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1

Pre-Variscan palaeogeographical structures in the Cantabrian Zone, Spain: some critical considerations regarding their origin, location and significance

Van Loevezijn Gerard B.S.

Geologos

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2023

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Vol. 29, No. 2

77--97

EN

An update of the main Devonian pre-Variscan palaeogeographical features of the southern Cantabrian Zone is presented. The approximal locations of these features are recorded in sections studied, with thin, incomplete developments for the highs and thick successions for the troughs. Generally, pre-Variscan palaeogeographical features were affected by Variscan and Alpine orogenic deformations, but with a different impact. Oroclinal bending, tectonic shortening by thrusts, movements along strike-slip faults and bending by folds all affected the Devonian palaeogeographical features, and only an approximation of their location and shape can be given. Nevertheless, the palaeogeography recorded in pre-Variscan sedimentary successions and their relative positions, provide specific, clear and objective evidence of the pre-Variscan elements.

2

Thermal history of Lower Palaeozoic rocks from the East European Platform margin of Poland based on K-Ar age dating and illite-smectite palaeothermometry - 481 – 509

Kowalska Sylwia, Wójtowicz Artur, Hałas Stanisław, Wemmer Klaus, Mikołajewski Zbigniew, Buniak Arkadiusz

Annales Societatis Geologorum Poloniae

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2019

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Vol. 89, No. 4

481--509

EN

Large-scale shale gas prospecting in the Polish part of the East European Platform did not discover large reserves of this resources. The article presents new research indicating that one of the reasons for the lack of shale gas relates to the thermal history of the Lower Palaeozoic rocks. Illite-smectite palaeothermometry was used to reconstruct the history of the platform and determine the maximum temperatures to which these rocks were subjected. The age of illitisation was also constrained using the K-Ar method. This method allowed precise dating of the maximum age of thermal transformations due to the deposition of numerous pyroclastic horizons (K-bentonite) throughout the entire geological profile from the Cambrian to the Silurian. Isotopic dating was made on over 53 samples of Lower Palaeozoic bentonites and low-grade metamorphic clays. These results were supplemented by analysis of the degree of thermal (smectite to illite) transformation in the profiles of 37 deep boreholes. 11 zones could be distinguished with different tectonic histories within the Polish part of the East European Platform edge. Maximum heating occurred in this region at about 320–340 Ma, corresponding to the Early Carboniferous or the turn of the Early and Late Carboniferous, phase A of the Variscan orogeny, known as the Sudetian phase. In the southern part of study area, the maximum of thermodiagenesis is slightly younger – 270–290 Ma, which responds to the Early Permian, the Asturian phase, the last phase of the Variscan orogeny. This means that the generation of hydrocarbons occurred before significant Mesozoic exhumation of the Polish part of the East European Platform, which led to the escape of a considerable amount of the gas generated. The study also presents the results of an interlaboratory comparison of illite age dating using the K-Ar and Ar-Ar methods. The comparison was conducted to find out what realistic error should be considered when interpreting geological K-Ar dating results.

3

Kopuła orlicko-śnieżnicka w świetle rozważań tektonicznych

Cymerman Z.

Przegląd Geologiczny

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2016

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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.

4

Podiform chromitites from the Variscan ophiolite serpentinites of Lower Silesia (SW Poland) : petrologic and tectonic setting implications

Wojtulek P. M., Puziewicz J., Ntaflos T., Bukała M.

