7th Meeting of the Czech Tectonic Studies Group Żelazno ...geolines.gli.cas.cz/fileadmin/pracovni...

7th Meeting of theCzech Tectonic Studies Group

Żelazno, Poland, May 9–12, 2002

published in Prague, April 2003

by the Institute of Geology,

Academy of Sciences of the Czech Republic

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Pred tento titulek nekam nahoru vloz mensim fontem nasledujici text "The following contributions on 7th Meeting of the Czech Tectonic Studies Group were erroneously not included in Geolines 14. We herein enclose these abstracts and express our apology to their authors" Ten nazev konference v teto omluve 7th meeting ...az 9-12,2002 udelej sikmo Pak nasleduje vse jak bylo-titulek a published in prague..atd-nezmeneno

svojtka

7th Meeting of the Czech Tectonic Studies Group Żelazno, Poland, May 9–12, 2002

GeoLines 15 (2003)2

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Dipmeter logging has recently become an integral part of stand-ard borehole geophysics procedures applied in hydrocarbon exploration and production wells both onshore and offshore. Quality interpretation of numerically processed dipmeter data provides structural, sedimentological and geodynamical data that describe geological aspects of reservoir formations in a much more detailed and informative way than those yielded by other types of wireline logs and by refl ection seismics. Of primary importance is the ability of the dipmeter data-based interpretation to locate, recognize and measure size and full orientation (with respect to the north and to a horizontal ref-erence plane) of a variety of tectonic and sedimentary struc-tures. General guidelines of handling the dipmeter raw data, principles of their processing and general rules of geological interpretation are presented in technical manuals issued by manufacturers of geophysical equipment and processing soft-ware (e.g. Goetz 1984, 1989; Schlumberger 1986; Halliburton 1992; Adams 1993), though the details of the methods are elaborated and refi ned in-house by structural geologists and sedimentologists professionally involved in this kind of in-terpretation, based on their knowledge and fi eld experience in understanding 3D anatomy of the whole spectrum of structures. Detailed geological analysis of data recorded using classical dipmeter or a more sophisticated tool, formation microimager, enables, among others: (1) continuous determination of the attitude of strata along borehole profi les, while monitoring all its changes and variations, (2) identifi cation of unconformities, (3) recognition and determining orientation of faults of various dimensions (down to centimeter-size events), (4) distinguish-ing fault-related drag zones, (5) analysis of the relative fault block rotations, (6) recognition of brittlely deformed zones, (7) fracture analysis (distinguishing and determining orientation of joint sets, assessment of fracture apertures, distinguishing between water and oil-fi lled fractures – possible only from for-mation microimager record), (8) identifi cation and geometrical analysis of folds, (9) orientating drill-cores with respect to the north, (10) distinguishing the types of internal bedding in clastic sediments and assessment of the directions of sediment palaeotransport and of the expected fi ltration anisotropy, (11) estimating 3D reservoir shapes (expected sandbody elonga-tion and reservoir thickening directions), (12) distinguishing parasequences, sequences and genetically uniform sedimentary complexes in drilled strata, (13) setting up palaeofacies and palaeogeographical models, (14) determining orientations of the present-day around-borehole in situ principal tectonic stress axes and, on this basis, optimizing trajectories of the

planned directional and horizontal drilling, estimating potential usefulness of hydraulic fracturing and/or water injection to be undertaken in order to enhance production, as well as setting up optimum confi guration of injection wells.

Case examples of applying dipmeter-based structural and sedimentological data in hydrocarbon exploration in a number of geological regions in Poland carried out by a team led by the present author (e.g. Aleksandrowski and Kiersnowski 1998; Jarosiński and Aleksandrowski 1998; Aleksandrowski 2001) and some examples from the Norwegian shelf (Aleksandrowski et al. 1992) are presented, including the Lower Permian red-beds of the fore-Sudetic monocline, Palaeozoic to Miocene platform basement of the Outer Carpathian fold-and-thrust belt and the Miocene to Pliocene succession of the Carpathian fore-deep. Running dipmeter and microimager can yield invaluable geological information in any deep drillings, in particular those aimed at scientifi c targets, at the same time partly replacing and complementing the costly extraction of drill-cores.

References

ADAMS J., 1993. Structural Interpretation Using Dipmeter and Borehole Image Data. In: Dipmeter and Borehole Image Interpretation, Z & S Geology Ltd, Short Course Notes, Aberdeen, 6/1-6/36.

ALEKSANDROWSKI P., 2001. Structural Analysis of Palaeo-zo ic-Triassic Complex in Tarnawa-1 Well (Western Out-er Carpathians) Based on Halliburton SED Dipmeter Data. Prace Państwowego Instytutu Geologicznego, 174, 133-142.

ALEKSANDROWSKI P., INDERHAUG O.H. and KNAP-STAD B., 1992. Tectonic Structures and Well bore Break-out Orientation. In: TILLERSON J.R. and W.R WA WER-SIK (Editors), Rock Mechanics. Proceedings of the 33rd U.S. Symposium, Santa Fe (U.S.A.), 29-37. Balkema, Rotterdam, The Netherlands.

ALEKSANDROWSKI P. and KIERSNOWSKI H., 1998. On the potential of structural, sedimentological and geody-namical analysis of borehole profi les based on modern dip-meter data. In: Najnowsze Osiągnięcia Metodyczno-Inter-pretacyjne w Geofi zyce Wiertniczej. Materiały VII Kra-jowej Konferencji Naukowo-Technicznej PGNiG i AGH, Kraków, 9-18.

JAROSIŃSKI M. and ALEKSANDROWSKI P., 1998. Inte-grated Geodynamic and Structural Investigations of

Structural geology and sedimentology from dipmeter data: the power of wireline loggingPaweł AleksandrowskiUniwersytet Wrocławski, Instytut Nauk Geologicznych, ul. Cybulskiego 30, 50-205 Wrocław, Poland

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Paweł Aleksandrowski

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

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Frac tured Reservoirs Based on Borehole Data. In: Ma te-ri ały Konferencji Najnowsze Osiągnięcia Metodyczne w Światowej Geologii Naftowej i Ich Wykorzystanie w Polskim Górnictwie Naftowym i Gazownictwie, PGNiG i Geonafta, Warszawa, 57-60.

GOETZ J.F., 1984. Dipmeter Interpretation: the Science and the Art. Gearhart Industries, Inc. Fort Worth, 51 pp.

GOETZ J.F., 1989. Dipmeter Interpretation: Pitfalls and Prefer-

red Practices. In: Halliburton Technical Papers, 1-16.HALLIBURTON, 1992. Introduction to the Six-Arm Dipmeter

and SHIVA Processing. HoustonSCHLUMBERGER, 1986. Dipmeter Interpretation. Fun da-

ment als. Schlumberger Ltd, New York, 76 pp.

Two large-scale seismic refraction experiments performed recently were aimed at the investigation of lithospheric structure in Central Europe. Experiment POLONAISE’97 tar-get ed the structure and evolution of the prominent European suture zone – TESZ and adjacent units. CELEBRATION 2000 experiment covered namely East European Craton and Pa-leozoic Platform, Western Carpathians, Panonian basin and partly also the neighbouring units including the Bohemian Massif. Both projetcs benefi ted from the new generation of small, portable, programmable seismic instruments TEXAN developed in the USA. This fact enabled their massive deploy-ment in the fi eld (1,200 stations during the CELEBRATION 2000 experiment) resulting in a dense coverage of the investi-gated area. Such methodology offers a possibility of 3-D mod-elling of seismic wave velocity distribution in the lithosphere in the advanced stage of interpretation. Both experiments were iniciated and realised as an international co-operation of ca. 30 institutes from Europe and North America (Guterch et al., 1999, 2000).

To cover suffi ciently the remaining areas of Central Europe, two new seismic refraction projects have been proposed

– project ALP2002 and project SUDETES 2003.Project ALP 2002, scheduled for summer 2002, will cover

the Eastern Alps, the Europe’s most prominent and complex mountain belt, and adjacent parts of Austria, Hungary, Italy, Czech Republic, Slovenia, and Croatia. The longest Trans-Alpian line of this experiment extending from Adriatic Sea will continue up to the northern part of the Bohemian Massif (Bílina in the Eger Graben region). University of Vienna (group of prof. Ewald Brueckl) is responsible for the project.

The experiment SUDETES 2003 is scheduled for summer 2003 and will cover the northern part of the Czech Republic, southwestern Poland and southeastern Germany. The overall scientifi c objective of the project is to investigate the deep

crus tal structure and geodynamics of the northern part of the Bo hemian Massif, the largest outcrop of the Late Paleozoic Variscan orogen in Central Europe. In addition to targeting this massif, its relationships with the adjacent Caledonides and TESZ will also be investigated. The project will also focus on Elbe Zone and Eger Graben regions and an unsolved question of the Late-Paleozoic through Recent history of their reactiva-tion. The NW-SE oriented Elbe Zone has for most of its history been active as an important strike-slip zone, parallel to the TESZ. The Elbe Zone produced a juxtaposition of terranes with different geodynamic histories, compositions, and geophysical properties. The WSW-ENE trending Eger Graben has been in-terpreted as a Neogene rift, characterized by signifi cant Oligo-Miocene volcanism (Kopecký, 1986). At a deep crustal level, the rift axis is generally associated with the southeast-dipping boundary between the Saxothuringian and Moldanubian ter-ranes. This boundary might be (?) associated with a major subduction zone within the Variscan belt that formed during the Middle-Late Paleozoic. The actual spatial characteristics of this boundary, its relationship with the intersecting Elbe Zone structures, as well as the history of its numerous reactivations at shallow crustal levels, remain a challenge to unraveling the geodynamic history of Central Europe.

The layout of the SUDETES 2003 project is suggested to consist of two orthogonal systems of recording profi les orient-ed perpendicular to and parallel with two main tectonic features of the region, the Elbe Zone and Eger Graben. To obtain dense ray coverage, not only in-line shots but also off-line ones are planned. The network of profi le measurements together with the fan records of off-line shots should provide a suffi cient 3-D coverage for 3-D modeling in the interpretation stages of the project.

