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1

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.

2

Chromium-rich illite/smectite in the basal Balinka Conglomerate of the Upper Carboniferous-Permian Boskovice Basin (Bohemian Massif). Annales Societatis Geologorum Poloniae

Hršelová Pavla, Houzar Stanislav, Buriánek David, Všianský Dalibor, Szczerba Marek, Ciesielska Zuzanna, Štelcl Jindřich, Nehyba Slavomír

Annales Societatis Geologorum Poloniae

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2023

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Vol. 93, No. 2

195--210

EN

The Upper Carboniferous polymictic Balinka Conglomerate was deposited along the western margin of the Boskovice Basin (eastern part of the Bohemian Massif). Angular aggregates of deep-green chromium-rich interstratified clay mineral R1-illite(0.8)/smectite (I/S) are present exclusively in the basal part of this unit. The textural position of chromium-bearing I/S (0.77–2.88 wt.% Cr2O3; 0.040–0.153 apfu Cr) in the conglomerate matrix indicates a genetic link with the highly altered chromium spinel, which is preserved in the relics. The source of Cr-rich spinelides was serpentinized peridotites in the adjacent Moldanubicum (Gföhl Unit). The formation of I/S is related to diagenetic processes in the conglomerate matrix. The fluids would have relatively high fugacity of CO2 and activity of K+. K/Ar ages of 284.1 ± 7.7 and 276.3 ± 7.4 Ma (lower Permian – Kungurian/Artinskian age) confirmed the diagenetic origin of this I/S.

3

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.

4

Tectonic pulse registered between 2013 and 2015 on the eastern margin of the Bohemian Massif

Briestenský Miloš, Stemberk Josef, Littva Juraj, Vojtko Rastislav

Geological Quarterly

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2021

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Vol. 65, No. 1

art. no. 14

EN

A significant period of increased tectonics was monitored between 2013 and 2015 on the eastern margin of the Bohemian Massif along ten faults. Nine of them showed a uniform scheme: dextral strike-slip along generally NW–SE striking faults, sinistral strike-slip along generally NE-SW striking faults and uprising of the southern blocks. The distinguished fault displacements displayed an NNW-SSE striking compressional component of the stress field during this remarkable tectonic episode.

5

Multistage structural evolution of the end-Cretaceous–Cenozoic Wleń Graben (the Sudetes, NE Bohemian Massif) : a contribution to the post-Variscan tectonic history of SW Poland

Kowalski Aleksander

Annales Societatis Geologorum Poloniae

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2021

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Vol. 91, No. 1

37--66

EN

Results of a new mapping and structural field study of the Wleń Graben (North Sudetic Synclinorium, SW Poland), made up of a post-Variscan volcano-sedimentary succession, were used to set up a new model of its multiphase tectonic evolution. The Wleń Graben constitutes a narrow tectonic trough, ca. 17.5 km long and up to 3.5 km wide, superimposed on the low-grade metamorphic rocks of the Kaczawa Metamorphic Unit and bounded by steep, NW−SE-oriented, normal and reverse faults. Previously, a simple, one-stage evolution of the graben was considered, with a single Alpine age intraplate compressional event responsible for the formation of the unit. The present study shows that the Late Cretaceous (post-Santonian?) evolution of the Wleń Graben was dominated by NW−SE-oriented, normal faults during the first, extensional stage of its formation. The central and southern parts of the graben were strongly affected by NW−SE-trending reverse faults and overthrusts, which reflect the second, probably latest Cretaceous to early Palaeogene(?) compressional event of tectonic deformation. Moreover, the whole area of the graben is dissected by sinistral strike-slip faults oriented perpendicular to the graben margins, representing the third stage of deformation (late Palaeogene–Neogene). The latest stage of evolution of the Wleń Graben includes a possible Neogene to Quaternary development of normal faults, interpreted here as gravitational collapse structures related to present-day morphology, rather than tectonically induced ones.

