Subduction- and non-subduction-related igneous rocks in the Central European Variscides: geochemical and Nd isotope evidence from the Kłodzko Metamorphic Complex, Polish Sudetes

Geodinamica Acta 16 (2003) 39–57 www.elsevier.com/locate/geoact

Original article

Subduction- and non-subduction-related igneous rocks in the Central European Variscides: geochemical and Nd isotope evidence from the Kłodzko Metamorphic Complex, Polish Sudetes Un ensemble magmatique composite dans la Chaîne varisque d’Europe centrale : étude géochimique et isotopique Sm–Nd du Complexe métamorphique de Kłodzko (Sudètes, Pologne) Ryszard Kryza a,*, Stanisław Mazur a, Christian Pin b b

a Institute of Geological Sciences, University of Wrocław, ul. Cybulskiego 30, 50-205 Wrocław, Poland Département de Géologie, CNRS, Université Blaise Pascal, O.P.G.C., 5, rue Kessler, 63038 Clermont-Ferrand cedex, France

Abstract The Kłodzko Metamorphic Complex (KMC) in the Central Sudetes is a composite outcrop of pre-Upper Devonian metasedimentary and metaigneous rocks, formed of several thrust units. The metaigneous rocks are geochemically diversified, and were interpreted to reflect a complex geodynamic setting of emplacement. The association of large amounts of felsic and mafic rocks is reminiscent of the model of Cambro-Ordovician bimodal, rift-related suites developed along the northern periphery of Gondwana. However, the felsic rocks are potash-poor, calc-alkaline in character, while the associated mafic rocks are, in part, metagabbros and cumulates resembling N-MORB, which is consistent with neither typical ensialic rift nor evolved MOR tectonic environments. Combined with published data, our new geochemical and Nd isotope results show that the metabasic rocks of the northeastern part of the KMC, not associated with felsic volcanics, are of within-plate type, with an eNd400 (assuming approximate youngest possible Silurian/Devonian age) of +6.8, typical of magmas derived from time-integrated depleted mantle sources. The metagabbros of the southwestern part of the KMC (associated with felsic rocks) range from slightly enriched to depleted rocks, and their eNd560 (assuming a Neoproterozoic age, K. Turniak, personal communication) scatters from +2.2 to +8.6, suggesting that hybrid sources and/or variable degrees of crustal contamination of a strongly depleted mantle source were involved. The intermediate and acidic rocks are peraluminous to metaluminous rhyolites, rhyodatites/dacites, and andesites (and volcaniclastics), with Na2O > K2O and large negative anomalies of Nb, Sr, and Ti. Their highly variable, but distinctly positive, eNd560 values (from +2.9 to +8.6, mostly clustered around +5.5) overlap those measured in the associated metagabbros, thereby substantiating close genetic relationships. Metarhyolites produced by crustal melting are conspicuously missing. A subduction-related environment is suggested for this peculiar mafic–felsic association of probable Neoproterozoic age. The overall geochemical variations, combined with the new age data, indicate that the KMC is a composite domain that displays fragments of a Pan-African active margin, telescoped during Variscan nappe tectonics, with rift-related volcanics and passive margin sequences probably related to the Palaeozoic break-up of Gondwana. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Résumé Le Complexe Métamorphique de Kłodzko (KMC), dans les Sudètes Centrales, correspond à un ensemble composite d’affleurements de roches métasédimentaires et orthodérivées d’âge anté-Dévonien supérieur, structurées sous la forme de plusieurs unités chevauchantes (fragments de nappes?) de contenus lithologiques et d’évolutions métamorphiques différents. Les roches orthodérivées, diverses du point de vue géochimique, ont jusqu’ici été interprétées comme les témoins d’un environnement géodynamique complexe. L’association de grandes quantités de roches felsiques et de roches basiques rappelle les suites bimodales d’âge Cambro-Ordovicien communément répandues à la marge septentrionale du Gondwana. Toutefois, les roches felsiques du KMC sont pauvres en potassium et de nature calco-alcaline, tandis que

* Corresponding author. E-mail address: [email protected] (R. Kryza). © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. DOI: 1 0 . 1 0 1 6 / S 0 9 8 5 - 3 1 1 1 ( 0 2 ) 0 0 0 0 4 - 9

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les roches basiques sont constituées, pour partie, de métagabbros et de cumulats à affinité N-MORB, ce qui ne s’accorde bien ni avec un environnement de rift ensialique typique, ni avec un contexte de ride médio-océanique. Avec les données déja publiées, nos résultats géochimiques et isotopiques Sm–Nd montrent que les métabasites de la partie nord-est du KMC, qui ne sont pas associées à des roches acides, sont de type intra-plaque, caractérisées par des eNdi (calculés en supposant un âge minimum de mise en place ignée de 400 Ma) de +6,8, ce qui indique un réservoir source mantellique appauvri en Terres Rares légères sur une base séculaire. Les métagabbros de la partie sud-ouest du KMC (associés à des roches felsiques) sont appauvris à légèrement enrichis du point de vue des éléments en traces incompatibles. Leurs eNdi, calculés pour un âge de 560 Ma (données U–Pb sur zircons, K. Turniak, comm. pers.) sont étalés entre +2,2 et +8,6, ce qui suggère l’implication de sources hybrides et/ou des degrés variables de contamination crustale d’une source mantellique fortement appauvrie. Les roches intermédiaires et acides associées sont des rhyolites peralumineuses à métalumineuses, des rhyodacites/dacites et des andésites, ainsi que des faciès volcanoclastiques, à caractère sodique (Na2O > K2O) et présentant de fortes anomalies négatives en Nb, Sr et Ti. Leurs signatures isotopiques du néodyme très variable, mais toujours nettement radiogénique (eNd560 de +2,9 à +8,6, pour la plupart regroupés autour d’une valeur de +5.5) se superposent à celle des métagabbros associés, et plaident ainsi en faveur d’un lien génétique. Deux interprétations sont a priori possibles : (a) les faciès intermédiaires et acides pourraient représenter les liquides différenciés (ou, dans quelques cas, des cumulats plagioclasiques) à partir des magmas basiques ; (b) ces faciès pourraient avoir été produits par fusion partielle en profondeur de roches basiques similaires à celles présentes à l’affleurement. Les caractéristiques géochimiques et isotopiques Sm–Nd des roches acides et intermédiaires, ainsi que l’absence de termes alcalins, semblent privilégier un environnement de type supra-subduction, dans lesquels de tels magmas felsiques sont souvent présents. L’absence de métarhyolites produites par fusion de matériaux crustaux anciens est un aspect important, démontré par les résultats isotopiques. Sur la base de ces données, un environnement de marge active paraît probable pour cette association mafique–felsique d’âge Néoprotérozoïque probable. L’ensemble de la variabilité géochimique observée, en accord avec les données radiométriques obtenues récemment (K. Turniak, comm. pers.), montre que le KMC est un domaine composite associant, par suite de la tectonique tangentielle varisque, des fragments d’une marge active d’âge Pan-Africain à des volcanites formées dans un contexte de rifting ainsi que des séquences de marge passive probablement liées à la dispersion du nord du Gondwana au Paléozoïque inférieur. © 2003 Éditions scientifiques et médicales Elsevier SAS. Tous droits réservés. Keywords: Geochemistry; Nd isotopes; Igneous rocks; Variscan Belt; Sudetes Mots clés : Géochimie ; Isotopes Nd ; Roches magmatiques ; Chaîne Varisque ; Sudètes

