Geochemical Evidence for Progressive, Rift-Related Early Palaeozoic Volcanism in the Western Sudetes

Journal ofthe Geological Society, London, Vol. 151, 1994, pp. 91-109, 10 figs, 3 tables. Printed in Northern Ireland

Geochemical evidence for progressive, rift-related early Palaeozoic volcanism in the western Sudetes

H. FURNES', R. KRYZA2,A. MUSZYNSK13, C. PIN4 & L. B. GARMANN' 1Geological Institute, University of Bergen, Allegt. 41, 5007 Bergen, Norway 21nstitute of Geological Sciences, University of Wroclaw, Cybulskiego 30, 50-205 Wroclaw, Poland 'Institute of Geology, Adam Mickiewicz University, Mako'w Polnych 16, 60-665 Poznan, Poland 4Universite' B. Pascal, U.R.A. 10 CNRS, 5, rue Kessler, 63038 Clermont-Ferrand, France

Abstrack The volcanigenicrocks of the KaczawaMts (western Sudetes, Poland), in theeastern Variscides, show changing geological and geochemical evolution during early Palaeozoic time. The lower part of the succession (Cambrian (?)-Ordovician) has three components. 1. Shallow marine to subaerial metabasalts, associated with limestones and volcaniclastics. The lavas are dominantly of a transitional tholeiitic-alkaline type and their trace element patterns typically represent a rift-related environment. They pass laterally (and upwards ?) into more depleted basalts resembling enriched MORB, with Nd-isotopic characteristics indicating contamination by continental crust. 2. Interlayered rhyodaciticlavas and volcaniclastics which show negative values, suggesting formation of the original magma by crustal melting. 3. An overlying alkaline bimodal suite of lavas and volcaniclastic rocks, as well as alkaline metabasites of shallow-intrusive character. The geochemistry of the latter resembles oceanic island volcanics, but they may well have been emplaced in the same evolving rift environment. The upper part of the Kaczawa succession, Ordovician-Silurian (?) in age, comprises a thick and monotonous sequence of deep-marine pillowed and massive metabasalts, associated with black shales and cherts. These lavas exhibit MORB trace element characteristics, with minor evidence of crustal contamination. During this stage of rifting, true oceanic crust probably formed. It is thus suggested that the studied part of the Kaczawa succession developed in a progressively evolving rift, initially within an ensialic environment, and finally reaching the stage of a basin underlain by oceanic-type crust. Together with similar Cambrian-Ordovician volcanic-sedimentary associations, widely distrib- uted in western Europe, from Portugal, through France and Germany, they represent a recordof the Early Palaeozoic rifting in the northern periphery of Gondwana.

The Variscan belt of Europe has recently been interpreted Theseand other questions may besolved through the asa complex obduction-collision belt, resulting fromthe establishment of stratigraphic and structural relationships of closure of Palaeozoicbasins during Ordovician to early volcanicand sedimentary successions, combined with Carboniferoustimes (Franke 1989; Neugebauer 1989; Pin geochemicalcharacterization. Indeed, detailed studies of 1989, 1990; Matte 1991). The continental collision, between time-equivalent, volcanic rocks from both the Saxothuring- Africaand Baltica, might have begun around380Ma, as ianand Rhenoherzynian zones, have shown striking inferredfrom Barrovian metamorphism and anatexis of similarities in their geochemicalevolution (Floyd 1982; continentalcrust at that time, recorded along the orogen Wedepohl et al. 1983; Grosser & Dorr 1986; Narebski et al. (e.g. Matte 1991). 1986; Bankwitz et al. 1989; Furnes et al. 1989; 1990; Kramer Incontrast tothe relatively well understoodpost- & Werner 1989; Munha et al. 1990; Prichystal 1990). collisional history of the Variscides, the record of which is This study provides major and trace element, andSm-Nd found mainly within weakly or unmetamorphosed volcanic- isotopic dataon greenschist-faciesmetamorphic volcanic sedimentary successions of the Saxothuringian and Rheno- rocks of the Kaczawa Mts in the western Sudetes, at the NE hercynianzones (Fig. la, insetmap), the pre-collisional edge of theBohemian Massif (Fig. la). Wepresent history of thisorogenic belt is still difficult to unravel. representative geochemical data from the whole area, and Difficulties mayarise due to: (1) the high metamorphic theseare discussed in the light of the recentlypublished grade of the early Palaeozoic rocks in the internal zones of geological,lithostratigraphic, and petrological background the orogen (including Saxothuringian) obliterating their age, (Baranowski et al. 1990; Kryza & Muszynski 1992; Kryza (2) ambiguousgeochemical character of volcanicrocks of 1993a; Muszynski in press). uncertain or unknownage, and (3) uncertain primary geographical relationships between different areas, and not clearly understood kinematics of early tectonic movements. Geological setting The main targets to which attention is focused include: The westernSudetes area displaysa mosaic composed of (a) time and opening of early Palaeozoic basins and their several suturedmetamorphic blocks amalgamated with relationships tothe Cadomian basement, (b) size of the Variscangranites. hasItbeen correlated with the basins and their possible development into basins underlain Saxothuringian zone (e. g. Kossmat 1927; Franke 1989), but by oceanic-type lithosphere, and (c) time and mechanism of the complex structureand important tectonic boundaries their closure. with adjacent areas are the reasons why many authors refer 91

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Fig. 1. (a) Simplified geological mapof the Kaczawa Mts, showingthe subdivi- sion of the sequence into tectonic units and sample location. The tectonic units are from north to south: Zlotoryja- Luboradz (ZL), Chelmiec (CH), Rzeszowek-Jakuszowa (W), Swierzawa (S), Bolkow (B), Dobromierz (D), and Cieszow (C). Other abbreviations are: MSF, Marginal Sudetic Fault; MISF, Main Intra-Sudetic Fault; SG, Swierz- awa Graben. Division of tectonic units modified from Teisseyre (1967) and Jerzmanski (1965). S Inset map in upper right corner shows location of the Kaczawa Mts in the European Variscides; BM, Bohe- mian Massif; RH, Rheno-Hercynian Zone; ST, Saxo-Thuringian Zone; MO, Moldanubian Zone, AF, Alpine Front. (Modified after Franke 1989). Inset map in lower left corner showsthe distribution of the above-mentioned tectonic

Yow lavas units. unlts D (L RJ) (a) General profiles through theS, B, Basic intruslves/ D, ZL, CH and RJ units of the Kaczawa Bbimodal lavas (LT) Ordovician Mts. Abbreviations: Or, Ordovician; Sil, Silurian; Dev, Devonian. Grey slates (c) Tentative composite profile through Volcanic sandstones. (GS)I the sequence of the Kaczawa Mts, si1 rhyodacitc volcanics (OR) indicating the development from Cam- Tuifaceous sedments (L brian (?) through to Permian. The vokaniclastics ? Cambrian broken line indicates uncertain strat- Wqcieszow igraphic relationships. Abbreviations: limestmes LT, Lubrza trachytes; GS, Gackowa Pillowed/?subaerial sandstones; OR, Oselka rhyodacites; hasalts 01 units S & (PVC) B PVC, Podgki volcanic complex.

to this area as a separate tectonostratigraphic unit. It was as the relationship to the main tectono-stratigraphic unitsof called Lugicum (Suess 1926; Stille 1951; Malkovsky 1984; theeastern Variscides, remainproblematic (Malkovsky Klominsky 1988; Chaloupsky1989), Sudeticum (Kossmat 1984; Oberc 1987; Chaloupsky 1989; Franke 1989; Don 1927; Misar 1984; Oberc 1987), or Lugosudeticum (Narebski 1990; Aleksandrowski 1990; Matte et al. 1990; Narebski 1990, 1993; Rajlich 1990). 1990; Paszkowski et al. 1990; Rajlich 1990). The Kaczawa Mts area comprises a Palaeozoic low grade The outcrop of epi-metamorphic rocks is divided by the volcanic-sedimentary succession (Fig. la), and has recently Swierzawa Graben(Fig. la), filled with Stephanianand been interpreted by Baranowski et al. (1990) as a fragment Permian molasse, into a northern and a southern part. Both of a Variscan accretionary prism. The succession spans the parts consist of several tectonic units comprising fragments timebetween the Cambrian (?) andEarly Carboniferous, of thrustsheets and, possibly, largernappes, and and has tentatively been correlated with the Bavarian facies polygeneticmelange bodies (Haydukiewicz 1987a, b; of theSaxothuringian zone (Franke 1989). However, its Baranowski et al. 1990). position within the structural mosaic of the Sudetes, as well In spite of considerable recent progress in stratigraphical