Geological Quarterly

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2016

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Vol. 60, No. 1

56--66

EN

The Gogołów-Jordanów Serpentinite Massif (GJSM) and the Braszowice-Brzeźnica Massif (BBM) are the largest serpentinite outcrops in the Fore-Sudetic Block (NE part of the Bohemian Massif, Central Europe). The GJSM is a peridotitic member of the Variscan Ślęża Ophiolite (SW Poland). Podiform bodies (veins and pockets) of chromitite are found on the Czernica Hill (GJSM) and on the Grochowiec Hill (BBM) within strongly serpentinized harzburgites which occur several hundred metres below Paleo-Moho. Chromitites consist of rounded chromite grains up to 3 cm across, and of chlorite filling the interstices. The veins are embedded in serpentine-olivine-chlorite aggregates. Relics of Mg-rich olivine (Fo95-96) occur in massive chromitite in the BBM. The bulk-rock total PGEs content is very low (42-166 ppm) and the PGE pattern is negatively sloped towards Pt and Pd and depleted relative to chondrite. The primary chromite I is aluminous (Cr# 0.50-0.52, Mg# 0.60-0.70). The highly aluminous and magnesian (Cr# 0.38, Mg# 0.80) chromite Ia occurs locally in the BBM. The secondary chromite II is enriched in Cr and impoverished in Al (Cr# 0.57-0.69), it replaces chromite I. Both chromite I and II contain small amounts of Ti (<0.14 wt% TiO2). Silicate inclusions in chromite are scarce. The composition and mode of occurrence of both the GJSM and the BBM chromitites are similar, thus they were formed probably under the same conditions. Textures of the chromitites suggest their magmatic origin. Their current geological position indicates their emplacement and crystallization in the uppermost mantle harzburgites occurring below the Moho Transition Zone (MTZ). The chromitites and hosting harzburgites were subjected to the greenschist-facies metamorphic overprint. The moderate Cr# and low PGEs contents suggest that the chromitites originated in the arc setting, thus their host ophiolite is of supra-subduction type.

5

An insight into a gneiss core of the Orlica–Śnieżnik Dome, NE Bohemian Massif : new structural and U-Pb zircon data

Redlińska-Marczyńska A., Żelaźniewicz A., Fanning C. M.

Geological Quarterly

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2016

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Vol. 60, No. 3

714--736

EN

The Orlica–Śnieżnik Dome in the Sudetes, the NE Bohemian Massif, embraces two formations of felsic gneisses of controversial origin and evolution. Our study shows that despite similar geochemical signatures, they carry systematic minor differences in mineral, isotope, zircon and geothermobarometric characteristics. Four variants of the Gierałtów gneisses include migmatites and have a longer structural history than the Śnieżnik augen orthogneisses. U-Pb SHRIMP analyses yielded U-Pb ages of ~500 Ma for cores and ~498 Ma for wide outer parts of zircon grains in the twice-folded Gierałtów gneisses, and an age of ~500 Ma for a discordant neosome vein. Neoproterozoic metasediments were among precursors of the lithologically diversified Gierałtów Gneiss Formation. First deformation, metamorphism, and migmatisation of these rocks occurred at 515–475 Ma and overlapped with the development and emplacement of a porphyritic S-type granite precursor to the Śnieżnik Gneiss Formation. The metagranite (= Śnieżnik augen orthogneiss) embraced migmatitic xenoliths. Zircon grains from such xenoliths revealed distorted and replaced cores which yielded U-Pb ages that dispersed around 507–487 Ma, whilst wide darker poorly zoned outgrowths yielded ages from ~343 Ma to ~325 Ma (mean ~340 Ma). These outgrowths were interpreted as a record of Carboniferous metamorphism assisted by rich Zr- and U-carrying fluids. The Variscan metamorphic overprint was heterogeneous, and variously affected rocks of the two gneiss formations.

6

Strefa kontaktu kaczawskiego kompleksu strukturalnego z depresją Świebodzic (Sudety Środkowe) w świetle nowych otworów badawczych Cieszów PIG 1 i Cieszów PIG 2

Cymerman Z.

