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    Wyświetlanie 1-14 z 14
    Tytuł:
    Tectonic pulse registered between 2013 and 2015 on the eastern margin of the Bohemian Massif
    Autorzy:
    Briestenský, Miloš
    Stemberk, Josef
    Littva, Juraj
    Vojtko, Rastislav
    Powiązania:
    https://bibliotekanauki.pl/articles/2058709.pdf
    Data publikacji:
    2021
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    tectonic pulse
    Bohemian Massif
    compression
    faults
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2021, 65, 1; 14
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Variscan multistage granitoid magmatism in Brunovistulicum: petrological and SHRIMP U-Pb zircon geochronological evidence from the southern part of the Strzelin Massif, SW Poland
    Autorzy:
    Oberc-Dziedzic, T.
    Kryza, R.
    Białek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059086.pdf
    Data publikacji:
    2010
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Variscides
    Bohemian Massif
    Strzelin Massif
    granitoids
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2010, 54, 3; 301-324
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Variscan Orogen in Poland
    Autorzy:
    Mazur, S.
    Aleksandrowski, P.
    Kryza, R.
    Oberc-Dziedzic, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/2058949.pdf
    Data publikacji:
    2006
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Bohemian Massif
    Sudetes
    Palaeozoic
    terranes
    metamorphism
    magmatism
    Opis:
    The structure and evolution of the Polish part of the Variscan Orogenic Belt is reviewed, based on published data and interpretations. The Sudetic segment of the Variscides, together with adjacent areas, experienced multi-stage accretion during successive collisional events that followed the closure of different segments of the Rheic Ocean. In SW Poland, Variscan tectono-stratigraphic units are tectonically juxtaposed and often bear record of contrasting exhumation/cooling paths, constrained by palaeontological and geochronological data. This points to the collage-type tectonics of this area. A three-partite subdivision of the Sudetes is proposed that reflects timing differences in deformation and exhumation of the respective segments. The Central,West and East Sudetes were deformed and amalgamated during the Middle/Late Devonian, at the turn from the Devonian to Carboniferous and during Early Carboniferous times, respectively. Problems in extending the classical tectono-stratigraphic zonation of the Variscides into the Sudetes are discussed and attributed to activity along Late Palaeozoic strike-slip faults and shear zones, disrupting and dispersing the initially more simply distributed tectono-stratigraphic units into the present-day structural mosaic. Relationships between the Variscan Externides and the foreland basin are explored. Sediments of the foreland basin locally onlap the external fold-and-thrust belt that had undergone an earliest Carboniferous partial tectono-thermal overprint. During the Late Carboniferous, the SW part of the foreland basin was heavily affected by thrusting and folding and incorporated into the Externides. DuringWestphalian C to Early Permian times, localized folding and thrusting affected the distal parts of the foreland basin, probably in response to dextral transpressional movements along NW–SE trending basement faults.
    Źródło:
    Geological Quarterly; 2006, 50, 1; 89-118
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The origin of the Popiel peridotite (Western Sudetes, SW Poland) : metamorphism of the island arc tholeiitic cumulate
    Autorzy:
    Kukuła, A.
    Puziewicz, J.
    Ntaflos, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060292.pdf
    Data publikacji:
    2015
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    peridotite
    cumulate
    supra-subduction
    Intrasudetic Fault
    Bohemian Massif
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2015, 59, 2; 239--247
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Gneiss protolith ages and tectonic boundaries in the NE part of the Bohemian Massif (Fore-Sudetic Block, SWPoland
    Autorzy:
    Oberc-Dziedzic, T.
    Kryza, R.
    Klimas, K.
    Fanning, M.C.
    Madej, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059703.pdf
    Data publikacji:
    2005
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Bohemian Massif
    East-West Sudetes boundary
    zircon ages
    Opis:
    Published geochronological data, petrology, geochemistry and geological context of orthogneisses in the Strzelin and the Stachów complexes (NE-part of the Fore-Sudetic Block), together with structural observations help to locate the northern extension of the boundary between the East and West Sudetes within the poorly exposed NE margin of the Bohemian Massif. The Strzelin complex, in the east, comprises the Strzelin gneiss, with zircon ages of 600š7 and 568š7Ma, and the Nowolesie gneiss with a mean zircon age of 1020_ 1Ma. The Stachów complex to the west, which forms several tectonic klippen in the Strzelin Massif and in the Lipowe Hills Massif, contains the Gościęcice gneiss and pale Stachów gneiss, both yielding Late Cambrian zircon ages (~500š5 Ma). The orthogneisses in both complexes correspond to peraluminous S-type granites, but have different inherited zircon ages and display contrasting trace element characteristics, indicating different sources and petrogenetic histories. Based on the ages, petrology and overall geological context, the Strzelin orthogneiss is similar to the Keprník orthogneiss of the East Sudetes, whereas the orthogneisses of the Stachów complex correspond to rocks known from theWest Sudetes (e.g. the Izera and Śnieżnik orthogneisses). The Stachów and the Strzelin complexes are separated by the Strzelin Thrust, which may be interpreted as the northern extension of the boundary between the East and West Sudetes, i.e. part of the boundary between the Brunovistulian and Moldanubian terranes of the NE part of the Bohemian Massif.