6

Triassic palaeogeography of NE Bohemian Massif based on sedimentological record in the Wleń Graben and the Krzeszów Brachysyncline (SW Poland)

Kowalski Aleksander

Annales Societatis Geologorum Poloniae

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2020

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Vol. 90, No. 2

125--148

EN

This paper presents a new sedimentological and palaeogeographic interpretation of the Early to Middle(?) Triassic continental deposits in the Wleń Graben and the Krzeszów Brachysyncline (Sudetes, SW Poland). These two tectonic subunits, located in the peripheral segments of the North Sudetic and Intra-Sudetic synclinoriums, respectively, represent the crucial elements for deciphering the post-Variscan palaeogeographic evolution of the NE termination of the Bohemian Massif. Sedimentological studies and facies analysis show that the Early Triassic siliciclastic deposition in both areas was dominated by fluvial sedimentation of the typical Buntsandstein facies within a gently sloping alluvial plain, locally followed by ephemeral lake environments in the late Early or Middle(?) Triassic. The lithofacies and the measured palaeocurrent directions indicate that the area was drained by braided streams flowing towards the northwest and north. Individual fluvial channels had depths not exceeding 1 m and widths of up to a few metres. Overbank deposits are poorly preserved due to the lateral shifting of channels. Based on available borehole data, an analysis of isopach maps was performed for the first time in the study areas. The study areas are presently separated by crystalline units devoid of sedimentary rocks, but the analysis indicate that they might have been in constant or periodical connection during the Triassic. It is concluded that the present-day extent of Triassic deposits is a result of the primary basin configuration combined with the Middle Triassic to Late Cretaceous erosion and post-Cretaceous tectonic uplift. The paper summarizes the present state of research on the continental Triassic preserved in the terminal parts of the North Sudetic and Intra-Sudetic synclinoriums, presents the first detailed sedimentological logs, and proposes new palaeogeographic interpretation. New findings include bioturbation structures, such as plant-root traces or tunnels formed by invertebrates and possible tetrapod footprints, which shed new light on the sedimentological interpretation of the continental Mesozoic deposits in the NE part of the Bohemian Massif.

7

Thermal history of the Carboniferous strata in the northern part of the Intra-Sudetic Basin (SW Poland): a combined Raman spectroscopy and organic petrography study

Botor Dariusz, Toboła Tomasz, Waliczek Marta

Acta Geologica Polonica

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2020

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Vol. 70, no. 3

363--396

EN

Raman spectroscopy and vitrinite reflectance measurements of dispersed organic matter from Carboniferous shales in boreholes in the northern part of the Intra-Sudetic Basin were used for thermal history reconstruction. Microscopic investigations have shown that the organic matter is dominated by the vitrinite maceral group. In analysed samples, organic matter shows a varied degree of thermal alteration determined by the mean random vitrinite reflectance (VRo) ranging from 0.72% to 3.80%. Mean apparent maximum vitrinite reflectance (R’max) values reached 4.98%. The full width at half maximum of D1 and G bands in Raman spectra are well-correlated with mean VRo and R’max. Thermal maturity in the boreholes shows a regular increase with depth. Geological data combined with Raman spectroscopy and mean vitrinite reflectance results indicate that the analysed Carboniferous strata reached maximum paleotemperatures from c. 110 to c. 265°C. The regional paleogeothermal gradient in the late Paleozoic was c. 80°C/km. The Variscan heating event presumably caused a major coalification process of organic matter. The Carboniferous–Permian magmatic activity must have contributed to high heat flow, adding to the effect of sedimentary burial on the thermal maturity.

8

Jurassic pebbles in the Cretaceous sandstones of the Bohemian Basin as a possible tool for reconstruction of the Late Jurassic and Late Cretaceous palaeogeography

