusions and the concurrent accumulation of sediments originated in an extensional setting of the peri-Gondwana rifted continental margin or a back-arc setting. The Pb/U and Pb/Th monazite data constrain the ca. 346–341-Ma peak of the Variscan regional metamorphism in the eastern Saxothuringian Terrane and the prolonged juxtaposition of now adjacent tectonic units at least until 330 Ma.

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Detrital zircon analysis of metasedimentary rocks of the Staré Město Belt, Sudetes : implications for the provenance and evolution of the eastern margin of the Saxothuringian terrane, NE Bohemian Massif

Śliwiński Marek, Jastrzębski Mirosław, Sláma Jiří

Geological Quarterly

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2022

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Vol. 66, No. 2

art. no. 21

EN

The Staré Město Belt (SMB) in the Central Sudetes forms a Variscan tectonic boundary zone that is located between the Saxothuringian and Brunovistulian terranes of the Bohemian Massif. The three thrust-bounded upper, middle and lower lithotectonic units of the SMB are composed of metasedimentary and Late Cambrian metavolcanic rocks. A new LA-ICP-MS zircon geochronology supported by zircon typology studies of the mica schists of the upper unit and the migmatitic paragneisses of the middle unit provides new insights into the provenance and evolution of the SMB. Our new data were obtained from metasedimentary rocks and compared to the previously published zircon ages of the SMB metavolcanic rocks. The results indicate that the metasedimentary and bimodal metavolcanic rocks in the separate lithotectonic units of the SMB originally formed Late Cambrian volcano-sedimentary successions. The source areas of the sedimentary basins studied were dominated by Neoproterozoic and Paleoproterozoic crystalline rocks that were presumably located near the West African Craton of Gondwana. A comparison of the detrital age spectra obtained with those previously published from the region indicates a strong association of the entire SMB with the Saxothuringian terrane of the Bohemian Massif. During partial melting of the metasedimentary rocks of the middle unit of the SMB, Cambrian and older zircon grains were affected by solid-state transformations that caused partial resetting of the U-Pb dates, changes in internal zircon textures and reductions in Th/U ratios.

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Evolution of Neoarchean-Paleoproterozoic basement in the Brunovistulia terrane, S Poland : geological, P-T and geochemical records

Żelaźniewicz Andrzej Ryszard, Jastrzębski Mirosław

Geological Quarterly

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2021

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Vol. 65, No. 2

art. no. 20

EN

Brunovistulia is a composite terrane of Gondwana descent that eventually was accreted to the SW margin of Baltica, central Europe. It is built of metagneous and metasedimentary rocks that originated mainly between 650 and 550 Ma. However in the Upper Silesian part of Brunovistulia, much older fragments have been drilled, which yielded U-Pb zircon ages between 2.75 and 2.0 Ga. They have been interpreted as an “exotic” constituent of the Brunovistulia superterrane, named the Rzeszotary Terrane. Our geological and geochemical studies of the Rzeszotary borehole cores yielded new data on the composition, provenance and evolution of that terrane. Precursors of the Rzeszotary complex were separated from the depleted mantle prior to or around 3.2-3.0 Ga. At 2.75-2.6 Ga, a juvenile magmatic arc edifice formed, beneath which oceanic lithosphere was subducted. Decompression melting of the mantle brought about tholeiite magmas of IAT/MORB composition with LILE additions. Tonalitic and trondhjemitic precursors of gneisses present today were formed at that time, probably due to partial melting of mantle-derived wet basalts at the base of the island arc. Around 2.0 Ga, the arc collided with an unspecified cratonic mass and was subject to orogenic deformation, metamorphism and migmatization. The entire arc edifice was then strongly shortened and forced down to depths equivalent to ~6-12 kbar where the rocks underwent contractional deformation and metamorphism (~500-700°C). Tonalites and trondhjemites were changed to gneisses, and basites to epidote- and garnet amphibolites. These rocks underwent syntectonic migmatization through the mechanism of segregation/differentiation in the presence of fluids and incipient partial melting. Synmetamorphic shortening of the rock pile, which led to folding and heterogeneous development of shear zones with thrust kinematics, terminated with intrusions of K-granites at 2.0 Ga, being followed by some brittle-ductile deformation of unconstrained timing. The 2.0 Ga event may have been connected with the 2.1-1.8 Ga global amalgamation of the Paleoproterozoic supercontinent of Columbia. Later the future Rzeszotary terrane was detached from the Gondwana mainland, reassembled and eventually, in the Neoproterozoic, it became part of the foreland of the Cadomian Orogen in Central Europe.