Prace Państwowego Instytutu Geologicznego

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2014

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T. 200

1--81

PL

W pracy przedstawiono wyniki badania rdzeni z dwóch płytkich (do gł. 200 m) nowych otworów badawczych Cieszów PIG 1 i Cieszów PIG 2 oraz uzupełniających prac terenowych w strefie kontaktu skał kompleksu kaczawskiego (jednostki Cieszowa) z waryscyjską molasą depresji Świebodzic. Wykonanie obydwu otworów umożliwiło szczegółowe rozpoznanie profilu litologicznego i charakterystyki strukturalnej spągowej (Cieszów PIG 2) i bocznej (Cieszów PIG 1) części jednostki Cieszowa. W otworze Cieszów PIG 1 występują licznie zieleńce, wapienie krystaliczne (marmury) z fyllitami i zmylonityzowane granitoidy. W tym otworze jest dużo stromo zorientowanych kataklazytów i brekcji tektonicznych. W otworze Cieszów PIG 2 nawiercono prawie wyłącznie zmylonityzowane granitoidy z niewielkimi wkładkami zieleńców i łupków chlorytowych. W otworze Cieszów PIG 2 procesy ścinania prostego w warunkach podatnych były penetratywne z rozwojem protomylonitów i mezomylonitów podczas deformacji D1. Prawie wszystkie wskaźniki zwrotu ścinania wskazują na nasuwczy zwrot przemieszczeń „góra” ku WSW. W otworze Cieszów PIG 1 procesy deformacji niekoaksjalnej w warunkach podatnych były bardziej zróżnicowane, co wynikało z większego zróżnicowania litologicznego skał oraz z mechanizmu porozdzielania deformacji (ang. strain partitioning) w warunkach lewoskrętnej, skośnej transpresji. Jednostka Cieszowa nie była nasunięta z „góry”, ale była skośnie „wciskana” od „dołu” z pakietu łusek tektonicznych podczas etapu D2 deformacji (w późnym wizenie). Etap deformacji D2 odbywał się głównie w warunkach kruchych, ale początkowo jeszcze w warunkach podatno-kruchych. Świadczy o tym następstwo różnych skał uskokowych. Kontakt jednostki Cieszowa z depresją Świebodzic został silnie zuskokowany po waryscyjskich procesach tektono-metamorficznych, prawdopodobnie podczas ekstensji późnokarbońsko-wczesnopermskiej. W czasie tej ekstensji powstał systemu podłużnych (względem foliacji S1) uskoków o prawie równoleżnikowym biegu, jak uskok Domanowa. Uskoki te były reaktywowane podczas ruchów alpejskich. Populacje uskoków w jednostce Cieszowa powstały w zmieniających się warunkach reżimu naprężeń. Uskoki inwersyjne z nasuwaniem głównie ku północy były wywołane reżimem kompresyjnym DK-A o prawie południkowej osi σ1 naprężenia głównego. Uskoki przesuwczo-inwersyjne z przemieszczeniami głównie ku E rozwijały się w reżimie kompresyjno-transpresyjnym DK-TR o osi σ1 nachylonej łagodnie ku WSW lub ENE. Dwa zespoły uskoków przesuwczych z przemieszczeniami ku W, SW i NW powstały w reżimie przesuwczym DP-B o osi σ1 nachylonej ku W i WSW lub ESE.

EN

The paper presents the research results of drill cores from two new shallow (up to 200 m depth) boreholes of Cieszów PIG 1 and Cieszów PIG 2, and supplementary field work in the contact zone of the Variscan Kaczawa Structural Complex (Cieszów Unit) rocks with molasse deposits of the Świebodzice Depression. The boreholes provided the opportunity to recognize the lithological section and structural characteristics of the bottom (Cieszów PIG 2) and lateral (Cieszów PIG 1) domains of the Cieszów Unit. The lithology in the Cieszów PIG 1 borehole is represented by abundant greenstones, crystalline limestones (marbles), phyllites and mylonitic granitoids. An abundace of steeply dipping cataclasites and tectonic breccias was also found in this borehole. The Cieszów PIG 2 borehole almost entirely penetrated mylonitic granitoids with thin intercalations of greenstones and chlorite schists. In the rocks of this borehole ductile simple shearing processes were penetrative, with the development of protomylonites and mesomylonites during D1 deformation. Almost all shear sense indicators show a reverse sense of ductile movements with top-to-the-WSW. In the Cieszów PIG 1 borehole, processes of non-coaxial deformation in ductile conditions were more variable, resulting from the large lithological variation of drilled rocks and deformation regimes, with the strain partitioning during sinistral, oblique transpression. However, the Cieszów Unit was not overthrust from the “top”, but was pushed obliquely from the “base” of a package of tectonic slices during the Late Visean deformation D2. Deformation D2 took place mainly under brittle conditions, but was initiated in ductile-brittle conditions. This is indicated by a sequence of various types of fault rocks from both boreholes. The contact of the Cieszów Unit with the Świebodzice Depression was strongly faulted after the main Variscan tectono-metamorphic processes, most likely during Mississipian - Early Permian extension. During this extension, a system of longitudinal (relative to the S1 foliation strike) faults formed, striking almost due W-E, such as the Domanów Fault. These faults were reactivated during the Alpine movements. Different populations of Alpine faults in the Cieszów Unit originated in various stress regime conditions. Inverse faults with mainly northward displacement were caused by the DK-A compression regime with almost meridional attitude of the σ1 axis of the main stress. A set of strike-slip-inversion faults with mainly eastward displacements developed in the DK-TR transpressional - to compressional regimes, with the σ1 axis of the main stress inclined gently towards the WSW or ENE. Two populations of strike-slip faults with displacements toward the W, SW and NW formed in the DP-B strike-slip regime, with the σ1 axis of the main stress inclined towards the Wand WSW or ESE.