Valecka Jaroslav

Volumina Jurassica

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2019

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Vol. 17, no. 1

17--38

EN

A new find of pebbles of Jurassic silicites in the Coniacian sandstones of the Bohemian Cretaceous Basin in N Bohemia has permitted analysis of the stratigraphic extent of Jurassic sediments in the NW part of the Bohemian Massif. The studied silicites are dominated by the rhax microfacies, while bioclastic and oolitic microfacies are less common. The thickest section of Jurassic sediments in the NW part of the Bohemian Massif has been obtained from the Doubice borehole. It is represented by basal clastics overlain by a 70 m thick succession of silicite-free carbonate rocks which range in age from Callovian to Lower Kimmeridgian. These deposits are dominated by the bioclastic microfacies whereas the rhax and oolitic microfacies are missing. The studied silicite-bearing sequence is younger than the carbonate rocks in Doubice borehole and was deposited mostly in a deeper zone probably during the Late Kimmeridgian transgression, much like in the Upper Frankenalb in SE Germany. The extensive Jurassic basin in the Bohemian Massif was connected with the S part of the Polish and German basins and – via the Hessian (Saxonian) Seaway – with the Jurassic basin in SE Germany. The Jurassic sediments were mostly eroded from the Bohemian Massif during the Early Cretaceous with the exception of small relics. The remnant of the Jurassic deposits preserved in the area of the West Sudetic Island supplied coarse debris during Late Cretaceous to the Bohemian Cretaceous Basin.

9

Polymetamorphic evolution of pelites inferred from tourmaline zoning – the Rędziny hornfels case study at the eastern contact of the Karkonosze Granite, Sudetes, Poland

Majka J., Sęk M. P., Mazur S., Gołębiowska B., Pieczka A.

Mineralogia

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2018

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Vol. 49, iss. 1/4

17--34

EN

Tourmaline occurring in hornfelses from the eastern envelope of the Karkonosze Granite (Western Sudetes, Poland) reveals at least two stages of crystallization expressed by its complex zoning. The cores and mantles of the crystals probably grew during prograde metamorphism under intermediate pressure-temperature conditions reflected by increasing Mg, Ti and Ca. Outermost rims show enrichment in Al and Ca, indicating growth during contact metamorphism in the presence of an Al-saturating phase. The Ti-content in biotite indicates that the temperature of the contact metamorphic event did not exceed 650ºC. The presence of andalusite and the lack of garnet and cordierite also indicates pressure conditions of ~ 2-3 kbar, typical of the C1 bathozone of Carmichael (1978) or the P1 bathozone of Pattison (2001).

10

Trace element variations as a proxy for reconstruction of palaeoenvironmental changes during the Late Aeronian faunal and carbon isotope perturbations: new data from the peri-Gondwanan region

Pašava J., Frýda J., Štorch P.

Geological Quarterly

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2017

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Vol. 61, No. 1

91--98

EN

Trace element variations in the Upper Aeronian (Llandovery, Lower Silurian), deep-water, black shale succession of the Barrandian area (Perunica) were studied across an interval associated with a graptolite mass extinction and global, positive carbon isotope anomaly. The main aim of the paper is to test whether distinct changes in graptolite diversity during Late Aeronian were linked with changes in deep sea water oxygenation. Using multiple geochemical proxies we documented high-frequency changes in oxygenation of sea water from sediments of the convolutus to linnaei (guerichi) biozones. Detailed comparison of graptolite diversity with those high-frequency oxygenation changes suggests that the long-term and step-wise Late Aeronian graptolite crisis was not significantly influenced by changes in oxygen level and thus it probably resulted by another causes. The collapse of global carbon cycle during the Late Aeronian probably only temporarily increased extinction rate of the long-term graptolite crisis and considerably decreased evenness of the uppermost Aeronian graptolite communities. The Aeronian graptolite mass extinction was thus primarily driven by other biotic and/or abiotic causes

11

Monazite stability and the maintenance of Th-U-total Pb ages during post-magmatic processes in granitoids and host metasedimentary rocks: A case study from the Sudetes (SW Poland)

Budzyń B., Jastrzębski M.

