The Early palaeozoic intracontinental rifting and incipient oceanic lithosphere development in the central West Sudetes (NE Bohemian Massif): the geochemistry of metabasites of the East Krknoše (Karkonosze) Complex

František Patočka¹ & Witold Smulikowski²

¹ Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 00 Praha 6, Czech Republic; pat@gli.cas.cz
² Institute of Geological Sciences, Polish Academy of Sciences, Ul. Twarda 51/55, 00-818 Warszawa, Poland; wsmulik@twarda.pan.pl

Key words: metabasites, petrography, geochemistry, Early Palaeozoic, intracontinental rift, oceanic basin, West Sudetes, Bohemian Massif, Variscides.

Abstract
Low- to medium-grade metabasites are the most abundant metaigneous rocks in the Early Palaeozoic metavolcanic (ąmetasedimentary) East Krkonoše (Karkonosze) Complex located at the Czech/Polish border in the central West Sudetes (NE Bohemian Massif). These mafic rocks are interpreted as metamorphosed equivalents of basic magmatites – both volcanics (lavas and pyroclastics) and subvolcanic intrusives. The correlation of lithostratigraphic units defined in the Czech (southern) and Polish (central and northern) parts of the East Krkonoše Complex is based on a comparison of the geochemical characteristics and petrography of the metabasites:
(1) The greenschists to greenstones (associated with abundant felsic metavolcanics) of the Czech East Krkonoše Complex, which are finely interfingered with low-grade metasediments, are correlated with the amphibolites forming small- to medium-sized bodies in medium-grade metasediments of the Polish East Karkonosze Complex. Both the low- and medium-grade metabasites are interpreted as comprising a range of metamorphosed tholeiitic, transitional and alkaline WPBs.
(2) The largest mafic rock suite, which dominates the Polish part of the East Krkonoše Complex, has a dismembered promontory along the eastern margin of the East Krkonoše Complex Czech component. Most of these mafic rocks (blueschists, greenschists, greenstones and amphibolites) correspond to N- and E-MORBs.
The above groups of rocks are broadly coeval and geochronologically overlap the Cambrian/Ordovician boundary. The similarity in magmatic ages and the diversity in geochemical features suggest that the East Krkonoše Complex metabasites are evidence for intracontinental rift development and the subsequent generation of incipient oceanic basin lithosphere in the NE Bohemian Massif during the Early Palaeozoic. Provided that the East Krkonoše Complex metabasites can be matched with similar rock suites in the West and Central European Variscides, their magmatic origin may be related to the rifting of northern Gondwana and large-scale break-up at the beginning of the Palaeozoic.

Geologia Sudetica, 33 (1): 17-22.

The granitoids of the Lipowe Hills (Fore-Sudetic Block) and their relationship to the Strzelin granites

Teresa Oberc-Dziedzic¹ & Christian Pin²

¹ Instytut Nauk Geologicznych, Uniwersytet Wrocławski, M.Borna 9, 50-204 Wrocław
² Département des Sciences de la Terre, 5, rue Kessler, 63038 Clermont-Ferrand Cedex

Key words: Fore-Sudetic Block, Lipowe Hills crystalline complex, Variscan granitoids, Rb/Sr dating.

Abstract
Muscovite-biotite granites, medium-grained biotite tonalites and fine-grained granodiorites from three boreholes situated in the middle part of the Lipowe Hills were characterized. It was found that the muscovite-biotite granites from the boreholes correspond to the Górka Sobocka granite known from the northern part of the Lipowe Hills. This granite was in turn compared to the light coloured granitoids, the so-called Gębczyce and Biały Kościół granites, from the Strzelin crystalline massif. The age link between the muscovite-biotite granites from the Lipowe Hills crystalline complex and those from the Strzelin massif was confirmed by the result of the whole-rock Rb-Sr analyse of a muscovite-biotite granite sample collected in the Górka Sobocka quarry. This result plots on the isochron obtained previously for the muscovite-biotite granites from the Strzelin and Gębczyce quarries at ca 330 Ma, with an initial 87Sr/86Sr ratio of 0.7055.

Geologia Sudetica, 33 (1): 23-31.

A rare mineral-bearing pegmatite from the Szklary serpentinite massif, the Fore-Sudetic Block, SW Poland

Adam Pieczka

University of Mining and Metallurgy, Department of Mineralogy, Petrography and Geochemistry, al. Mickiewicza 30, 30-059 Kraków, Poland; pieczka@uci.agh.edu.pl

Key words: Szklary, serpentinite, pegmatite, rare minerals.