The SUDETES 2003 and the ALP 2002 projects are designed to merge not only with CELEBRATION 2000 and

Projects ALP 2002 and SUDETES 2003 – Continuation of 3D Refraction Seismic Experiments in Central EuropeALP 2002 and SUDETES 2003 Organizing Committee (E. Brueckl1, M Grad2, A. Guterch3, P. Hrubcová4, A. Špičák4)1 Vienna University of Technology, Gusshausstrasse 27-29, A-1040 Wien, Austria2 Institute of Geophysics, University of Warsaw, Pasteura 7, 02-093 Warsaw, Poland3 Institute of Geophysics, Polish Academy of Science, Ks.Janusza 64, 01-452 Warsaw, Poland4 Geophysical Institute, Academy of Sciences of the Czech Republic, Bocni II/1401, 142 00 Prague, Czech Republic


POLONAISE’97 experiments, but also with the seismic tomography experiment BOHEMA 2001/02, and numerous Czech-German projects on the geodynamics of the West Bohemia/Vogtland area that is repeatedly experiencing earth-quake swarms. The projects should contribute to delineation of basement structure in regions covered by sedimentary ba-sins, to better knowledge of crustal rheology, and deep-seated crustal inhomogeneities and will be complemented by concur-rent geological/geophysical research projects focused on the shallower crustal levels. Warsaw and Prague groups with the support of NSF through University of Texas at El Paso will be responsible for the performance of the SUDETES 2003 experi-ment.

References

GUTERCH A., GRAD M., KELLER G.R., 2001. Seismologists Celebrate The New Millennium with an Experiment in Central Europe. EOS, Transactions, American Geophysical Union, 82 (45), 529, 534, 536.

GUTERCH A., GRAD M., THYBO H., KELLER G.R. and POLONAISE Working Group, 1999. POLONAISE’97

– An international seismic experiment between Precambrian and Variscan Europe in Poland. Tectonophysics 314, 101-121.

KOPECKÝ L., (1986). Geological development and block structure of the Cenozoic Ohře rift (Czechoslovakia). Proc. 6th Int. conf. basement Tect., 114-124, Utah.

Peraluminous leucogranites with accessory tourmaline derived from crustal sources are widespread in mountain belts formed by continental collision (London et al., 1996). In eastern part of the Moldanubicum they are spatially associated with the Třebíč pluton, and three distinct types of leucocratic, medium- to fi ne-grained, biotite and muscovite-biotite granites with accessory tourmaline were distinguished.

(i) Two mica granites with tourmaline concentrated in orbi-cules (OTG) compose small intrusive bodies and dykes, scarce-ly up to 200 m thick. Quartz + tourmaline ± feldspars orbicules, up to 10 cm in diameter, or rare veins, up to 2 cm thick, are randomly distributed or concentrated in several m thick zones within bodies of leucocratic granites. Subhedral tourmaline is intersticial between euhedral grains of feldspars and quartz, and it replaces dominantly plagioclase. The accessory minerals include apatite, andalusite, cordierite, ilmenite, zircon, allanite, xenotime and monazite in granite; apatite is fairly abundant in orbicules. The tourmaline-quartz orbicules and veins seem to be a product of crystallization of evolved, B-rich medium (melt and/or fl uid) during late solidus to early subsolidus stage of the granite formation.

(ii) Two mica granites with disseminated tourmaline (DTG) form relatively large intrusive bodies and dykes, up to several km2. They do not exhibit such apparent spatial relationship to durbachite plutons as OTG. Euhedral to subhedral tourmaline grains, up to several mm long, are rather regularly distributed in the rock. The accessory minerals include apatite and zircon. In contrast to the OTG, disseminated tourmaline crystallized from granitic melt.

(iii) Biotite granites with tourmaline (MTG) typically oc-cur in marginal zone of the Třebíč pluton. They form relatively small bodies (up to several hundred m thick) and are associated with migmatites and aplites. Euhedral tourmaline grains oc-

cur in coarse-grained pegmatoid facies, subhedral intersticial grains in rare quartz + tourmaline ± feldspars orbicules, up to 5 cm in diameter. Poikilitic garnet forms grains from 5 to 25 mm in diameter, randomly distributed in the rock, further accessory minerals include apatite, zircon and sillimanite.

All types of tourmaline granites have very similar geo-chemical signature corresponding to leucocratic and peralumi-nous (ASI = 1,0–1,3), syn- to post-collisional S-type granites: K2O = 2.77–6.14; Fe2O3tot = 0.42–2.08; Rb = 194–234 ppm; Mg/Fe = 0.08–0.33; Rb/Sr = 1.00–5.56 in OTG, 5.24–7.34 in DTG and 0.5 in MTG; CaO = 0.49–0.87, 0.36–0.66 and 1.67, respectively. The normalized REE patterns are very similar for OTG and DTG granites; low REE concentrations ∑REE

= 20.08–99.81 ppm and slight LREE enrichment (LaN/LuN = 1.9–6.8). The MTG indicate HREE depletion (LaN/LuN = 10.14) with distinct positive europium anomaly (Eu/Eu* 2.5). Similar mineral assemblages, whole rock major, minor and trace chem-istry suggest that positive and negative europium anomalies (Eu/Eu* 0.5–1.6) found in both OTG and DTG rather refl ect different fO2 during crystallization. Lower CaO/Na2O ratios (0.10–0.22) in OTG and DTG are typical for melts derived from clay-rich, plagioclase-poor pelitic rocks (Sylvester, 1998). The high CaO/Na2O ratios (0.53) in MTG are typical for melts generated from plagioclase-rich psammitic rocks.

The zircon saturation temperatures 784–725 °C obtained for durbachitic rocks in Třebíč pluton (Watson and Harrison 1983) are similar to those the MTG (778 °C); DTG and OTG provided 660–713 °C, and 660–746 °C respectively.

The geochemical signatures suggest relatively primitive character of all granite types. The OTG and DTG had similar protoliths (metapelites) and conditions of melting (probably muscovite dehydration melting). Geochemical and minera-logical signatures of MTG exhibit less primitive character and

Tourmaline-bearing leucogranites from the Třebíč pluton in the MoldanubicumBuriánek, D and Novák, M. Department of Mineralogy, Petrology and Geochemistry, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic

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higher temperature of melting (probably biotite dehydration melting).

References

LONDON D., MORGAN G.B., and WOLF M.B., 1996. Boron in granitic rocks and their contact aureoles. In: BORON

(Editor). Mineralogy, Petrology and Geochemistry (Grew, E.S. & Anovitz, L.M. eds.). Rev. Mineral., 33: 299-330.

SYLVESTER P. J., 1998: Post-collisional strongly peralumi-nous granites.- Lithos 45, 29-44.

WATSON E. B. and HARRISON T. M., 1983. Zircon satura-tion revisited: temperature and composition effects in a variety of crustal magma types.- Earth. Planet. Sci. Lett., 64: 295-304.

In the West Carpathians, there are two principal groups of granitic rocks that originated during the peak stadium of the Variscan collision processes and/or after the slab breakoff (or delamination). The older one is pretty peraluminous (ASI = 1.1 – 1.5) dominated by two-mica granites and granodiorites, whereas biotite granodiorites to tonalites being less common. Accessory mineral association comprising monazite and il-menite and presence of host (metamorphic) rock xenoliths are typical of these rocks. From geochemical point of view, Ba, Sr and Rb range widely (up to 2000, 1000, and 200 ppm, respec-tively) with Rb/Sr generally <1. The REEs are moderate with fractionated pattern and small negative Eu anomaly. Initial Sr 0.706 – 0.708, ε Nd(350) = −0.62 to −4.24, the 206Pb/204Pb ratios of the whole rock samples range from 18.39 to 19.28 and the 207Pb/204Pb ratios from 15.59 to 15.74, stable isotopes (O and S) with values δ 18O(SMOW) = 8.8–11.3‰ and δ 34S(CDT) from −0.9 to +5.7‰. Magmatic intrusion age of these granites is between 350–330 Ma with majority around 340 Ma. These granitic rocks resemble in classical alphabetic nomenclature common S-type and/or Ilmenite Series granites.

The younger group of granites is rather metaluminous to subaluminous (ASI = 0.8 – 1.1) dominated by biotite tonalite to granodiorite with scarce hornblende. Muscovite-biotite granodiorite to granite are in less extent. Accessory mineral association of magnetite + allanite and occurrence of mafi c microgranular enclaves (MME) are characteristic of this group. Lower SiO2 concentrations are compatible with higher trace el-ements Zr, Ba, Sr, LREE and Fe group element contents. REE patterns are typically steeper with higher LREE and without Eu anomaly. The initial Sr = 0.704 – 0.707 with Rb/Sr = 0.05 – 0.7 which are consistent with Rb-poor crustal source and/or mixed lower crustal or mantle component. Few Nd data fall within the S-type group – εNd(i) = −1.7 to −3.5 although mafi c dioritic enclaves with ε Nd(i) = 1.8 – 0.5 clearly indicate interaction with a basic or intermediate, dioritic lower crustal melt. The 206Pb/204Pb ratios of the whole rock samples range from 17.99

to 18.85 and the 207Pb/204Pb ratios from 15.53 to 15.70. Stable isotopes (O and S) with values δ 18O(SMOW) = 7.8 – 9.9‰ and δ 34S(CDT) from −2.9 to +2.3‰ also support melting of more basic lower crustal protolith. Magmatic intrusion ages of these gran-ites vary between 310 – 300 Ma and these granitic rocks can be compared to I-type and/or Magnetite Series granites.

Generally we suppose that collisional processes that result in the formation of crustal-scale nappe structures and gen-eration of collision-related felsic “S-type” granite magmatism characterize the main Meso-Variscan collisional period. Neo-Variscan stage is connected with collapse of the collisionally thickened crust. The fi nal collisional shortening was followed by the gravitational instability of thickened lithosphere, which resulted in the process of thinning of lithosphere (lithospheric delamination, detachment of lithospheric root from the light continental lithosphere, or slab breakoff). As a result of the slab-breakoff, the asthenosphere upwelled and thermal perturbation led to melting of the metasomatised lithospheric mantle and subsequent formation of “I-type” granites at the base of the crust. This period was characterized by a shift from compres-sional towards extensional tectonics.

Indeed there are small differences between both groups of granitic rocks in the isotopic picture, neither younger metalu-minous nor older peraluminous granitic suites have typical geo-chemical characteristics of continental collisional granites. It is interesting that these isotopic characteristics suggest rather for the origin in volcanic arc with granite melting during subduc-tion of oceanic crust under continental margin, than melting in the consequence collisionally thickened crust.