7

Ambiguous geological position of Carboniferous rhyodacites in the Intra-Sudetic Basin (SW Poland) clarified by SHRIMP zircon ages

Kryza R., Awdankiewicz M.

Geological Quarterly

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2012

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Vol. 56, No 1

55-66

EN

Rhyodacite sheets (the Sady Górne Rhyodacites) in the lowermost part of the Permo-Carboniferous Intra-Sudetic Basin molasse fill have been mapped as intrusives but, later on, based on ambiguous field and petrographic evidence, reinterpreted as lower Carboniferous lavas and tuffs; if so, they would mark the earliest episode of late-orogenic volcanism in the Intra-Sudetic Basin and in the whole Sudetes region in SW Poland. However, re-examination of field relationships and new observations are consistent with an intrusive emplacement of the rhyodacites as conformable to semiconformable, simple to composite sheets. SHRIMP zircon study indicates that the rhyodacites contain rare inherited zircons of ca. 560 Ma, and ca. 470 Ma (or slightly older), and a main population of zircons with an average concordia age of 306.1 š2.8 Ma. This latter age documents the emplacement of the rhyodacites during a mid/late late Carboniferous (Westphalian) stage of volcanism in the Intra-Sudetic Basin in the Central European Variscides. This post-orogenic volcanism was possibly initiated several million years later than previously assumed, and could have comprised a few pulses over a relatively prolonged time span of millions of years.

8

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).

9

The tectonometamorphic evolution of the marbles in the Lądek-Śnieżnik Metamorphic Unit, West Sudetes

Jastrzębski M.

Geologia Sudetica

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2005

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Vol. 37

1-26

EN

Together with the adjacent rocks, the marbles of the Lądek-Śnieżnik Metamorphic Unit (LSMU), West Sudetes, SW Poland underwent a polyphase structural evolution that occurred in metamorphic conditions changing from medium-grade to low-grade and in deformation regimes changing from ductile to semi-brittle. The structural evolution of the marbles began with E-W subhorizontal shortening resulting in the tilting of the Cal-Dol layering (which had generally originated as a pre-tectonic and pre-metamorphic feature) and its transposition to a steeply dipping metamorphic S1 foliation. The subsequent vertical flattening occurred at the temperature peak of regional metamorphism and produced the N-S trending tight, recumbent F2 folds. This event is also documented by the subhorizontal S2 axial-plane carbonate grain shape fabric and the parallel alignment of Phl-MsšTršCzo in the marbles, and the S2 axial-plane schistosity in the adjacent mica schists. The temperature increase was associated with the progressive mineral sequence Phl › Tr › Di in the dolomite-bearing marbles, which probably initially equilibrated at low to moderate X(CO2). Under peak temperatures, the observed arrangement of the metamorphic zonation of the Stronie formation developed, overprinting the folded planes. Subsequently, under retrogressive conditions, younger deformations were localised in the dynamically recrystallised shear zones that mostly reactivated the S2 planes and were associated with a late top-to-the-N (NE) directed tectonic transport. The D3 mylonitisation was associated with the elongation and size reduction of carbonate grains within the S-C' or S-C mylonites. It produced the S3 planes and the N-S trending L3 stretching lineation. Both groups of the tectonic structures and D2-established mineral isograds (Tr-in and Di-in) were together reoriented during the late compressional stages D4 and D5, related respectively to the SW-NE (WSW-ENE) and NW-SE (NNW-SSE) directed tectonic shortenings. This is visible in the large scale F4 folds, the diversity of the D2-and D3-related mineral assemblages, and the temperature estimations related to both tectonic stages, which indicate decreasing metamorphic conditions from ? 600°C in the SE to ? 490°C in the NE of the LSMU during D2, and from ca. 510°C to 430°C for the respective domains during D3. The incomplete pattern of the Di-in and Tr-in isograds, which still refers to the geometry of gneiss-schist boundary, confirms that the macrostructures of the LSMU mainly developed in tectonic event(s) following the temperature peak of metamorphism.