Abstract
In the Szklary serpentinite massif, besides serpentinites, amphibolites, rare rodingites and altered gabbros, rather common light-coloured aplites occur. Occurrences of pegmatites are very rare. A small fragment of a pegmatite, basically composed of feldspars, quartz, micas and tourmaline, is exposed only on Mt. Szklana. During detailed mineralogical investigations on it, numerous and sometimes rare or very rare minerals have been identified: chrysoberyl, spessartine, manganocolumbite and manganotantalite, stibiocolumbite, holtite, pyrochlore, beusite, paradocrasite and stibarsen, manganoan apatite and others, occurring in small or very small grains. The pegmatite from Szklary probably represents a product of the crystallization of silicic magma generated from the partial melting of older sediments during high-grade metamorphism. Its structural and textural development (graphic intergrowths), and to some extent its mineral composition make it comparable to some anatectic pegmatites of the gneissic block of the Góry Sowie Mts.

Geologia Sudetica, 33 (1): 33-48.

Genetic relationships between metabasalts and related gabbroic rocks: an example from the Fore-Sudetic Block, SW Poland

Kazimierz Dziedzic¹ & Helena Dziedzic²

¹ Instytut Nauk Geologicznych, Uniwersytet Wrocławski, 50-205 Wrocław, Cybulskiego 30
² Polska Akademia Nauk, Instytut Nauk Geologicznych, Zakład Geologii Sudetów, Podwale 75, 50-449 Wrocław, Poland

Key words: Sudetes, Variscan, metabasalts, gabbro, trace elements, geochemical modelling, granulite facies metamorphism.

Abstract
The metabasalts occurring within the gneisses of the eastern part of the Góry Sowie gneiss block, have either enriched or depleted LREE patterns. However, these two types of metabasic rock are indistinguishable in terms of their major elements and many trace elements. Their intimate association indicates that their parent magmas erupted nearly contemporaneously. They originated through the decompressional, two-stage incremental melting of a mantle diapir source. The LRRE enriched variety of the basalts was formed from a spinel/garnet peridotite melt mixture which was followed by spinel peridotite melts. From the latter melts, cumulate gabbros crystallized and extracted portions of these melts provided the LRRE depleted variety of basalts. This strongly suggests that the metabasalts are compatible in age with the gabbros.
Both of the metabasalts varieties developed mainly by AFC processes involving mantle source melts and lower continental crust components. From a comparison of these metabasalts with those in adjacent areas, it is possible to draw the conclusion that volcanic activity in the whole region had the same time-span.
The metabasalts were metamorphosed to LP hornblende granulites, synchronously with the surrounding amphibolite facies gneisses of the margins of the Góry Sowie Block, which were metamorphosed to LP-HT cordierite gneisses. They originated due to the transition from high-grade amphibolite to granulite facies conditions associated with a near-isothermal decompression, during the time of the late Variscan (Carboniferous).

Geologia Sudetica, 33 (1): 49-65.

Heavy minerals in the Carboniferous sediments of the Intra-Sudetic Basin as palaeogeographic indicators

Elżbieta Felicka

Instytut Nauk Geologicznych Uniwersytetu Wrocławskiego, Cybulskiego 30, 50-205 Wrocław, Poland

Key words: heavy minerals, alimentary areas, Carboniferous, Intra-Sudetic Basin.

