Wyniki wyszukiwania - BazTech

1

Kopuła orlicko-śnieżnicka w świetle rozważań tektonicznych

Cymerman Z.

Przegląd Geologiczny

|

2016

|

Vol. 64, nr 10

814--830

EN

The paper presents tectonic considerations on the geology of the Orlica-Śnieżnik Dome (OSD), based on the published geotectonic, structural and kinematic data and reports on the OSD geotectonic setting, relating to the evolution of the Variscan collisional belt. Further progress has been done in the recognition of the structure and evolution of the OSD, and for many decades the dominant structural geology has been replaced with multithreading researches. However, the current tectonic interpretations are matched against pre-established schemas of structural evolution of the OSD. The OSD is most likely a fragment of the Moldanubian Terrane with the Variscan collisional sutures. The dextral transpression in a general shear regime and with the participation of strain partitioning has formed a thrust sheet package with the dominant tectonic transport top-to-the NNE, N and NW, with the exception of the NE part of the OSD. The development of regional-scale ductile shear zones in the OSD took place during the progressive tectono-metamorphic evolution from about 360 to 335 Ma. These processes resulted from the highly oblique collision of the Moldanubian Terrane (with the OSD) with the Brunovistulicum on the east and the Tepla-Barrandian Terrane on the W, and with a frontal collision with the Central Sudetic Terrane on the N.

2

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

|

2016

|

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.

3

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

|

2015

|

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.

4

The Orlica–Śnieżnik Dome, the Sudetes, in 2002 and 12 years later

Żelaźniewicz A., Jastrzębski M., Redlińska-Marczyńska A., Szczepański J.

Geologia Sudetica

|

2014

|

Vol. 42

105--123

EN

During the 2002 meeting of Czech, Polish and Slovak tectonic community in Żelazno, the Sudetes, the Central European Tectonic Studies Group (CETeG) was established. 12 years ago, participants of the meeting made an excursion to the eastern part of the Orlica–Śnieżnik Dome (OSD), which was focused on a variety of gneisses with inserts of (U)HP eclogites and various enclaves. The 2014 meeting brought members of the CETeG to the OSD again and an accompanying field excursion was dedicated mainly to evolution of metasedimentary and metavolcanogenic rocks in the region. This paper is a short review of the results of the studies undertaken in the OSD by different research groups in the last 12 years. The review is set against a background of what we knew about the geology of the dome in 2002. A significant progress was made. P-T paths were determined for mica schists and marbles as well as for metarhyolites originated from the continental crust and metabasites derived from the mantle. New light was shed on the origin of various types gneisses in the OSD and their genetic and structural relationships. A plethora of isotopic studies helped to better constrain timing of igneous and metamorphic events in the Orlica–Śnieżnik complex. Ages clustered around 350–340 Ma are repeatedly obtained, yet scarcer older ages up to 390 Ma and their geological significance are open to debate. Tectonic evolution of the dome was revised and new geodynamic concepts were proposed. However the new data has created some new problems and some old problems are still to be resolved in the future.

5

The CETeG 2014 excursion to crystalline basement of the Orlica–Śnieżnik Dome, the Sudetes

Żelaźniewicz A., Budzyń B, Ilnicki S., Jastrzębski M., Murtezi M, Redlińska-Marczyńska A., Stawikowski W., Szczepański J.

Geologia Sudetica

|

2014

|

Vol. 42

125--136

6

Paleomagnetism and magnetic mineralogy of metabasites and granulites from Orlica-Śnieżnik Dome (Central Sudetes)

Kądziałko-Hofmokl M., Szczepański J., Werner T., Jeleńska M., Nejbert K.

Acta Geophysica

|

2013

|

Vol. 61, no. 3

535--568

EN

The results of palaeomagnetic, rock magnetic, and microscopic study of Early Paleozoic metabasites and granulites from the Orlica Śnieżnik Dome (OSD, Sudetes) have been combined with geochronological data. In the eastern part of the OSD (Śnieżnik Massif, SM) ferrimagnetic pyrrhotite is prevalent, accompanied by various amounts of Fe-oxides. In the western part of the OSD (Orlica-Bystrzyca Massif, OBM) Fe-oxides dominate. All magnetic minerals originated during hydrothermal and weathering processes. The palaeomagnetic study revealed the presence of three secondary components of natural remanence: Late Carboniferous, Late Permian, and Mesozoic. Two Paleozoic components are related to volcanic activity in the Sudetes. They are carried by pyrrhotite and Fe-oxides and were isolated only in SM rocks. The Mesozoic component was determined in both parts of the OSD and is carried by Fe-oxides. It covers a time span, from ~160 to ~40 Ma, corresponding to a long period of alteration.