10

The boundary zone of the East and West Sudetes on the 1:50 000 scale geological map of the Velké Vrbno, Staré Město and Śnieżnik Metamorphic Units

Don J., Skácel J., Gotowała R.

Geologia Sudetica

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2003

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Vol. 35

25-59

EN

The results of field investigations carried out by the authors were used together with existing Czech and Polish cartographic publications to compile a digital geological map (1:50 000) of the boundary zone of the East and West Sudetes. This map is supplemented with a text presenting a tectonic interpretation of the cartographic picture, preceded by a brief description of all 61 of the lithostratigraphic units of the area. Apart from this printed version, the map has also been published as a digital version on CD for the first time. The map covers an area of 1875 km2, in which three entire regional geological units occur: the Velké Vrbno dome and the Śnieżnik metamorphic unit, divided by the relatively narrow Staré Město paleorift zone, which is meridionally-stretched along a 55-kilometre long section. The Keprnik and the Vidnava domes, the Zábřeh crystalline unit, and the upper Cretaceous Nysa Kłodzka graben are all partially included in the map. The authors experienced major difficulties regarding the correlation of lithostratigraphic units to tectonic structures interpreted in a different way; this mainly concerned those lying on opposite sides of the international border. Thus the awareness exists that necessary, although sometimes arbitrary and subjective solutions may not be upheld by the results of future investigations. The digital version of the map should facilitate the supplementation of its contents and should enable a direct correction of the present picture in the course of such future investigations. The digital version is available on a CD-ROM at the Institute of Geological Sciences, Wrocław University

