The fabric of the Culm conglomerates in the eastern parts of the Nizký Jesenik and Drahany Uplands, eastern margin of the Bohemian Massif, the Czech Republic

Josef Havíř

Institute of Physics of the Earth, Masaryk University Brno, Tvrdého 12, 602 00, Czech Republic; havir@ipe.muni.cz

Key words: Bohemian Massif, Nízký Jeseník, Drahany Uplands, Variscan, Culm, conglomerates, deformation.

Abstract
The fabric of the Culm conglomerates was studied by geometrical strain analysis methods in the eastern parts of the Nízký Jeseník and the Drahany Uplands on the eastern margin of the Bohemian Massif. The shapes and orientations of pebbles were used as strain markers and the average final ellipsoids (Shimamoto & Ikeda, 1976) were calculated (final fabric ellipsoids representing both depositional and deformational influence on the sediments).
The geometric strain analysis shows a predominantly depositional or only partially deformational fabric. Only at some sites in the eastern part of the Nízký Jeseník Uplands a deformational fabric of the conglomerates occurs. But there is evidence of a very weak effect of ductile shortening in the Drahany Upland probably connected with rotation of the more rigid pebbles in the viscous graywacke matrix of the conglomerates. The orientations of the long axes of the final fabric ellipsoids are more or less uniform. The long axes are predominantly orientated N-S to NE-SW in the eastern parts of the Nízký Jeseník and the Drahany Uplands, which means nearly parallel to the major structures of the Variscan orogen in this region.

Geologia Sudetica, 32 (1): 13-47.

Volcanism in a late Variscan intramontane trough: Carboniferous and Permian volcanic centres of the Intra-Sudetic Basin, SW Poland

Marek Awdankiewicz

Uniwersytet Wrocławski, Instytut Nauk Geologicznych, Zakład Mineralogii i Petrologii, ul. Cybulskiego 30, 50-205 Wrocław, Poland, fax: 48 71 3201371; mawdan@ing.uni.wroc.pl mawdan@ing.uni.wroc.pl

Key words: Sudetes, volcanism, Carboniferous, Permian.

Abstract
The Intra-Sudetic Basin represents a late Variscan intramontane trough situated near the NE margin of the Bohemian Massif. The Carboniferous-Permian molasse succession in the northern part of the basin provides evidence of three stages of volcanic activity during: 1) the latest Visean/earliest Tournaisian, 2) the late Westphalian-Stephanian, and 3) the early Permian, the latter corresponding to the climax of volcanism. Rhyodacites, andesites and basaltic andesites were characteristic of the earlier stages (1 and 2), while basaltic trachyandesites, trachyandesites and rhyolites erupted during the later stages (2 and 3). The earliest volcanism occurred near the northern margin of the Intra-Sudetic Basin and the successive Carboniferous and Permian volcanoes shifted SE-wards with time, consistently with the intrabasinal depositional centres. The location of the volcanoes was controlled by NNW-SSE to NW-SE aligned fault zones. The magmas intruded thicker accumulations of sedimentary rocks within intrabasinal troughs, and erupted through thinner sequences outside the troughs. Effusive to extrusive activity created lava-dominated, composite volcanic centres to the north and west. In the eastern part of the basin the most evolved acidic magmas erupted explosively, with the formation of: 1) a maar belt (late Carboniferous) and 2) a major caldera (early Permian), with subsequent emplacement of subvolcanic intrusions in both cases. The volcanic edifices represented intrabasinal elevations subjected to substantial erosion, with the largest supply of volcanogenic debris into the basin following the most voluminous rhyolitc eruptions in Permian times. The caldera was a centre of lacustrine sedimentation.

Geologia Sudetica, 32 (1): 49-53.

A review of Rb-Sr isotope patterns in the Carboniferous granitoids of the Sudetes in SW Poland

Pádhraig S. Kennan¹, Helena Dziedzic², Marek W. Lorenc² & Michał P. Mierzejewski³

¹ University College Dublin, Geology Department, Belfield, Dublin-4, Ireland
² Polska Akademia Nauk, Instytut Nauk Geologicznych, Zakład Geologii Sudetów, 50-449 Wrocław, ul. Podwale 75, Poland
³ Uniwersytet Wrocławski, Instytut Nauk Geologicznych, 50-205 Wrocław, ul. Cybulskiego 30, Poland

Key words: Sudetes, Variscan granites, Rb-Sr ages, Sr-isotope systems, magma source.

Abstract
Carboniferous granite intrusions are a relatively uncontroversial element in the geological history of the Sudetes in SW Poland. The Sr-isotope systems in these granites show geological scatter indicative of contamination by crustal rock, failure to homogenise during intrusion/crystallisation and inheritance from source. Rb-Sr ages are thus somewhat compromised and imprecise. The granites originated from a relatively primitive source that underlay much of the region in Carboniferous times.

Geologia Sudetica, 32 (1): 55-71.