7

Gneisses in the Orlica-Śnieżnik Dome, West Sudetes : a single batholitic protolith or a more complex origin?

Redlińska-Marczyńska A., Żelaźniewicz A.

Acta Geologica Polonica

|

2011

|

Vol. 61, no. 3

307-339

EN

Detailed structural and petrographic studies confirmed the presence of two major units of ca. 515-480 Ma gneisses in the Orlica-Śnieżnik Dome (NE Bohemian Massif) and enabled the distinction of two formations which differ in their mineral composition (modal and chemical) and structural records. An intrusive contact between rocks of the two formations was observed. The Gierałtów Gneiss Formation is composed of rocks having at least two sets of folded metamorphic foliations, with relics of compositional banding and records of early shearing prior to migmatization and metablastesis which produced quartzofeldspathic segregations (D1-D2 events). Such aggregates, even if isometric and shared (D3) may, but must not be mistaken for original augens (porphyroclasts in the original granite). Modal contents of the feldspars differ widely (20-40% of plagioclase feldspar, 16-40% of alkali feldspar) as well as their composition (Ab[0-90], An[6-38]); the biotites can be either poor or enormously enriched in Al (0.26-1.07 Al[^VI]). Such heterogeneities are consistent with the inferred metamorphic transformations of originally diversified sedimentary-volcanogenic protoliths. in contrast, the Śnieżnik Gneiss Formation is composed of metagranites, dynamically metamorphosed into the augen gneisses. They possess only one set of mylonitic foliation and one rodding lineation, both developed during a regional shear event (D3). Nearly equal modes of feldspars and quartz, uniform composition of plagioclase feldspar (An6-23) and a rather stable amount of Al (0.3-08 AlVi) in the biotites are indicative of homogenization of a granitic protolith. Anatectic provenance of the gneisses is evidenced by enclaves. Felsic microgranular enclaves are chilled fragments of the parental intrusion, while xenoliths and surmicaceous enclaves are akin to rocks of the Gierałtów Formation, thus the latter or equivalent rocks formed a migmatic envelope of the Śnieżnik granite pluton.

8

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

Jastrzębski Mirosław

Geologos

|

2008

|

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).

9

Tectonic evolution of the late Cretaceous Nysa Kłodzka Graben, Sudetes, SW Poland

Don J., Gotowała R.

Geologia Sudetica

|

2008

|

Vol. 40

51-63

EN

The Nysa Kłodzka Graben, located in the Sudetes of SW Poland, developed as a result of Coniacian (middle Upper Cretaceous) N-trending faulting of the Variscan crystalline basement rocks that comprise the crest of the Orlica-Śnieżnik Dome. The graben was transgressed by a late Cretaceous sea that encroached during the Cenomanian from the northwest. Up to 700 m of Coniacian shales, sandstones and conglomerates were deposited in the graben, with shales (the ~500 m thick Idzików 'clays') dominating the graben's central section. On the western side of the graben, shales grade upwards to greywackes in a style that resembles a turbidite sequence; on the eastern side, shales are overlain by sandstones and conglomerates (the Idzików conglomerates) that represent extensive late Cretaceous fan deltas. These within-graben fan deltas date the onset of fault-block movements that uplifted the Sudetes region during the late Cretaceous-Cenozoic. By the end of the Cretaceous, both the sedimentary infill and the underlying Cenomanian and Turonian strata were steepened at the graben margins and were gently folded, the fold axes paralleling the graben's marginal faults. Subsequent Cretaceous-Paleocene ('Laramian') deformations resulted in NW-trending reverse faulting, which restructured the earlier N-S template of the graben, and in transcurrent faults, which cut the N-trending folds, modified the north and south ends of the graben and strongly affected the graben's western walls. The total thickness of the Upper Cretaceous strata of the Nysa Kłodzka Graben is 3 times that of the Intra-Sudetic Synclinorium, implying that the two units developed independently.

10

The acid metavolcanic rocks of the Orlica-Śnieżnik Dome (Sudetes): their origin and tectono-metamorphic evolution

Murtezi M.