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research(Urbanek et al. 1975; Chorowska 1978; Hay- theunits (Haydukiewicz 1987b; Baranowski et al. 1990). dukiewicz & Urbanek 1986; Urbanek & Baranowski 1986), The Radzimowice slates, traditionally regarded as the oldest itis still difficult to establisha precise lithostratigraphic (Eocambrian)rocks of thecomplex (Teisseyre1967), are scheme for larger parts of the area (Baranowski et al. 1990; nowdocumented by conodonts(Urbanek & Baranowski Kryza & Muszynski 1992). Lithologicallogs for the main 1986) as no older than Ordovician; the upper age limit is tectonic units are shown in Fig. lb, and a composite profile unknown, but it is tentatively proposed that they may be of from possible Cambrian through to Permianis shown in Fig. earlyCarboniferous age (Fig. lc).Baranowski (1988) lc.The biostratigraphic controls whichallow tentative interprets them as trench-fill deposits; they probably form a correlations of the profiles are mainly from graptolitic black thrust-bounded tectonic unit separating the Swierzawa and slates of Silurianage (Haydukiewicz 1987a, b,and Bolkow units (Fig. la). references therein). Apart from this, the sequential orderin The volcanic rocks which are dominant in the lower to the logs is based on indications of the younging direction middle part of the succession (Cambrian (?)-Silurian) were preserved in sedimentaryand volcanicrocks (Kryza & found in previousgeochemical work (Narebski 1980) to Muszynski1992), andon fewa conodont findings in represent a rather uniform suite formed in a within-plate, Ordovician andDevonian strata (Urbanek et al. 1975; probablyoceanic-island regime. Morerecent studies Haydukiewicz & Urbanek 1986; Baranowski et al. 1990). (Baranowski et al. 1984; Narebski et al. 1986; Kryza & The lower part of the Kaczawa succession is considered Muszynski 1988; Furnes et al. 1989, 1990) revealeda to be Cambrian (?)-Ordovician in age, and is represented considerable geochemical variation of volcanic rocks within by the sequences of the Swierzawa and Bolkow units (Fig. the sequence and suggested an ensialic rift environment as a lb). Bothsequences comprise composite volcanic- probable emplacement setting. sedimentary rock assemblages, and in particular the Bolkow unit displays pronounced lithological variations. It contains, in ascending order,the followingmain lithological units (Kryza & Muszynski 1992): thick andpredominantly Petrography subaqueous mafic volcanicrocks (Podgorki volcanic Comprehensive petrographic description of the various rock complex),Wojcieszow limestone, rhyodacitic lavas and types compiled in Fig. lc have been provided in a number of volcaniclastics (Oselka rhyodacites)-all threeincluded in papers(e.g. Ansilewski 1954; Narebski 1964; Pacholska the Milek succession. It further contains grey slates, bimodal 1975; Lorenc 1983; Baranowski 1988; Kryza & Muszynski lavas and volcaniclastics(Lubrza trachytes), thelatter 1988; Fumes et al. 1989), and particularly in Kryza (1993a, locally grading upwards into Silurian black slates and cherts, b) and Muszynski(in press). Hence, in this paper only a and, in turn,into siliceous slatesbearing Devonian condensedpetrographic description of the rocktypes for conodonts(Haydukiewicz & Urbanek 1986). theIn which we present geochemical analyses, will be given. Swierzawaunit, some of the above-mentionedlithologies are lacking,while shallow-watera volcanic sandstone Metavolcanic rocks Cambrian (?)-Ordovician age formation(Gackowa sandstone, see Kryza et al. inpress) of appears to be time-equivalent and genetically related to the Oselka rhyodacites. Tuffaceous sedimentary rocks appear as Metabmalts of the Podgorkivolcanic complex. The Pod- intercalations throughout the lower and middle parts of both gorkivolcanic complex comprises themetabasalts at the sequences. lowest parts of the Swierzawa and Bolkow units (Fig. la, b). The stratigraphicalposition of thickgrey slates is In the Swierzawaunit, they are representedmainly by uncertain. They are mostly of turbiditic character and often slightly vesicular,pillowed and massivelavas in the lower host numerous basic sills. In the eastern part of the Bolkow part of the succession, and by shallow-water and subaerial unit,they seem to separate the Mileksuccession and the basaltic flows and hyaloclastites in theupper part. These Lubrzatrachytes, but their thickness varies considerably volcanicrocks are associatedwith shallow-water vol- along this unit. Similar thick sequences of grey slates, locally canigenicsandstones and other tuffaceoussedimentary interlayered with volcaniclastic rocks and intruded by basic rocks. Generally, similar lithologiesare found in the western sills, are found in the Swierzawa,Zlotoryja-Luboradz, part of the Bolkow unit, whilein its central andeastern Chelmiec and Rzeszowek-Jakuszowaunits (Fig. lb). All part, massive and locally pillowed metabasalts predominate, theserocks arethought to be of Ordovicianage, though in association with the Wojcieszow limestones, Oselka rhyo- such anage has been proved by conodonts only in the dacites, and tuffaceous metasediments. Rzeszowek-Jakuszowaunit of Fig. lb (Urbanek et al. Ingeneral, all thesemetabasalts are petrographically 1975). similar. They are fine-grained, mostly aphyric rocks, weakly Two units, the Rzeszowek-Jakuszowa and Dobromierz or moderately cleaved. Occasionally, small augite phenocry- (Fig. lb), consist of largeuniform masses of pillow lavas, sts are the only igneous mineral preserved. The rocks are minor hyaloclastites and other volcaniclastics, and subordin- composed of variousproportions of albite,actinolite, ate black shales, locally with Silurian graptolites (Jerzmanski chlorite, epidote, sphene and opaque minerals, and locally 1965). The mafic volcanic rocks are supposed to be Silurian calcite, stilpnomelane,green biotite and phengitic mica. or Ordovician to Silurian in age(Jerzmanski 1965; Pumpellyite and aegirine-augite have been found in a few Baranowski et al. 1990). localities (Kryza 1993a, b). Sodic amphiboles (glaucophane The youngest rocks of the complex are melanges which andcrossite) are quite common, often partly replaced by are considered, at least in part, to be of early Carboniferous actinolite. This is evidence of a high to medium pressure low age(Haydukiewicz 19876; Baranowski et al. 1990, and grademetamorphic path (Kryza et al. 1990). Pumpellyite references therein). They represent tectonized sedimentary andaegirine-augite have been found in a few localities breccias, and are found as thrust-bounded bodies inmost of (Kryza 1993~).

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Rhyodacitic rocks. These are represented by felsic metavol- intermediate pressure conditions (Kryza & Muszynski 1988; canic rocks of the Bolkow unit (Oselka rhyodacites). They Kryza et al. 1990). define rather regularlyaligned outcrops of tensto 150m wide, within metabasalts, tuffaceous rocks, and Wojcieszow Metabasalts of Ordovician-Silurian (?) age limestones. The felsic rocks are veryfine-grained, often strongly cleaved, and contain small quartz and, more rarely, These are represented by voluminous pillowed and massive feldspar phenocrysts in places. The mineral composition is basaltic flows, and minor volcanic breccias and hyaloclastites quartz, K-feldspar and phengite, as well as occasional albite, of the Rzeszowek-Jakuszowa andDobromierz units (Fig. chlorite, carbonate and opaque minerals. These rocks have la). Minorsedimentary intercalations comprise very been interpreted as derived from felsic volcaniclastics and fine-grained tuffaceous rocks, as well as the stratigraphically minor rhyodacitic lavas (Kryza & Muszynski 1992; Muszyn- important graptolite-bearing Silurian black slates and cherts. ski in press). Themetabasalts of the Rzeszowek-Jakuszowaunit The volcanigenicsandstones of the Swierzawaunit usually display well defined pillow structures, with primary (Gackowa sandstones), which are probably time-equivalent features such as vesicle distribution, joints and drain-outs. and genetically related to the Oselka rhyodacites, form an Typically,they are slightly to moderatelyvesicular, outcrop c. 100 mthick within mafic lavas. These light- aphanitic lavas, composed of partly altered clinopyroxene, coloured,fine-grained and mostlymassive rocks are albite, chlorite, epidote and titanite. Greenish pumpellyite is composed of quartz,albite, K-feldspar, phengite, and alsowidespread, while amphibole (actinolite) is rare. The various amounts of carbonate and opaque minerals. They latterfeature, together with the generallyweak deforma- have been variably interpreted as lavas, tuffs or sandstones, tional imprint, suggest a probable lower metamorphic grade butrecently Kryza et al. (inpress) documented their within the Rzeszowek-Jakuszowaunit compared with the sedimentary derivation, and interpreted them as reworked other tectonic units of the Kaczawa Mts area (R. Kryza & felsic volcanicrocks (most probably of Oselkarhyodacite A. Muszynski, unpublished data). type), deposited in a shallow marine environment. Themetabasalts of theDobromierz unit are mostly massive, or of coarse platy or lensoid appearance, though typical pillow lavas are also found frequently. The dominant Bimodalshallowvolcanicintrusiveand suite rocks are fine-grained, andcontain characteristically metabasites. The bimodalsuite comprises alkaline lavas, abundant clinopyroxenemicrophenocrysts. The matrix widespread in the upper parts of the Swierzawa and Bolkow consists of chlorite,epidote, albite, sphene and opaque units. Theyrange in composition from alkali-basaltic to minerals. Glaucophane, partly replaced by actinolite, as well pantelleritic,and trachytic lavas aredominant (the whole as pumpellyite are also quite common. suite is therefore referred to as the Lubrza trachytes). The The largeproportion of commonlymassive lavas lavas form small domes or extrusions up to afew hundred m observed in the Rzeszowek-Jakuszowaand Dobromierz thick, embedded in volcaniclastic rocks (including pyroclas- units, and the scarcity of interlayered sediments, indicate a tic flows) of intermediate to felsic composition. The lavas rather high rate of lava effusion, probably in a deep marine are dark grey to light-cream coloured, aphanitic, and mostly setting. aphyric, with occasionallysmall feldspar phenocrysts. The The basic metavolcanic rocks of the small Cieszow unit matrix is composed of K-feldspar, albite, quartz, phengite, (Fig. la)are fine- to medium-grainedfeldspar-rich lavas. titanite, and opaque minerals. Sodic amphibole, and green They often show evidence of brecciation and alteration, the biotite are locally present.Recently, Muszynski & Kryza latter by net-veining of quartz,epidote and pumpellyite. (1993) reported relicts of pyroxene of nearly pure jadeitic Their relationships to the neighbouring Dobromierz unit is composition in these rocks. This confirmed the early high- uncertain. pressuremetamorphic episode inferred by Kryza et al. (1990) from the presence of relict glaucophane in metabas- Analytical methods ites of the complex (see below). Major oxides and the trace elements Cr, Ni, Rb, Sr, Y, Zr and Nb The metabasite sills (shallow intrusive alkaline metaba- were determined by wavelength dispersive X-ray fluorescence. The salts) are widespread within the grey slates in the northern glass-bead technique of Padfield & Gray (1971) was used for the part of the Swierzawa unit, in the Zlotoryja-Luboradz and major elements, and pressed powder pellets for the trace elements Chelmiecunits, and to less extent along the Bolkowunit using international standards for calibration and Flanagan's (1973) (Fig. la). These bodies usually reach several tens of meters recommended values. The REE (rare earth elements) together with in thickness. Rarely exposed conformable contacts with the Hf,Ta, Th, Uand Sc were determined by instrumental neutron surroundingbedded slates suggest that the bodies are activation,using international standards for calibration.The predominantly shallow sills (Kryza & Muszynski 1988). gamma-ray activities were measured with a large Ge(Li) detector. In all localities thepetrographic features of the Methods are described by Brunfelt & Steinnes(1969, 1971). metabasitesare similar. They are massive,fine- to Instrumentalprecisions for trace elements in this account are as medium-grained,locally porphyritic rocks. Generally, they follows:better than or c. f5%: Sm, Tb, Ta, Y, Zr,Sr, Cr; c. f5-10%: La, Eu, Yb, Hf; c. 10-15%: Ce, Nd, Gd, Ho, Tm, U, contain well-preserved clinopyroxene phenocrysts (augite to Rb, Ni. diopside), and rarely igneous brownish amphibole (kaersut- Sm-Ndisotopes were analyzed on a VG 54 E mass ite). The matrix is composed of various amounts of albite, spectrometer. After total spiking using a mixed '4ySm-'""Nd tracer sodic(glaucophane or crossite)and calcic (actinolite) and dissolution in closedPFA Teflon vessels, Sm andNd were amphiboles,chlorite, epidote, green biotite, titanite, isolated by cation exchange in HCI and HNO,, then separated from magnetite and hematite, and calcite. The observed sequence each other and adjacent lanthanides by extraction chromatography of metamorphic amphiboles, from glaucophane to actinolite, using HDEHP on teflon powder (Richard er al. 1976). Procedural stronglysuggests a metamorphicpath from high to blank was c. 0.1 ng Nd and <0.03 ng Sm. Sm was analysed as the