Geological Quarterly

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2016

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Vol. 60, No. 1

106--123

EN

The stability and maintenance of the age record of monazite during post-magmatic processes were studied in granitic and host metasedimentary rocks from the Sudetes (SW Poland). Unaltered monazite in the Kłodzko–Złoty Stok granitoid provided a Th-U-total Pb age of 329 ± 5 Ma, which was related to the late stage of pluton emplacement. In contrast, monazite in the Jawornik granitoid remained unaltered or was partially replaced by secondary phases, including (1) allanite, epidote and, occasionally, apatite; (2) cheralite, allanite and a mixture of clays, Fe oxides and possible unknown rare earth element (REE) phases; and (3) K-feldspar and cheralite with subsequent formation of titanite. Different alteration products on the thin section scale indicate the local character of the post-magmatic processes affecting monazite induced by alkali-rich fluids. The altered and unaltered monazite grains both yielded a Th-U-total Pb age of 343 ± 4 Ma. The Th-U-total Pb ages of the monazite in the accompanying metasedimentary rocks thermally affected by intruding magmas were also constrained. In the paragneiss in contact with the Jawornik granitoid, the unaltered monazite and monazite partially replaced by allanite yielded an age of 344 ± 5 Ma. The monazite from the mica schist, farther from the contact with the granitoids, exhibited an age of 336 ± 4.5 Ma. The 344–336 Ma ages exhibited a record of monazite (re)growth during prolonged Variscan metamorphism. The predominant early Viséan ages constrain the timing of the development of the Złoty Stok Skrzynka Shear Zone and the emplacement of the Jawornik granitoid intrusion. The age results, which are consistent with previous geochronology, indicate that the partial alteration of the monazite did not affect the internal domains or the maintenance of the monazite ages. Thus, this study reveals that monazite geochronology can provide meaningful data in crystalline rocks affected by fluid-induced post-magmatic processes.

12

Gold deposits of the Czech Republic from a mineral policy perspective

Janíková P., Starý J., Klika R., Kavina P., Jirásek J., Sivek M.

Gospodarka Surowcami Mineralnymi

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2015

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T. 31, z. 4

35--49

EN

Gold production in the region that currently makes up the Czech Republic has a thousand-year-old tradition with peaks around the third century BC, 14th century AD and 20th century AD. In general, approximately 100 metric tonnes were produced by the end of mining in 1994, of which nearly 9 tonnes were produced in the 20th century and approximately 3 tonnes were produced after World War II. Significant gold deposits were discovered during the last extensive exploration conducted in the 1970s to 1995, motivated by the sharp rise in the price of gold at the beginning of the 1970s and in the 1980s. Fifteen deposits with 239 tonnes of geological resources of gold were registered. Another 112 tonnesare recorded as prognosticated resources. None of these deposits are mined, due to unresolved issues involving environmental protection. The exploitation of these deposits is restricted primarily due to concerns regarding the environmental impacts of the mining and processing of extracted minerals. A key aspect of these restrictions is likely the existing ban on the use of cyanide mining technologies. A new and yet-to-be-approved proposal for an updated mineral policy in the Czech Republic is attempting to gradually change this stance. Yet another problem lies in the unfinished surveys of mineral deposits, which would specify the total amount of gold and upgrade the resources to higher categories concerning the level of exploration. Without these, it is impossible to prepare the necessary economic assessments of potential production and of the deposits to the fullest extent of activities involving exploration, mineral extraction and processing, including subsequent reclamation of affected areas, elimination of mining impacts and regeneration of post-mining landscapes. The future of gold deposits in the Czech Republic also greatly depends on future trends in the price of gold and accompanying (by-product) minerals occurring together with gold in mined ores.