1. Introduction Lower Palaeozoic–Devonian metaigneous rocks, represented mostly by the so-called “bimodal” suites, are widespread in the Variscan Belt. Geochemically, they often correspond to recent within-plate volcanics (including alkali- and transitional-tholeiitic series) and are interpreted to have been emplaced in a continental rift system, active along the northern periphery of Gondwana in Cambrian–Ordovician times [1–6]. In many places, these suites are associated with tholeiitic metabasites of E-MORB to N-MORB affinities, often being assumed to represent more evolved (and broadly coeval or subsequent, e.g. Silurian?–Devonian) rifting stage, within oceanic crust [3,7]. According to Floyd et al. [6] and Crowley et al. [8], the alkali basalts were extracted from an enriched (tentatively ascribed to a plume) source, while the variably enriched MORB-like basalts resulted from the interaction of depleted and enriched mantle reservoirs. In some areas, the MORB-type basic rocks are associated with a large amount of acidic rock types (orthogneisses, metarhyolites, etc.), which often appear to be genetically related to the basites. This large proportion of the acidic rocks within the MORB-type complexes is unusual, compared with magmatic suites produced in recent mid-ocean ridge environments. To elucidate the genetic relationships between these acidic rocks and different basic associations (including ophiolitic assemblages, such as those of the S´ lVz˙ a and Nowa Ruda Massifs; see e.g. Majerowicz [9] and Pin et al. [10]), and to interpret their geodynamic emplacement

settings, we need more detailed geochemical and isotopic studies and better age constraints for these magmatic suites. Typical examples of such specific basic–acidic associations are found in Lower (and Middle?) Palaeozoic metaigneous complexes in the West Sudetes (Southwest Poland), i.e. in the eastern metamorphic envelope of the Variscan Karkonosze Pluton (Rudawy Janowickie) and in the Kłodzko Metamorphic Complex (KMC). The former has recently been studied in detail [11–14], whereas the latter still remains rather poorly understood [15,16]. The aim of this paper is (a) to present new geochemical and Sm–Nd isotopic data from the KMC and to combine them with earlier published results to get a more comprehensive image of the geochemical variation of mafic and felsic suites, and (b) to interpret the geochemistry of these rocks in terms of magma sources, possible differentiation processes, and likely tectonic settings for complex magmatic activities recorded in the eastern part of the Variscan Belt.

2. Geological setting 2.1. Outline tectonics and lithostratigraphy The KMC displays a composite outcrop of metasedimentary and metaigneous rocks in the Central Sudetes (Fig. 1). In spite of its small size (<200 km2), it is one of the key areas for regional geological interpretations, e.g. for timing of Palaeozoic orogenic processes in the eastern part of the Variscan

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Fig. 1. Geological position of the Kłodzko Metamorphic Complex in the Central Sudetes (map B) and Bohemian Massif (map A). Inset map A: EFZ—Elbe Fault Zone, ISF—Intra-Sudetic Fault, MGH—Mid-German Crystalline High, MO—Moldanubian Zone, MS—Moravo-Silesian Zone, NP—Northern Phyllite Zone, OFZ—Odra Fault Zone, RH—Rhenohercynian Zone, SX—Saxothuringian Zone. Map B: BU—Bardo Unit, ISF—Intra-Sudetic Fault, KMC—Kłodzko Metamorphic Complex, KZG—Kłodzko–Złoty Stok Granitoid, NZ—Niemcza Shear Zone, OSD—Orlica–S´ niez˙ nik Dome, RT—Ramzova Thrust, SBF—Sudetic Boundary Fault, SZ—Skrzynka Shear Zone. Abbreviations in the legend: C1—Lower Carboniferous, Cm3—Upper Cambrian, D—Devonian, D3—Upper Devonian, Or1—Lower Ordovician, Pt3—Upper Proterozoic, Pz1—Lower Palaeozoic, S2—Upper Silurian.

Belt [17–21]. Its important role in tectonic models comes from the early recognized sedimentary contact between palaeontologically documented, unmetamorphosed Upper Devonian carbonates and underlying folded and metamorphosed basement rocks [22,23]. The basement rocks contain crystalline limestones with coralline fauna, originally assigned to the Ludlowian [24,25]. This post-Silurian and preUpper Devonian unconformity was taken as evidence for an important role of the Caledonian orogeny in that part of the Variscides. However, more recently, the coralline fauna has been re-defined as Mid-Devonian [26], and the tectonic exhumation of the metamorphic basement rocks interpreted as an Eo–Variscan event [21,27]. The metaigneous rocks of the KMC were found to display diversified geochemical characteristics, which were interpreted in terms of the complex geotectonic setting of their emplacement [28]. This interpretation assumed that these rocks form parts of a single, and generally coherent, sedimentary–magmatic succession [28,29]. However, various parts of the KMC, which consist of various lithologies of

different magmatic and metamorphic histories, may represent individual tectonic units derived from originally separate settings, subsequently juxtaposed by tectonic displacements [22]. Recent petrological and structural studies [30] provide arguments in favour of the latter interpretation. According to Kryza and Mazur [30] and Mazur and Kryza [31], the KMC is formed of several thrust units (fragments of nappes?) with different protoliths and metamorphic paths (Figs. 2 and 3). In the northeastern part of the area, they include: (a) Mały Boz˙ ków Unit (MBU)—a progradational shelf–sedimentary succession deposited at a passive continental margin (with Early Givetian coralline fauna [26]); (b) ŁTczna Unit (LU)—a mélange emplaced, most likely, on a continental slope; (c) Bierkowice Unit (BU)—a mafic volcanic suite probably emplaced in a rift environment; (d) Kłodzko–Twierdza Unit (KTU)—a variegated volcano–sedimentary succession with features indicating active continental margin affinities. In the southwestern part of the KMC, the unit(s) of S´ cinawka (SU) and Orla–Gołogłowy (OGU) can be distinguished, which possibly represent fragments of

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Fig. 2. Geological sketch of the Kłodzko Metamorphic Complex (partly based on Emerle-Tubielewicz [32]).

oceanic-type crust associated with minor pelagic metasedimentary rocks; the position of the southernmost part of the KMC adjoining the Variscan Kłodzko–Złoty Stok Granitoids remains uncertain. 2.2. Metaigneous rocks: distribution and petrography 2.2.1. Mały Boz˙ków and ŁTczna Units No metaigneous rocks occur in the MBU, whereas relatively small bodies of metabasites, associated with chlorite schists, are found in the ŁTczna mélange. The metabasites are mostly fine-grained, strongly foliated rocks, composed of amphibole (ACTI, MG-HORN, and ACTI, from core, through mantle, to rim, respectively), albite, epidote, quartz, chlorite, calcite, and iron oxides. 2.2.2. Bierkowice Unit This tectonic unit is formed of massive to moderately foliated fine-grained metabasic rocks, traditionally referred to as greenstones, with minor intercalations of chlorite schists. The greenstones are composed of amphibole (TSCHto-Mg-HORN, rimmed by ACTI), albite, epidote, calcite, chlorite, and opaques. Scarce garnet is locally found.