    Źródło:
    Geological Quarterly; 2005, 49, 4; 363--378
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Calcareous nannoplankton in the Upper Jurassic marine deposits of the Bohemian Massif: new data concerning the Boreal–Tethyan communication corridor
    Autorzy:
    Holcová, K.
    Holcová, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059943.pdf
    Data publikacji:
    2016
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    calcareous nannoplankton
    Late Jurassic
    North Bohemian Massif
    biostratigraphy
    paleoecology
    Opis:
    Calcareous nannoplankton assemblages from the Jurassic relict deposits in the northern part of the Bohemian Massif are described here for the first time. They are generally of low diversity and dominated by watznaueriaceans. Some of them are diagenetically affected, probably due to dolomitisation. Calcareous nannoplankton enables the stratigraphical range of the Northern Bohemia Jurassic succession to be extended to the Tithonian by reference to the stratigraphical range of Jurassic platform sequences in Central Poland and the eastern part of the Bohemian Massif. The Oxfordian–Kimmeridgian nannofossil assemblages indicate a generally oligotrophic condition of the restricted sea with episodic fluvial input containing terrestrial nutrients. The character of the upper part of the water column was generally uniform and did not reflect variability at the sea-floor expressed by lithofacies diversity. The palaeoenvironment interpreted for the famous former palaeontological locality “Sternberk Quarry” was characterized by a higher nutrient content and more stable environment. The Tithonian nannofossil assemblages contain warm-water Tethyan taxa which suggest south-north migration of nannoplankton due to warming during the Jurassic–Cretaceous boundary interval.
    Źródło:
    Geological Quarterly; 2016, 60, 3; 624--636
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hydrothermal veins linked with the Variscan structure of the Prague Synform (Barrandien, Czech Republic): resolving fluid-wall rock interaction
    Autorzy:
    Halavínová, M.
    Melichar, R.
    Slobodník, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059098.pdf
    Data publikacji:
    2008
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Bohemian Massif
    Palaeozoic
    Variscan veins
    carbonates
    isotope geochemistry
    fluid systems
    Opis:
    Variscan syntectonic hy dro ther mal veins of the Prague Synform are important traces of small-scale fluid migration in Lower Palaeozoic sedimentary rocks — a process induced by late Variscan tectogenesis. Two main structural types of Variscan syntectonic calcite veins were recognised during fieldwork. Veins of Type I have an irregular or sigmoidal shape and are often arranged in en echelon arrays. A shearing regime during the formation of this type is deduced. Veins of a second structural type (Type II) have a more regular and straight shape relative to those of Type I and in some places form a dense network. The structural position of the Type II veins is related to structural elements of Variscan folds. Veins were formed due to interlayer-slip combined with fold- related fracturing that gave rise to the infilling of dilational structures. A tensional regime also permits growth of the fibrous veins. Two princpal directions were distinguished within the Type II veins. The first one is NNW–SSE and the second one shows a perpendicular ENE–WSW orientation. These directions seem to be parallel and/or perpendicular to the nappearchitec ture of the Prague Synform. Variscan syntectonic veins crystallised in a relatively closed, rock-buf fered system. Extraction of chemical components from surrounding rocks is indicated by a combined microprobe/cathodoluminescent study and by isotope geochemistry. The carbon isotope values of hydrothermal calcites reflect the carbon isotope composition of the host rocks. The delta exp.13C values of vein calcites and their host Silurian rocks are between –0.29 and –1.98‰ PDB. The same relationships were found between the veins and the host Devonian limestones (from 1.72 to 2.52‰ PDB). Samples close to the Silurian/Devonian boundary show transition values between 0.25 and + 1.16‰ PDB. The Sr-isotopic signature supports a genetic link between the calcite veins and the host rocks. The 87Sr/86Sr ra tio in calcites ranges between 0.708619 and 0.708738 and in wall rocks be tween 0.708755 and 0.709355. Aqueous and hydrocarbon-rich fluid systems have been found in fluid inclusions. Liquid hydrocarbons show mostly a light blue fluorescence suggesting the presence of higher hydrocarbons. They are more abundant in dark Silurian rocks, which are rich in organic matter. Lower salinities (0.5–8.9 eq. wt.% NaCl) and homogenization temperatures with a maximum around 140gradeC are typ i cal for the aqueous (H2O–NaCl) system. The oxygen isotopic composition of fluids ranges between –2.80 and +3.33‰ SMOW. This indicates that transformed formation waters in teracted with the host rocks and/or deeply circulating isotopically depleted meteoric waters. Intersections with the isochore specify border trapping temperatures between 127 and 160grade C and pressures from 300 to 1070 bars.