PL

Produkcja złota w Czechach ma ponad tysiącletnią tradycję sięgającą trzeciego wieku przed naszą erą. Ogółem do końca 1994 roku wyprodukowano około 100 ton złota, z czego prawie 9 ton zostało wyprodukowanych w XX wieku i około 3 tony − po II wojnie światowej. Znaczne złoża złota odkryto podczas ostatnich rozległych badań, przeprowadzonych w latach 1970−1995, które determinowane były gwałtownym wzrostem cen złota w latach 1970−1980. Odkryto 15 złóż złota o zasobach geologicznych wynoszących 239 ton. Kolejnych 112 ton złota oszacowano w zasobach prognostycznych. Żadne z tych złóż nie jest eksploatowane z powodu nierozwiązanych problemów dotyczących ochrony środowiska. Eksploatacja tych złóż jest ograniczana przede wszystkim ze względu na obawy dotyczące wpływu na środowisko procesów wydobywczych i przetwórstwa wydobywanych kopalin. Kluczowym aspektem tych ograniczeń jest istniejący zakaz stosowania technologii wydobywczych z wykorzystaniem cyjanku. Nowy, jeszcze nie zatwierdzony, wniosek o zaktualizowanej polityce surowców mineralnych w Czechach, stopniowo stara się zmienić tę postawę. Jeszcze innym problemem są niedokończone badania złóż kopalin, które określą całkowitą ilość złota i spowodują przeszacowanie zasobów do wyższych kategorii. Bez nich niemożliwe jest przygotowanie niezbędnych analiz ekonomicznych, potencjalnej produkcji, rekultywacji obszarów dotkniętych działalnością górniczą. Przyszłość złóż złota w Republice Czeskiej zależy również od przyszłych trendów cen tego surowca i towarzyszących mu (produkt uboczny) minerałów.

13

Granite tors of Waldviertel (Lower Austria) as sites of geotourist interest

Michniewicz A., Różycka M., Migoń P.

Geotourism / Geoturystyka

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2015

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nr 1-2

19--36

EN

Granites of the South Bohemian Pluton are among the main rocks in the region of Waldviertel in the northern part of Lower Austria. The overall topography is gently rolling, with higher elevations and medium-altitude mountainous relief present only in the south-western part. Tors are the most characteristic residual landforms and occupy different settings, from mountain tops to valley floors. They vary in shapes and dimensions, with castle koppies and boulder clusters being most common. Many tors host well-developed microforms such as weathering pits, karren, runnels, and flared slopes. Balanced rocks are among the highlights of the region. Because of good access residual granite landforms of Waldviertel are well suited to be developed as geosites and geotourist destinations, but there is clearly a deficit of explanation and interpretation. In this paper 15 representative tors are presented, tourist infrastructure is summarized, and a thematic one-day drive is proposed.

PL

Granity plutonu południowoczeskiego należą do głównych skał występujących w regionie Waldviertel w północnej części kraju związkowego Dolna Austria. Region ten odznacza się lekko falistą rzeźbą, z większymi wysokościami i górzystym ukształtowaniem jedynie w części południowo-zachodniej. Skałki stanowią najbardziej charakterystyczny element rzeźby denudacyjnej, zajmując różną pozycję morfologiczną, od szczytów wzniesień po dna dolinne. Są zróżnicowane pod względem kształtu i wymiarów, z dominacją zamczysk skalnych i zgrupowań bloków (skałek rumowiskowych). Morfologię wielu z nich urozmaicają mikroformy, takie jak kociołki wietrzeniowe, żłobki, rynny i nisze kloszowe. Szczególnie interesującym elementem rzeźby regionu są chybotki. Dobra dostępność sprawia, że rezydualne formy granitowe regionu są odpowiednie do zagospodarowania jako geostanowiska i atrakcje geoturystyczne, choć uwagę zwraca brak szerszego zaplecza edukacyjnego i interpretacyjnego. W artykule przedstawiono 15 reprezentatywnych skałek granitowych, podsumowano zagospodarowanie turystyczne obszaru oraz zaproponowano przebieg jednodniowej tematycznej trasy samochodowej.

14

The origin of the Popiel peridotite (Western Sudetes, SW Poland) : metamorphism of the island arc tholeiitic cumulate

Kukuła A., Puziewicz J., Ntaflos T.