2.2.3. Kłodzko–Twierdza Unit In this unit, the dominating phyllites are associated with mafic and felsic metavolcanic and volcaniclastic rocks. The mafic rocks form a 500 m wide outcrop along the northeastern edge of the unit and, also, minor intercalations within phyllites elsewhere. The metabasites vary in texture and composition, from massive rocks composed of amphibole (Fe-HORN rimmed by ACTI), coexisting with albite, oligoclase, and epidote, to various types containing different proportions of quartz, chlorite, and white mica. The felsic rocks are represented by thin bodies of pinkish and massive metarhyolites, mostly within Ab–Chl schists in the area of Kłodzko. The metarhyolites are composed of small K-feldspar phenocrysts and a microcrystalline matrix of quartz, feldspar, and white mica, accompanied by chlorite, calcite, and iron oxides. Laminated and strongly foliated varieties probably represent felsic metavolcaniclastics. The metarhyolites in the largest outcrop in the southern part of the KTU (Fig. 2) are pinkish-grey, fairly massive, and fine-grained rocks, composed of abundant plagioclase phenocrysts (1–5 mm in size) enclosed in a matrix of quartz and subordinate feldspar and white mica. Aligned re-crystallized

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quartz domains and fine white mica aggregates define indistinct foliation. 2.2.4. S´ cinawka Unit This unit is formed only of metabasic rocks represented by slightly deformed metagabbros and more strongly foliated amphibolites (flaser gabbros), grading into each other. The metagabbros are medium- to coarse-grained (1–5 mm grain size) and rather massive rocks composed of macroscopically blackish amphibole (TSCH and Mg-HORN, with partly inherited igneous form and composition?), plagioclase (up to 60% An), epidote, minor chlorite, and ilmenite largely replaced by sphene. Grossularite- and almandine-rich garnet is occasionally found. The amphibolites display distinct foliation and lineation, while the modal composition and mineral chemistry are similar to those of the metagabbros. 2.2.5. Orla–Gołogłowy Unit The metagabbros of this unit range from fine- to coarsegrained and are variably deformed, up to common gabbroic mylonites. Typical massive, coarse-grained metagabbros from Orla Hill display well-preserved ophitic texture and are composed of large prismatic, pale-green-to-brownish amphibole, 3–5 mm in size, and of primary, igneous? appearance, and interstitial plagioclase (intensely saussuritized), with minor epidote, chlorite, apatite, and opaques. Orthogneisses of the OGU can be subdivided into two petrographic varieties: Gołogłowy plagioclase gneisses and two-feldspar S´ cinawka gneisses. The Gołogłowy gneisses, associated with metagabbros (Fig. 2), typically are grey, medium-grained rocks, with distinct foliation and augen or layered texture. They consist of quartz, plagioclase porphyroblasts (up to 5 mm in size), white mica, and minor epidote, chlorite, biotite, garnet, and opaques. The gneisses are often mylonitized. The S´ cinawka gneisses are found as subordinate bodies, from tens of centimetres up to several tens of metres thick, within amphibolites of the northwestern part of the OGU (indicated as “amphibolite, minor gneiss” in Fig. 2). They range from undeformed porphyritic metagranites to strongly foliated varieties. The main components are plagioclase (phenocrysts and in matrix), quartz, and K-feldspar, with accessory biotite, white mica, garnet, and epidote. Locally, aplite veins, up to ca. 20 cm thick, are common. Dark, amphibolite-like rocks surrounding the S´ cinawka gneisses in the western part of that unit appear to have andesitic composition (sample M75). Felsic metaigneous rocks of the OGU form numerous, usually foliation-parallel bodies, from tens of centimetres up to tens of (or a few hundred?) metres thick, within metagabbros and orthogneisses. Most commonly, they are massive to weakly foliated, aphanitic to fine-grained, porphyritic rocks, with fairly variable mineral composition, reflecting variable chemistry. Chemically less evolved rocks, corresponding to dacite/rhyodacite (some andesite?), are light grey in colour and often show an igneous microtexture composed of abun-

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dant plagioclase phenocrysts (0.1–1 mm long) in a very fine-grained (<0.05 mm) matrix of secondary albite, epidote, amphibole, and chlorite. The bluish-green amphibole also forms scarce phenocrysts, 1–3 mm in size. Rocks of more evolved rhyolitic composition also display rather massive fine-grained, porphyritic texture, and contain K-feldspar and plagioclase phenocrysts (0.2–3 mm large) in a matrix of quartz, feldspars, and white mica (grain-size <0.1 mm). Garnet phenocrysts, usually partly replaced by chlorite, are fairly common. 2.3. Metamorphic and structural evolution According to Wojciechowska [29], the KMC experienced, in general, a greenschist and, locally, epidote–amphibolite facies metamorphism, with metamorphic grade increasing south- and westwards. However, Kozłowska-Koch [33] showed that the rock assemblage went through a complex metamorphic evolution, under the amphibolite facies, followed by the greenschist facies. Recent petrological and tectonic research highlighted in greater detail the metamorphic and structural evolution of the KMC [30,34,35]. The MBU (Fig. 2), comprising mainly phyllites and clastic metasediments, experienced only weak metamorphism and deformation under the lower range of the greenschist facies. The other units of the northeastern area went through significantly stronger metamorphism and deformation. In the LU, metabasic rocks bear evidence of P–T conditions of the epidote–amphibolite or lower range of the amphibolite facies (Mg- or Fe-HORN, or Fe-EDEN + albite). The metabasic rocks of the BU have evidence of similar peak PT conditions (Mg-HORN + albite + rare garnet). In two samples of these rocks, relict Na–Ca amphiboles were found, indicating an early metamorphic episode, at relatively high P/T conditions. The rocks of the KTU display roughly similar metamorphism (coexisting albite and oligoclase, together with Fe-HORN or Fe-PARG rimmed by ACTI). The southwestern area of the KMC, in general, displays higher metamorphic grades compared to the northeastern and eastern area, but particular rock complexes there seem to record different P–T paths. The metagabbros and amphibolites of the SU are relatively strongly metamorphosed under amphibolite facies conditions (TSCH, Mg-HORN, or FePARG + plagioclase up to 60% An, and garnet Alm51, Grs30, Prp11, Sps2). The “metamorphic maturity” of these rocks is confirmed by the lack of earlier metamorphic assemblages and no significant chemical zonation in the minerals. Preliminary PT estimates indicate possible high P of metamorphism, ca. or above 15 kbar [35]. The lithologically variable OGU bears distinct records of complex metamorphic evolution. The peak metamorphic conditions correspond to the amphibolite facies (MgHORN/TSCH + calcic plagioclase + Mn-poor garnet. However, the peak metamorphism was preceded by an earlier lower-grade event (within the greenschist or epidote– amphibolite facies), as inferred from (a) common relict

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amphibole cores (often corroded) of actinolite composition, overgrown by Mg-HORN and TSCH, (b) garnet zonation, with outward increasing Alm and Prp and decreasing Sps, and (c) usually distinct ‘inverse’ zonation of plagioclase (An content increasing from core to rim). The peak assemblage is partly replaced by a greenschist facies paragenesis. The eastern part of the southwestern area, between Kłodzko and Krosnowice (Fig. 2), is strongly influenced by thermal metamorphism along the contact with the Variscan Kłodzko–Złoty Stok Granitoids (cordierite hornfelses, grossularite–pyroxene metabasites). Wojciechowska [29,36] interpreted the KMC as forming a single 1500–2000 m thick succession that, as a whole, had gone through a sequence of five deformation events. The main phase of deformation and metamorphism was connected with a northnortheast–southsouthwest compression. The rock complex was interpreted (op. cit.) to form a large south-verging isoclinal anticline, with the axis dipping to the east. According to Wojciechowska, the S´ cinawka Fault, separating the northern and southern parts of the KMC [37], formed after the main metamorphic event, at shallow crustal levels. According to Kryza and Mazur [30], the structure of the KMC is the result of a series of tectonic events. First, the nappe-like units were thrust to the westnorthwest, probably at the turn of Mid- and Late Devonian (the sense of thrusting typical of the northern flank of the Variscan Belt). The contemporaneous, and partly subsequent, metamorphism was connected with ductile shearing in a dextral transpressional regime, resulting in localized mylonitization. The latter deformation modified the earlier nappe contacts, changing them into dextral strike–slip shear zones. The dextral transpression caused the exhumation of the basement rocks and the formation of the pre-Upper Devonian unconformity. The subsequent westnorthwest–eastsoutheast sinistral strike–slip displacements occurred under vanishing meta-

Fig. 3. Tectonic subdivisions and lithology of the Kłodzko Metamorphic Complex (see previous page). Legend:

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morphic conditions and, apparently, were contemporaneous with the development of the Bardo Basin (Fig. 2). The final deformation, during Carboniferous times, folded the metamorphic basement rocks, together with the Upper Devonian limestones and sediments of the Bardo Basin.