Magnetic susceptibility of granites worldwide displays a bimodal distribution, with one mode corresponding to the values of 10-3 to 10-2 and the other one to those of 10-5 to 10-4 [SI]. The former mode granites, with magnetite representing magnetic minerals, are often represented by an I (igneous) type. The latter mode granites, in which magnetic minerals are repre-sented by ilmenite, often correspond to an S (sedimental) type.

Tectonic environment and magnetic susceptibility of the West Carpathian granitesDagmar GREGOROVÁ1, Milan KOHÚT2, František HROUDA3,4

1 Geophysical Institute of Slovak Academy of Sciences Bratislava, Slovak Republic2 Dionýz Štúr Institute of Geology, Bratislava, Slovak Republic3 Institute of Petrology and Structural Geology, Charles University, 128 43 Praha, Czech Republic4 AGICO Inc., 621 00 Brno, Czech Republic


Magnetic susceptibility of the West Carpathian granites is in general low, in the order of 10-4 [SI]. In the minority of specimens it is in the order of 10-5 and in exceptional speci-mens it is higher, in the order of 10-3. The susceptibility values of the most West Carpathian granites correspond to the values

typical of S-types. This is in contradiction with the granite origin revealed geochemically. The preliminary explanation of this contradiction is that magnetite originally present in the I-types was destroyed during Alpine deformation indicated by magnetic fabric.

The Gföhl gneiss is an important lithological unit of the most deeply buried part of the Moldanubian root domain. It is sug-gested by some authors that this gneiss complex together with HP granulites, eclogites and mantle fragments form the highest structural position of the Moldanubian zone due to exhuma-tion associated with large-scale nappe tectonics (Matte, 1990, Petrakakis, 1995). The Gföhl gneiss complex is rather hetero-geneous in composition, and consists of nebulitic migmatites, stromatitic biotite-rich migmatites and locally of banded or-thogneisses. The detailed outcrop observations reveal gradual transitions from porphyritic orthogneiss via high-grade mylo-nites to entirely molten rock. The question arises, whether the large volumes of felsic medium-grained migmatites originate through partial melting of orthogneiss protolith or whether the main proportion of migmatitic domain was originally formed by fertile metasediments rich in hydrous minerals (Thompson, 2000).

Several key outcrops were investigated from the structural, textural and petrological point of view. The earliest structures are represented by steep solid state high-grade foliations in strongly sheared orthogneisses marked by alternations of monomineralic feldspar and quartz layers and large amount of biotite. This fi rst fabric is W dipping (at an angle of 60–80º) and N-S trending. The early fabric is folded and transposed by fl at foliation associated with the development of fi ne-grained mylonites. These high-grade mylonites progressively pass into migmatitic gneiss rich in sillimanite and garnet, and fi nally into completely molten felsic leucosomes. The new planar system is E-W trending (at an angle of 15–40º) and bears N

– S oriented mostly subhorizontal lineation.We sampled two sections in which the above transition from banded orthogneiss to nebulitic migmatite was observed. The aim of this work is to understand the melting process of high-grade orthogneiss, i.e., relatively refractory rock using a detailed petrologial and textural analysis.

We have distinguished and documented four textural stages from the orthogneiss to nebulitic migmatites. The fi rst one is represented by fi ne-grained banded ortogneiss with distinctly separated monomineral layers. The K-feldspar layers

0.75–2 mm thick consist of grains 0.5 mm in size with straight boundaries. Numerous rounded inclusions of quartz (0.01 mm in size) occur mostly at triple points. A polygonal mosaic of well-equilibrated plagioclase 0.2–0.3 mm large forms layers 0.25–1.25 mm thick. Quartz occurs in 0.7–0.1 mm thick poly-crystalline ribbons. Large fl akes of biotite, locally overgrown by sillimanite (< 5%), form bands separating quartz from plagioclase aggregates. Small garnet (0.07–0.1mm in size) is associated with biotite aggregates.

The second stage is characteristic of grain coarsening and disappearance of monomineralic layering. The K-feldspar-rich aggregates are composed of K-feldspar (80%) grains (0.6 mm in size) with straight boundaries and numerous inclusions of quartz (20%) and biotite. Plagioclase-rich layers are composed of plagioclase (80%), quartz (20%), biotite fl akes, and rounded garnet grains (0.5 – 0.9 mm in size) + sillimanite. Quartz forms irregular aggregates composed of large grains (0.4–0.6 mm in size) with strongly lobate boundaries.

The third stage is marked by change in the proportion and size of individual minerals and by the increase in sillimanite content. Former plagioclase-rich layers show almost granite-like texture being composed of almost equivalent amount of plagioclase and quartz as well as minor amount of K-feldspar. The K-feldspar layers consist of large irregular grains of K-feldspar and small plagioclase grains. The K-feldspar/quartz ratio is 1:1. The plagioclase and K-feldspar layers are separated by sillimanite aggregates. No relics of original layering can be observed in the nebulitic migmatite.

The grain boundaries of minerals in individual stages were “traced” in the GIS Arc View environment and analysed using The Matlab™ Poly LX toolbox (Lexa, 2001), where statistical analysis of grain size, grain contact frequencies, modal compo-sitions and grain boundaries and shapes were performed. This study permits to quantify the textural evolution of mineral aggregates from solid state to random anatectic structure. The detailed microprobe work, currently in progress, is carried out to estimate the PT conditions of textural annealing and melting. Basing on these data, an attempt is made to propose a model of textural annealing and melting explaining the disintegration of

Development of the Gföhl migmatites through partial melt-ing and textural annealing of high-grade orthogneiss via process of disintegration of solid state texturePavlína HASALOVÁ and Karel SCHULMANNInstitute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43, Prague 2, Czech republic

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the original solid state texture and development of large vol-umes of nebulitic migmatites in the Gföhl unit.

References:

PETRAKAKIS K., 1995. High – grade metamorphism and retrogression of Moldanubian granulites, Austria. Eur J Mineral, 7(5): 1183 –1203.

MATTE P., MALUSKI H., RAJLICH P. and FRANKE W., 1990. Terrane boundaries in the Bohemian Massif; result of large-scale Variscan shearing. Tectonophysics,177: 151-170.

THOMPSON A.B., GARDIEN V. and ULMER P., 2000. Melting of biotite plus plagioclase plus quartz gneisses: the role of H2O in the stability of amphibole. J Petrol, 41(5): 651-666.

The Klodzko - Zloty Stok massif (KZS) is one of the Variscan plutonic bodies located within the Lugian Zone at NE margin of the Bohemian Massif in southern Poland. Though the rocks were described petrographically in a great detail (namely by Wierzcholowski 1976) and many silicate analyses were pub-lished, the trace element contents and geochemical characteris-tics are still poorly known.

The plutonic rocks from the KZS are dominantly intermedi-ate and only marginally acidic. The whole compositional range of major plutonic rocks (excluding enclaves) is from about 54 to 68 wt.% with rare leucogranites up to 75%.

Lorenc (1991) stressed the metaluminous chemistry of the major rock types, their hybrid nature and abundance of dark in-clusions that he interpreted as typical mafi c magmatic enclaves (MME). According to him the role of mafi c magma in petro-genesis of granitoids forming the KZS was principal.

Geochemical study of a new set of samples displays highly variable composition of major rock types as well as of MME. These data enabled us to differentiate at least 3 compositional groups (Table 1) that differ in petrochemical parameters.

Mafi c varieties of rocks from the KZS display typical fea-tures of mantle-derived magmas or hybrid magmas dominated in composition by the mantle end-members (high mg-values, high contents of MgO, Cr, Ni). However, composition of the

mafi c members vary and they cannot represent single magma batch.

The most potassic plutonic rock yet analysed are mon-zonites from the endocontact of the KZS at Żelazno. These and some other dark and K-rich rock varieties from KZS are similar in chemical composition to “vaugneritic” and “syenitic” intrusions in the Niemcza Zone, namely at Kożmice and Piława Górna (cf. Puziewicz 1987, 1988). Their chemical composition cannot be due to contamination of a common basaltic magma with crustal rocks or melts as these rocks have not only high K and Rb but also the highest MgO, Cr and Ni and the mg-values.

Composition of the prevailing relatively dark and K-rich granitoids resemble that of shoshonitic rocks (SHO). Some granitoids from surroundings of Laskówka and Laski corre-spond to the high-K calc-alkaline series (HKCA) with different composition of MME.

Compared to durbachitic rocks from the Moldanubian Zone of the Bohemian Massif, even the most potassic rocks from the KZS and the Niemcza Zone display signifi cantly lower contents of K2O, P2O5, Rb, Cs, Th and U. However, their geochemical signature, namely in the “spider diagrams”, seems to be similar. We consider existence of some similarities in his-tory of their mantle sources.

Geochemical variability of the Kłodzko – Złoty Stok Massif: possible role of multiple mafi c end-members of hybrid granitoids

František V. HOLUB and Jerzy ŻABA 1 Inst. of Petrology and Structural Geology, Charles University Prague, Albertov 6, CZ 12843 Praha 2, Czech

Republic2 Department of General Geology, University of Silesia, ul. Bedzinska 60, PL 41-200 Sosnowiec

Group Rocks SiO2 K2O K2O/Na2O mgUK monzonite to melagranodiorite 54–58 3.4–4.7 1.3–2.2 72–65.3SHO melagranodiorite to granodiorite 58.7–62.5 3.4–4.2 1.1–1.3 55.7–53.1HKCA biotite granodiorite to monzogranite 64–68 3.1–3.5 1.0–1.1 46.4–43.1

mg = MgO/(MgO + FeOtot.) (from molar values)

Tab. 1. Comparison of selected petrochemical parameters for major compositional groups of plutonic rocks from the Klodzko – Zloty Stok massif and similar rocks from the Niemcza Zone


Rocks of the KZS display high LILE/HFSE elemental ratios and also the high Th/Ta ratios are typical for igneous rocks derived from sources geochemically modifi ed in the supra-subduction environment at destructive plate margins. However, as the mantle may retain the “subduction signature” after cessation of subduction, derivation of the K-rich mantle magmas may not be contemporaneous with active subduction in the area.

The compositional diversity and signifi cant differences in incompatible elemental ratios between members of in-dividual compositional groups from the KZS cannot be as-cribed to increasing degree of enrichment superimposed on a common mantle lithology, or to decreasing melting degrees. Geochemical characteristics and variability of K-rich magmas can be due to distinctive sources within the heterogeneous sub-continental lithospheric mantle with complex history.