Abstract
The Intra-Sudetic Basin, a Variscan intramontane trough in the central Sudetes (NE part of the Bohemian Massif), is filled with Carboniferous, Permian, Triassic, Upper Cretaceous and Cenozoic deposits. The Carboniferous sediments display considerable lateral and vertical facies variation, which reflects intense synsedimentary, tectonic and volcanic activities. The sedimentary material was transported from various directions, and both the pebble lithology and the heavy minerals present are good palaeogeographic indicators of the alimentary areas.
This paper presents the results of heavy mineral analyses of the Carboniferous deposits of the Intra-Sudetic Basin and discusses the possible usage of the heavy mineral spectra as palaeogeographic and stratigraphic indicators. Samples representing all the Carboniferous formations were taken along two profiles: between Ciechanowice and Kamienna Góra (profile W), and between Sady Górne and Głuszyca (profile E).
The heavy mineral analyses show the variation of the heavy fraction, both in the stratigraphic column and laterally. The Upper Tournaisian sediments display a characteristic heavy mineral assemblage: epidote, biotite, and chlorite - pointing to the Kaczawa Mts as the source area. In the Visean sediments, a clear regional distinction can be seen: in profile W there are no significant differences compared to the older sediments; in profile E - garnet appears as a major component, pointing to possible transport from the Góry Sowie Block. In the Upper Visean, the regional differences disappear, probably as a result of redeposition of the older material. There is an important change in the mineralogy of the heavy fraction in the middle part of the Biały Kamień Formation. A considerable decrease in the garnet and ZRT (zircon+rutile+tourmaline) -mineral content is observed, and minerals formed during diagenesis (e.g. haematite) and/or hydrothermal processes (barite and siderite), become more abundant.
The chemical composition of some minerals (especially garnet and chlorite) appears to be very useful for establishing the alimentary areas. The garnets of the Ciechanowice and Lubomin Formations are rich in Grs and resemble the garnets from the contact-metamorphic basic rocks of the Rudawy Janowickie (garnets rich in Sps, typical of HP rocks of the eastern cover of the Karkonosze Pluton, were not found). In the Sady Górne Formation, garnets similar to those from the gneisses and migmatites of the Góry Sowie Block are the most common (a few grains rich in Sps, typical of low-grade metamorphic rocks are also found). The younger deposits display a wide variation of garnet formulae, which indicates various source areas and an important role of resedimentation.
The heavy mineral analyses confirm that the alimentary areas for the oldest sediments of the Intra-Sudetic Basin were the Kaczawa Mts and the eastern cover of the Karkonosze granite, whereas for the younger deposits, most probably, there was not a single source area; rather the materials derived from different sources and were redeposited. The distinct change in the heavy mineral spectra in the middle part of the Biały Kamień Formation suggests an important change in the factors controlling sedimentation in the basin. The heavy mineral analyses, in general, confirm previous interpretations based on sedimentological research; however, the direct transport from the Góry Sowie Block area is questionable (apart from garnets, other minerals typical of the rocks of that area do not occur).

Geologia Sudetica, 33 (2): 71-83.

The petrology and geochemistry of mantle-derived basic and ultrabasic rocks from the Szklary massif in the Fore-Sudetic Block (SW Poland)

Piotr Gunia

Instytut Nauk Geologicznych Uniwersytetu Wrocławskiego, Zakład Mineralogii i Petrologii, Pl. M. Borna 9, 50-204 Wrocław, Poland; guniap@ing.uni.wroc.pln

Key words: ultrabasites, serpentinites, amphibolites, plagiogranites, petrology, geochemistry, Szklary, Fore-Sudetic Block.

Abstract
This paper presents the results of petrological investigations of rocks from the Szklary serpentinite massif in the eastern margin of the Góry Sowie Block. Among the weakly serpentinised ultrabasites present, harzburgites, lherzolites and pyroxenites have been distinguished. Small enclaves of metabasites within the serpentinites represent low-Ti varieties and - like rodingites - they developed from initial gabbroides or picrites. They reveal a characteristic depletion in incompatible elements. This feature is reminiscent of high-Mg (boninite) basic magmas formed in island arc or back-arc basin environments. Plagiogranites, present within the serpentinites, most probably represent trondhjemites - more acid derivates formed during the fractional crystallisation of the same initial basic magma.
On the basis of the petrological investigation results, the hypothesis was put forward that - with regard to their initial composition - the ultrabasites of the Szklary massif may represent heterogeneous spinel residual peridotites impregnated with pyroxenite veins. Enclaves of metabasites and plagiogranites, having the properties of mafic cumulates and/or fractional differentiates, may reflect a stage of further magmatic processes which took place in a zone of lithospheric plate convergence.

Geologia Sudetica, 33 (2): 85-105.

Layer silicates from Szklary (Lower Silesia): from ocean floor metamorhism to continental chemical weathering

Elżbieta Dubińska¹, Boris A. Sakharov², Grzegorz Kaproń¹, Paweł Bylina³ & Jan A. Kozubowski ⁴

¹ Warsaw University, Faculty of Geology, Institute of Geochemistry, Mineralogy and Petrology, al. Żwirki i Wigury 93, 02–089 Warsaw, Poland; dubinska@geo.uw.edu.pl, kapron@geo.uw.edu.pl
² Institute of Geology, Russian Academy of Sciences, Pyzhevsky per. D7, 107017 Moscow, Russia;  sakharov@ginran.msk.su
³ Institute of Geological Sciences, Polish Academy of Sciences, Twarda 51/55, 00-818 Warsaw, Poland; bylina@twarda.pan.pl
⁴ Warsaw Technical University, Department of Material Engineering, Narbutta 85, 02-524 Warsaw, Poland; jankozu@inmat.pw.edu.pl

Key words: Szklary, Ni-layer silicates, corrensite, serpentine-smectite, nickeliferous laterite, kerolite-pimelite, sepiolite, clintonite, chlorite.

