Geochemical constraints of origin and evolution of migmatites in the central part of the Moldanubian Zone (Temelin area), Bohemian Massif.
High-temperature metamorphism accompanied by partial melting and migmatite formation is a common feature in collisional belts (Bohlen 1987, Harley 1989, Kohn et al. 1993, Schnetger 1994, Kalt et al. 1999). The geodynamic processes responsible for such P-T-conditions in medium to shallow crustal levels are not yet well understood. They are generally assessed by models that combine the results of high-PT experiments with P-T paths deduced from rock complexes in collisional zones (e.g., Brown 1993, Holtz and Johannes 1996, Kalt et al. 1999, Kriegsman 2001).
High-temperature and low-pressure (HT-LP) migmatitic gneisses and migmatites are the dominant metamorphic lithologies within the high-grade metamorphic parts of the Variscan Belt in the western and central Europe. In particular, the Bohemian Massif displays continuous areas with high-grade metamorphic rocks, including various types of migmatites (metatexites and also diatexites). The highest concentrations of migmatites occur in the Moldanubian Zone of the Bohemian Massif. The first comprehensive study of the origin of migmatites in the Moldanubian Zone was published by Zoubek (1927). Description of the origin and evolution of migmatites of the Moldanubian Zone mostly followed the original genetic model and terminology of Sederholm (1913) (e.g., Suk 1964, Krupicka 1968, Chab and Suk 1977, Vrana et al. 1995).
The origin of migmatites is the subject of many studies discussing different migmatite-forming processes: a) Injection of externally derived granitic melts (Sederholm 1913, Zoubek 1927), b) metasomatism (Misch 1968), c) metamorphic differentiation (Robin 1979, Ashworth and McLellan 1985), and partial melting of the host rocks (Mehnert 1968, Johannes 1988, Kriegsman 2001). The latest, commonly accepted model of migmatite formation considers these rocks a result of partial melting (Sawyer 1987, Jung et al. 1998, Milord et al. 2001, Solar and Brown 2001). The currently most widely accepted descriptive terminology of Mehnert (1968) and Brown (1973) subdivides migmatites into metatexite migmatites and diatexite migmatites. Metatexite is defined as migmatite containing evident original layering, metamorphic foliation or banding, which survived partial melting (Brown 1973). Metatexites are migmatites that retained a low melt fraction, and mostly underwent only a short-range transport of melt (Sawyer 1996, 1999). Diatexite has been defined as migmatite in which premigmatization structures are destroyed (Brown 1973), and homogenization and coarsening of texture occurs. A characteristic feature is banding caused by flow in which mafic minerals form schlieren (Sawyer 1996). Diatexites thus represent rocks in which the melt fraction was high. According to the definition given by Brown (1973), diatexis is considered to be the process of high-grade anatexis in which fusion may be complete.
In the last years, some detailed studies were carried out to determine the role of partial melting in the origin and evolution of migmatites and anatectic granites in the Moldanubian Zone of the Bohemian Massif (e.g., Matejka 1991, Kalt et al. 1999, Adelt 2001, Rene 2001, Leichmann et al. 2002). This paper presents a detailed analysis of migmatites from the area between Tyn nad Vltavou and Temelin. Field relations, petrography and rock chemistry were used to constrain the conditions of origin and evolution of migmatites in the Monotonous group of the Moldanubian Zone in this area.
The Moldanubian Zone is a part of the Variscan orogenic belt, which resulted from the collision of Laurasia and Gondwana, and several small microplates between these, in the Devonian to Carboniferous times (Matte 1986). In the area of the Bohemian Massif, the Variscan belt is deeply eroded and partly covered by Mesozoic and Tertiary sediments, with only isolated basement units exposed in the central and southern part of this important geological unit. The Moldanubian Zone of the Bohemian Massif can be divided into several tectonometamorphic units (Matte 1986, Franke 1989, 2000). An obvious distinction exists between 1. the Monotonous group with migmatites and gneisses of pelitic to psammitic composition, and 2. the more variegated gneiss complex with intercalations of calc-silicate rocks, marbles, amphibolites and orthogneisses (Varied group). Both groups contain isolated lenses of peridotites and eclogites that document a collisional event in the Moldanubian Zone before the HT-LP metamorphic event (e.g., Medaris et al. 1995). Recently, terrane criteria (Matte et al. 1990) rather than original lithostratigraphic criteria (Zoubek 1988) have become increasingly used for the description of the evolution of the Moldanubian Zone. The original lithostratigraphic groups (monotonous and varied) are now defined as distinct terranes, namely the Ostrong terrane and Drosendorf terrane. Franke (2000) even implemented these two original groups within the Drosendorf assemblage.