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metal species on single Ta filament. Nd was measured as Nd+ on element variation and REE diagrams, and a concentration triple Ta-Re-Ta assembly.143Nd/144Nd ratios are corrected for mass level similar to MORB (Fig. 3). In the easternmost part of fractionation by normalizationto 146Nd/144Nd= 0.7219, and are the unit, two samples (R045.4 and GOE, Figs la and 3) given relative I4?Nd/IuNd = 0.511860 for the La Jolla standard. exhibit pronounced negative Ta and Nb anomalies and high (up to 10 times MORB) Th values.

Alteration effects Rhyodaciticrocks. The rhyodaciticlavas and pyroclastic rocks of the Bolkow unit (samples N20A and OK9.8, Fig. 3) Theminor and trace element as wellas Nd-isotope data show a progressive enrichment in the incompatible elements have been used to characterize the rocks. Hence, only the towards Th, with negative anomalies for Ta, Nb, P and Ti. behaviour of these particular elements during alteration and Apparently related are the volcanigenic sandstones and vol- low-grade metamorphism will be discussed here. Elements canigenic rocks of the Swierzawa unit (R3.2 and G9.5, Fig. such as Ti, Zr, Nb, and Ta are reported to remain Y, Hf 2), which display a similar pattern, but with generally lower stable (e.g. Cann 1970; Hart 1970; Hart er al. 1974; Coish abundances, except for the high Cr value of sample G9.5 1977; Ludden et 1982;Staudigel & Hart 1983). The al. (Figs 2 & 3). The differencebetween the lavas and vol- behaviour of Th is uncertain,but Wood et al. (1979) caniclastics iswell demonstrated by their REE patterns. reportedthat the Th/La ratio remains stable in altered Whereasthe volcaniclastic rocks of the Swierzawaunit rocks. On the basis of exceedingly low solubility of Th in (G9.5 & R3.2)show smooth and progressive enrichment water,Chen et al. (1986) and Krauskopf (1986) argue from Yb through to La (Fig. 2), the lavas of the Bolkow unit againstany significant mobility of Th. Studiesconcerning (N20A & OK9.8) are relatively high in their heavy REE, thebehaviour of REE duringvarious types of alteration defining a slight downward convex pattern, with pronounced have shown that heavy REE can be regarded as immobile. negative Eu-anomalies (Fig. 3). The behaviour of light REE, however, is debatable. Thus, someauthors (e.g. Ludden & Thompson 1979) have documented some mobility, whereas others (e.g. Dungan et Alkaline bimodal suite. The basic lavas are represented by al. 1983) reportedno mobility.Since the volcanicrocks the two samples C14.2 and P4.1 of unit S. They are high in reported in this account generally show smooth normalized the incompatible trace elements, and in the multi-element REE patterns (Figs. 2-5),we believe thattheir composi- variation- and REE diagrams they show progressive enrich- tions largely reflect that of the original magma. ments from Yb through Th, and Lu through to La, respectively (Fig. 2). Thepatterns of the associatedtrachytes (C14.15 of the Swierzawa unit, and LA2of the Bolkow unit) arerather similar, except for pronouncednegative ano- Major, minor and trace element characterization malies with respect to PzOs, Ti02, and Eu for sample LA2 Alarge number of geochemicalanalyses of the volcanic (Figs 2 & 3). rocksfrom the various above-mentioned units (Fig. la, b) have been carried out by XRF. For this account we report Shallow intrusive metabasalts. These occur at various strat- full analyses only of representative samples, for which the igraphic levels within the Cambrian (?)-Ordovician sequence rare earth and other trace elements, as well as Nd-isotopes in the Swierzawa and Bolkowunits, and invariably in as- havebeen analysed. The resultsare presented in Tables sociation with the thick grey slates sequences in the Swierz- 1-3. awa, Zlotoryja-Luboradz and Chelmiec units (Fig. la, b). Theyare represented by samples W2 and C1.15 of the Swierzawa unit (Fig. 2), 38/S542 and CHG of the Chelmiec Cambrian (?)-Ordovician metavolcanic rocks unit, and sample ZL1 of the Zlotoryja-Luboradz unit (Fig. 4). Exceptionally, sample CHG is not an intrusive rock, but representsa minor pillowed basalt body within the grey Metabmalts of the Podgorki volcanic complex. In the multi- slates which are densely intruded by metabasite sills. This element variation diagrams (Figs 2 and 3) defined by Th, spatial relationship and close geochemical similarity (Fig. 4) Ta,Nb, Ce, P, Zr,Hf, Sm, Ti, Y, Yb,Sc and Cr,the stronglysuggests thatthe intrusivesand thesubordinate elementshave been arranged in such a way thatthey in pillow basalts represent the same magmatic episode. Thus, it generalbecome progressively more incompatible towards can be assumed that the emplacement of the basic sills was Th. All the samples from the Swierzawa unit (014.4, 018, mostprobably contemporaneous or slightly later than the Swie 1 and 05.7, Fig. 2), and the samples from the western deposition of the surrounding slates. part of the Bolkow unit (D81C and C39B, Fig. 3), show a The samplesmentioned are all verysimilar in their progressiveenrichment towards Th, which atthe most is multi-elementvariation- and REE-patterns,andare around30 times MORB (mid-oceanridge basalt), andY moderatelyenriched in the mostincompatible elements. similar to MORB concentration. This is similar to the con- They are all lower than MORB with respect to the heavy centrations and patterns characteristic of basalts transitional REE (represented by Yb in the Rock/MORB diagram), but between tholeiitic MORB and alkaline basalts, or continen- considerably higher with respect to TiOz, thusdefining slight tal tholeiites (e.g. Holm 1985; Thompson et al. 1984). The positive Ti anomalies (Figs 2 & 4). corresponding FEE patterns confirmthis by showinga continuous increase in the chondrite-normalized values from Lu through to La (Figs 2 & 3). However, the metabasalts of Ordovician (?)-Silurianmetabasalt thecentral and eastern part of the Bolkowunit (KOF, The mostextensive development of thesemetabasalts is OK9A and R07.3, Fig. 3) show flat patterns in the multi- found in the Dobromierz and Rzeszowek-Jakuszowa units

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Swierzawa Rock 1 Chondrite .( Unit lop4.111~1

Th Ta Nb Ce P Zr Hf Sm Ti Y Yb SC Cr La Ce Nd Sm Eu Gd Tb Ho Tm Yb LI 100 1 10

0.1

1M) 0 R3.2 + G9.5 10 10 :

0.1

I t014.4 10

1 t I

0.1

1- 1- Nd Th Ta Nb Ce P Zr Hf Sm TiYb Y Sc Cr La Ce Nd Sm EuTb Gd Ho Tm Yb Lu Fig. 2. Geochemical data for metavolcanic rocks from the Swierzawa unit, showing data, multi-element variation and REE diagrams. Chondrite data for normalization are from Haskinet al. (1968). MORBvalues: Ta = 0.18 ppm, Nb = 4 ppm, Ce = 10 ppm, P,O, = 0.12%, Zr = 90 ppm, Hf = 2.4 ppm, Sm = 3.3 ppm, TiO, = 1.5%, Y = 30 ppm, Yb = 3.4 ppm, Sc = 40 ppm and Cr = 250 ppm from Pearce (1980), and Th = 0.2 ppm from Tarney et al. (1980).