Abstract
The weathering crust at Szklary is known as a classical location of a nickeliferous laterite deposit derived from the chemical weathering of ultrabasic rocks. The layer silicates from the Szklary massif have been studied since the eighteenth century; moreover, this locality is considered to be an exceptional location of different minerals including nickel containing corrensite, interstratified kerolite-stevensite, interstratified serpentine-smectite, kerolite-pimelite, and clintonite. Ni-corrensite and irregularly mixed-layer serpentine-smectites with a variable layer ratio were found in Szklary for the first time.
The origin of the layer silicates from Szklary is complex: (1) serpentine, chlorite, and clintonite are products of hydrothermal metamorphism related to the serpentinization of ultramafic rocks and posterior metamorphism and (2) the mixed-layer minerals, sepiolite, and kerolite-pimelite formed due to the hydrothermal and supergeneous alteration of ultrabasic rocks and various metamorphic schists.

Geologia Sudetica, 33 (2): 107-130.

Pokrywa zwietrzelinowa masywu Szklar i jej niklonośność
[The Szklary massif nickel-bearing weathering cover]

Jerzy Niśkiewicz

Instytut Nauk Geologicznych Uniwersytetu Wrocławskiego, Pl. Maksa Borna 9, 50-204 Wrocław, Poland

Key words:serpentinite weathering, metamorphic rock weathering, magmatic rock weathering, nickel-bearing capacity, Szklary massif, Fore-Sudetic Block.

Abstract
The thickness of the weathering cover on the Szklary Massif ranges from zero (no cover) to 76 metres. The weathered rock forms troughs and sinks of different shapes and depths. Its form indicates that a fissure network played an important role in the evolution of the weathering processes. The fissures allowed the weathering processes to penetrate deeply. The weathering cover is composed of alteration products of three rock varieties: serpentinites, metamorphic and magmatic rocks. The author distinguished 9 varieties of serpentinite, 6 varieties of metamorphic rock and 3 varieties of magmatic rock weathering covers. The thickness of these covers ranges from several cm to 47.9 metres. The weathering cover types of the three different rock varieties generally have sharp boundaries, while within a given rock variety, the weathering cover types have boundaries which, as a rule, are poorly expressed.
The nickel in the weathered rocks of the Szklary massif is genetically related to serpentinite rocks containing from 0.18 to 0.28 wt % Ni. The largest nickel concentration occurs in the weathering cover of the central area, at Mount Szklana Góra. The serpentinite weathering covers are the main centre of nickel concentration, while the metamorphic and magmatic rock weathering covers have higher nickel contents where they are in contact with the serpentinite weathering covers, or if they were within the scope of activity of local nickel-bearing weathering solutions.

Geologia Sudetica, 33 (2): 131-141.

Heavy minerals in the serpentinite weathering cover of the Szklary massif

Michał Sachanbiński, Robert Piórewicz & Roman Michalik

Instytut Nauk Geologicznych Uniwersytetu Wrocławskiego, Pl. Maksa Borna 9, 50-204 Wrocław, Poland

Key words: heavy minerals, the Szklary massif, serpentinite, serpentinite weathering cover, laterite.

Abstract
Forty minerals were identified belonging to the heavy mineral (d > 2.98 g/cm3) suite of the Szklary massif. They are: actinolite, almandine, anthophyllite, apatite, biotite, brunsvigite, chlorite, chromite, chrysolite, zircon, enstatite, epidote, ferroplatinum, goethite, haematite, hornblende, clinochlore, leucoxene, magnesioferrite, magnetite, magnesite, molibdenite, monacite, muscovite, niggliite (PtSn), olivine, orthopyroxenes, an osmium-bearing phase (Ba₂CaOsO₆), native palladium, pyrope, native platinum, pleonaste, rutile, native silver, talc, tremolite, trevorite, tourmaline, native gold and zoisite. The mineralogical characteristics of the most common phases are presented in this paper, and three paragenetic groups of heavy minerals are distinguished.