The Ostrong terrane (Ostrong unit in Austria, Fuchs and Matura 1976) encompasses the previous Monotonous and Kaplice groups of Zoubek (1988). The two groups show mutual transitions with different intensities of HP-LP metamorphic overprint (Fiala et al. 1992). These monotonous sequences of quartz-pelitic and greywacke lithologies containing several orthogneiss bodies and rare intercalations of amphibolites and calc-silicate rocks are probably not older than Late Proterozoic (Kroner et al. 1988). The Drosendorf terrane (Drosendorf nappe in Austria, Tollman 1982), largely identical with the previously used the Varied group, consists essentially of a thick supracrustal sequences of greywacke-pelitic lithology with locally frequent intercalations of marbles, calc-silicate gneisses, graphitic rocks, quartzites, leptynites and amphibolites. These sequences, probably Late Proterozoic to Early Palaeozoic in age, were at least partly deposited on an old crystalline basement (Wendt et al. 1993).
The peak metamorphism of migmatites in the Moldanubian Zone of the Bohemian Massif was dated at 323-326 Ma by concordant U-Pb single monazite grains dating (Kalt et al. 2000). Cooling of the migmatites below about 300[degrees]C is recorded by K-Ar biotite ages of 325-315 Ma (Kreuzer et al. 1989) and Ar-Ar biotite ages of 312-315 Ma (Kalt et al. 1999).
The area between Tyn nad Vltavou and Temelin is formed by metamorphic series of the Monotonous group, which are deformed in more independent tectono-metamorphic stages (Fig. 1). An older geological model (Zelenka 1927, Hejtman et al. 1964) presumes the presence of complicated brachyanticlinal closures accompanied by sigmoidal folds. A totally different tectonic model of this area was formulated by Vrana et al. (1977) in their explanations to the detailed geologic map 1:25,000 of the Tyn nad Vltavou area. In their opinion, the metamorphic series in this area is characterized by the presence of three successive fold stages and/or shear deformations with various deformation fabrics. The youngest fold stage of Vrana et al. (1977) is connected with the formation of an extensive area of the so-called refoliated gneisses. The process of refoliation took place at the boundary of ductile and brittle deformations (Vrana et al. 1977) and affected the already migmatized metamorphic complex. In connection with this complicated geological fabrics, the above mentioned authors suppose that the formation of this geologic structure probably resulted from polyorogenetic evolution rather than from polyphase evolution in the same orogen. A similar tectonic model was used later by Vrana (1979) also in his explanation of the tectonic style of the South Bohemian Moldanubian Zone as a whole.
New detailed geologic mapping to scale 1:10,000 aimed at the recognition of a deeper geological structure of the Moldanubian Zone in the area of the Temelin nuclear power plant (Klecka et al. 1988) revealed that the idea of metamorphic refoliation of the Moldanubian series in the Tyn nad Vltavou area can be refused. This mapping supported by tectonic investigations of metamorphic fabrics defined older ductile and younger ductile-brittle deformation stages. The older stage gave rise to a strike-slip accompanied by thrusting of the northern block formed by metamorphic rocks of the Podolsko complex over the gneisses of the Monotonous group. Lineations trending ENE-WSW originated during this stage. The younger deformation stage of Klecka et al. (1988) was governed by tensional regime and generated lineations trending NW-SE. The younger deformation stage also involved the origin of the Vodnany regional shear zone, also reactivated in the Neogene. Neogene movements along this regional shear zone were proved by occurrence of small isolated basins filled with Neogene sediments (see also Vrana et al. 1977). In the metamorphic series of the Moldanubian Zone, the younger deformation stage is characterized by regional muscovitization of sillimanite-biotite paragneisses or biotite-bearing metatexites. This idea is also consistent with an older geological model for this area defined by Machart (1987). In this model, the Vodnany shear zone copied an older shear zone along which rock complexes of the lower crust represented by ultrabasites and granulites were uplifted to the Earth's surface.
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FIELD RELATIONSHIPS AND SAMPLE SELECTION
Paragneisses, migmatized paragneisses and migmatites of the Monotonous group in the area between Tyn nad Vltavou and Temelin were well exposed during geological investigations aimed at the construction of the Temelin nuclear power plant and also during the construction activities at this site. A construction of a deep deposit of high-level waste at the same site was also supposed at the time of the construction. To reveal deeper geological structure of the metamorphic series, Js-799 structural borehole was drilled in this area (Pazdernik 1987). This borehole was situated on the northern margin of the area of the nuclear power plant, on the SW edge of the village of Krtenov and reached a final depth of 731.25 m. The metamorphic series uncovered in the Js-799 structural borehole showed highly monotonous modal composition of gneisses, migmatized gneisses and migmatites. The main rock types in this borehole are biotite gneisses and sillimanite-biotite gneisses to metatexites (stromatitic migmatites) with relatively rare intercalations of diatexites (leucocratic migmatites). Relatively rare are also irregular lenses of calc-silicate rocks. Two systems of lineations were found in this rock complex (see Klecka et al. 1988). The older system of lineations is characterized by the presence of quartz-feldspar lenses in paragneisses and by ENE-WSW trends of the lineation. The origin of this lineation is also connected with ductile movements during incipient migmatization, or during incipient partial melting of the original paragneisses. The younger lineation is a very conspicuous structural element both in the original paragneisses and younger migmatites. Its trend NW-SE is also indicated by the orientation of sillimanite nodules in sillimanite-biotite paragneisses and migmatites. Dykes and lenses of pegmatitic granites, pegmatites and aplites 8-50 centimetres thick, rarely 80 cm thick, were also found in the Js-799 borehole. The orientation of these dykes and lenses is usually conformable with the foliation of the metamorphic series.