3. Geochemistry 3.1. Previous studies, the database and methods Based on 12 major and trace-element analyses and Sm–Nd data for five samples, NarVbski et al. [15,28] distinguished four geochemical types of the metabasites in the KMC. Type 1, in the middle part B of the lithostratigraphic sequence [36], corresponds to WP (e.g. rift-related) basalts. The remaining three types (all in the upper part C of the sequence) included: (2) high-Ti amphibolites of T-MORB character; (3) low-Ti amphibolites, geochemically transitional between magmas of constructive and destructive plate margins; (4) gabbro-amphibolites of variable geochemical character, some indicative of cumulation processes. According to NarVbski et al. [28] and NarVbski [38], the latter three types could have developed in a complex geotectonic setting: “within a narrow oceanic basin (Red Sea type), possibly cut by a transform fault, and subsequently influenced by a subduction zone and/or mantle plume”. Taking into account the described geochemical variation and the consequent complex interpretation, Kryza and Mazur [30] analysed major and trace elements in 12 new samples of metaigneous rocks of the KMC, including three felsic metavolcanics. Later on, six more samples of felsic rocks were analysed for major and trace elements, and a set of 12 representative samples of mafic and felsic rocks were measured for Sm–Nd isotopes (C. Pin). Altogether, the database considered here in this paper (Table 1) includes 29 analyses

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of major and trace elements (11 from NarVbski et al. [28]), and Sm–Nd isotope data for 17 specimens (five from NarVbski et al. [28]; Table 2). The above mentioned 18 new analyses of major and trace elements were made in Actlabs, Canada, using combined XRF and ICP-MS techniques (Actlabs code “4Lithores”). Sm–Nd isotopic data were obtained in Clermont-Ferrand, using methods described by Pin and Santos Zalduegui [39]. In order to take into account that the igneous emplacement age of the studied rocks is still poorly constrained, the Nd isotope data have been corrected for in situ decay of 147Sm for two dates believed to encompass the plausible range of formation age of the igneous protoliths: 400 Ma and 560 Ma (see Section 4). The age-corrected isotope ratios are reported using the usual epsilon notation (Table 2). In most cases, the eNd values calculated for the two ages differ by less than one unit, and can be used to draw inferences on the source reservoirs and possible genetic links of the studied samples. 3.2. Geochemical characteristics The analysed samples show varying degrees of low- to medium-grade metamorphic alteration, which may have caused selective element mobility, especially for the largeion-lithophile (LIL) elements [40]. For this reason, our characterization and interpretation of the metaigneous rocks is based mainly on elements that are considered relatively stable during alteration, such as the high-field-strength (HFS) elements, Th and the rare earth elements (REE) [41]. Good linear relationships between pairs of stable elements, together with generally smooth normalized patterns for a sequence of incompatible trace elements, including the REE, suggest that these elements reflect magmatic chemical variations [6]. 3.2.1. Metabasites of the northeastern area The metabasic rocks of the northeastern part of the KMC, i.e. from the BU (referred to as Group M1, comprising samples 25, 27, 77 (= IW664), 78, 85, M65 and M66B), belong to the subalkaline, tholeiitic series, and plot within basalt composition, close to the alkali basalt field in Winchester and Floyd’s [42] diagram (Fig. 4). They display moderate to strong enrichment in most incompatible elements (Zr/Y 5–7, Zr/Nb 9–12). Several samples have a negative Sr anomaly (Fig. 6a and b), indicating possible plagioclase fractionation or Sr mobility during metamorphism. Negative anomalies of Nb are conspicuously absent, as shown by Th/Nb ratios (0.06–0.08), well within the range of values typical of within-plate and MOR basalts not affected by crustal contamination. Indeed, the analyses plot mostly into the WPT or T-MORB fields of discrimination tectonic setting diagrams. The high positive eNd400 values of +6.1 and +6.8 (+6.1 and 6.9 for a 560 Ma age) for two samples point to an origin from a mantle reservoir that was markedly depleted in LREE on a time-integrated basis (i.e. which evolved with Sm/Nd ratio higher than that of the chondritic reservoir during most of its history). However, this source suffered a

LREE enrichment process at the time of or shortly before magma generation, as shown by the LREE-enriched patterns of the metabasites. The metabasalt representative of the KTU (sample M61) is relatively less enriched in LREE and in most incompatible trace elements (e.g. low Nb—Fig. 6a), and it deviates from the main cluster of the BU samples on various trace-element diagrams (e.g. it corresponds to Andesite/Basalt in Winchester and Floyd’s [42] diagram—Fig. 4, but its Ti/V ratio is around 50, typical of OFB). 3.2.2. Metabasites of the southwestern area Metagabbros and amphibolites of the S´ cinawka and Orla– Gołogłowy Units of the southwestern part of the KMC (Group M2) are also of subalkaline tholeiitic character, although predominantly plotting near the boundary with the calc-alkaline series on the AFM diagram (Fig. 5). These rocks are geochemically variable and can be subdivided into several groups. Group M2a comprises four samples of metagabbros (35, 108, M67, and M69), which are slightly enriched, E-MORBlike rocks (Fig. 6c and d), broadly similar to Group M1, with Th/Nb ca. 0.06–0.07 (with the exception of M69, 0.12, possibly indicating crustal contamination or a subduction influence), Zr/Y 4–7, and Zr/Nb 11–16. Group M2b of metagabbros and amphibolites (M68, 40 and, possibly, 50/1) has clear N-MORB incompatible traceelement patterns (Fig. 6c and d): LREE depletion, flat HREE, and high Zr/Nb (64 in sample M68). This is consistent with their very high eNd, irrespective of their geological age (+7.3 to +8.8), typical of magmas extracted from a source that was severely depleted in Nd relative to Sm on a time-integrated basis. The amphibolite IW662 from KsiTz˙ ek (southwest of Kłodzko) has also a fairly high eNd560 = +7.4, but its geological position is obscure. Group M2c comprises metagabbros (30, M71A, and 50/1) with distinct trace-element anomalies (Fig. 6e and f). All three samples display rather flat and convex-shaped REE patterns (Fig. 6f), resembling those of MORB-type magmas. However, their trace-element anomalies (e.g. negative for Zr and Hf, and positive for Sr and P) reflect fractionation and crystal accumulation processes, suggesting that the convex REE patterns probably result from clinopyroxene or amphibole accumulation, and do not necessarily reflect an N-MORB derivation. Indeed, their eNd560 values (+2.2 to +4.5) are much lower than those measured in all other mafic rocks in the KMC, and rule out an origin from the MORB-source reservoir (eNd ca. +9 in Late Precambrian–Early Palaeozoic times [46]). In general, the mafic rocks of the southwestern area of the KMC tend to be rather dispersed on discrimination tectonic setting diagrams (keeping in mind that such diagrams should be used for basaltic liquids, not cumulates), with most analyses plotting within the N-MORB and T-MORB fields. On the Zr/Y–Zr diagram (not shown here), several samples plot within the IAB field; however, this

R. Kryza et al. / Geodinamica Acta 16 (2003) 39–57

47

Table 1 Chemical analyses of metaigneous rocks from the Kłodzko Metamorphic Complex (* from NarVbski et al. [15], ’ after Kryza and Mazur [30], ’’ – this study) Unit Sample

B 25/1*

B 27*

B 77*

B 78*

B 85*

BU M65’

BU M66B’

KTU M61’

C 35*

C 108*

SU M67’

SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total

48.40 1.22 14.10 12.00 0.19 7.87 12.40 1.48 0.28 0.16 1.68 99.78

50.15 2.57 13.05 15.85 0.22 2.50 5.78 6.14 0.57 0.90 1.91 99.64

45.90 3.25 13.15 16.20 0.22 6.78 7.50 3.40 0.08 0.40 3.06 99.94

49.60 3.21 12.70 16.90 0.24 4.66 6.66 4.00 0.33 0.47 1.09 99.86

47.80 3.31 12.70 16.40 0.21 5.14 7.79 4.26 0.18 0.51 1.46 99.76

46.98 3.08 12.94 16.34 0.25 5.65 8.31 3.55 0.21 0.34 2.55 100.20

52.35 2.90 12.38 12.82 0.27 2.25 13.33 0.43 0.12 0.45 3.52 100.82

46.20 1.96 14.49 12.64 0.19 8.65 8.82 2.71 0.30 0.30 3.42 99.68

51.10 1.94 13.40 11.20 0.19 7.16 8.60 3.50 0.54 0.31 1.10 99.04

45.90 2.23 14.00 13.10 0.24 5.29 11.30 4.15 0.20 0.30 3.08 99.79

46.56 2.30 14.29 14.36 0.25 5.72 10.37 3.00 0.25 0.23 2.16 99.49

Cr Ni Co Sc V Cu Pb Zn Sn W Sb K Rb Cs Ba Sr Tl Ga Li Ta Nb Hf Zr Ti Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

325 89 50 55.0 290 12 12 81

7 8 31 23.6 194 49 15 138

91 57 50 38.4 400 251 9 148

16 23 40 29.0 340 111 13 116

42 47 49 32.0 408 106 8 127

664 1

2739 4

1494 3

4483 7

1660 3

37 265

172 99

25 149

56 180

63 174

182 242

25 181

15 9

25 6

20 11

23 5

25 5

392 242 42 30.0 227 51 0 133 1 1.5 1.60 2490 3 1.30 121 249 0.00 20

64 45 41 41.0 389 139 11 105

4732 5

47 39 25 30.0 447 23 0 79 2 6.1 0.03 996 0 0.00 34 829 0.00 28

273 124 35 33.0 252 46 10 104

2324 9

68 67 51 38.0 411 167 0 125 2 5.2 0.00 1743 0 0.00 59 204 0.00 23

15 3

17 5

66 54 43 43.0 402 213 0 121 1 4.7 0.00 2075 3 0.00 45 172 0.00 21

8.0 0.0 69 7314 22.0 0.60

36.0 8.6 352 15407 64.0 0.00

20.0 5.2 201 19484 39.0 1.30

29.0 6.1 261 19244 39.0 1.70

28.0 6.7 283 19843 49.0 1.90

17.10 43.60

21.90 50.90

22.70 53.30

9.36 22.60

9.92 24.70

2.46 1.30

11.10 3.44

6.50 2.26

7.58 2.42

8.08 2.73

4.05 1.36

4.73 1.73

0.65

1.95

1.14

1.29

1.54

0.71

0.93

2.51 0.41

5.77 0.85

3.18 0.49

3.16 0.48

4.13 0.61

0.5 7.5 3.8 167 11720 32.4 0.75 0.26 11.40 28.10 3.60 18.60 5.04 1.91 5.60 0.93 5.78 1.21 3.46 0.48 2.96 0.44

12.0 3.7 141 13369 35.0 0.70

33.50 79.40

1.6 20.2 4.8 203 17415 35.9 0.12 0.63 17.60 41.10 5.07 24.40 6.46 2.32 6.77 1.08 6.51 1.33 3.73 0.51 3.12 0.42

14.0 5.8 159 11630 23.0 0.90

3.00 9.44

1.3 16.4 5.1 206 18441 35.9 1.24 0.37 16.00 38.00 4.86 24.60 6.71 2.22 6.85 1.15 6.79 1.39 3.85 0.53 3.14 0.43

2.32 0.40

2.83 0.42

0.7 8.8 3.6 141 13771 33.8 0.63 0.22 8.86 22.30 3.04 15.90 4.81 1.80 5.46 0.98 6.05 1.27 3.74 0.54 3.31 0.47

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Unit Sample

SU M69’

C 40*

C 50/1*

SU M68’

C 52*

C 30*

OGU M71A’

KTU K102’’

KTU K114’’

OGU K242’’

OGU K197’’

SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total

52.23 1.89 14.13 10.81 0.15 6.56 9.23 3.54 0.40 0.19 1.69 100.82

48.80 0.51 14.60 8.67 0.19 9.88 12.60 2.40 0.07 0.08 1.25 99.05

50.50 1.64 13.20 15.30 0.25 5.70 9.92 2.33 0.18 0.20 0.62 99.84

53.00 1.10 14.20 12.41 0.22 6.21 9.24 3.07 0.23 0.10 1.16 100.94

43.00 0.93 17.60 12.10 0.25 8.28 11.90 1.66 0.79 0.32 2.84 99.67

49.70 0.48 15.80 5.64 0.12 10.00 12.30 1.95 0.80 0.80 3.12 100.71

42.81 0.71 20.09 10.06 0.22 6.31 14.31 1.50 0.80 0.40 3.26 100.47

63.83 0.56 15.98 5.10 0.07 2.73 2.07 4.81 1.54 0.16 3.59 100.44

70.51 0.40 14.11 3.21 0.06 1.35 1.45 5.86 0.86 0.10 2.07 99.98

79.48 0.14 10.92 2.11 0.02 0.40 1.16 4.18 0.96 0.04 0.86 100.27

61.45 0.59 16.85 5.10 0.09 3.06 4.96 4.86 1.14 0.15 2.10 100.34

Cr Ni Co Sc V Cu Pb Zn Sn W Sb K Rb Cs Ba Sr Tl Ga Li Ta Nb Hf Zr Ti Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

178 98 40 41.0 329 0 0 92 1 7.7 0.03 3321 5 0.00 152 284 0.00 19

435 107 48 72.0 218 67 11 117

101 51 41 43.0 398 123 0 105

175 52 38 0.0 310 17 9 100

515 45 29 39.0 151 31 9 38

581 2

1494 2

6558 18

6641 19

14 149

0 108

280 658

238 295

11 3

0 3

222 59 40 42.0 318 21 0 102 0 9.6 0.00 1909 5 0.00 40 138 0.00 18

14 15

11 13

176 40 27 39.0 275 10 0 75 0 10.4 0.07 6641 15 0.30 241 775 0.08 19

22 0 27 13.0 95 16 12 60 1 44.0 0.90 12785 36 0.80 473 233 0.30 17

0 0 12 8.0 44 27 7 53 1 32.0 0.90 7140 13 0.00 430 118 0.00 15

62 425 17 3.0 16 0 7 0 4 93.0 1.10 7970 15 0.00 844 157 0.10 13

36 0 24 13.0 93 0 10 103 0 54.0 0.80 9465 24 0.00 341 620 0.20 19

3.0 0.8 37 3057 16.0 0.00

4.8 2.3 0 9832 0.0 0.60

5.0 0.0 34 5575 20.0 0.00

4.0 0.5 28 2878 12.0 0.00

1.39 4.50

4.53 13.00

4.51 17.10

0.98 3.28

1.54 0.65

3.03 1.16

4.20 1.31

0.92 0.41

0.47

0.80

0.00

0.26

1.89 0.32

2.96 0.48

1.91 0.28

1.01 0.17

0.0 1.0 0.6 14 4262 17.0 0.09 0.10 3.98 11.50 1.78 10.50 3.31 1.17 3.33 0.51 3.19 0.67 1.93 0.26 1.62 0.23

0.30 5.0 3.4 129 3381 18.0 3.20 1.40 16.50 35.60 4.08 17.10 3.50 0.95 3.20 0.50 2.80 0.60 1.80 0.29 1.90 0.27

0.50 5.0 4.6 176 2404 18.0 5.30 1.60 11.90 29.70 2.82 11.90 2.70 0.65 2.80 0.50 3.00 0.60 2.10 0.33 2.20 0.34