An extreme composition has to be considered for source of the peralkaline dyke rock of karlsteinite composition intruding the SHO plutonites at Rogówka.

References

LORENC M.W., 1991. Uwagi o genezie intruzji kłodzko-złotostoskiej (studium porównawcze na bazie enklaw).

–Archiwum Mineralogiczne, 47, (1), 79-98.PUZIEWICZ J., 1987. Petrografia, geneza i autometamorfizm

syenitu kwarcowego z Piławy Górnej i jego pegmatytów. – Archiwum Mineralogiczne, 43, (1), 5-18.

PUZIEWICZ J., 1988. Plagioclase-pyroxene-biotite rock from the Koźmice quarry, Niemcza zone (Sudetes, SW Poland): the fi rst occurrence of vaugnerite in Polish Sudetes.

– Mineralogia Polonica, 19, (2), 59-68.SMULIKOWSKI K., 1979. Skała ultramaficzna z Droszkowa

koło Kłodzka w Sudetach. – Archiwum Mineralogiczne, 35, (2), 55-66.

WIERZCHOŁOWSKI B., 1976. Granitoidy kłodzko-złoto-stockie i ich kontaktowe oddziaływanie na skały osłony (studium petrografi czne). – Geologica Sudetica, 11, (2), 147 pp. Warszawa.

Fig. 1. The K2O versus MgO plot for rocks of the Klodzko – Zloty Stok massif and the Niemcza Zone. Averages of common plutonic rocks are from Le Maitre (1976).

During last 20 years, numerical methods of paleostress recon-structions were very well developed, but progress in graphi-cal methods was nearly stopped, however modern computers enable good graphical presentation of data. Merit of graphi-cal methods is illustrative relation between data and results. Two basic graphical methods include right dihedra method (Angelier and Mechler 1977) and M-plane method (Arthaud 1969). These two methods are the two marginal cases of general inverse method based on one-fault inverse analysis.

Using fault coordinate system, where l-axis is striae linea-tion, n-axis is normal to fault plane and m-axis complete right-

Generalized Angelier-Mechler‘s/Arthaud‘s methodMiroslav HROZA and Rostislav MELICHARDepartment of Geology and Paleontology, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic

Fig. 1. Equal-area plots for different methods of σ1-deter-mination based on one-fault inversion: Angelier-Mechler’s method (µ ≤ 1), descripted method (vari-able µ, e.g. µ ≤ 0.2), Arthaud’s method (µ = −1, no solution in this case).

GeoLines 15 (2003)10

hand orthogonal system lmn, it is easy to derive equation for Lode parameter µ = (2σ2 − σ1 − σ3)/(σ1 − σ3) in dependence on direction of σ1 and σ3 respectively. This function limits fi eld of possible σ1-directions with decreasing of µmax (Fig. 2a) and

σ3-fi eld with increasing of µmin. The fi eld of σ1 is equivalent to right dihedra quadrant for µ ≤ 1 as one extreme and is reduced to part of M-plane for µ = −1 as the second extreme (Fig. 1). Base on this idea we can make equal-area plot for fi elds of σ1 and σ3 with isolines of µ (Fig. 2b, c). With these plots we can determine upper and lower limits of µ (µmax, µmin), and corre-sponding fi elds of σ1 and σ3 respectively.

References

ANGELIER J. and MECHLER P., 1977. Sur une méthode gra-phique de recherche des contraintes principales également utilisable en tectonique et en séismologie: la méthode des dièdres droits. Bull. Soc. géol. France, 19: 1309–1318. Paris.

ARTHAUD F., 1969. Méthode de détermination graphique des directions de raccourcissement, ďallongement et intermé-diaire ďune population de failles. Bull. Soc. géol. France, 11: 729–737. Paris.

Fig. 2. Equal-area plots of distribution σ1 and σ3 showing fi eld reduction in dependence on µmin and µmax: a – one fault, σ1-plot with µmin isolines; b – σ1-plot of µmin for two faults from Fig. 1; c – σ3-plot of µmax for the same faults. Isolines of µ: −1.0, −0.9, −0.8, −0.6, −0.3, 0, 0.3, 0.6, 0.8, 0.9, 1.0.

Hydrogen and oxygen isotope ratios in mafi c and ultramafi c rocks of Ślęża (Sl) and Nowa Ruda (NR) ophiolites complexes (N margin of Bohemian Massif, Sudetes Mts., SW Poland), have been analysed. This was done to assess the role of ocean fl oor metamorphism and continental processes in the evolu-tion these two ophiolites.

These ophiolites belong to the mafi c-ultramafi c massifs sur-rounding the signifi cantly older Precambrian Sowie Mts. gneis-sic block (SM). The NR ophiolite is situated at the SW margin of the SM. Its northern part is composed of variable petrologic types of altered gabbro (metagabbro) and the southern, subvol-canic part, consist of metadiabases and altered pillow lava. The northern and southern parts are divided by the Słupiec cata-clastic zone. The Ślęża ophiolite represents almost complete ophiolite sequence composed of: Gogołów-Jordanów (G-J) ser-pentinite massif (ultramafi c member), Ślęża Mt. gabbro (mafi c, plutonic member) and Wieżyca Hill (WH) metadiabases and amphibolites (volcanic member). The ophiolite is in overturned position and the pillow lava and sedimentary members have not been found. The Sl ultramafi cs contact on S to the N border of SM, and all the Sl members contact on N and NW to the SE border of slightly younger Variscan Strzegom-Sobótka (S-S) granite massif. Comparison of mesostructural features of the ophiolite to such features of other Sudetic units of known age, suggests that the emplacement of these ophiolites took place during Variscan orogenesis (continental collision with NE-SW suture zone). Sm-Nd age determination of the mafi c member

A record of oceanic and continental stages in evolution of the Sudetic ophiolites – new evidence from stable isotope composition of silicate minerals.Mariusz O. JĘDRYSEK and Anita WEBER-WELLERLaboratory of Isotope Geology and Geoecology, University of Wrocław, Cybulskiego 30, 50-205 Wrocław, Poland

confi rmed that thesis. The Sm-Nd age of the mafi c member of Sl is 353 ± 21 Ma and that of NR is 351 ± 16 Ma.

Structural evolution of rocks is not necessary accompa-nied by formation of new minerals however, apparently may result in a redistribution of isotope ratios in the deformed primary minerals. Thus, isotope analysis may be a good tool to reconstruct geological condition of structural evolution of rocks. Mesostructural observations in Sl revealed presence of the primary magmatic lamination S0 and metamorphic and/or tectonic foliations S1, S2, S3 and S4. Moreover, 6 systems of slickensides have been observed. In case of the sheeted dykes member (amphibolites) the S0 may be considered as sequence of rhythmic variations of the structure, parallel to the margins of the dykes. In lower members of the ophiolite the S0 is a dark and light lamination. In the metagabbro the leucocratic laminae are composed predominantly of feldspars and products of their hydrothermal decomposition. The melanocratic laminae are composed mostly of diallage and uralitic hornblende. In the ul-tramafi c cumulates the light laminae consist mostly of chlorites, tremolite and primary calcite, and the dark ones are relics of pyroxenes and amphiboles. In the tectonites (serpentinites) the S0 exists in presence of fl at sectors composed predominantly of pyroxene relics, and the overlying spaces are fi lled mostly with olivine and products of its decomposition.

The S1, in general, is parallel to S0, but sometimes one can observe centimetre-scale intrafoliation folds F1 formed during the D1 deformation. Despite that in the outcrop-scale the F2

GeoLines 15 (2003) 11

folds have not been noticed, the S2 foliation is very clear, espe-cially in ultramafi c rocks. It is developed as typical schistosity possibly formed during deformation D2. Generally, the S2 is perpendicular to S0 and S1. The D3 deformation of S2 yielded meter-scale open folds F3. The S3 surfaces are not penetrative and occur only in ultramafi c rocks as the axial cleavage in F3 folds. The F4 folds have been noticed in schistose serpentinites and amphibolites as small knick folds with cataclasis devel-oped along axial planes (S4). The S4 in ultramafi c cumulates occur only in a few zone of cataclasis.

In non-mineralised (ore minerals are accessory or not observed) rocks, the δ18Ο whole rock (wr) value varies from 3.97 ‰ (Słupiec tectonised gabbro) to 8.35 ‰ (G-J serpen-tinites). These values are typical for ophiolitic sequences. It was suggested earlier that ocean water was an important factor controlling hydrogen isotope ratios in chlorite from rodingites in GJ and sulphur isotope ratios amphibolites in SM. Therefore, it could be expected that advances in oceanic fl oor metamorphism (higher w/r ratio and lower temperature) would leave hydrogen and oxygen isotope offprint in whole rocks too. Therefore, vertical profi les in Sl () and NR (δD and ) ophiolites have been constructed, and isotope values versus the distance from petrologic Moho have been plotted (Figs 1, 2, 3). In general, overall vertical distributions of δD and values do not show regular pattern. Nonetheless, the upper horizons of gabbro (dominantly fi ne-grained) close to the contact to sub-

volcanic rocks (amphibolites), show clear upward decrease in δD value in NR (Fig. 1), increase in value in NR (Fig. 2) and decrease in value in Sl (Fig. 3).

Temperature and mineralogical composition are the domi-nant factors governing D and O isotope fractionation in water

– rock system. Metagabbro is composed of minerals showing slightly negative O and D fractionation factors in mineral-water system, and the α factor decreases with temperature decrease. However, amphibolites show signifi cant content of albite, quartz, carbonates and zeolites which, in turn, show strongly positive O isotope fractionation in the mineral-water system. Therefore, it is expected, that an increase in seawater alteration during potential ocean fl oor metamorphism, in temperatures between 100 to 500 oC, and decrease in temperature of this alteration, should result in decrease in in metagabbro, and higher values in the amphibolites. This is the case in the Sl profi le (Fig. 3) but not the in the NR one (Fig. 2). This suggest that the Sl ophiolite rocks were strongly altered due to an ocean fl oor metamorphism, but the NR rocks much less or oceanic traces were overwhelmed by later continental processes. The NR δD profi le, support this thesis, as the D/H ratios in the NR are very low and the NR δD value decreases upward suggesting decrease in temperature of the rock alterations and increasing role of meteoric origin fl uids. Likewise, and δD values and profi les in GJ serpentinites do not show any relation to oceanic alteration (Fig. 3 and 4) or potential infl uence of S-S granite.