(Fig. 5), and a minor occurrence within a supposed tectonic to normal MO-, is observed in the Rzeszowek-Jakuszowa slice in theChelmiec unit (sample CHB in Fig. 4). The and Dobromierz units.

types. A progressively increasing depletion in incompatible Figure 6 shows a tentative geochemical development of the elements towards Th, from that typical of enriched MORB, magmaticproducts of the KaczawaMts with time.In

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Bolkow Rock l Chondrite Unit C Rock'MoRB r loo0 1 V loo0 E 100 U 10

IiV,," 0.010.11 Tgmd: 101 Th Ta Nb Ce P Zr Hf Sm TI Y Yb ScNdCe La Cr Srn Eu TbGd Ho Trn LuYb

100

0.1

100

10 OK.9A

1 D 0.1 A R045.4 0.01

100 10

10 - 1 n 1 A- m 0.1 J 14,. , ,..., ,'""' &' n Th Ta CeNb P Zr Hf Sm Ti Y Yb Sc LaCr Ce Nd Srn Eu TbGd Ho LuYbTm n Nd

Fig. 3. Geochemical data for metavolcanic rocks from the Bolkow unit, showing data, multi-element variation and REE diagrams. Normalizing chondrite and MORB values as in Fig. 2.

general, the earliest development of basaltic shallow water volcanigenicsediments. At ahigher stratigraphic level, a to subaeriallavas, associated with shallow water clastic typical alkaline suite of shallow water to subaerial lavas and sediments,andthe Wojcieszowlimestones, canbe volcaniclastics is developed.Locally abundant alkalic characterized as transitional between tholeiitic and alkaline basaltic shallow intrusive bodies occur which are similar to basalts. However, in thecentral and eastern part of the the basic members of the bimodal suite. Bolkow unit,more depleted lavas,resembling MORB, The metabasalts representing the latest intense volcanic occur,some of whichdisplay negative Taand/or Nb episode of the Kaczawa Mts are developed as deep-water anomalies. All these basaltic volcanic rocks are intercalated pillow lavas of dominantly MORB-type, associated in the with rhyodacitic lavas and pyroclastics, as well as siliclastic upper part with Silurian black slates and cherts. These can

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Zlotoryja- Luboradz Nd Rock / MORB Rock / Chondrite Unit 0 r 100 10 r

10 'i 1 0 +7 0.1 J Th Ta NbCe P Zr HfSmTi Y YbScCr La Ce Nd Sm EuGdTb Ho TmYb Lu c Nd

Chelmiec Unit 10 D Nd 0 +Q 1 ? CHB L 3 0.1 3

0.1l 1

1007 10 [038/s542) ...... 1. I ...- . :. 10 0 +9 +l\ Nd 0.1- 1 l1111111,111111 Th Ta NbCe P Zr Hf SmTi Y Yb Sc Cr La Ce Nd Sm Eu Gd Tb Ho Tm YbLu

Fig. 4. Geochemical data for metavolcanic rocks from the Zlotoryja-Luboradz and Chelmiec units, showing data, multi-element variation and REE diagrams. Normalizing chondrite and MORB valuesas in Fig. 2.

furtherbe subdivided intonormal MORB andenriched basaltsshow the largest spread in thevalues, between 0 MORB. The latter type has lower &Nd than the former, and and +7.2, averaging +4.9. The highestvalue of +7.2 in may show negative Ta anomalies (Fig. 6). sample KOF from thecentral part of the Bolkowunit is ratherexceptional, and most samples do notexceed +6.3 Nd-isotopic characterization (Table 3). The associated rhvodacitic rocks exhibit entirelv The values of thediffferent volcanicrocks areshown in different eNdvalues (-3.6 to -4.8), thus demonstrating no Fig. 7. The transitionaltholeiitic-alkaline, andtholeiitic geneticrelationship between the two. The values of the

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Rzeszowek- Jakuszowa Unit

Rock / MORB Rock / Chondorite Nd 0 fl -m 0.1 1 ,I I,)II,IlI 1111 Th TaNbCe P Zr HfSmTi Y YbScCr Lace NdSm EuGdTb Ho TmYbLu 0 +7 E Nd

Dobromierz Unit Nd -+ U 10

1 0 b

0.0o,’l1

m Th TaNbCe P Zr HfSm Ti Y Yb Sc Cr Lace Nd Sm EuGdTb Ho Tm Yb Lu 0 +9 Nd F%. 5. Geochemical data for metavolcanic rocks from the Rzeszowek-Jakuszowa and Dobromierz units, showing data, multi-element variation and REE diagrams. Normalizing chondrite and MORB values asin Fig. 2.

alkaline bimodal suite show a range between +2.7 to +3.7, The basalticlavas range from typical alkaline basalts, to averaging +3.1,and is rather similar tothe alkaline transitionalbetween alkaline basalts and MORB, and to intrusions with theslightly lower values (+l.8 to +3.1). The typical MORB.The acidicmagmas arerepresented by stratigraphicallyhighest MOR-typebasalts, intercalated rhyodacitic lavas and volcaniclastic rocks, as well as by the withSilurian slates show the highest E,.,~ values,ranging dominant trachytic member of the alkaline bimodal suite. between +3.2 and +8.7, averaging +6.4. There is furthermorea significant change in the magmatic evolution with time. Thus, the most widespread Magma genesis basalttype theearlyat stage is thetransitional The compilation of the geochemical data (Fig. 6) shows that tholeiitic-alkaline type. Lavas resembling MORB occur only avariety of basalticmagma compositions is represented. locally. Evidence of crustalcontamination, exemplified by

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Table 1. Major element analyses of representotive samplesfrom the Koczowo Mts CommentsTiO,SiO, Al,O, FeOtMnOMgOP,O,Na,OCaOK,O L01 Total Sweierzuwu Unit C14.2 Alk. basite 49.97 3.37 18.04 10.52 0.18 2.87 3.46 0.58 7.55 99.892.301.05 P4.1 Alk. basite 51.71 2.82 17.43 11.62 0.04 1.92 1.38 0.81 7.58 98.762.381.07 C14.15 Trachyte 61.52 0.56 16.59 4.08 0.10 0.81 1.82 3.83 8.15 99.502.150.16 SWIE 4 Trachyte 63.70 0.90 16.80 4.90 0.12 0.61 2.00 6.25 2.80 99.060.98 C1.15 Massive basalt 42.70 1.82 14.47 14.39 0.24 12.77 6.11 2.50 0.30 100.174.960.19 05.7 Pillow lava 44.18 2.46 14.85 11.56 0.11 3.53 8.88 4.49 2.12 99.206.560.46 G9.5 Volcaniclastics 83.62 0.29 8.59 1.71 0.01 0.80 0.05 0.47 3.12 101.342.600.07 R3.2 Volcaniclastics 72.77 0.25 11.55 1.95 0.05 0.43 4.10 1.13 4.48 0.123.36100.19 014.4 Pillow lava 47.33 2.72 15.04 12.52 0.17 5.30 8.40 3.68 0.08 98.893.39 0.27 018 Pillow lava 49.20 2.71 11.90 13.20 0.16 7.21 8.41 3.20 0.68 99.632.560.43 SWIEl Pillow lava 46.21 2.74 15.19 11.88 0.16 5.69 7.56 3.89 0.33 98.984.680.37 W2 Intrusive alk. basalt 43.60 3.12 9.50 14.30 0.19 11.86 11.62 1.66 0.62 0.64 101.003.92 SWIE 5 Intrusive alk. basalt 43.10 3.75 10.30 12.02 0.19 11.63 12.30 2.40 0.40 3.7699.85

Bolkow Unit LA2 Trachyte 67.32 0.17 15.28 4.25 0.09 0.02 5.30 5.39 98.370.500.04 C39B Pillowy basalt 49.62 3.71 15.86 9.99 7.562.600.17 4.55 1.49 0.68 99.533.30 R07.3 Massive basalt 45.86 1.82 14.43 10.23 8.367.120.33 4.28 0.06 100.007.300.21 OK9A Pillow lava 46.02 1.65 16.05 10.44 9.217.370.18 3.66 0.02 99.744.900.24 N20A Rhyodacite 76.55 0.11 12.31 0.48 0.45 0.64 8.91 0.70100.122 OK9.8 Rhyodacite 80.98 0.09 12.07 0.17 0.50 0.20 3.59 99.071.430.04 R045.4 Pillow lava 54.48 1.04 15.70 7.15 5.886.300.14 6.59 0.16 99.902.300.16 KOF Massive basalt 45.03 1.19 15.09 11.00 0.1611.379.23 1.45 0.76 99.734.300.16 D81C Pillow lava 45.85 3.20 12.44 12.17 7.695.680.15 4.44 0.43 95.703.030.62 GOE Pillow lava 50.46 1.os 15.42 9.26 5.305.670.18 5.41 0.35 100.497.200.19