1.30 15.0 8.1 253 833 59.0 8.80 3.50 36.20 81.10 9.17 39.60 9.10 1.43 9.30 1.70 9.90 2.10 6.80 1.06 7.00 1.02

0.20 3.0 3.0 106 3513 14.0 1.70 0.80 12.70 28.40 3.54 15.70 3.30 1.03 3.10 0.50 2.60 0.50 1.60 0.23 1.50 0.21

1.1 10.8 3.8 147 11361 36.0 1.32 0.84 12.10 27.10 3.19 15.50 4.33 1.62 5.23 0.95 6.16 1.36 3.99 0.58 3.61 0.53

0.2 1.1 1.9 70 6571 24.0 0.06 0.06 1.94 5.90 0.93 5.70 2.11 0.84 2.82 0.55 3.72 0.87 2.68 0.40 2.50 0.40

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Unit Sample

OGU M72’

OGU M74’

OGU M75’

OGU K174’’

OGU M71B’

KTU? K135’’

OGU M62’

SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total

77.92 0.02 12.10 0.52 0.00 0.11 0.12 3.82 3.37 0.02 0.92 98.92

76.99 0.08 12.56 1.13 0.01 0.09 0.15 4.36 3.58 0.03 0.73 99.71

56.12 1.14 14.54 8.61 0.16 4.72 6.48 3.66 0.77 0.11 1.85 98.16

76.17 0.10 12.43 1.64 0.03 0.19 1.61 6.04 0.66 0.02 1.57 100.46

64.55 0.06 20.86 1.17 0.03 0.47 4.36 6.17 0.91 0.05 1.31 99.94

74.29 0.10 14.41 1.64 0.03 0.49 0.83 5.21 1.92 0.04 1.23 100.19

78.04 0.28 12.56 1.00 0.02 0.23 0.11 4.28 1.38 0.07 1.34 99.32

Cr Ni Co Sc V Cu Pb Zn Sn W Sb K Rb Cs Ba Sr Tl Ga Li Ta Nb Hf Zr Ti Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

71 0 16 1.0 0 0 15 37 3 58.4 3.20 27975 99 1.60 208 24 0.61 19

0 0 19 2.0 0 0 6 56 4 70.0 0.03 29719 65 0.30 905 24 0.26 24

84 33 47 27.0 174 31 0 128 2 67.1 0.05 6392 17 0.20 312 130 0.11 20

0 0 15 3.0 10 0 6 39 6 82.0 0.70 5479 14 0.00 465 102 0.10 21

0 0 8 2.0 12 0 0 34 0 24.0 0.00 7554 23 0.60 278 941 0.11 16

0 0 19 2.0 7 0 8 0 0 106.0 1.10 15940 45 3.30 746 227 0.40 11

0 0 5 8.0 17 17 9 58 1 12.6 1.20 11456 35 0.07 376 82 0.22 14

4.4 29.9 4.6 75 144 64.0 17.50 4.56 7.88 18.20 2.03 8.75 3.39 0.13 4.43 1.16 8.45 2.00 6.81 1.16 7.61 1.15

1.1 10.4 7.3 192 456 53.6 8.12 3.24 20.10 47.20 5.34 22.90 6.43 0.42 6.64 1.29 8.77 1.99 6.23 1.07 7.21 1.08

0.4 4.8 4.7 179 6864 43.6 2.03 0.93 13.20 30.90 3.90 19.20 5.56 1.43 6.11 1.14 7.45 1.60 4.83 0.73 4.54 0.67

1.00 9.0 6.7 202 576 34.0 7.60 2.90 15.50 41.80 4.43 19.60 5.10 0.61 4.90 0.90 5.70 1.30 4.30 0.78 5.70 0.92

0.0 0.0 0.8 50 378 2.0 0.12 0.13 3.72 5.10 0.47 1.79 0.36 0.50 0.35 0.05 0.32 0.06 0.20 0.03 0.24 0.04

0.20 3.0 1.5 63 600 3.0 2.00 0.60 8.90 13.90 1.42 5.10 0.80 0.29 0.70 0.00 0.40 0.00 0.30 0.05 0.40 0.08

0.3 3.3 4.7 181 1709 36.0 3.88 2.77 18.20 40.00 4.62 20.80 5.02 1.15 5.15 0.00 5.38 1.25 3.90 0.60 4.18 0.66

Lithostratigraphic/tectonic units after Wojciechowska (in [28]): B – middle part, C – upper part of the KMC succession; after Kryza and Mazur [30]: BU – Bierkowice, KTU – Kłodzko-Twierdza, SU – S´ cinawka, OGU – Orla – Gołogłowy Units.

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Table 2 Sm–Nd isotope data for metaigneous rocks of the Kłodzko Metamorphic Complex (for sample location see Appendix 1) Sample 77 (IW664) M65 50/1 (IW657) M68 52 (IW655) 30 (IW663) M71A IW662 K102 K242 K197 M72 M74 M75 K174 Gorz Orla K135 M62

Sm 2.65 6.63 3.52 2.35 3.63 2.16 3.46 3.69 3.56 8.87 4.28 3.19 6.69 6.18 5.03 0.281 3.28 0.872 5.42

Nd 8.20 25.6 10.9 4.40 12.1 6.43 11.8 13.5 17.3 38.0 16.3 10.1 24.9 22.4 20.0 1.53 14.3 5.49 23.9

147

Sm/144Nd 0.1951 0.1567 0.1949 0.2222 0.1823 0.2031 0.1769 0.1649 0.1245 0.1410 0.1592 0.1907 0.1622 0.1670 0.1521 0.1109 0.1390 0.0960 0.1371

143

Nd/144Nd 0.512986 0.512847 0.513009 0.513174 0.512819 0.512775 0.512796 0.512904 0.512523 0.512630 0.512731 0.512880 0.512791 0.512853 0.512806 0.512563 0.512587 0.512455 0.512864

± 12 8 11 9 12 10 8 9 8 7 8 6 9 7 7 17 10 9 11

eNd400 Ma +6.8 +6.1 +7.3 +9.1 +4.2 +2.3 +4.1 +6.8 +1.4 +2.6 +3.7 +5.0 +4.7 +5.7 +5.5 +2.9 +1.9 +1.5 +7.4

eNd560 Ma +6.9 +6.9 +7.3 +8.6 +4.5 +2.2 +4.5 +7.4 +2.9 +3.8 +6.4 +5.1 +5.4 +6.3 +6.4 +4.6 +3.1 +3.6 +8.6

3.2.3. Intermediate and acidic metaigneous rocks Felsic metavolcanic rocks (intermediate to acidic) are widespread in the OGU. Apart from that, small bodies of such rocks, mostly thin veins and volcaniclastic intercalations, are found in the variegated sequence of the KTU. The position of the two large rhyolitic outcrops, (a) northeast of Gołogłowy and Kłodzko and (b) south of Kłodzko, is rather obscure. They may represent separate tectonic units or continuations of (a) the OGU and (b) the KTU, respectively. Characteristically, no felsic rocks are associated with the Bierkowice metabasalts and with the S´ cinawka metagabbros.

Most of the felsic rocks show general geochemical similarity, although specific differences are observed between the samples. The analysed samples are peraluminous (seven samples) to metaluminous (three samples), have Na2O >> K2O (except M72), and all of them plot within the calcalkaline field on the AFM diagram (Fig. 5). In Winchester and Floyd’s [42] classification diagram (Fig. 4), the samples are dispersed between the rhyolite, through rhyodacite/ dacite, to andesite fields. Conventionally, based on some systematic differences in trace-element patterns, in particular on light to heavy REE fractionation, the intermediate/acidic rocks are subdivided into three groups. Group F1 (samples K102 and K114 from KTU and K197 and K242 from OGU) is moderately LREE

Fig. 4. Metaigneous rocks of the KMC on Winchester and Floyd’s [42] diagram. Open circles—metabasalts of the northeastern part of the KMC (group M1); full circles—metabasites, and full diamonds—metacumulates of the southwestern part of the KMC (Group M2a–c); intermediate/acidic rocks: + group F1; × group F2; * sample M72; full triangles—group F3.