PL

Obserwacje polowe autorów oraz publikowane czeskie i polskie materiały kartograficzne posłużyły do zestawienia cyfrowej mapy geologicznej w skali 1 : 50 000 strefy granicznej Sudetów Wschodnich z Sudetami Zachodnimi. Uzupełnia ją tekstowa interpretacja tektoniczna uzyskanego obrazu kartograficznego, poprzedzona krótkim opisem wszystkich 61 wydzieleń litostratygraficznych. Oprócz prezentowanej wersji papierowej po raz pierwszy mapa publikowana jest również w formie cyfrowej na dysku CD. Obejmuje obszar 1875 km2 na którym występują w całości trzy regionalne jednostki geologiczne: kopuła Velkého Vrbna i metamorfik Śnieżnika, obie rozdzielone południkowo wydłużoną na odcinku ponad 55 kilometrowym stosunkowo wąską strefą paleoryftu Starého Města. Graniczące od wschodu i zachodu dalsze jednostki, czyli kopuła Keprnika i Vidnavy oraz strefa krystaliniku zabřeskiego i górnokredowy rów Nysy Kłodzkiej, ujęte zostały w częściach ograniczonych ramą mapy. Przedstawiony obszar obejmuje sudecki wycinek jednego z najważniejszych lineamentów podłoża krystalicznego nie tylko Sudetów, ale i środkowej Europy. Strefa wczesnopaleozoicznego paleoryftu Starého Města, wykorzystana następnie przez waryscyjski zespół nasunięć, stanowi północne przedłużenie nasunięcia moldanubskiego, oddzielającego Masyw Czeski od bloku Bruno-Vistulikum. Dalej ku północy przecina przedgórze sudeckie aż po okolice Wrocławia. Po obu stronach tego głębokiego i konsekwentnie odnawianego rozłamu występują jednostki różniące się rozwojem facjalno-strukturalnym. Na wschodzie pierwsza konsolidacja struktur nastąpiła przed wendem (~560 Ma), natomiast po stronie zachodniej na przełomie kambru z ordowikiem (~500 Ma). Ponowna bardzo silna przebudowa strefy granicznej tych jednostek połączona z intensywnymi procesami metamorfozy - ale szybko zanikającymi na zewnątrz zarówno ku wschodowi jak i ku zachodowi - miała miejsce podczas rozpoczętego w dewonie rozwoju waryscyjskiego łuku orogenicznego. Badany wycinek Sudetów wszedł wtedy w skład środkowoeuropejskiego progu krystalicznego, rozdzielającego internidy od eksternidów tego orogenu (Pożaryski 1992; Don 2000, 2002). Podobnie jak wzdłuż całego łuku, polaryzacja tektoniczna na jego wschodnim skrzydle - przecinającym pra-Sudety - skierowana była wyraźnie na zewnątrz, czyli na wschód. W tej konwencji badana strefa jest przedłużeniem niemieckiego odcinka środkowowaryscyjskiego progu krystalicznego, skręcającego wzdłuż Odry koło Wrocławia na południe w starą strefę rozłamową. Apogeum waryscyjskiej przebudowy tej strefy nastąpiło pod koniec wczesnego karbonu (~340 Ma). Autorzy mapy natrafili na znaczne trudności związane z korelacją wydzieleń litostratygraficznych różnie interpretowanych struktur tektonicznych, szczególnie po obu stronach granicy państw. Zdają sobie sprawę, iż konieczne niekiedy arbitralne i subiektywne rozwiązania nie zawsze zostaną w przyszłości potwierdzone. Wersja numeryczna opracowanej mapy w znacznym stopniu ułatwi wprowadzanie uzupełnień oraz bezpośrednią korektę obecnego obrazu w toku przyszłych badań. Równolegle z artykułem zawierajacym analogową wersję mapy przygotowana została jej numeryczna wersja (na poziomie szczegółowości skali 1:50 000), rozprowadzana na dysku CD. Informacja o warunkach nabycia w/w dysku dostępna jest pod adresem e-mail: romgot@ing.uni.wroc.pl. .

11

Pre-Late Devonian unconformity in the Kłodzko area excavated: a record of Eo-Variscan metamorphism and exhumation in the Sudetes

Kryza R., Mazur S., Aleksandrowski P.

Geologia Sudetica

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1999

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Vol. 32, nr 2

127-137

EN

The results of excavation works aimed at exposing the pre-Late Devonian unconformity in the vicinity of Kłodzko (Middle Sudetes, NE Bohemian Massif) are reported. The unconformity, first described by Bederke in 1924, provides important constraints on the timing of the exhumation of metamorphic complexes in the Sudetes. However, despite its importance, the unconformity is nowhere exposed at present (with the possible exception of the gabbro blocks at one locality - Mt.Wapnica in Dzikowiec), and has been inaccessible for direct observation for decades. Therefore, new excavation works were conceived and done to confirm the unconformity's existence and to describe details of the contact between the metamorphic basement and the Devonian sedimentary cover. Two localities, at Łączna and Gołogłowy, were selected for the excavation, based on detailed mapping and an EM31 conductivity survey. In both localities, four trenches, 2.5-3 m deep and up to 24 m long, were dug across the expected contact zone. Along the trenches in both sites the unconformity was excavated. At each site, the metamorphic rocks are in primary, sedimentary contact with the overlying basal sedimentary breccias and conglomerates. There is no evidence of tectonic disturbance at the contact. This angular unconformity must have formed during a relatively narrow time interval of c. 10-15 Ma, between the early Givetian and late Frasnian or Famennian. This timing is constrained by the late Frasnian?- to Famennian age of the limestones directly overlying the basal conglomerates and by the recently revised early Givetian age of a coralline fauna from the metamorphosed limestones of the Kłodzko Metamorphic Unit at Mały Bożków. The existence of this unconformity implies that at the turn of the Middle and Late Devonian times, freshly deformed and metamorphosed rocks were exhumed and onlapped by sediments of the Bardo sequence, which, eventually, became folded during latest Visean/Namurian times.