Granitoids of the Odra Fault Zone: late- to post-orogenic Variscan intrusions in the Saxothuringian Zone, SW Poland

Teresa Oberc-Dziedzic¹, Andrzej Żelaźniewicz² & Stefan Cwojdziński³

¹ Instytut Nauk Geologicznych, Uniwersytet Wrocławski, M. Borna 9, 50-204 Wrocław, Poland
² Instytut Nauk Geologicznych PAN, Zakład Geologii Sudetów, Podwale 75, 50-449 Wrocław, Poland
³ Państwowy Instytut Geologiczny, Oddział Dolnośląski, Jaworowa 19, 53-122 Wrocław, Poland

Key words: Fore-Sudetic Block, granitoid, Mid-German Crystalline Rise, Odra Fault Zone, Saxothuringian Zone, Variscides, Sudetes.

Abstract
There are 5 occurrences of granodioritic to monzogranitic rocks found subsurface along the Odra Fault Zone a Permo-Mesozoic horst defining the northeastern edge of the Bohemian Massif. These are generally unfoliated,  I-type granitoids with low A/CNK and initial Sr/Sr ratios making them geochemically and petrographically akin to late- to post-kinematic Variscan granitoids of the West Sudetes, being closest to those of the eastern part of the Fore-Sudetic Block (Strzelin, Niemcza). They represent late/post-orogenic, collisional intrusives of  Early-Late Carboniferous age which are widespread throughout the Saxothuringian and Moldanubian zones in the Bohemian Massif. The country rocks to the granitoids are mica schists and paragneisses attaining staurolite-grade. The granitoids lack evidence of ductile or brittle strike-slip movement of  Late Carboniferous-Permian age along the Odra Fault Zone, which thus has to be taken as a dip-slip fault zone, rather than a late Variscan dextral strike-slip feature. Brittle to semi-brittle deformation of the Odra granitoids relates to the formation of the horst during Permo-Mesozoic times. A Silurian-Early Devonian magmatic arc of the Mid-German Crystalline Rise, identified further to the west in Germany, probably does not have an easterly prolongation into Poland because there is no evidence for arc-related magmatism of that age in the Sudetes and Fore-Sudetic Block.

Geologia Sudetica, 32 (2): 83-111.

Volcanism in a late Variscan intramontane trough: the petrology and geochemistry of the Carboniferous and Permian volcanic rocks of the Intra-Sudetic Basin, SW Poland

Marek Awdankiewicz

Uniwersytet Wrocławski, Instytut Nauk Geologicznych, Zakład Mineralogii i Petrologii, ul. Cybulskiego 30, 50-204 Wrocław, Poland; mawdan@ing.uni.wroc.pl

Key words: Intra-Sudetic Basin, Carboniferous, Permian, late- to post-collisional volcanism, geochemistry, petrology.

Abstract
The Carbonifeorus-Permian volcanic rocks of the Intra-Sudetic Basin represent products of late- to post-collisional volcanism associated with extension within the eastern part of the Variscan belt of Europe. The volcanic succession is subdivided into the older, calc-alkaline suite (the early and late Carboniferous) and the younger, mildly alkaline suite (the late Carboniferous and early Permian). The rhyodacites with subordinate basaltic andesites and andesites of the older suite show convergent plate margin affinities. The rhyolitic tuffs, rhyolites with less widespread trachyandesites and basaltic trachyandesites of the younger suite are largely characterised by within-plate affinities, with some gradations towards convergent plate margin affinities. This geochemical variation compares well with that found in some Tertiary-Recent extensional settings adjacent to former active continental margins (e.g. the Basin and Range province of the SW USA). The parental magmas for each suite of the Intra-Sudetic Basin possibly originated from similar, garnet free mantle sources at relatively shallow depths (within the subcontinental mantle?), but at variable degrees of partial melting (lower for the mildly alkaline rocks). The convergent plate margin-like geochemical signatures of the volcanic rocks may either have been inherited from their mantle sources, or be related to the assimilation of crustal rocks by the ascending and fractionating primary magmas. The intermediate-acidic rocks within each suite mainly originated due to fractional crystallisation of variable mineral assemblages equivalent to the observed phenocrysts (mainly plagioclase and pyroxenes, with hornblende and biotite in the calc-alkaline suite, and K-feldspar in the mildly alkaline suite). The trace element patterns of the volcanic rocks were also strongly influenced by fractionation of accessory minerals, such as spinels, ilmenite, zircon, apatite and others. The petrographic evidence (e.g. quartz phenocrysts with reaction rims, complexly zoned or sieve-textured feldspar phenocrysts) suggests that assimilation and/or magma mixing processes might also have taken place during the evolution of the magmas.

Geologia Sudetica, 32 (2): 113-126.