Geological Quarterly

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2015

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Vol. 59, No. 2

239--247

EN

A small (280 x 140 m) outcrop of peridotite occurs on Popiel Hill (Sudetes, SW Poland) within the low-grade metabasic rocks of the Rudawy Janowickie Complex, which form the eastern and north-eastern cover of the Variscan Karkonosze granite. The peridotite is situated on the Intra-Sudetic Fault, one of the major Variscan dislocations in the region. The rock consists of strongly tectonised olivine (Fo84-88) and orthopyroxene (Mg# 0.84–0.88) aggregates, overgrown by tremolite-magnesiohornblende, locally forming large crystals, embedded in serpentine. Spinel and magnetite are subordinate; ilmenite, Fe-sulfide, and apatite are accessories. The bulk-rock chemical composition suggests a lherzolitic composition and the occurrence of primary clinopyroxene, now completely replaced by tremolite and magnesiohornblende. Rare Earth Element patterns are flat, slightly enriched relatively to primitive mantle, as is typical of island arc tholeiites. Olivine, orthopyroxene, and spinel were the first to crystallize, and they represent relics of a primary igneous assemblage. They were followed by tremolite and serpentine, formed during uplift and related metamorphism. The last mineral to crystallize was magnesiohornblende, which originated due to contact metamorphism by the Karkonosze granite magma. The Popiel peridotite probably represents a small slice of lherzolitic cumulate, which originated in a tholeiitic magma chamber at the roots of a supra-subduction volcanic arc.

15

Pleistocene speleothem fracturing in the Western Carpathian orogenic foreland : A case study from transtensional setting at the eastern margin of the Bohemian Massif

Babek O., Briestenský M., Přecechtělová G., Štěpančíková P., Hellstrom J. C., Drysdale R. N.

Geological Quarterly

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2015

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Vol. 59, No. 3

491–-506

EN

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 hájovnou, Javoříčko, and Mladeč 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 14C 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 Mladeč 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.

16

Monazite Th-U-total Pb geochronology and P-T thermodynamic modelling in a revision of the HP-HT metamorphic record in granulites from Stary Gierałtów (NE Orlica-Śnieżnik Dome, SW Poland)

Budzyń B., Jastrzębski M., Kozub-Budzyń G. A., Konečný P.

Geological Quarterly

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2015

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Vol. 59, No. 4

700--717

EN

Thermodynamic modelling and monazite Th-U-total Pb dating via electron microprobe were used to improve the pressure, temperature and timing constraints of the HP-HT metamorphic record in granulites from Stary Gierałtów (NE Orlica-Śnieżnik Dome (OSD), SW Poland). The thermodynamic calculations constrained the P-T conditions to 20-22 kbar and ca. 920ºC in the felsic to intermediate granulites and 20-22 kbar and ca. 970ºC in the mafic granulite. These conditions are considered to closely represent the peak temperatures experienced by these rocks. In the intermediate granulite, the matrix monazite and monazite inclusions in garnet and allanite yielded an age of 349±2.5 Ma. An HP-HT metamorphic event with temperature conditions exceeding 900ºC, which are greater than the closure temperatures of most geochronometers, must have disturbed and completely reset the isotopic systems, including the Th-U-Pb system in the monazite. Consequently, this resetting prevented us from constraining the age of potential earlier metamorphic events or the igneous protolith. The 349±2.5 Ma age reflects the timing of the late-stage HP-HT event and cooling below 900ºC related to the initial exhumation of the granulites. A comparison of the new P-T-t constraints with previous data from the NE Orlica-Śnieżnik Dome indicates that the activation of the channels that exhumed the HP rocks to mid-crustal depths most likely initiated at ca. 350 Ma, and all the metamorphic rocks in the OSD likely shared a common Variscan evolution after ca. 340 Ma.

17

The origin of atoll shaped garnets in the Tepla Crystalline Complex, Bohemian Massif

Peresty V, Racek M, Lexa O

Geologia Sudetica

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2014

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Vol. 42

71--71

18

The Clay and Zavist faults - one large strike-slip fault in the east part of Barrandian (Bohemian Massif)

Knizek M, Melichar R.

Geologia Sudetica

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2014

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Vol. 42

36--37

19

Relative reactivation and kinematic potential analysis of some faults in the NE part of the Bohemian Massif

Havir J.

Geologia Sudetica

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2014

|

Vol. 42

29--29

20

Deformation and metamorphic record within the subduction exhumation channel as recorded in the Krkonose-Jizera Mountains, Bohemian Massif

Jerabek P, Konopasek J, Zackova E

Geologia Sudetica

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2014

|

Vol. 42

35--35