    Źródło:
    Geological Quarterly; 2008, 52, 4; 309-309
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pleistocene speleothem fracturing in the Western Carpathian orogenic foreland : A case study from transtensional setting at the eastern margin of the Bohemian Massif
    Autorzy:
    Babek, O.
    Briestenský, M.
    Přecechtělová, G.
    Štěpančíková, P.
    Hellstrom, J. C.
    Drysdale, R. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059654.pdf
    Data publikacji:
    2015
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    speleothems
    U/Th series dating
    palaeoseismicity
    Pleistocene
    Bohemian Massif
    Western Carpathians
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2015, 59, 3; 491--506
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    New biostratigraphic evidence (calcareous nannofossils, ostracods, foraminifers, ammonites, inoceramids) on the Middle Coniacian in the eastern Bohemian Cretaceous Basin
    Autorzy:
    Svobodova, Andrea
    Kočí, Tomáš
    Kočová-Veselská, Martina
    Ferré, Bruno
    Košťák, Martin
    Čech, Stanislav
    Chroustová, Markéta
    Powiązania:
    https://bibliotekanauki.pl/articles/2058594.pdf
    Data publikacji:
    2019
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    biostratigraphy
    Coniacian
    Late Cretaceous
    Březno Formation
    Bohemian Cretaceous Basin
    Czech Republic
    Opis:
    The classical locality of Svinary in the eastern Bohemian Cretaceous Basin is the site of new biostratigraphic investigations. Besides some scarce macrofossil evidence, bulk sediment samples were processed to retrieve micropalaeontological assemblages, and calcareous nannofossil smear slides were analysed. The studied material provided calcareous nannofossil assemblages including Micula staurophora, Lithastrinus septenarius and Broinsonia parca expansa, thus documenting the Middle Coniacian (upper part of UC10 Zone and lower part of UC11 Zone). The foraminifera assemblage is relatively rich, planktonic species show a wide stratigraphical range, while the benthic association represented by Neoflabellina suturalis suturalis and Gaudryina carinata is very similar to the Coniacian biozone of Stensioeina granulata-Eponides whitei, valid for the Bohemian Cretaceous Basin. Ostracods are represented by two common cytherellid species, and two rare ornamented species: Imhotepia marssoni? and Pterygocythereis spinosa. Inoceramid bivalves, namely Platyceramus mantelli, and a newly recorded ammonite, Tridenticeras tridens, support the late Middle Coniacian age of the Svinary outcrop. New biostratigraphic results are given along with palaeoecological interpretations of newly collected fossil material.
    Źródło:
    Geological Quarterly; 2019, 63, 3; 586--602
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    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
    Autorzy:
    Pašava, J.
    Frýda, J.
    Štorch, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060353.pdf
    Data publikacji:
    2017
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    Aeronian
    graptolite mass extinction
    redox-sensitive trace elements
    Barrandian area
    Bohemian Massif
    Opis:
    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
    Źródło:
    Geological Quarterly; 2017, 61, 1; 91--98
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    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
    Autorzy:
    Śliwiński, Marek
    Jastrzębski, Mirosław
    Sláma, Jiří
    Powiązania:
    https://bibliotekanauki.pl/articles/2187195.pdf
    Data publikacji:
    2022
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    detrital zircon age spectra
    provenance
    Variscan terranes
    Staré Mìsto Belt
    Bohemian Massif
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2022, 66, 2; art. no. 21
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    A vestige of an Early Devonian active continental margin in the East Sudetes (SW Poland) - evidence from geochemistry of the Jegłowa Beds, Strzelin Massif
    Autorzy:
    Szczepański, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2059534.pdf
    Data publikacji:
    2007
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    East Sudetes
    Moravo-Silesian Zone
    Bohemian Massif
    Variscides
    provenance studies
    geochemistry of metasandstones
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2007, 51, 3; 271-284
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    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)
    Autorzy:
    Budzyń, B.
    Jastrzębski, M.
    Kozub-Budzyń, G. A.
    Konečný, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060006.pdf
    Data publikacji:
    2015
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    monazite
    Th-U-total Pb dating
    thermodynamic modelling
    granulite
    Orlica-Śnieżnik Dome
    Bohemian Massif
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2015, 59, 4; 700--717
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    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)
    Autorzy:
    Budzyń, B.
    Jastrzębski, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2060191.pdf
    Data publikacji:
    2016
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    monazite stability
    Th-U-total Pb dating
    Jawornik granitoids
    Kłodzko–Złoty Stok Pluton
    Orlica-Śnieżnik Dome
    Bohemian Massif
    Opis:
    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.
    Źródło:
    Geological Quarterly; 2016, 60, 1; 106--123
    1641-7291
    Pojawia się w:
    Geological Quarterly
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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