Fig. 5. Irvine and Baragar’s [43] AFM diagram. Symbols as in Fig. 4.

might result, for example, from fractionation of zircon from the magma.

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Fig. 6. N-MORB-normalized multi-element variation diagrams (left) and “primitive-mantle”-normalized REE plots (right) for the KMC metabasites: group M1—a and b, group M2a and M2b—c and d, and group M2c “cumulates”—e and f. Normalization values for N-MORB are from Pearce [44] and Sun and McDonough [45]—for REE, and for “primitive mantle”—from G.A. Jenner (“NewPet” computer software).

enriched (Fig. 7a and b), with (La/Yb)N 3.5–5.8. Group F2 (samples M74, M75, and K174) displays flat HREE patterns (Fig. 7c and d) and slight LREE enrichment: (La/Yb)N 1.8–2.9. The eNd560 values in both F1 and F2 group felsic rocks range from +2.9 to +6.4. Similar Nd isotope characteristics are found in two other samples of felsic rocks: specimens Gorz and Orla (Table 2). Importantly, the observed range of eNd560 corresponds, in broad terms, to that measured in the mafic cumulates of Group M2c. Sample M72, of

strongly sheared metarhyolite, has a distinctly flat REE pattern ((La/Yb)N 0.70), but roughly similar eNd560 (= +5.1) as in the other felsic rocks described. Group F3 is represented by two samples: metarhyolite K135 and metaplagioclasite M71B, both having very low trace-element concentrations (0.1–1.0 that of MORB), unusually high LREE/HREE ratio ((La/Yb)N 10.5–15.0), and concave REE pattern (Fig. 7g and f). The eNd560 for sample K135 is +3.6. Metarhyolite M62 has an extremely high

52

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Fig. 7. N-MORB-normalized multi-element variation diagrams (left) and “primitive-mantle”-normalized REE plots (right) for the KMC intermediate/acidic metaigneous rocks: group F1—a and b, group F2—c and d, and group F3—e and f).

eNd560 of +8.6 (+7.4 at 400 Ma), indicative of a derivation from a strongly time-integrated LREE-depleted source. It represents a relatively large and massive rhyolitic body northeast of Gołogłowy, at the boundary between the KMC and the Bardo Unit to the east (Fig. 2), but the age of this rock and its geological position remain uncertain. Most of the acidic rocks, except for those of Group F3, show negative Sr (± Eu), P, and Ti anomalies, typical of highly evolved magmas, and indicating probable plagioclase, apatite, and Ti-rich

phase fractionation and removal. All the samples, excluding M72, also display pronounced negative Ta and Nb anomalies. 4. Discussion: magma types and emplacement settings Geochemically, the metabasalts of the BU in the northeastern part of the KMC correspond to WPT or T-MORBtype volcanics, whereas metaigneous rocks of the southwest-

R. Kryza et al. / Geodinamica Acta 16 (2003) 39–57

Fig. 8. V—Ti/1000 diagram [47]. Symbols as in Fig. 4.

ern part of the KMC are dominated by metagabbros of uncertain affinity, with numerous geochemical anomalies, probably reflecting intense fractionation and cumulation processes. This clear distinction can be seen in the V–Ti diagram (Fig. 8), on which the WPT metabasalts show much higher Ti contents and Ti/V ratios (around 50), in contrast with those in the MORB-type metagabbros (Ti/V ratios mostly between 15 and 35). In so far as their composition reflects that of basaltic liquids, these metagabbros correspond to the “low-Ti meta-tholeiites” of Floyd et al. [6], which were attributed to the melting of the sediment-contaminated subcontinental lithosphere. The distinction between the two groups of metabasites is also evident on the Ti/V–Nb/Y plot (Fig. 9). In this diagram, the most depleted metagabbros from the southwestern part of the KMC correspond well to the plutonic members of the S´ lVz˙ a ophiolite (S´ lVz˙ a-P; [48]). (It is worth noting that the felsic rocks of the KMC have Nb/Y ratios similar to those of the metagabbros.) Summing up, the metabasalts of the BU, in accordance with NarVbski et al. [28], can be considered as magmas

Fig. 9. Ti/V—Nb/Y diagram. S´ lVz˙ a ophiolite plutonic (P) and subvolcanic (V) rocks shown for comparison [48]. Symbols as in Fig. 4.

53

derived from a rather strongly depleted mantle source, probably generated within an extensional setting. In contrast, the metaigneous rocks of the southwestern part of the KMC are geochemically more diversified, with dominating metagabbros, often with cumulative characteristics. They might have been emplaced in an oceanic-crust environment, but the observed diversity of eNd values, and the high proportion of geochemically related felsic rocks, clearly precludes an N-MORB derivation and rather suggests a subductionrelated tectonic setting for their origin. All the intermediate/felsic metaigneous rocks of the KMC display positive eNd values, specifically, from +3.6 to +8.6 for acidic rocks and from +2.9 to +6.4 for intermediate rocks. These Nd isotope signatures provide an important constraint on their petrogenesis, because they rule out materials with low time-integrated Sm/Nd ratios (i.e. old continental crust or derived metasediments) as suitable sources. Instead, a depleted mantle reservoir is indicated. The incompatible trace-element patterns of these rocks often have negative anomalies of Nb, Sr (except the meta-andesite K 197), Eu, and Ti, suggesting that they might have evolved from mafic parental melts through removal of crystal assemblages rich in plagioclase and Fe–Ti oxides. The field association and the similar range of eNd values observed in these felsic rocks and in the cumulate metagabbros suggest their genetic relationships, possibly in a supra-subduction zone environment. Sample M72 (Orla “porphyroid”) departs from the other samples in having high Nb and Ta contents. Together with its radiogenic Nd isotope signature (+5.1 at 560 Ma), these trace-element characteristics are reminiscent of alkaline rhyolites. Radiometric dating of the igneous protolith of these metarhyolites is needed to better assess their possible geodynamic significance. The general geochemical features of the intermediate/acidic rocks, i.e. their peraluminous– metaluminous and calc-alkaline characteristic, together with the widespread occurrence of amphibole (if it proves to be, at least in part, primary), are in line with a probable subductionrelated emplacement setting [49] or with a model of remelting of crustal material comprising older, geochemically similar components. Although the dispersion of analyses on Pearce et al. [50] discrimination diagrams (e.g. Rb vs. Y + Nb, not shown here) resembles that of “oceanic SSZ and back-arc basin” granitoids [51], similar distribution may display rocks the emplacement setting of which remains at least controversial (e.g. the Klamath Mts granites in California, interpreted to have formed either in immature oceanic islandarc setting or by no-subduction-related partial melting of a heterogeneous metabasaltic source; see [52] and references therein). The new results show that the intermediate/acidic rocks of the Orla–Gołogłowy and Kłodzko–Twierdza Units (including large rhyolitic bodies northeast of Gołogłowy and south of Kłodzko) display general geochemical similarity, although they occur in contrasting lithological associations. The former unit is dominated by plutonic rocks, including metagabbros and cumulates, whereas the latter represents a