Paleomagnetism and remagnetization of Upper Devonian synorogenic clastic sediments from the Pogorzała Formation (Świebodzice Depression, West Sudetes, Poland

Magdalena Kądziołko-Hofmokl¹, Maria Jeleńska¹, Tahar Aifa², Jean B. Edel³ & Andrzej Żelaźniewicz⁴

¹ Instytut Geofizyki, Polska Akademia Nauk, Ks. Janusza 64, 01-452 Warszawa, Poland, e-mail: magdahof@igf.edu.pl
² Géoscience - Rennes, University of Rennes 1, Campus de Beaulieu, 35042, Rennes, France
³ École et Observatoire de la Terre, 5 rue Descartes, 67084 Strasbourg, France
⁴ Instytut Nauk Geologicznych, Polska Akademia Nauk, ul. Podwale 75, 50-449 Wrocław, Poland; mail

Key words: Upper Devonian, conglomerates, sandstones, remagnetization, Sudetes, Variscides.

Abstract
The Upper Devonian highly polymict conglomerates (site 26) and sandstones with clasts (site 27) of the Pogorzała Formation in the synorogenic Świebodzice Depression, West Sudetes, are hydrothermally altered and show signs of penetration by mineralized fluids. Nearly all the magnetic minerals present (mainly Fe-oxides and pyrrhotite accompanied by Fe-hydroxides) are of secondary origin. Rocks from each site carry multicomponent natural remanence composed of Mesozoic/post-Mesozoic and Palaeozoic components. In the conglomerates (site 26) two Palaeozoic components, labelled P and C, occur in the matrix and pebbles, whereas in the sandstones with large clasts (site 27) only one Palaeozoic component labeled C1 occurs. This means that the results of the conglomerate test for both sites are negative and the studied rocks were remagnetized during several remagnetization episodes. The overprints present in site 26 closely fit the reference data for the Baltica Plate for the Early Permian component (P) and Viséan component (C). The overprint present in site 27 is slightly shifted from the Westphalian (C1) segment of the reference path. The P component is also close to the path of polar wander for Variscan Europe.

Geologia Sudetica, 32 (2): 127-137.

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

Ryszard Kryza, Stanisław Mazur & Paweł Aleksandrowski

Uniwersytet Wrocławski, Instytut Nauk Geologicznych, ul. Cybulskiego 30, 50-205 Wrocław, Poland

Key words: Variscan orogeny, Caledonian orogeny, Devonian, Sudetes, Bohemian Massif.

Abstract
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.

Geologia Sudetica, 32 (2): 139-146.

Low-hafnium zircon from alluvial and colluvial placeres of northern Bohemia: composition and possible sorces

Jaromír Ulrych¹ & Pavel Uher²

¹ Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Praha 6, Czech Republic
² Geological Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 842 26 Bratislava, Slovak Republic

Key words: zircon, Zr/Hf ratios, placer deposits, Bohemia, Czech Republic.

Abstract
Low-hafnium zircon is, together with pyrope, sapphire and magnesian ferri-ilmenite, a widespread heavy mineral in three historical placers of precious stones in N Bohemia. The chemical compositions of zircon from all three localities (Třebenice area, Jizerská louka Meadow, Sýkoří důl Valley) are appreciably similar. Zircon forms large, 1 to 7 mm long homogeneous or oscillatory zoned crystals, generally low in Hf (0.45-1.27; aver. 0.77 wt.% HfO₂), Y, REE, U, Th and Ca. The genetic association of this zircon with nepheline syenite or pegmatite is doubtful as zircon from this rock found in xenoliths in a nearby alkali basalt pipe breccia from Košťálov Hill represents the Hf-rich type (1.57-1.97; aver. 1.73 wt.% HfO₂). Consequently, low-hafnium zircon most probably originated from unknown coarse-grained products of early magmatic crystallisation of an alkali basalt magma forming explosive pipe breccias.

Geologia Sudetica, 32 (2): 147-161.

Tunnel valleys and alluvial fans in the western Sudetic Foreland (southwestern Poland): the lithostratigraphy of Quaternary deposit

Krzysztof Urbański

Państwowy Instytut Geologiczny, Oddział Dolnośląski, Jaworowa 19, 53-122 Wrocław, Poland

Key words: Quaternary, stratigraphy, tunnel valleys, alluvial fans, Wrocław-Magdeburg Pradolina, Sudetic Foreland.

Abstract
The western Sudetic Foreland between the Nysa Łużycka and Bóbr rivers consist of deposits of two glaciations, the Elsterian and Saalian, and the extensive fluvial sediments. The Elsterian glacial deposits (the lower glacial complex) are only preserved in deep troughs. These structures, which were formerly interpreted as buried valleys, are actually of glacial origin and represent tunnel valleys. The glacial sediments of the Odranian glaciation (the upper glacial complex) are very thin and are only represented by a single till bed which occurs throughout the area, although only in patches. In the study area there are extensive series of fluvial deposits (the lower fluvial complex) between the Elsterian and Odranian tills, which are correlated with the Holstenian to early Saalian fluvial horizon in Germany (the Middle Terrace). The Wartanian sediments are represented by another fluvial series (the middle fluvial complex) which is composed of local alluvial fans deposited by Sudetic rivers, the Wrocław–Magdeburg Pradolina valley and the outwash plains formed at the front of the Wartanian ice sheet. The youngest sediments are represented by one Weichselian and two Holocene fluvial terraces (the Bóbr, Kwisa and Nysa Łużycka Terraces).