Dobromierz Unit JS6 Massive basalt 51.14 0.99 18.73 11.15 0.19 3.58 4.97 4.98 0.73 0.31 3.30 100.10 PA40 Pillow lava 43.54 1.60 14.83 12.90 0.22 7.93 14.60 3.57 0.16 0.27 3.00 102.62 PL3A Massive basalt 46.77 1.41 15.83 11.14 0.32 7.72 9.68 3.49 0.01 0.19 3.70 100.25 JS4 Massive basalt 46.23 1.15 14.08 9.55 0.19 6.65 12.83 2.90 0.07 0.12 6.30 100.07 D02 Massive basalt 45.99 1.70 13.79 12.84 0.19 5.35 10.92 2.20 0.22 0.26 8.20 101.66 PA18 Pillow lava 48.67 2.11 14.72 12.27 0.20 6.96 8.12 3.43 0.76 0.29 2.60 100.13

Chelmiec Unit CHB Massive basalt 50.66 1.53 14.26 11.17 0.21 5.08 11.81 1.48 0.33 0.17 2.70 98.63 CHG Pillow lava 43.28 3.04 14.01 12.87 0.18 5.06 10.03 2.78 0.88 0.36 6.80 99.27 38lS.542 Intr. alk. basalt 40.69 3.01 13.83 13.28 0.52 5.66 11.23 1.79 0.28 0.29 12.24 101.73

Zlotoryjo-Luborodz Unit ZL1 Intr. alk. basalt alk. Intr. ZL1 43.9 3.31 15.40 12.629.24 8.02 0.17 1.133.18 100.743.300.44

Rzeszowek-Jokuszowo Unit M YC Pillow lava Pillow MYC 43.71 1.43 15.70 9.72 0.16 6.45 13.72 2.97 0.14 0.28 8.30 102.58 1 Massive basaltMassive LI 1 45.98 1.17 18.01 9.27 0.19 6.75 7.83 3.43 1.34 0.19 4.40 98.56

samplesshowing negative Taand Nb anomalies and low The E,,-Sm/Nd diagram (Fig. 8) allowsdiscussion of &Nd, is common at this magmatic stage. All these basaltic possible magma genetic relationships of the basic and acid magmas are associated with rhyodacitic rocks, and overlain rocks.generalIn the &,,-Sm/Nd showpositive a in many places by the alkaline bimodal suite. relationship for the metabasalts and trachytic rocks (except Atthe higheststratigraphic level, enriched to normal for sample no. 21 = GOE, Fig. 8a). In Fig. 8b the various MORB lava types are dominant, with no acidic derivatives, rocks have been grouped according to their trace element and withvery minor, if any,evidence of crustal characteristicsandage(i.e. eitherCambrian (?)- contamination. The time-related change in the composition Ordovician, or Ordovician-Silurian). The Cambrian (?)- of the basaltmagma is also indicated by the Nd-isotope Ordovician metabasalts show a large range in both the E~~ composition. Thus, the E~,values of theCambrian(?)- values and Sm/Nd ratios, thus suggesting that not all have Ordovicianbasalts areon the average slightly lower,and experiencedthe same magmatichistory. Some of these show larger variations that those of Ordovician-Silurian age lavas, which onthe basis of theirtrace element (Fig. 7). characteristics can be classified as either transitional basalts

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Table 2. Trace element analyses of representative samplesfrom the Kaczawa M@ Sc Cr Ni Rb Sr Y Zr Nb Hf Ta Th U La Ce Nd Sm Eu Gd Tb Ho Tm Yb Lu

Swierzawa Unit (214.2 15 (214.2 17 12 132 27 62 473 108 10 6 8.3 1.1 74 15914 61 4.8 1.8 2.2 0.53.90.9 P4.1 17 P4.1 11 77 27 45 333 76 6.6 4.6 5.5 0.4 73 14912 69 4.4 13 1.5 1.5 2.6 C14.15 2.9 33 11 99 63 55 736 101 17 8.5 18 1.2 106 21314 76 2.61.2 11 1.15.90.9 SWIE4 181 93 468 1559 650 110 86 174.4 4.6 15 0.7 c1.15 37 345 145 262 25 1202.6 10 0.6 8.2 0.2 4.7 1.222 3.7 14 0.7 0.5 2.2 05.7 28 322 145 1 127 27 193 1.423 1.2 4.3 19 0.8 31 16 5.6 1.9 1.30.9 0.42.30.5 G9.5 4.9 G9.5 181 14 36 27 8 105 2.8 200.1 42 5.223 3.4 0.8 4 0.3 0.9 R3.2 3 79 106 17 1090.5 4.410 0.5 3.4 20 39 3.7 15 1 0.5 1.7 014.4 28 143 60 86 310 29 173 3.7 1.1 1.2 0.8 15 58 22 6.6 2.2 1 0.5 2.5 0.3 018 29 281 183 2 280 34 1.4213 4.5 23 0.2 1.935 47 22 6.3 1.9 8.2 1 0.5 2.7 SWlEl 33 508 207 11 210 36 236 21 5.1 1.6 1.421 1.2 26 104 2.3 7 1.2 2.9 0.5 W2 41 W2 482 154 8 0.4633 3.622 3 280 5.4 50 44 98 55 8.6 1.62.2 0.4 0.9 SWIES 3.2 18 535 2811 273 50 54 45 8.3 1.9

Bolkow Unit LA2 12 2577 12992 1.2 138 14 31 24 1186 25 568 92 20 0.2 1.9 4.2 2.8 C 39B 24 C39B 10137498 21 35 322 63 456.7 103 523.3 0.8 4.9 2.5 7.9 1.21.2 2.2 R07.3 41 357 73 41 441 143 0.1 317 4.7 0.6 0.4 1.5 4.4 13 1.5 1 0.53.5 0.7 O K9A 34 OK9A 314 722.5 0.529208 0.7 1.4150 3.56 2.511 180.3 6.3 0.3 N20A 8 2 21275 53 219 124.70.9 13 7.2 8 0.6 12 1.7 0.1 1 0.9 5.3 OK9.8 41 19 54 0.768 3.5 8 15 37 15 2.9 9.7 0.2 5.1 0.91.91.2 0.95.4 R045.4 30 274 93 108 26 0.1123 2.8 3 1.14.6 1 17 3.4 13 1.1 7.9 0.6 0.5 0.42.5 KOF 28 830 306 20169 28 80 5 1.8 3.30.2 0.6 0.2 3 3 8.4 1.1 0.60.3 2 0.4 0.9 D81C 29 176 42 4 41277 273 29 5 1.5 1.228 48 2.821 0.6 1.5 1.1 2.4 6.8 GOE 35 146 13 2 30149 117 3 14 2.7 19 8.10.2 1.2 1.8 0.4 2.5 0.5 0.7 1.2 3.8

Dobromierz Unit JS6 20 33 18 21 285 20 91 1.8 1.5 0.1 0.3 1.5 0.30.9 0.7 0.56.6 1.1 15 3 10 PA40 48 82316 11734 171 0.1 2.3 0.12.7 0.5 9.1 3.7 8.4 1.3 0.8 0.41.3 3.1 0.6 PL3A 34 248 96 102 32 58 1.9 0.2 3.1 9.9 3.2 1.1 0.6 1 0.5 3 JS4 85 27 15535 114 348 1.9 0.1 0.12.2 0.7 8.1 9.1 1.2 3 0.31.80.30.7 0.6 D02 48 220 64 4 565 40 130 0.2 0.2 2.8 0.8 7.8 1.411 4.2 13 1 1.60.7 3.9 0.7 PA18 35186 15 38 87 40 2090.2 1.9 1.4 4.5 31 15 6.9 1.6 5.2 1 1 0.7 1.2 3.2

Chelmiec Unit CHB 41 340.9 53 5.5 1.2 3.84111 35 11410 15 5 0.3 0.2 2.4 1.33.6 0.6 CHG 33 70184 83261010 22 31 4.1 1.51.5 43 19 0.9 25 2.16.4 0.9 1.9 0.2 38lS.542 1156 3189 98 3.5 2628 206 1.3 0.442 19 22 1.8 5.1 0.7 1.7 0.3

Zlotoryja-Luboradz Unit 34 129 31 459 25 210 27 4.7 27 210 25ZL1 459 31 129 34 1.7 1.7 0.2 23 50 5.7 28 0.3 0.91.8 0.8 5.4 1.6