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Age constraints on the Pre-Variscan and Variscan thermal events in the Kamieniec Ząbkowicki Metamorphic belt (the Fore-Sudetic Block, SW Poland)

Jastrzębski Mirosław, Żelaźniewicz Andrzej, Budzyń Bartosz, Sláma Jiří, Konečny Patrik

Annales Societatis Geologorum Poloniae

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2020

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Vol. 90, No. 1

27--49

EN

The Kamieniec Ząbkowicki Metamorphic Belt (KZMB) is a narrow zone of mainly mica schists, subordinate acid metavolcanics and scarce eclogites, sandwiched between Brunovistulia and the northern tip of the Teplá-Barrandia microplates. Locally occurring high-pressure relics indicate subduction of the metasedimentary succession of the KZMB, the origin and provenance of which remain unclear. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) investigations of detrital zircons show that the metapelites represent an Ediacaran-Cambrian sedimentary basin, with a maximum depositional age of 561±9 Ma. This basin was filled with detritus from a source or sources, composed of rocks containing zircons that are mainly Cryogenian-Ediacaran and Palaeoproterozoic in age. No younger component was found in the zircon population studied. The isotopic U-Pb LA-ICP-MS and chemical U-Th-total Pb electron probe microanalysis (EPMA) monazite geochronology data indicate an important regional tectono-metamorphic event at ca. 330 Ma. Though these data do not permit determination of the peak pressure from the peak temperature stages, the event was part of a complex collision of the Saxothuringian plate with Brunovistulia.

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Ewolucja tektonometamorficzna marmurów i otaczających łupków łyszczykowych formacji strońskiej (Sudety)

Jastrzębski Mirosław

Geologos

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2008

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Vol. 14, No. 1

51--71

PL

Połączone badania strukturalne, petrograficzne oraz geochronologiczne nad relacjami P-T-d (ciśnienie-temperatura-deformacja) w marmurach i otaczających łupkach łyszczykowych kopuły orlicko-śnieżnickiej (KOŚ) przyczyniły się do rekonstrukcji ewolucji tektonicznej wschodniej krawędzi Sudetów Zachodnich. Wyniki przeprowadzonych badań wykazały, iż na wskutek skrócenia tektonicznego w kierunku E-W (etap D1), związanego z waryscyjską kolizją domen kontynentalnych Sudetów Zachodnich oraz Brunowistulii, doszło do powstania stromej foliacji SI, pogrubienia skorupy i pogrążenia skał formacji strońskiej na głębokości odpowiadające ciśnieniom 0.9-1.0 GPa. Początkowe fazy wynoszenia skał, stowarzyszone ze pionowym skracaniem tektonicznym (etap D2), były powiązane z progresją metamorfizmu regionalnego od warunków facji zieleńcowej do facji amfibolitowej. Pod koniec etapu D2, podczas ustalenia się piku temperaturowego metamorfizmu, ukształtowała się strefowość metamorfizmu zapisana w skałach formacji strońskiej. Etap D2 doprowadził do wykształcenia leżących wąskopromiennych fałdów F2, deformujących foliację S1, oraz do spłaszczania więźby wewnętrznej zakonserwowanej w granatach. Progresywna deformacja etapu D2 ostatecznie doprowadziła do ukształtowania się subhoryzontalnej foliacji osiowej S2, którą w łupkach łyszczykowych stanowi powszechnie obserwowane złupkowanie. Podczas dalszego wynoszenia skał doszło do lokalnej reaktywacji foliacjj S2 w reżimie góra-ku-N, odpowiedzialnej za wytworzenie się stref ścinania. Późniejsze skracanie tektoniczne w kierunku NE-SW (etap D4) mogło wiązać się z regionalnym fałdowaniem i reorientacją powierzchni strukturalnych S2 || S3 oraz powierzchni izoterm/izograd metamorficznych, zaś na wskutek skracania tektonicznego w kierunku NW-SE (etap D5), doszło do nachylenia tych powierzchni w kierunku W/NW. Oba końcowe etapy mogły być odpowiedzialne za obserwowany kształt izograd metamorficznych, a także zmniejszanie się stopnia metamorfizmu w kierunku W/NW.

EN

Integrated structural, petrographic and geochronological studies on P-T-d record in marbles and adjacent mica schists of the Orlica-Śnieżnik Dome (OSD) contribute to a model of the tectonic development of the eastern borderland of the West Sudetes. The results of these studies show that marbles of the OSD experienced E-W directed subhorizontal shortening (D1 stage), which resulted from the Variscan collision between the West Sudetes domain and the Brunovistulian terrane. These processes led to crustal thickening, development of a steep metamorphic fabric, and the burial of the Stronie Formation to depths corresponding to 0.9-1.0 GPa. Subsequent vertical shortening (D2 stage) was related to the onset of uplift and progression of metamorphism from greenschist to amphibolite facies conditions. Under peak conditions in the temperature, metamorphic zonation was established in the Stronie Formation. The D2 shortening led to folding of the 51 planes to form recumbent tight folds (F2), and to flattening of the inclusion trails in syn-D2 garnet porphyroblasts. Ongoing D2 deformation led to the development of subhorizontally disposed S2 axial-plane foliation. In mica schists, it is preserved as a penetrative schistosity. During progressive uplift, S2 planes were reactivated as a result of subsequent top-to-N directed transport (D3 stage). The S2 || S3 planes and S2-related metamorphic isograds were regionally folded during the D4 tectonic stage, which was characterised by NE-SW directed tectonic shortening. During stage D5, due to NW-SE directed tectonic shortening, the structural and metamorphic sur- faces became inclined toward west (or north-west). The D4 and DS stages were presumably together responsi- ble for the observed metamorphic isograds and their overall tilting toward W (or NW).