Fig. 1. δD versus distance to the N border (the potential Moho) of the Nowa Ruda massif

Fig. 2. δ18Ο versus distance to the N border (the potential Moho) of the Nowa Ruda massif


Therefore, we suggest that the S1 formed in the oceanic stage of the evolution of these ophiolites.

The δD values show gradual increase and δ18Ο values show gradual decrease, from margin into the centre of the GJ serpen-tinite body. It suggests that during serpentinization(s), w/r ratio was (were) much higher in the marginal parts than in the centre of the serpentinite body. This suggestion may be supported by D/H isotope analysis in whole rocks and carbon and oxygen isotope analysis in scattered ophimagnesites. On the other hand,

Fig. 3. versus distance to the ultramafi c cumulates (the po-tential Moho zone) of the Ślęża massif

tectonic deformations in GJ, which are considered as a result of D2, are extensive and seem more “plastic” at the marginal parts of the serpentinite body. We suggest that possibly this is caused by gradient of water fl ow penetrating the massif during deformations and the main antigoritic serpentinization. Low hydrogen and oxygen isotope ratios evidence signiffi cant infl uence of meteoric origin fl uids during serpentinization and formation of the S2.

It is expected that hydrothermal alteration due to S-S intru-sion should result signiffi cant variations in isotope ratios, espe-cially in δD in the western part of the GJ. However, this is not very clear pattern. Thus, apparently, the S-S intrusion could be regarded to D3 deformation, however, likewise to the potential D4 deformation, no clear isotope evidence has been found in the scale of the massif. Nonetheless, earlier isotope study evidence that vein chrisotile from the S-S contact zone has been formed due to the granite intrusion, and lizardite formed at surfi cial temperatures under isotope equilibrium with water of meteoric origin.

Fig. 4. δD versus distance to the contact with S-S granite massif

7th Meeting of theCzech Tectonic Studies Group

Żelazno, Poland, May 9–12, 2002

published in Prague, April 2003

by the Institute of Geology,

Academy of Sciences of the Czech Republic

Excursion Guide


GeoLines 15 (2003) 15

Introduction to the field tripLate Palaeozoic Sedimentation in the Intra-Sudetic Basin (Western Sudetes, SW Poland)Leszek Kurowski

The Intra-Sudetic Basin, situated at the northern margin of the Bohemian Massif in the West Sudetes, represents one of the larger intramontane throughs widespread along the Variscan belt of Europe (Fig. 1). It is fi lled with the Lower Carboniferous to Lower Permian volcano-sedimentary succession. The total thickness of the basin fi ll attains 12,000 metres (Fig. 2). The Intra-Sudetic Basin constitutes a large fault-bounded synclino-rial structure, 70 km long and 35 km wide, which extends in the WNW-ESE direction. The basin is framed by various crystalline basement units of the Variscan consolidation and by another Late Palaeozoic sedimentary basins. The basin fi ll suc-cession is overlain by the Lower Triassic continental and Upper Cretaceous shallow-marine deposits.

Development of the Intra-Sudetic Basin was initiated at the beginning of Early Carboniferous as an intramontane depression bounded by tectonically active margins (Teisseyre 1968). Its NW part was framed by the Góry Kaczawskie and Rudawy Janowickie metamorphic complexes and, hypotheti-cal, “Southern Massif”, which were rapidly uplifted and eroded during the Early Carboniferous. Since the Late Tournaisian to Middle Visean the basin was fi lled with non-marine, clastic deposits mainly comprising coarse-grained conglomerates and sedimentary breccias. This part of the Lower Carboniferous molasse sequence of 5 km thick was formerly referred to as

"Older Culm” (Dathe 1892; Teisseyre 1975). It represents de-posits of transverse alluvial fans developed along active fault scarps bounding the basin. Alluvial fans grew centripetally towards the axial fl uvial belt with easterly inclined paleoslope (Teisseyre 1968, 1975; Dziedzic & Teisseyre 1990). The Upper Tournaisian - Middle Visean succession shows a distinct cyclic organisation (Teisseyre 1968, 1975). It comprises several meg-acyclothems which are distinguished as individual lithostrati-graphic units: Ciechanowice, Stare Bogaczowice and Lubomin Formations (Stop 1).

During the Late Visean a marine transgression invaded westwards along the northern margin of the Intra-Sudetic Basin (Dathe 1892; Żakowa 1963).

The western part of the basin was occupied by a shallow marine embayment passing southward into extensive fl uvial/

deltaic system. At the same time, the eastern part of the basin was submerged, in contrast, by a relatively deeper sea. The Upper Visean sedimentary succession is referred to as the Szczawno Formation (formerly "Younger Culm”) (Stop 2). Its thickness increases gradually from 600 m in vicinities of Wałbrzych (most probably not complete stratigraphic interval) to approximately 2 000 metres in the western part of the basin. The succession includes fossiliferous shales containing brack-ish marine fauna (Żakowa 1963).

Tectonic uplift of the eastern and southern basin borders led, at the turn of the Early and Late Carboniferous, to rearrange-ment of the Intra-Sudetic Basin and its depositional system. In consequence of a marine regression, the consecutive Upper Carboniferous to Lower Permian sedimentary successions accumulated in continental settings. The Upper Carboniferous succession consists of few individual fi ning upwards mega-cyclothems, typical of alluvial environment. The succession attains up to 2000 metres in thickness and is, predominantly, of coal-bearing character.

The Early Namurian Wałbrzych Formation consists of quartz arenites and minor conglomerates interpreted to rep-resent an upper delta-plain facies association which evolved into a meandering alluvial plain association (Nemec 1984). Northward directed paleocurrent indicators show a distinct fan-like arrangement were related to northward propagation of allu-vial-deltaic system. The Wałbrzych Formation is approximately 300 metres thick and contains some 30 coal seams.

The Biały Kamień Formation comprises up to 400 metres of the Upper Namurian to Lower Westphalian (Gothan & Gropp 1933) conglomerates and sandstones. Sedimentation was domi-nated by in-channel processes (Kurowski 1998). Braided style of channel pattern evolved upwards into a meandring channel system of an upper delta plain. Paleocurrent indicators, in vi-cinities of Wałbrzych, point to the NNW-directed transport of clastic material which was derived from the easterly and south-erly located source areas.

The Biały Kamień Formation grades upwards into fi ne-clastics and sandstones of the Žacler Formation (Westphal A-C), which contains numerous coal seams (Fig. 2, compare also Tab. 1). This up to 900 metres thick succession represents diverse in-channel and overbank facies associations of an ex-tensive alluvial plain. The paleocurrent indicators suggest the N and NW-directed transport of the clastic material derived from the S and SE margins of the basin.

The Žacler Formation is conformably overlain by the monotonous succession of the Glinik Formation (Westphal

The Intra-sudetic Basin – a Record of Sedimentary and Volcanic Processes in Late – to Post-Orogenic Tectonic SettingMarek Awdankiewicz1, Leszek Kurowski1, Krzysztof Mastalerz2, Paweł Raczyński21 Institute of Geological Sciences, University of Wrocław, pl. Maksa Borna 9, 50-204 Wrocław, Poland2 14076 – 115th Ave., Surrey, B.C., V3R 2P6, Canada


Fig. 1. Simplifi ed geological map of the Intra-Sudetic Basin (after Sawicki, 1995; modifi ed) with outline map of the Bohemian Massif (after Franke, 1989, modifi ed) to show its location (ISB). Ruled – crystalline domains, crosses – Variscan granites, blank – sedimentary basins; ISB – Intra-Sudetic Basin.

GeoLines 15 (2003) 17

D – Stephan). The latter represents a 600 m thick sequence of transitional character between coal-bearing Namurian to Westphalian successions and barren Stephanian and Lower Permian sediments. The Glinik Formation consists of pink to yellow sandstones and fi ne conglomerates interlayered with red mudstones. They represent deposits of braided channels and restricted overbank areas.

The Late Stephanian sedimentation in the Intra-Sudetic Basin produced up to 400 m thick, fi nning upwards sequence of

the Ludwikowice Formation (Fig. 2, Tab. 1). This sedimentary succession comprises mostly red sandstones and conglomer-ates, which accumulated in alluvial-fl uvial settings. Coarse- to medium-grained sediments grade upwards into mudstones and claystones, which include thin intercalations of bitumi-nous limestones. This uppermost portion of the Ludwikowice Formation resulted from sedimentation in lacrustine environ-ments.

The Autunian sediments of the Intra-Sudetic Basin are simi-lar in many respects to the underlying Ludwikowice Formation. They comprise two successive megacyclothems: the Krajanów and Słupiec Formations (Fig. 2, Tab. 1) (Stop 5), which col-lectively attain up to 900 m in thickness. Both fi nning upwards cyclothems comprise clastic deposits of alluvial fan, fl uvial and lacustrine environments (Kurowski 2001). Sedimentation took place in the NW-SE elongated paleovalleys which were fed in clastics by the axial NW-sloping fl uvial systems and transverse, marginal alluvial fans.

Intense tectonic activity during the Saxonian led to the signifi cant uplift of the southern and southeastern frames of the Intra-Sudetic Basin and resulted in a diversifi ed relief (land-scape rejuvenation). Elevated margins of the basin became sub-jects to effective erosion. Sedimentation took place in elongated valleys bounded by fault-related steep slopes. The valley fl oors were occupied by fl uvial plains dominated by accumulation in braided-type channels. The axial fl uvial belts were effectively fed in coarse-clastic material by transverse, mass-fl ow-domi-nated alluvial fans. The Saxonian period of sedimentation in the Intra-Sudetic Basin resulted in 100 to 400 metres thick succes-sion of predominantly red-coloured, coarse-clastic conglomer-ates of the Radków Formation (Fig. 2, Tab. 1).

Carboniferous and permian volcanism in the intra-sudetic basinMarek Awdankiewicz

The Carboniferous and Permian development of the ISB has been associated with three stages of volcanic activity during: 1) the latest Tournaisian/earliest Visean, 2) the late Westphalian and Stephanian, and 3) the early Permian, the latter correspond-ing to the climax of volcanism. Recent studies in the Polish part of the basin (Awdankiewicz et al. 1998; Awdankiewicz 1998, 1999 a, b and references therein) show that geochemical and petrographic characteristics of the volcanic rocks changed with time, the location of volcanic centres was strongly controlled by tectonics, and the volcanic activity and sedimentary proc-esses were closely interrelated.