12

Litologia i geneza zmetamorfizowanych skał osadowych i wulkanicznych jednostki Chełmca (Góry Kaczawskie)

Baronowski Z., Haydukiewicz A., Kryza R., Lorens S., Muszyński A., Urbanek Z.

Geologia Sudetica

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1998

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Vol. 31, nr 1

33-59

EN

Based on detailed drill core studies from fourteen boreholes (up to 1500 m deep) and on field observations, the Chełmiec tectonic unit in the northern part of the Kaczawa Mts appears to contain two types of tectonostratigraphic elements. The first is fragments of a stratigraphic sequence, composed mainly of dark muddy slates (metamudstones) and variegated laminated silty-clayey slates (both considered as Ordovician), and of volcaniclastic rocks, greenstones and dia-bases. The second element is represented by mélange bodies which consist of dark muddy slates (matrix) enclosing fragments of various lithologies: dark siliceous and graphitic slates, light siliceous slates, quartzites, greywackes, variegated silty-clayey slates etc. (probably Upper Devonian or Lower Carboniferous). Due to the lack of biostratigraphic evidence, the stratigraphic subdivision is based on lithological criteria. Using e.g. the rule of superposition and analysis of lithological contacts and sedimentary and volcanogenic structures, the stratigraphic succession was defined, and three informal lithostratigraphic units were distinguished: (a) an association of metamudstones and diabases, (b) an association of metavolcaniclastic rocks (both within the stratigraphic sequence), and (c) a mélange association. The dark metamudstones and variegated silty-clayey slates of the association of metamudstones and diabases are interpreted as turbidites. The volcaniclastic rocks, of clearly epiclastic character, were delivered episodically from marginal parts of the basin or volcanic heights by denser turbiditic currents and other types of gravity flows. Simultaneously, volcanic activity occurred within the basin itself producing basaltic lavas (now observed as subvolcanic diabases and effusive greenstones), which geochemically correspond to recent mildly alkaline within-plate basalts. The geotectonic setting of the basin is difficult to define precisely but the sequence was probably emplaced in an outer fan or in a basin at a continental margin. The mélange represents a later stage of the evolution of the Kaczawa Complex. Most probably, it was deposited from gravity flows and slumps in a trench or on a trench slope. Its origin is thought to have been connected within the formation of a Variscian accretionary prism in Late Devonian and Early Carboniferous times. The rock complex of the Chełmiec Unit experienced several stages of deformation during the Variscian orogeny. The first event resulted in a system of thrusts (and associated folds?) and it was related to (or partly preceeded by) the formation of mélange. It is likely that deformation at this stage (and in particular in its later phase) took place under blueschist facies conditions. The second deformation event, probably under greenschist facies conditions, was associated with folding which steepened the earlier foliation and produced new asymmetric folds. The third deformation event, partly under semi-brittle/brittle conditions, is responsible for new thrusts cutting the earlier structures and the formation of large open folds, such as the Bolków-Wojcieszów antiform. The deformation of the rocks of the Chełmiec Unit was associated with greenschist facies metamorphism. In general, primary sedimentary and volcanic structures are well preserved in the rocks of this unit which often seem to have suffered weaker deformation and metamorphism than that observed in other units of the Kaczawa Mts. No clear evidence of the early high-pressure episode which is widespread in other tectonic units of the Kaczawa Complex has been found in the Chełmiec Unit so far.