Rzesrowek-Jakrrszowa Unit M Y C 28 177 161 177 28 MYC 6 0.4 232.2 121 7 0.6 3.8 14 0.9 3 0.4 L11 45 10430127 188 12 183 4 0.2 0.8 116.5 120.3 0.3 3.10.7 1.4

or MORB, have rather similar &Nd values, but with Sm/Nd stronglycontaminated by such a component. As tothe ratios varying between 0.23 and 0.33. The variations in the alkaline bimodal suite it is rather obvious, both on the basis Sm/Ndratios, might indicate different degrees of partial of trace element patterns and concentrations, as well as the melting, or thatthose with the highest Sm/Ndratios values, that the basaltic and trachytic rocks are related representmelts from previously melted mantle (e.g. to each other (Figs 6-8). Also the intrusive alkaline basalts, Pedersen & Hertogen 1990). In general those with MOW as well assome samples near the boundary between the characteristics, have the highest Sm/Nd ratios (Fig. 8b). The transitionallavas and the bimodalsuite (e.g. C39B), have similarity in the valueswould indicate thatthe two were trace element patterns comparable to the alkaline bimodal generatedfrom similar sources, and the variations in the suite, and a common magmatic history is hence suggested. Sm/Nd may be explained by partial melting and fractional It is also noteworthy that a few samples, mainly from the crystallizationprocesses. Since Nd in general is a more lower part of thesequence within the Bolkowunit (i.e. incompatible element than Sm (e.g. Arth & Hanson 1975), samples R045.4 and GOE), display high Th, and negative the Sm/Nd will progressively increase with repeated melting Taand Nb anomalies. This is reminiscent of subduction- from onesource, but will decrease withfractional generated magmatic rocks (e.g. Wood et al. 1979; Saunders crystallization processes, as indicated by arrows in Fig. 8b. et al. 1980;Thompson et al. 1984). However,the same The rhyodaciticrocks define traceelement patterns samplesalso exhibit low &Nd values,particularly sample which hardly can be related to differentiation from any of GOE, which shows the largest Ta and Nb anomaly (Fig. 3), the basaltic rocks (Fig. 6), and this supposition is strongly and also has the the lowest cNdvalue of zero (Fig. 8). This supported by their distinctly negative &Nd values (Fig. 7). On relationshipwould ratherfavour continental crustal this basis we therefore suggest thatthe rhyodaciticrocks contamination, as it is well known that continental crust is most likely representproducts of partialmelting of generally low in Ta and Nb, but may be high in Th (e.g. continentalcrustal material, or, thatthey at least are Thompson et al. 1980; Wood 1980;Taylor & McLennan

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Table 3. Sm-Ndisotope anaIyses of representatiave samples from the Kaczawa Mts

Sm Nd '47Sm/'"Nd '43Sm/1"Nd'47Sm/'"NdRef. no. Nd Sm &Nd

Swierzawa Unit T = 500Ma C14.2 1 17.6 89.2 0.1192 0.512530 f 12 +2.8 P4.1 2 13.7 69.5 0.1190 0.512574 f 13 +3.7 C14.15 3 13.8 79.2 0.1057 0.512495 f 13 +3.0 SWIE4 3* 15.1 83.1 0.1097 0.512453 f 7 +1.9 C1.15 4 3.73 13.8 0.1631 0.512835 f 11 +6.0 05.7 5 5.52 22.1 0.1509 0.512813 f 12 +6.3 G9.5 6 2.84 15.8 0.1092 0.512166 f 12 -4.6 R3.2 7 4.14 18.6 0.1345 0.512192 f 12 -4.8 014.4 8 5.57 22.0 0.1531 0.512813 f 12 +6.2 018 9 6.90 29.1 0.1434 0.512760 f 11 +5.8 SWIEl 10 6.81 28.7 0.1434 0.512739 f 9 +5.3 W2 l1 9.13 48.6 0.1134 0.512459 f 19 +1.8 SWIE5 11* 9.13 48.7 0.1133 0.512466 f 9 +1.9

Bolkow Unit T = 4500 Ma LA2 12 21.5 106 0.1222 0.512537 f 16 +2.7 C39B 13 9.30 48.8 0.1147 0.512471 f 12 +1.9 R07.3 14 3.99 12.2 0.1984 0.512941 f 22 +5.8 OK9A 15 3.72 12.7 0.1764 0.512862 f 13 +5.6 N20A 16 1.44 6.13 0.1418 0.512274 f 13 -3.6 OK93 17 4.43 15.4 0.1739 0.512376 f 15 -3.7 R045.4 18 2.91 10.5 0.1674 0.512771 f 14 +4.4 KOF 19 2.48 8.21 0.1823 0.512960 f 14 +7.2 D81C 20 7.48 30.0 0.1507 0.512735 f 14 +4.8 GOE 21 3.12 11.6 0.1635 0.512534 f 12 0.0

Drobromierz Unit T = 420 Ma JS6 22 2.69 10.6 0.15531 0.512757 f 10 +4.6 PA40 23 3.28 9.71 0.2040 0.513077 f 12 +8.1 PL3A 24 3.11 8.75 0.2148 0.513092 f 16 +7.8 JS4 25 2.65 7.77 0.2063 0.513020 f 12 +6.9 D02 26 3.60 10.3 0.2104 0.513123 f 10 +8.7 PA18 27 5.55 21.8 0.1538 0.512686 f 18 +3.2

Chelmiec Unit T=500Ma CHB 28 3.71 11.3 0.1982 0.512988 f 10 +6.7 CHG 29 5.72 24.9 0.1392 0.512664 f 27 +4.2 38/S.542 30 5.36 23.5 0.1379 0.512605 f 16 +3.1

Zlotoryja-Luboradz Unit T=500Ma ZL1 31 ZL1 6.28 28.5 0.1333 0.512572 f 13 +2.7

Rzeszowek-Jakuszowa Unit T = 420 Ma MYC 32 MYC 3.18 11.9 0.1611 0.512812 f 13 +5.1 L1 1 33 2.66 8.64 0.1858 0.512937 f 10 +6.3

1985;Wilson 1989). TheTh content of continentalcrust and/or that the source is more depleted with respect to the may,however, vary widely. Thus, in amphibolites the Th incompatible elements. content is generally high, whereas in granulites it is low (e.g. Wilson 1989). The Th/Ta ratio of a basalt contaminated by continental crustal material, may hence differ pronouncedly, Discussion dependingon the crustal level at which themagma is In the discussionbelow wewill combine our present temporarily stored. knowledge of the geochemicalcharacteristics and the The MORB-like Ordovician-Silurian metabasalts show a geologicalevolution of the volcanigenicrocks of the ratherrestricted range both with regard to valueand Kaczawa Mts, in an attempt to propose a tectonic model, Sm/Nd ratios, but are slightly higher with respect to both shown in Fig. 9. We will further attempt a correlation of the parameters, compared with the older, MORB-like metaba- volcanicsuccession of the Kaczawa Mts withtime- salts (Fig. 8b). This would imply that the latest magma in equivalent,apparently similar volcanic sequences in the general is less contaminated by continental crustal material, Sudetes and elsewhere in central Europe (Fig. 10).

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10 p, @ E-MORB @ N - MORB 5 -. 2 1 1 -5 -5 ThTaNbCePZrHfSrnTiYYbScCr -1 b (4a+4b) ThTaNbCe PZrHfSrnTi YYbScCr 200

100 4a: PA18 (e),, MYC (A), JS6 (0) units D & RJ \o 4b: Average and std.dev. of: D02, PL3A, JS4, L11 & CHB lkaline 10 units D & RJ modal Jite (3) 3: LA2 (A), P4.1 (a), W2 (0) m units B & S m1 0 z 2: Lava (X) of unit B: Average of . N20A & OK9.8

Volcaniclastics (0)of unit S Average of R3.2 & (39.5

la: Average and std.dev. of: 014.4,018, SWlE 1,05.7,Cl.l5,D8IC&C39B Rhyodacitic units S and B (western part) 1 b: Average and std.dev. of: KOF, OK9A

& R07.3 (0) nnn Average of GOE & R045.4 (X) Transitional unit B (central and eastern part) tholeiitic- alkaline and tholeiitic basalts @ Tholeiitic (la+lb) I1

.. I I -” ThTaNbCePZrHfSrnTiYYbScCr ThTaNbCe P ZrHfSmTi YYbScCr Fii. 6. Geochemical compilation of the metavolcanics from the Lower Palaeozoic sequence of the Kaczawa Mts. Thestratigraphic column is part of that shown in Fig.lc.

Geotectonic model latter,indicate that these represent melts from a less depletedmantle source than those of MORB-like The earliest, transitional tholeiitic-alkaline basalts (Fumes composition. The verylow eNd values of some of the et al. 1989), associated with volcanigenic sandstones (Kryza samplesmight also indicate thatthe magmahad some et al. in press) andlimestones (Lorenc 1983), are all of residence time in the continental crust, and thus becoming shallowwater deposition. In Fig. 9A wesuggest that the contaminated. The association of highlyenriched alkali volcanic sequence is entirely underlain by continental crust, basalts with depleted normal MORB is a feature that may probably attenuated. The main part of the metabasalts show beaccounted for by theinteraction of plume-likea trace element patterns (Figs 2, 3 & 6) that are similar with componentwith the convecting asthenospheric mantle. those of rift environments (e.g. Holm 1985). However, both Mixing of thesetwo end members mayaccount for the the trace elements and the Nd-isotopes of the metabasalts generation of thetransitional basalts. In anextensional showdifferences in theirpatterns, indicating thattheir setting, influenced or driven by mantle plume activity, such genesiswas not uniform. Thus,the MORB-like trace basaltassociations areto beexpected. Minor amounts of elementpatterns of some of thesamples, combined with crustal contamination may further be a complicating factor, their high values,give evidence that these represent and may offer one explanation to the subordinate Nb-Ta melting fromamantle source withlow time-integrated negative anomalies. The rhyodacitic lavas and volcaniclastics Nd/Sm ratios, that had suffered long-term depletion prior to definetrace elementpatterns that cannot be related to the formation of the transitional basalts. The relatively high fractionalcrystallization from any of the associatedbasic content of incompatible elements and low &Nd values of the magmas (Fig. 6). This is even better demonstrated by the