Geochemistry and petrogenesis

The volcanic succession of the Intra-Sudetic Basin can be sub-divided into the older, calc-alkaline suite, emplaced in the early and late Carboniferous, and the younger, mildly alkaline suite, erupted in the late Carboniferous and early Permian times

Fig. 2. Stratigraphic scheme for Carboniferous and Permian of Intra-Sudetic Basin (Nemec et al., 1982; Odin et al., 1982).


STRATIGRAPHY

CZECH PART POLISH PARTFormation Member Formation Member

Lower Triassic Bohdašin “Buntsandstein”Thuringian BohuslaviceSaxonian Trutnov Radków

Chełmsko Slaskie

WambierzyceUpper

Autunian

Lower

Słupiec

Walchia Shale

Building Sandstone

Broumov

Martinkovice

Olivĕtin

Nowa Ruda

Chvaleč

Bečkov

Verneřovice

KrajanówUpper Anthracosia Shale

Stephanian

LudwikowiceLower Anthracosia Shale

GlinikOdolov Jivka

Svatoňovice

WestphalianŽacleř

Petrovice

Ždarky-Dul

Lampertice

Żacler

Upper Coal-Bearing

Middle - Barren

Lower Coal-BearingNamurian Biały Kamień

Wałbrzych Upper

Visean Middle

Lower

Błażków SzczawnoLubominBogaczowice

Upper Tournaisian Ciechanowice

Fig. 2. Stratigraphic scheme for Carboniferous and Permian of Intra-Sudetic Basin (Nemec et al., 1982; Odin et al., 1982).

GeoLines 15 (2003) 19

(Figs. 3, 4, 5). The calc-alkaline suite comprises mostly rhyo-dacites with minor andesites and basaltic andesites. These rocks show convergent plate margin-like geochemical characteristics (Fig. 5). The mildly alkaline suite comprises, in a decreasing volumetric abundance, rhyolitic tuffs, rhyolites, trachyandesites and basaltic trachyandesites. These rocks are largely character-ised by within-plate geochemical features, with some gradation towards convergent plate margin affi nities (Fig. 5).

Geochemical data suggest that parental magmas of both volcanic suites originated from similar, garnet-free mantle sources at relatively shallow depths (within the subcontinental lithospheric mantle ?), but at variable degrees of partial melting, lower for the mildly alkaline suite. Convergent plate margin-like signatures of the volcanic rocks may either be inherited form the mantle sources of magmas or may refl ect crustal con-tamination of the ascending and fractionating magmas. Both

Fig. 3. Geological sketch of the northern part of the Intra-Sudetic Basin. The map shows distribution of the main types of vol-canic rocks, together with distribution of lavas vs. intrusions and location of eruption centres and magma feeders.


suites comprise moderately to strongly evolved rock types. The major and trace element variation can largely be modelled as a closed system fractional crystallisation of variable mineral assemblages, equivalent to the observed phenocryst phases: mainly plagioclase, pyroxenes and olivine, with hornblende and biotite in the calc-alkaline suite, and with K-feldspar in the mildly alkaline suite. Trace element patterns of the more evolved rocks were also strongly infl uenced by fractionation of such accessory minerals as spinels, ilmenite, apatite, zircon and others. Both geochemical and petrographic evidence (e.g. resorbed quartz phenocrysts with reaction rims, complexly

zoned and sieve-textured plagioclase phenocrysts) suggest also that assimilation of crustal rocks and magma mixing processes might have been infl uential.

Considering the regional geological context, the geochemi-cal characteristics of the volcanic suites of the Intra-Sudetic Basin can hardly be interpreted as resulting from a changing geodynamic regime, e.g. from an active continental margin in the Carboniferous to a within-plate extensional setting in the Permian. Apparently, the volcanic rocks were related to a late/post-orogenic setting and their geochemistry refl ects rather the source characteristics (e.g. a metasomatic enrichment pre-

Fig. 3. Geological sketch of the northern part of the Intra-Sudetic Basin. The map shows distribution of the main types of vol-canic rocks, together with distribution of lavas vs. intrusions and location of eruption centres and magma feeders.

GeoLines 15 (2003) 21

ceding volcanism) and variable differentiation processes (e.g. crustal contamination) of the primary magmas. Similar geo-chemical variation is typical of many volcanic suites emplaced in extensional settings adjacent to former active continental margins (e.g. the Basin and Range Province of the USA).

Volcanic centres, subvolcanic intrusions and the interrelationships of volcanism, tectonics and sedimentation.

The earliest volcanism in the Intra-Sudetic Basin occurred near its northern margin and the successive Carboniferous and Permian volcanic centres shifted SE-wards with time, consist-ently with depositional centres of the basin (Fig. 3). The loca-tion of magma feeders and volcanoes can be tentatively linked with basin margins and, in most cases, intrabasinal elevations and their boundary faults (NNW-SSE to NW-SE aligned in the

Polish part of the basin). The emplacement style of the magmas was strongly infl uenced by palaeogeographic controls: the magmas intruded into thicker accumulations of sedimentary rocks within intrabasinal troughs and erupted through thinner sequences on the intrabasinal elevations. In general, effusive to extrusive activity was typical to the northern and western parts of the basin where lava-dominated, composite volcanic centres were created. In the eastern part of the basin the most evolved acidic magmas erupted explosively with the formation of a maar belt (late Carboniferous) and ca. 10 km in diameter cal-dera (Permian), with subsequent emplacement of subvolcanic intrusions in both cases.

The volcanic activity affected sedimentary processes. Volcanic edifi ces related to major eruptions represented topo-graphic highs subjected to substantial erosion, with the largest supply of volcanogenic debris into the basin following the most voluminous rhyolitic eruptions in the Permian times. On the other hand, the caldera in the eastern part of the basin was an intrabasinal depositional centre.

Contrasting development of Permian volcanic activity in the east and west of the Intra-Sudetic Basin

During the fi eld trip three volcanic complexes related to the Permian climax of volcanic activity will be visited: Kamienna Góra Basaltic Trachyandesites (Stop 3), Góry Krucze Rhyolites (Stop 4) and Tłumaczów Trachyandesites (Stop 5). All the complexes belong to the Słupiec Formation (see previous chapters). In the area of the Permian depositional centre of the Intra-Sudetic Basin near Nowa Ruda, the Słupiec Formation is thickest and most completely developed. In contrast, the west-ern part of the Formation near Kamienna Góra and Lubawka, which accumulated away from the depositional centre over an intrabasinal elevation, is characterised by a hiatus at its base, lower total thickness, lack of some lithostratigraphic members and transgressive development of younger members. Volcanic rocks within the Słupiec Formation also show a different devel-opment in the east and west. In the east the volcanic rocks are subordinate relative to sedimentary rocks, and they comprise tuffs (largely ignimbrites) and several rhyolitic and trachy-andesitic intrusions, including the Tłumaczów Trachyandesites. In the west the volcanic rocks strongly prevail over sedimen-tary rocks and comprise basic/intermediate and rhyolitic lavas, including the Kamienna Góra Basaltic Trachyandesites and the Góry Krucze Rhyolites.

The Kamienna Góra Basaltic Trachyandesites (Awdan-kiewicz 1997, 1999 a, Awdankiewicz et al., 1998) crop out in the western part of the Intra-Sudetic Basin in the lowermost part of the Słupiec Formation (Fig. 6). This volcanic rock complex is interpreted as a small shield volcano formed due to effusive eruptions of basic/intermediate lavas (SiO2 content around 52 %). The vent area of the volcano was located SE of Kamienna Góra, in the area now covered with younger de-posits. The volcano possibly represented a very fl at cone with a basal diameter of ca. 10-12 km and a height of ca. 100 m. The total volume of erupted lavas can be roughly estimated at

Fig. 5. Geochemical variation of selected trace elements in the volcanic rocks of the Intra-Sudetic Basin. A – Zr-Ti plot (Pearce, 1982). Symbols as in Fig. 1. B – MORB-normalised trace element patterns of the basaltic andesites and the basaltic trachyandesites (normalisation after Pearce, 1983).


Fig. 6. Geological sketch of the Permian deposits in the western part of the Intra-Sudetic Basin (based on Awdankiewicz, 1999 a, b, Bossowski and Czerski, 1987, 1988, Don et al., 1981 a, b, Grocholski, 1994, Mastalerz et al., 1995 a, b, Tasler et al., 1990, 1995).

GeoLines 15 (2003) 23

1-4 km3. The lavas represented various types (aa, pahoe hoe and block lavas, Fig. 7) and some lava fl ows carried abundant sedimentary xenoliths and lava-sediment breccias refl ecting interaction of hot lava with wet, poorly consolidated sediments in the basal part of fl ows and in their vent area. Sporadic explo-sive (phreatomagmatic?) eruptions resulted in the deposition of up to 1 m thick laminated tuff layers between successive lava fl ows. Intercalations of sandstones and mudstones accumulated between successive eruptive products, in particular in the distal parts of the volcano. Various lavas with sedimentary and pyro-clastic intercalations are exposed at Stop 3.

Correlation of successive lava fl ows in well exposed sec-tions (Fig. 8) shows a general westward younging of the fl ows. Possibly, the volcano formed on an easterly inclined palaeos-lope (Fig. 9). Consequently, the oldest lavas fl owed to the east, and younger fl ows were successively shifted to the north and west due to accumulation of lavas and aggradation of relief east of the vent. In the latest stages of activity the vent pos-sibly shifted SW-wards, as suggested by the distribution of the youngest lavas near Przedwojów.

The Góry Krucze Rhyolites represent the major com-ponent of the Słupiec Formation on the western limb of the Intra-Sudtic Basin, found above the Kamienna Góra Basaltic Trachyandesites. The rhyolites show an asymmetric thickness variation and a strong lithological variation, with the southern and central areas dominated with massive to laminated lavas, and vesicular lavas and abundant rhyolitic breccias in the north-ern part (Figs 6 and 10). The breccias formed by autoclastic processes and epiclastic redeposition of rhyolitic debris.

This rock complex refl ects a major effusive eruption of acidic lavas with total volume of several tens of cubic kilo-metres. The rhyolitic lavas possibly erupted from vents near Chełmsko Śląskie and fl owed largely to the north and east. The eruption formed an oval extrusion ca. 15 km in diameter, several hundred metres thick in its proximal part and possibly composed of a few overlapping lobes (Fig. 11).