Geologia Sudetica

|

2006

|

Vol. 38

1-38

EN

The Orlica-Śnieżnik Dome (OSD) belongs to the mosaic of geological units forming the Sudetic part (NE margin of the Bohemian Massif) of the Variscan belt. Acid metavolcanic rocks referred to as leptites appear in the OSD as intercalations in the mica schists of the Stronie Formation - the supracrustal cover of the gneiss core of the unit. Two types of acid meta-volcanogenic rocks have been distinguished: massive leptites (ML) and biotite-bearing leptites (BBL); together they are referred the leptite series. The ML originate from acid volcanic rocks that could have contained only small amounts of sedimentary material. The BBL are metamorphosed tuffites with a variable share of sedimentary material. All the analysed leptites from the entire OSD area reveal similar geochemical characteristics. The high concentration of strongly incompatible elements such as REE, as well as the enrichment in large-ion-lithophile elements indicates the continental crust affinities of the leptites' protolith. On the other hand, ascertained the high Th/Ta ratios, negative Nb and Ta anomalies, and low Ti, Zr and Hf content can be interpreted as indicators of magmatism connected with a suprasubduction environment. Such ambiguous characteristics may indicate that an ensialic rift environment, considered as the place of origin for the magmatic rocks dated at c. 500 Ma and occurring in the OSD, developed due to extension behind a collisional zone of Lower Palaeozoic age. An extensional environment created during this event could be the location for the postulated early deformation and metamorphism of the Stronie Formation. The Śnieżnik metagranites would have been emplaced into such, already deformed, supracrustal cover. The signature of an active margin found in these continental crust rocks that were stretched and melted due to the increased heat transfer resulted from an earlier (Neoproterozoic?) tectono-thermal episode. The reconstructed path of the tectono-metamorphic evolution of the leptites entirely results from a Variscan collisional episode occurring in the borderland of the West and the East Sudetes. The sequence of the deformations established for the studied rocks is interpreted as an effect of the continuous convergence of crustal units in an E-W direction. Structural and phase-equilibria lines of evidence show that the tectono-metamorphic evolution of the Stronie Formation was that of early burial (D1) to a depth not exceeding upper amphibolite facies conditions, and subsequent uplift connected with subvertical shortening and flattening strain (D2). As a result of the continuous convergence, thrusting took place along the edges of the colliding units. The final adaptation of the colliding crustal slices led to zonal lateral oblique displacements (D3). This latter event is treated as the cause for disturbance of the isograd and isotherm pattern observed within the rocks of the Stronie Formation. It is also responsible for zonal shearing, generally taking place in a N-S direction. During the collision that occurred along the eastern margin of the OSD, the rocks of the Stronie Formation reached the highest P-T conditions of metamorphism at c. 9 kbar and 650°C. The presented data shows a considerable decrease in the peak-metamorphic conditions from the east to the west of the OSD.

11

Mesostructural and kinematic characteristics of core gneisses in western part of the Orlica-Śnieżnik Dome, West Sudetes

Dumicz M.

Geologia Sudetica

|

1998

|

Vol. 31, nr 1

105-111

EN

The Orlica-Śnieżnik Dome in the West Sudetes consists of an orthogneissic core and a schist-phyllite mantle. It is subdivided into two parts tectonically separated by the Upper Cretaceous Nysa Graben. In this paper structures developed during polyphase deformation of the c. 500 Ma core gneisses in the western part (Orlické hory, Góry Orlickie, Góry Bystrzyckie) are compared with those of the eastern part (Śnieżnik massif). The effects of deformations D1 to D4 structures are, in general, mutually comparable in the gneissic series of the Góry Orlickie (Mountains) and the Śnieżnik complex. D5 structures, manifested in the Góry Orlickie as S-C structures which show a top-to-the-south or top-to-the-southwest sense of displacement, are, however, not known in this shape from the eastern part. Structures of such geometry in the gneisses of the latter region were ascribed to deformation D3. The C element of the S-C structures is represented in the Góry Orlickie by a rough S5 domainal cleavage, spatially related to the NW-SE fault zone of Olešnice-Uhřínov, which separated the gneissic core from the Nové Město series and the Zabřeh series of the mantle. This relationship suggests that both the S5 cleavage and the fault zone are associated with the same deformation event D5 and originated under similar rheological and kinematic conditions. In both cases cataclastic deformation was accompanied by only local and limited recrystallization of white micas. Kinematic analysis of the D5 tectonic structures shows that these structures were formed in a sinistral transtension regime. In the Góry Bystrzyckie the tabular crystals of microcline, usually preserving their original shapes, are, in general, arranged along the S3 gneissosity planes in which they show a considerable scatter. They are more or less lenticularly deformed, in concordance with the SSW-trending L3 mineral recrystallization lineation, and point to a top-to-the-north sense of shearing during D3 event.