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volcano–sedimentary succession, with rather subordinate metabasalts. It is possible that the OGU represents a deeper, plutonic crustal fragment, while the KTU is a surface equivalent (and contemporaneous?) succession, formed in a suprasubduction or back-arc basin. Better age constraints would be crucial to verify such models. The KMC appears to comprise magmatic products and parts of a volcano–sedimentary succession probably emplaced in the supra-subduction environment. In that aspect, it is as yet a unique tectonic unit in the West Sudetes, and it differs, for example, from the Kaczawa and South Karkonosze Units, which mostly recorded effects of the Cambro-Ordovician rifting along the northern Gondwana margin [3,6,11,12,52]. This difference could be readily explained in the light of preliminary U–Pb zircon data (K. Turniak, 2001, personal communication), indicating Neoproterozoic 600–560 Ma ages for protoliths of the metaigneous rocks from the Orla–Gołogłowy and Kłodzko–Twierdza Units. Indeed, a magmatic arc setting is widely proposed for Neoproterozoic volcano–sedimentary and plutonic complexes forming the pre-Variscan basement in adjacent parts of Central Europe. Arc- or back-arc-related provenance reveal greywackes from the Cadomian Units of the Saxothuringian Zone [53], Neoproterozoic volcanics of the Barrandian Syncline [54], and Late Proterozoic metaigneous rocks of the Brno Massif ([55] and references therein). In the KMC, fragments of such a Neoproterozoic magmatic arc are thrust over the Mały Boz˙ ków, ŁTczna and Bierkowice Units, of which only the first one is palaeontologically documented as Mid-Devonian [26]. Nevertheless, the BU, with a withinplate, rift-related geochemical signature, displays close affinities to other Palaeozoic volcanic successions of the West Sudetes. The juxtaposition of these two contrasting parts of the KMC took place due to the westnorthwest-directed thrusting [34] and was followed by their final exhumation between the Early Givetian and Late Frasnian [26].

5. Conclusions 1. The metaigneous rocks of the KMC belong to two geochemically distinct groups: (a) the “within-plate” group (mafics only) in the northeastern part of the area (BU) and (b) the “subduction-related” group, comprising both metagabbros (often cumulates) and intermediate-felsic rocks, in the southwestern area (S´ cinawka, Orla–Gołogłowy and, probably, Kłodzko– Twierdza Units). The two groups derived from variably depleted mantle sources. 2. The intermediate/acidic metaigneous rocks, associated with the metagabbros and amphibolites, are found in large proportion in the southwestern area (the position of some outcrops, however, is obscured by poor exposure). Geochemical features, including similar eNd values, of the felsic and mafic rocks suggest that they are broadly co-genetic.

3. The general geochemical characteristics and Sm–Nd isotopic data of the intermediate/acidic rocks indicate the extraction of magmas from a source that was strongly depleted in Nd relative to Sm on a timeintegrated basis. Together with the absence of alkaline rocks, the new results seem to favour a subductionrelated setting in which similar felsic magmas are common. 4. The possible inter-relationships between the intermediate/acidic rocks and the metagabbros can be considered in terms of several models, e.g.: (a) the intermediate and acidic rocks are fractionates (or in a few cases plagioclase cumulates) derived from the basic magmas; (b) the intermediate/acidic derivates may have formed from re-melting of similar metabasites at depth. 5. The discrete distribution of different geochemical types of rocks in different parts of the KMC corroborates the hypothesis that the KMC is a composite stack of tectonic units, variable in terms of geodynamic settings and, probably, ages. 6. The recognition of Neoproterozoic(?) subductionrelated magmatism in the Sudetes has significant implications for the geodynamic reconstructions of the preVariscan history of Central Europe. It provides new evidence for the existence of rock units representing remnants of a Pan-African active margin in the West Sudetes. 7. The Neoproterozoic(?) plutonic and volcano–sedimentary sequences in the southwestern part of the KMC can be interpreted, following the general model of Nance and Murphy [56], as evidence for the subduction of an oceanic domain beneath the Gondwana active margin. In contrast, the metamorphosed volcanic and sedimentary successions of the northeastern part of the KMC, showing affinities to rifting processes and passive continental margin settings, may represent subsequent events related to the Palaeozoic break-up of Gondwana.

Acknowledgements The study was carried out as part of the cooperation project between the Université Blaise Pascal, ClermontFerrand and Wrocław University. We acknowledge financial support from the Polish Research Committee KBN project no. P04D 023 12, and from Wrocław University internal grants 2022/W/ING and 1017/S/ING/01-II. This is a contribution to IGCP Project N° 453 “Modern and Ancient Orogens”. Profs. I. Wojciechowska, J. Don and W. NarVbski are thanked for their help and advice at the early stages of our studies. Thanks are due also to Jan Kosler and to an anonymous reviewer for their constructive comments and corrections.

R. Kryza et al. / Geodinamica Acta 16 (2003) 39–57

55

Appendix 1 List of samples No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Symbol 25a 27a 77a (IW664) 78a 85a M65b M66Bb M61b 35a 108a M67b M69b 40a 50/1a (IW657) M68b

Rock Metabasalt Metabasalt Metabasalt Metabasalt Metabasalt Metabasalt Metabasalt Metabasalt Metagabbro Metagabbro Metagabbro Metagabbro Metagabbro Metagabbro Metagabbro

Unit Complex B Complex B Complex B Complex B Complex B BU BU KTU Complex C Complex C SU SU Complex C Complex C SU

16 17 18 19 20 21

52a (IW655) 30a (IW663) M71Ab IW662a K102c K114c

Metagabbro Metagabbro Metagabbro Amphibolite Meta-andesite Metadacite

Complex C Complex C OGU Complex C KTU KTU

22 23 24 25 26 27 28 29 30 31

K242c K197c M72b M74b M75b K174c Gorza,d Orlaa,d M71Bb K135c

Metarhyolite Meta-andesite Metarhyolite Meta-aplite Meta-andesite Metarhyolite Felsic dike Felsic rock Plagioclasite Metarhyolite

OGU OGU OGU OGU OGU OGU Complex C Complex C OGU KTU (S)

32

M62b

Metarhyolite

OGU (E)

Location No precise location Czerwionka Czerwionka No precise location No precise location Kopiec Hill, quarry 500 m west of top S´ wiVcko–Huberek, quarry west of road to ŁTczna Kłodzko, Połwiejska 5, 5 m west of house S´ cinawka Sr., hill east of Dzik river Chmielnik Hill, quarry at south foot Chmielnik Hill, quarry at south foot S´ cinawka Sr., east bank of Dzik river S´ cinawka Dln., Kapliczna Hill Gorzuchów S´ cinawka Dln.–Wygwizdów, quarry north of railway Gorzuchów Bierkowice–Gołogłowy, quarry north of railway Orla Hill, quarry at north foot Kłodzko–KsiTz˙ ek, quarry Kłodzko–Twierdza, east slope of hill (metatuf?) Kłodzko–Twierdza, northwest slope of hill (metatuf?) Orla Hill, crags at southeast slope Orla Hill, quarry at northwest slope Orla Hill, crag on stream, at west foot S´ cinawka–Mill, north bank of S´ cinawka river S´ cinawka–Mill, behind the house Gołogłowy, gorge north of railway Gorzuchów (dike in metagabbro) Orla Hill (“leptinite”) Orla Hill, quarry at north foot (in metagabbro) Kłodzko, Wyspian´ skiego, quarry southsoutheast of town Gołogłowy, quarry north of railway

Lithostratigraphic/tectonic units: after Wojciechowska (in [28]): B—Middle part (mostly equivalent to Bierkowice Unit), C—upper part of the KMC succession (mostly equivalent to S´ cinawka and Orla–Gołogłowy Units); and after Kryza and Mazur [30]: BU—Bierkowice, KTU—Kłodzko–Twierdza, SU—S´ cinawka, OGU—Orla–Gołogłowy Units. a Chemical analyses after NarVbski et al. [28]. b Chemical analyses after Kryza and Mazur [30]. c Chemical analyses of this study. All Sm–Nd analyses performed by C. Pin. d No chemical data Sm–Nd only.

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