The formation of the Góry Krucze rhyolitic extrusion cre-ated and intrabasinal high several hundred metres thick in the western part of the Permian Intra-Sudetic Basin. This volcanic edifi ce has then been subjected to a strong erosion. In the south-ernmost part of the edifi ce a distal lava fl ow lacks 30 to 50% of its original thickness and the overlying alluvial deposits contain abundant angular clasts derived form the rhyolitic fl ow (Stop 4). Similar rhyolitic debris and deposits are common within the Radków Formation above the Góry Krucze Rhyolites along

Fig. 7. Types of lava fl ows forming the Kamienna Góra Basaltic Trachyandesite unit and their schematic logs.

Fig. 9. A model of the evolution of the Kamienna Góra Basaltic Trachyandesite complex. The complex is interpreted as a small shield volcano. Lava fl owage directions changed in successive stages of activity (from A to C; comments in the text).


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GeoLines 15 (2003) 25

Fig. 10. A schematic S-N section of the Góry Krucze Rhyo-lite unit.

Fig. 11. A possible reconstruction of the Góry Krucze rhy-olitic edifi ce at a mature stage of its development. At its northern periphery the rhyolitic lavas partly buried the older trachyandesitic shield volcano (the Kamienna Góra Basaltic Trachyandesites).

Stop 1. Miszkowice; natural outcrop northwestwards from the village (Fig. 12).Stratigraphy: Lubomin Formation, Visean.Krzysztof Mastalerz, Leszek Kurowski

A complex of very coarse-grained, sedimentary breccias and associated deposits is exposed along the 500 metres long bluff. The breccias form thick to very thick beds, which dip towards NE at an angle of 25–30°. The beds show usually fl at lower surfaces with no signs of erosive relief. The deposits are very poorly sorted and contain abundant matrix. The matrix-sup-ported grain framework predominates. Common is bimodal

grain size distribution (diamicts). All the components of the grain framework are angular and/or sub-angular. The largest clasts attain 1 metre in diameter. The matrix consists of a sand-mud-granule mixture. There occur a few moulds of large "tree" trunks locally. The deposits do not usually show any evidence of internal organization. Subhorizontal parallel orientation of elongated clasts appears in a few beds. Some of the beds dis-

the whole western limb of the Intra-Sudetic Basin, indicating a substantial erosion of the whole rhyolitic edifi ce.

A different sequence of Permian volcanic events is recorded in the Słupiec Formation in the eastern part of the Intra-Sudetic Basin. In that area volcanism started with a major ignimbrite-forming eruption (ca. 50 km3 dense rock equivalent?) with the formation of pyroclastic deposits over 300 m thick in places. It is suggested that the eruption created a 10 km wide caldera in the Broumov-Nowa Ruda area, which subsequently acted as a depositional centre of the basin (Awdankiewicz, 1998, 1999 a). Younger activity included emplacement of numerous rhyolitic and trachyandesitic laccoliths and sills into sedimentary strata below the pyroclastic deposits along the caldera margin near Rybnica Leśna, Głuszyca, Świerki and Tłumaczów (Stop 5). The Permian volcanism in the Intra-Sudetic Basin ceased after the eruptions of intracaldera basic lavas and acidic pyroclastic deposits near Šonov.


play indistinct inverse-to-normal coarse-tail grading. Gneissic rocks, greenstones and amphibolites are the dominant litholo-gies of the clasts.

The moderately thick bedded, fi ner-grained breccias occur subordinately. They show relatively better sorting. Discoidal and/or elongated clasts are imbricated in places. Some beds dis-play indistinct, channel-like erosive basal contacts. A few thin beds of sandstone to granule-grade conglomerates accompany these breccias. These deposits are moderately to well sorted and can be classifi ed as subgraywackes and lithic arenites. They show indistinct parallel horizontal- and low angle cross stratifi cation.

Most of the beds resulted from gravity fl ow transport and deposition. The matrix-supported, thick-bedded breccias are related to powerful debris fl ows. However, the low content of clay-grade particles within these sediments points against the classic model of the cohesive debris fl ow deposits. Thus, it is doubtful that cohesion was the dominant clast support mecha-nism in these fl ows. Most fl ows resulted in sheet-like bed

forms and the erosive features are confi ned to solitary, shallow scoures. The beds of sand- to granule-grade deposits resulted, most probably, from high-concentration fl uidal fl ows. It was also suggested that some beds have been formed under the up-per fl ow regime conditions as inferred from the antidune-type backset stratifi cation (Teisseyre, 1977).

The sediments exposed nearby Miszkowice accumulated in a proximal zone of an alluvial fan, which was attached to the western marginal fault of the Intra-Sudetic Basin. The very immature detrital material came from the northwest, from the deeply dissected Rudawy Janowickie Range, which was built of crystalline metamorphic complexes. The alluvial fan (“Miszkowice fan”) was an element of the piedmont-like sys-tem which developed in the Visean along the western margin of the basin (Teisseyre, 1975). The clastic material was transferred further eastwards, to the basinal axial zone. The development of the piedmont settings and the resultant thick accumulation wedge, were related to the normal faulting along the western basin edge at the beginning of the Carboniferous.

Fig. 12. Excursion route with stops.

GeoLines 15 (2003) 27

A 20 metre thick sequence exposed in the quarry contains main-ly fi ne conglomerates and pebbly sandstones, which form thick, commonly composite, sedimentary units (Fig. 13). Their bases commonly display distinct erosive relief and contain various sole and fl ame structures. The pebbles reach up to 5-6 cm in di-ameter and show good to moderate roundness. Pebble imbrica-tion appear commonly in conglomerates and pebbly sandstones. Mudstone intraclasts and moulds of plant twigs/logs commonly occur in the lower parts of the beds. Some conglomerates and, most frequently, sandstones display planar- or trough cross stratifi cation. The large-scale sets of inclined cross stratifi ca-tion, with composite internal structure occur only in places.

The fi ner-grained sediments (mudstones and siltstone) are the minor components of the exposed sequence. They form thinner beds which interlayer with and pinch out in conglomer-ates and sandstones. The fi ne-grained deposits commonly show ripple cross lamination. However, the primary sedimentary structures are commonly obscured and /or completely obliter-ated in these deposits due to intense root penetration (Stigmaria sp. with abundant "appendices"). Abundant imprints of pteri-dosperms (leaves, fructifi cations) appears in the beds of thinly, parallel laminated mudstones and siltstones. A mould of a large, thin-shelled bivalve was recently discovered in these deposits.

The sequence of the beds displays cyclic organization. Individual cyclothems are characterized by fi ning upwards grain size. The coarse-grained deposits, frequently with intra-clasts of mudstones, occur above erosive soles. The complete cyclothems contain fi ne-grained deposits with abundant root moulds in their upper parts.

Pebbly and sandy deposits of the exposed sequence have accumulated in fl uvial channels. The large-scale composite inclined stratifi cation is attributed to point bar facies of the high-sinuosity channels. Finer-grained sediments were de-posited in various overbank settings. The rooted horizons are related to periods of intense plant colonization of overbank areas. However, relatively frequent fl ood episodes prevented development of peat bogs. Palaeocurrent indicators suggest that paleoslope was inclined towards the NE. Clastic material was mainly derived from the Rudawy Janowickie Metamorphic Complex. General palaeogeography and distribution of facies suggest that deposition took place in distributary channels

and overbank areas of a large delta plain. The occurrence of bivalves was related to the development of the brackish-marine embayments between individual depositional lobes.

Stop 2. Kamienna Góra; old quarry in the SW part of the town (Fig. 12).Stratigraphy: Szczawno Formation (upper Visean).Krzysztof Mastalerz, Paweł Raczyński, Leszek Kurowski

Fig. 13. Facies relationships of the Upper Visean fl uvial/deltaic sequence of the Szczawno Formation exposed near Kamienna Góra (Stop 2; southeastern wall of the quarry).


Locality 3 comprises three abandoned quarries located on the southern slopes of Łysina Hill near Czadrówek, on the SE pe-ripheries of Kamienna Góra (Figs 6 and 12). The volcanic rocks exposed there are distinguished as the Kamienna Góra Basaltic Trachyandesites and represent the lowermost member of the Słupiec Formation in that part of the Intra-Sudetic Basin. The geology, petrography and geochemistry of these volcanic rocks are characterised in detail in Awdankiewicz (1997, 1999 a, b) and Awdankiewicz et al. (1998).

The volcanogenic sequence at locality 3 (Figs 14 and 15) is ca. 30-40 m thick and dips gently to the SE. The sequence con-sists of three successive lava horizons with sandstones and tuffs interbedded between the two lowermost lava fl ows (Fig. 16). The most complete section can be observed in northernmost of the three quarries.

The lowermost lava fl ow is ca. 8-10 m thick and consist of massive lavas in its lower part grading upwards into vesicular lavas and breccias of vesicular lavas. The top of the fl ow is uneven and cracked. Above, nearly 1.5 m thick sequence of sedimentary and pyroclastic rocks is found, including:

· 20–40 cm thick brown, poorly consolidated, laminated sand-stones composed largely of vesicular basaltic trachyandesite clasts,

· a 1.5 cm thick layer of green sandstone devoid of volcano-genic clasts,

· ca. 100 cm thick brown and white, laminated tuffs. Lamination is lacking adjacent to the overlying breccias and in places the tuffs are cut by clastic dykes of green sandstones.

The main part of the section represents a 25 m thick lava fl ow of a complex structure. Its inner portion consists of mas-sive lavas grading upwards into vesicular to amygdaloidal lavas, and the outer parts are composed of lava-sandstone brec-cias. The basal breccias are 20–100 cm thick, and the top brec-cias are 5–10 m thick. In general, the breccias consist of lava blocks in a sedimentary matrix, or the opposite, and a strong variation of clast sizes, shapes and arrangement is observed. In places the lavas host sedimentary rafts up to 0.5×8 m large as well as numerous clastic dykes (Fig. 17). In the upper part of the described fl ow specifi c forms of lava are locally found. These are oval in shape with a diameter of 5 to 20 m and con-sist of massive lavas mantled by vesicular lavas. The largest one in the northern quarry shows radial and concentric joints (Fig. 15, section 1), and another one in the southern quarry shows U-shaped platy joints along the margins (Fig. 15, sec-tion 3). These forms, best exposed on NE-SW trending quarry walls, are interpreted as diagonal sections of NW-SE aligned lava-fi lled tubes.