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Fig. 7. Compilation of Nd-isotope data of the volcanogenic rocksof the Lower Palaeozoic sequence of the Kaczawa Mts. MOR-type basalts: solid and open W inverted triangles representN-MORB ww and E-MORB, respectively. Alkaline V bimodal suite: Solid and open circles vv represent intrusives and lavas, respectively. Rhyodacitic suite: Solid and open 880 squares represent lavas and volcaniclastics, respectively. Transitional tholeiitic- alkaline and tholeiitic basalts: solid and A open triangles represent tholeiitic and transitional basalts, respectively. The A stratigraphic column is partof that A shown in Fig.lc. A AA~A A A

r1h111111111'1 -4 -2 0 24 68 Nd

negativevalues (Figs. 7 & S),and we therefore suggest believe thatthis is rather reflection a of crustal thatthese rocks originated by melting of thecontinental contamination. crust (Fig. 9A). The youngest(Ordovician (?)-Silurian) deep-marine The stratigraphicallyhigher (probably Ordovician) pillowed and massive lavas, partly associated with Silurian alkalinebimodal suite of lavas and volcaniclastics, the graptolite-bearingblack shales, are in generalterms intrusivealkaline basalts, as well assome of the pillow different from those of Cambrian (?)-Ordovician age. The basalts classified as the transitional basalts, have lower &Nd main part of these lavas are characterized by a MORB-like values and Sm/Nd ratios (Fig. 8). This, combined with the trace element pattern (Figs 5 & 6), and both their &Nd values trace element characteristics (Figs 2-4 & 6), would suggest and Sm/Nd ratios arehigher than the stratigraphically lower that they largely may be derived from a common source, as lavas (Fig. 8).We interpret this asrepresenting a more indicated inFig. 9B. On the basis of previously published advanced stage in the rifting process, and suggest that true traceelement data, it wassuggested thatthese alkaline oceanic crust may have developed at this stage (Fig. 9C). rocks compare closelywith themagmatic products of continental rifts, or oceanicislands (Fumes et al. 1989). Regional correlations There may be no contradictionin these two alternatives; Basic and bimodal volcanic rocksof assumed or documented indeed, aplausible comparative moderntectonic situation Earlyand Mid-Palaeozoic age arefound withinseveral may be represented by the southern part of the Red Sea, tectonostratigraphicunits of theSudetes area (Fig. 10a). wherealkaline oceanic islands are built uponrifted, However, in mostcases uncertain ages anddisputable attenuated continental crust (Gass et al. 1973). The intrusive structural relationships between these units, make correla- alkalinebasalts areassociated withthick sequences of tions speculative (Kryza 1992). mudstoneswhich are mostly of turbiditiccharacter The metabasalts intercalated with the Lower Cambrian (Baranowski et al. 1990), and this may indicate deepeningof limestones 'and slates of the Gorlitzer Schiefergebirge may the marine basin. be time equivalent to the Podgorki volcanic complex of the Throughout the volcanic succession of the Kaczawa Mts, KaczawaMts. Basic volcanic and subvolcanic rocks also and in particular in its lower part, some of the samples show occur within the Devonian clastic sequence of the Gorlitzer trace-element patterns reminiscent of those in subduction- Schiefergebirge(Hirschmann & Brause1969), and their influencedmagmas, reflected by negative Taand Nb majorelement characteristics (Rosler & Werner 1979) anomalies (Fig. 6).However, the presence of alkaline indicatea within-plate affinity. Similarbasic rocks, mainly basalts as well as the crustally derived rhyodacites would not shallowintrusives, occur within low-grade metamorphic indicateformation in an arc environment, unless in a sequences of the western andcentral part of the back-arcsetting, which again appears unlikely due to the Fore-SudeticBlock, and theyprobably represent the generallack of greywackes andarc-type volcaniclastics. eastern continuation of the Kaczawa complex (Kryza 19936, Whencompared with the Nd-isotopedata of the Lower and references therein). Ordovicianmetabasalts of some of the Scandinavian To thesouth of the KaczawaMts, thepredominantly ophiolites, in which thesubduction imprint invariably is mafic volcanicrocks of thesouthern andeastern dominant (Pedersen & Hertogen 1990; Fumes et al. 1992), Izera-KarkonoszeBlock show destructive plate margin the Kaczawa Mts MORB-like Ordovician-Silurian metaba- characteristics (mostly island arc tholeiites). They have been salts only show minor overlap (Fig. 8b). Furthermore, these interpreted to indicatechangea from extensional to samplesoften show the lowest &Nd values, andhence we subduction-relatedsetting during Silurian times (Narebski

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'lENd

SmINd

Fig. 8. (a) cNd versus Sm/Nd for the

volcanogenic rocks of the Lower Palae- -5 ozoic sequence of the Kaczawa Mts. The numbers correspond to the ref. nos. given in Table 3. 'O- E. (b) cNdversus Sm/Nd diagram in which the Kaczawa Mts volcanic rocks have been classified according to the trace element characteristics, and further compared with metabasic rocks from 5- Devonian and Lower Palaeozoic ophiolites from the Polish Sudetes (PS) and Norwegian Caledonides (NC), respectively. The data from the Sudetic ophiolites are from Pin et al. and J , , , , , , , , , , , , SmlNd (1988), 0 ::::i::::l:~..,....,.,..,::::I~ those from the Norwegian ophiolites 0.20 0.25 0.30 0.35 0.40 0.45 from Pedersen & Hertogen (1990) and Furnes et al. (1992). The line CEP Kaczawa Mis extending from cNd c. -8 to -16 at Rhyodacltlc lavas Sm/Nd c. 0.2 shows variation in con- C,'::) Ordoviclan to Sllurlan -5 temporary continental erosion products 0Cambnan (?) to Ordoviclan (data from Chester et al. 1979). Arrows i 1 show the effects of partial melting (PM), : Upper (Polish Sudetes (PS) and Lower .. ., , . . . .. (Norwegan Caledonldes (NC)) crystal fractionation (CF),crustal con- Paleozoic ophiolites tamination (CC), and metasomatic enrichment (ME).

1980; 1990; Narebski et al. 1986; Pin 1990); however, recent KlodzkoMetamorphics, in thenorthern part (Woj- U-Pb dating give ages around 500 Ma (Oliver et al. 1993), ciechowska et al. 1989). However, metabasic rocks of the consistentwith recent modifiedstratigraphic scheme of Stare Mesto unit at the SE margin of the Orlica-Snieznik Zelzny Brod complex (Chaloupsky 1989). dome(OSD in Fig.10a) display mostly destructive plate Thecomposite metavolcaniccomplex of theKlodzko margingeochemical affinity (Poubova & Sokol1993; Metamorphics, of assumedpost-Ludlow andpre-Upper Narebski 1993). They have been considered by Misar (1984) Devonianage (Wojciechowska 1990), comprises within- to be of ophioliticorigin, whereas Narebski (1990) has plate, MORB and supra-subduction magma types, and has attributed them to small but typical Alaskan-type intrusions. been interpreted in terms of acomplex transform-fault Therelationship between the rift-related KaczawaMts relatedemplacement setting (Narebski et al. 1989). volcanic rocks and the mafic-ultramafic bodies to the NE,E, However, one cannotexclude the possibility thatthese and S of the Gory Sowie Block, as well as the mafic igneous geochemicallydifferent magmatic rocks are of different rockswidespread along the boundarybetween the west ages,thus questioning the above-mentioned geodynamic Sudetes and the Moravo-Silesian zone (Fig. 10a), is one of interpretation (Narebski 1993). the key questions in the geotectonic evolution of the eastern Correlations of the Kaczawa complex with metavolcanic Variscides (Narebski 1990). The circum-Gory Sowie Block rocks of the Orlica-Snieznik Dome, as well as with those in mafic-ultramaficcomplexes have been petrologically and the eastern part of the Fore-Sudetic Block (Fig. lOa), are geochemically documented as typical MORB-type ophiolites evenmore difficult, dueto highermetamorphic grades, (Majerowicz1990), andtheir Upper Devonian ages obliterating their ages, and still rather limited geochemical constrained both by geological evidence and Sm-Nd isotopic data. The volcanic rocks of the Orlica-Snieznik Dome are dating (Pin et al. 1988), though recent U-Pb zircon dating thought to be earlyPalaeozoic in age,and the available have yielded younger ages of around 420Ma (Oliver et al. geochemical datapoint to apredominantly MORB-type 1993). The values andSm/Nd ratios for theseophiolites affinity of the rocks in the southwestern part (Domecka & overlap with the Ordovician (?)-Silurian metabasalts of the Opletal 1980; Sokol & Sokolova 1989; Opletal et al. 1990), Kaczawa Mts (Fig. 8b). Thus, it is possible that the matured and tomore complex affinities, resembling those in the Devonian ocean developed as a consequenceof the evolving

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3 3

I' '/ MOR-type basal&

crust ? 2 L 2

Alkaline 9. Cartoon showing the develop- blrnodal Fig. ment of the volcanigenic rocksof the Kanawa Mts, as inferred from the geological and geochemical information. (A) The earliest (Cambrian?- Ordovician) development. At this stage it is indicated that mantle-generated, basaltic magma may become contaminated at different crustallevels, and 1 1 further that the rhyodacitic magma was produced by crustal melting. (B) Development of the alkaline, bimodal suite of mantle-generatedmelts. nn It is inferred at this stage that the Transltlonal continental crust has suffered continued tholeiitic- attenuation. alkaline and (C) During Silurian time the pre- tholeiitic basalts dominance of basaltic melts are gen- L,Magma erated from a depleted mantle, and at this stage atrue oceanic crust was Mantle probably developed.

earlyPalaeozoic rifting processes,evidence of which is French Massif Central,Armorican Massif, and Galicia in recorded in the described part of the Kaczawa succession. It Spain (Pin 1989, 1990, and references therein), to Portugal has also been suggested (Narebski et al. 1989; Pin 1990) that (Ossa Morena Zone; Muhna et al. 1990). These sequences some of the within-plate metavolcanic rocks in the Klodzko locally appear to comprise sedimentary rocks with features Metamorphicsmay give enidence of a later (Silurian- indicating a rather shallow water environment of deposition Devonian) rifting episode. (e.g. review by Erdtmann 1991). Typically, the lavas are of The mafic complexesalong the boundary with, and within-plate affinity. Localoccurrences of supposed within the Moravo-Silesianzone areconsidered to be at subduction-relatedmagmatism could equally result from least partly of Devonianage (Misar 1984). Recent contamination by the continental crust. Thus the described geochemicalstudies (Prichystal 1990; Jedlicka & Peciva volcanicrocks of the KaczawaMts can be regarded as a 1990) have shownthat in addition to volcanics of dominantly well-documentedexample of LowerPalaeozoic volcanic calc-alkaline character(Jakes & Patocka 1982; Patocka sequenceswidespread within the internalpart of the 1984), also representatives of within-plate and MORB-type European Variscides, and which havebeen interpreted to occur. They have been interpreted to represent arc/back-arc develop in a system of ensialic, rift-related basins along the relatedmagmatism connected with subduction onthe northern periphery of Gondwana. The evolving rift system easternside of theBohemian Massif (Narebski1990; mostprobably attained astage of basinsunderlain by Paszkowski et al. 1990; Pin 1990). oceanic-typelithosphere, already during Ordovician and Fromthe discussion above, it is evidentthat we need Siluriantimes. This has been inferred from preserved moreinformation on ages,geochemistry andstructural fragments of metamorphosedMORB-type ophiolitic com- relationships to construct a consistent geotectonic model for plexes found along the internal part of the Variscides (Fig. this part of the Variscan belt. However, on a larger scale, lob) anddated aroundat 500Ma (Pin 1990). The thedescribed volcanic succession of the KaczawaMts is MORB-typevolcanic rocks in theupper part of the lithologically and geochemically very similar to, and may be described Kaczawa succession, associated with the Silurian correlatedwith theso-called 'bimodal volcanic (or pelagicsediments, are further arguments that the early spilite-keratophyre)association' (Perekalina 1981), wide- Palaeozoic rifting reachedthestage of oceanic-type spread in isolated outcropsalong the west-European spreading. Whetherthe Cambrian-Ordovician and Devo- Variscides,through theSaxothuringian Zone in Germany nianextensional phases were separated by aconvergence (e.g.Vesser areain Thuringia; Bankwitz et al. 1989), episodeduring theLate Silurian/Early Devonian, as

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Conclusion The LowerPalaeozoic volcanigenic rocks of the Kaczawa Mts(western Sudetes) in theeastern Variscidescan be characterized as follows. (1) Cambrian (?) to Ordovicianshallow marine to subaerialmetabasalt lavas, intercalatedrhyodacitic lavas andvolcaniclastic rocks, associated with limestones. The metabasaltshave trace element patterns typically of transitional tholeiitic-alkaline affinity, and their Nd-isotopes suggest some crustal contamination. The Nd-isotopes of the rhyodacitic suite show thatthese rocks most likely originated-~ by melting of continental crust. (2) An alkaline bimodal suite of extrusive and intrusive metabasalts and trachytes of Ordovician age, associated with volcaniclastics. (3) A thick,monotonous sequence of Ordovician to Silurian (?) deep marine pillow lavas, associated with black shalesand cherts. Thesemetabasalts have trace element pattern typical of MORB, and show only minor Nd-isotopic evidence of crustal contamination. The geotectonic model presented for this assemblage of volcanic and sedimentary rocks invokes progressive rifting, initially in a continental setting, and finally, in Silurian (?) time,resulting in anoceanic basin. The volcanics of the KaczawaMts arefurther discussed andcorrelated with similar, time-equivalent rock sequences in the Sudetes and elsewhere in the Variscides.

This paper is a result of a long-term cooperation between University ofWroclaw, University of Bergen,and UniversitC B. Pascal and CNRS in Clermont-Ferrand. We thank for the financial support and forthe possibility of using the analyticalfacilities in the geology departments of these universities. R. K. acknowledges the support given by the grant MEN 251/1/ING/W.U.Wr, and H. F. for grants given by the University of Bergen to travel to Poland for doing field Fig. 10. (a) Lower and Mid-Palaeozoic volcanic rocks and work.We further gratefullyacknowledge theadvantageous mafic-ultramafic complexesof the Sudetes area. Inset map shows long-term cooperation with our colleagues of the Kaczawa team: Z. the location of the area in the Bohemian Massif (BM). Volcanic Urbanek, S. Lorenc,and our late friends Z. Baranowskiand A. rocks (solid symbolsare mafic, open are felsic): circles, Proterozoic Haydukiewicz.F. Vidal helped with the Sm-Ndanalyses and J. ? to Lower Palaeozoic (uncertain age); squares, Cambrianto Ellingsen with the illustrations. We further express our thanks to Ordovician; triangles, Silurian and Devonian. Fine grid, Mafic and thereviewers W. Narebski and P. A. Floyd for constructive ultramafic complexes (JE, Jesenik; NR, Nowa Ruda; SL, Sleza; critisism and helpful information. SO, Sobotin). Crosses, Variscan granitoids. Tectonic subdivisions: FSB, Fore-Sudetic Block; GK, Kaczawa Mts; GS, Grlitzer Schiefergebirge; GSB, Gory Sowie Block; IKB, Izera-Karkonosze References Block; KM, Klodzko Metamorphics; LAZ, Lusatian Anticlinal Zone; MS, Moravo-Silesian Zone; NZ, Niemcza shear zone; OSD, ALEKSANDROWSKI,1990.P. Early Carboniferous strike-slip displacements at Orlica-Snieznik Dome; MIF, Main Intra-Sudetic Fault. Based on the northeast periphery of the Variscan belt in Central Europe. InternationalConference on PaleozoicOrogens inCentral Europe, Kryza (1992). Gouingen-Giessen, Aug.-Sept. 1990. (b). Lower Palaeozoic volcanic rocks(squares, Cambrian: dots, ANSILEWSKI,J. 1954. The keratophyres of the Kaczawa Mts. Archiwum Ordovician; triangles, Silurian) and MORB-type mafic complexes Mineralogicme, 131-162. (In Polish, English summary). (stars) of the European Variscides. Main Variscan massifs ARTH,J. G. & HANSON,G. N. 1975. Geochemistry and origin of early (stippled): AM, Armorican Massif; BM, Bohemian Massif; IM, Precambriancrust of northeastern Minnesota. Geochimica et Cos- mochimica Acta, 39, 325-362. Iberian Massif; MC, MassifCentral. Tectonic zones:CI, Central BANKWITZ,P., BANKWITZ,E. & KRAMER,W. 1989. Tectonic development and Iberian; MO, Moldanubian; MS, Moravo-Silesian; OM, Ossa magmatism of a Cambro-Ordovician sequence, Vesser area, Thuringian Morena; RH, Rhenohercynian; SP, Southern Portuguese; ST, Forest. In: KRAMER, W.& WERNER, C.-D.(eds) Prevarixan mafic rocks Saxothuringian; LS, Lugosudetic;AF, Alpine Front. Based on inthe Saxothuringian zone. Guidebook of excursions in the GDR, Perekalina (1981) and Pin (1990). May/June 1989, 73-85. BARANOWSKI,Z. 1988. Lithofacies characteristic of trench-fill metasedirnents in the Radzimowice Slate (Paleozoic),Sudetes, SW Poland. Annales assumed from palaeomagnetic and some geochemical data SocietatisGeologorum Poloniae, 58, 3-4, 325-383. (In Polish, English (subduction-relatedvolcanic rocks), wellas fromas summary). indications of high-pressuremetamorphism inwestern - & LORENC,S. 1986. A volcanic-carbonate association in the Gory Kaczawskie, Western Sudetes. Geologische Rundschau, 75, 595-599. Europe (e.g. Franke 1989; Neugebauer 1989; Pin 1989, --, , HEINISCH, H.& SCHMIDT, K.1984. Der kambrische Vulkanismus 1990; Matte 1991), can not be convincingly answered based des Bober-Katzbach-Gebirges (Gory Kaczawskie, West-Sudeten, Polen). on the current data from the study area. Neues Jahrbuch fiir Geologie und Palaonrologie Monaohefte, 1, 1-26.

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Received 20 January 1992; revised typescript accepted 20 April 1993

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