The uppermost part of the described section comprises a discontinuous horizon of several 1–5 m thick fl ows composed of massive to vesicular lavas. The bases of the fl ows are sharp and uneven, refl ecting the morphology of their basement. These lavas possibly form aligned lobes with a variable, wind-ing orientation.

The rock succession at locality 4 is interpreted as a se-quence of lavas with minor pyroclastic and sedimentary rocks accumulated in a proximal part of a small shield volcano. Location of the eruptive centre of the volcano within 1–2 km E-SE of the locality (Fig. 8) is inferred from indirect geological relationships within the Kamienna Góra Basaltic Trachyndesite unit, and it is consistent with transport directions of tuffs and lavas inferred from structures at this locality (see below). The sedimentary rock found within the sequence and as various xenoliths within the fl ow (in breccias, as rafts and clastic dikes) are tentatively interpreted as alluvial deposits equivalent to the Walchia shales of the Słupiec Formation.

The described sequence formed due to essentially two eruptions separated with a relatively long quiescence period. The fi rst eruption was effusive and resulted in the emplacement of aa-type lava fl ow forming the lowermost part of the section. These lavas were subjected to a prolonged subaerial exposure and weathering. Redeposition of loose lava fragments resulted in accumulation of the overlying brown, poorly consolidated volcanogenic sandstones composed of the local material. The following thin layer of green sandstones represents an “exter-nal” alluvial deposit, lacking the local volcanic debris.

The second eruption started with an explosive (freatomag-matic?) phase with the deposition of the laminated tuffs.

Stop 3. Czadrówek near Kamienna Góra; abandonned quarries on the southern slopes of Łysina Hill (Fig. 12).Stratigraphy: Słupiec Formation, Kamienna Góra Basaltic TrachyandesitesMarek Awdankiewicz

Fig. 14. A log of the volcano-sedimentary succession at local-ity 3 (Czadrówek).

GeoLines 15 (2003) 29

Subhorizontal lamination and poorly developed low-angle cross lamination of the tuffs suggest deposition by a pyroclastic surge, with possible NW-ward transport directions. The next phase of the eruption was effusive and a thick, aa-type fl ow forming the major part of the described section was erupted. The lava-sandstone breccias, sedimentary xenoliths and clastic dikes abundant in the fl ow resulted from the interactions of lava with wet, poorly consolidated sediments. These interactions possibly occurred in the vent area, where lava must have bro-ken through a sedimentary cover, and at the base of the fl ow on its way down slope. The lava interacted also with the tuffs and sediments at the visited locality, causing homogenisation of the

tuffs within ca. 10 cm near the tuff-basal breccia contact and formation of sandstone dikes in the tuffs. The SE-NW aligned lava structures within the fl ow are interpreted as lava-fi lled tubes - former feeder channels of the lava fl ows – and suggest NW-ward lava fl owage (the fl ow sense cannot be directly deter-mined but it is constrained by geological relationships).

The fi nal, waning phase of the eruption was still effusive and resulted in the emplacement of a thin, discontinuous horizon of pahoe-hoe type fl ows found at the top of the sec-tion. The pahoe-hoe lavas fl owing over a rugged top of the underlying xenolitic aa fl ow preferentially fi lled depressions in the latter.

Fig. 15. Sketches of selected quarry walls at Stop 3 (Cza drówek).


The volcanic rocks exposed at Stop 4 are distinguished as the Góry Krucze Rhyolites and represent the main rock unit of the Słupiec Formation in that part of the Intra-Sudetic Basin. The rhyolites are unconformably overlain by sedimentary rocks of the lowermost part of the Radków Formation. The contact of these two formations is well exposed (Awdankiewicz et al., 1998).

The volcano-sedimentary sequence at locality 4 (Fig. 18) is ca. 25 m thick and dips gently to the north-east and east. The lower 20 m represents a rhyolitic lava fl ow which consist of two lithologically and structurally distinctive parts. The lower part of the fl ow, 5-10 m thick, consists mainly of strongly al-tered, brown and greenish, laminated lavas with sparse feldspar phenocrysts. Macroscopically these rocks resemble a poorly consolidated mudstone, and preliminary XRD and DTA deter-minations suggest alkali feldspars and smectite-type mineral as the main components. The upper part of the lava fl ow, ca. 10 m thick, is composed of pink-coloured, massive to laminated, sparsely porphyrytic rhyolites with prismatic and platy joints.

The boundaries of the lower, altered rhyolites with the up-per, fresh rhyolites, are sharp, but in a transitional zone these two lithologies interdigitate (Fig. 18). Other lithologies found in the boundary zone are spheroidal rhyolites (containing abun-dant spherical structures up to 5 cm in diameter) and vesicular rhyolites. Well developed fl ow folds are characteristic of the lower to middle part of the rhyolitic fl ow (Fig. 19), and are less common in its upper part. Autoclastic breccias composed of angular rhyolite clasts are observed locally. In addition, hydro-

Stop 4. Okrzeszyn; abandonned quarry north of the Okrze-szyn village (Figs 6 and 12)Strarigraphy: Słupiec Formation, Góry Krucze Rhyolites.Marek Awdankiewicz

Fig. 16. Basaltic trachyandesite lavas with ca. 1.3–1.5 thick intercalation of sandstones and tuffs. The photo-graphs shows the interval from ca. 5 to 12 m from the log in Fig. 14.

Fig.17. Sandstone xenoliths (light, with platy joints) in massive to vesicular basaltic trachyandesites (dark). Largest xenoliths, up to ca. 1 m in diameter, can bee seen near the centre and in the lower right parts of the photograph. Thin clastic dykes and trails of aligned small xenoliths are found between the large xenoliths (e.g. left of the hammer).

Fig. 18. A log of the rhyolitic lavas and the overlying sedi-mentary rock at Stop 1 (Okrzeszyn).

GeoLines 15 (2003) 31

thermal mineralisation (calcite, barite, malachite) is found as veins and breccia cement in the lower part of the fl ow.

The rhyolites are overlain by a 5 m thick complex of brown to green rhyolitic breccias, sandstones and mudstones (Fig. 20). The breccias form a lensoidal bed ca. 2 m thick and 50 m wide which seems to fi ll a wide, shallow depression within the rhy-olitic fl ow. The breccias consist of angular rhyolite clasts up to 10 cm long set in a sandy to muddy matrix and show a chaotic structure, and in places subhorizontal lamination, imbrication of rhyolite clasts and cross lamination. The sequence above, ca. 4 m thick, consists mainly of laminated sandstones and mud-stones with a 0.5 m thick breccia bed.

The volcano-sedimentary sequence at locality 4 documents effusive rhyolitic volcanism and subsequent processes of ero-sion and sedimentation at the southern edge of the Góry Krucze rhyolitic extrusion.

The rhyolitic lava fl ow at locality 4 shows many features typical of acidic lavas worldwide, including fl ow lamination and folds, autoclastic breccias and, in particular, a vertical lithological variation. A characteristic feature of many rhyolitic lava fl ows are glassy, obsidian margins mantling “stony”, crys-talline interior. This zonal structure apparently develops due

to a faster cooling of fl ow margins. At the visited locality the strongly altered “mudstone-like” rhyolite in the lower part of the section is interpreted as a basal glassy (obsidian) layer of the fl ow, devitrifi ed, decomposed and replaced with alkali feld-spars and clay minerals due to weathering and/or hydrothermal processes. The fresh rhyolites (including the spherolidal vari-ety) found above represent the interior of the lava fl ow, formed at a slower cooling rate. Apparently, the upper glassy layer of the fl ow is lacking here. This, together with abundant local rhyolitic debris in the overlying deposits indicate that the upper part of the fl ow (the whole glassy layer and partly the crystal-line layer, representing 30-50 % of the original fl ow thickness ?) was removed by erosion.

The sedimentary complex above the rhyolites is tentatively interpreted (Awdankiewicz et al., 1998) as an alluvial deposit, composed of interbedded channel deposits (breccias) and over-bank deposits (sandstones, mudstones), with poorly developed soil horizons in places. The depositional structures suggest the NE-ward transport. The clastic material of the deposits is large-ly local and derives from the underlying rhyolites, as indicated by lack of rounding and petrographic features of the clasts.

Fig. 19. A layer of platy-jointed, fl ow-folded, and locally au-tobrecciated rhyolite within strongly altered obsidian in the lower part of the lava fl ow at Okrzeszyn.

Fig. 20. Eroded top of the rhyolitic lava fl ow at Okrzeszyn overlain by breccias, sandstones and mudstones.


Stop 5. Tłumaczów; quarry of trachyandesites (Fig. 12).Stratigraphy: Słupiec Formation (Building Sandstone member); Tłumaczów Trachyandesites (Rotliegend).Krzysztof Mastalerz, Paweł Raczyński, Leszek Kurowski, Marek Awankiewicz

The quarry pit exposes a few tens of metres thick section of vol-canic rocks and associated siliciclastic deposits. The volcanic rocks, of trachyandesitic composition, form a shallow-level subvolcanic intrusion (laccolith?). The contacts of this body are generally conformable with bedding in enveloping deposits. However, distinct disturbances occur locally in the surrounding sedimentary strata. The sedimentary rocks show evidence of a weak thermal alteration and brecciation along the contacts with volcanic rocks.

The sedimentary rocks exposed in the quarry comprise reddish-brown fi ne clastics and sandstones. Ripple cross lamination is the dominant primary structure in these rocks. The upper surfaces of the beds commonly display wave ripple morphology. Some sediments reveal parallel horizontal lamina-tion. Mud-crack polygons and raindrop imprints are commonly found on the lamination surfaces. The primary structures are commonly obliterated due to bioturbation and/or cementation.

Numerous imprints of the Walchia twigs and fructifi cations constitute the most common record of fossil organisms. There were also discovered footprints of reptiles and/or amphibians preserved in these deposits.

Sediments exposed in the quarry have accumulated on a mud-sand fl at closely related to the shore of a shallow, most probably, ephemeral lake. The water level in the lake varied frequently and its oscillations are well documented by the close association of the structures of subaerial exposure (mud cracks, raindrop imprints, footprints and trackways) and wave ripples. The development of the fl at onshore plain was, most probably, related to accumulation of the clastic material derived from the SE. The local shoreline was directed from the NNE to SSW as inferred from the wave ripple orientation. The fresh, unconsoli-dated sediments were, most probably, subsequently invaded by the thick, sill-like intrusion of basaltoids.

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