Detailed petrographic and geochemical investigations of migmatization of paragneisses of the Monotonous group in the Temelin area employed borehole cores from above mentioned Js-799 structural borehole. Two types of migmatized gneisses and migmatites were distinguished in the Temelin area on the basis of abundance, geometric relationship, modal composition and microstructures of mesosome and leucosome. Moreover, both types are medium-grained and heterogeneous on the millimetre to centimetre scale in terms of modal composition. Twelve samples of unaltered metatexites (stromatitic migmatites) and diatexites (leucocratic migmatites) were used for detailed petrographic and geochemical investigations. Both rock types are of semipelitic to psammitic composition. Migmatized gneisses of psammitic composition were often described as greywacke paragneisses in the original description of borehole Js-799 (Pazdernik 1987).
Metatexites (stromatitic migmatites) are characterized by a pronounced interlayering of mesosome with leucosome and pronounced foliation. They contain millimetre- to centimetre-sized leucosome layers concordant to foliation. Metatexites are sometimes characterized also by phlebite-stromatititic structure. Semipelitic to psammitic composition of metatexites in borehole Js-799 alternates on the order of magnitude of 0.X to X0 m. Metatexites were described as migmatized sillimanite-biotite paragneisses and greywacke paragneisses in the original description of borehole Js-799 (Pazdernik 1987). Diatexites (leucocratic migmatites) are characterized by massive structure. Millimetre- to centimetre-sized and patchy light areas can only by vaguely distinguished from dark areas. These migmatites also typically display poorly discernible foliation. In the original description of borehole Js-799, these rocks were described as leucocratic or nebulitic migmatites (Pazdernik 1987).
The proportion of mesosome and leucosome in metatexites is highly variable; the amount of leucosome sometimes prevails over the amount of mesosome. Biotite and muscovite are the most abundant mineral phases (35-50 vol.%) in mesosome, quartz and plagioclase ([An.sub.19-24]) occur in less significant amounts. Mesosome is characterized by two deformation phases. Muscovite originated usually in the younger deformation stage. Biotite was probably formed in the older deformation stage but younger, second-generation biotite was also encountered. The second generation of biotite typically shows more intensive pleochroism. Fibrous aggregates of sillimanite, which was formed together with muscovite, sometimes occur near muscovite tables. The amount of sillimanite is 2-6 vol.%. Biotite of the main generation is vaguely pleochroic, light yellow-brown along X, light brown to brown along Y and Z. Biotite is sometimes chloritized; very fine-grained aggregates of newly formed chlorite form transverse veins several millimetres thick. Leucosome in metatexites mostly consists of K-feldspar, plagioclase ([An.sub.18-22]) (30-40 vol.%) and accessory garnet, often forming inclusions in K-feldspar. The amount of quartz is 15-25 vol.%. K-feldspar is slightly perthitic. Accessory phases are apatite, zircon, ilmenite and magnetite. Accessory cordierite also occurs in some cases, forming small xenoblastic grains.
Migmatites with nebulitic structure, which can be described as diatexites in the terminology of Brown (1973), are formed by weakly foliated rocks. Texture of these migmatites is lepidogranoblastic. Diatexites are formed by biotite, plagioclase ([An.sub.18-25]), quartz, K-feldspar and accessory phases. Very typical accessory mineral is garnet, which occurs in isometric grains 0.01-0.02 mm in size. Muscovite is rare. K-feldspar is characterized by the occurrence of myrmekite. Biotite is usually significantly pleochroic, light yellow-brown along X, brown to dark brown along Y and Z. Individual tables of biotite are characterized by the absence of preferred orientation.
The present study is based on 12 rock samples collected from the Js-799 structural borehole. After a detailed field study, representative samples of various structural types of migmatites were selected for major and minor element analyses. Borehole cores of 1-2 kg in weight were used for chemical analyses of rocks. The rocks were crushed in jawbreaker and agate ball mill. After each step of grinding, the samples were systematically reduced in quantity. Major elements were analysed by classic wet methods in the laboratory of the Institute of Rock Structure and Mechanics of the AS CR (IRSM) (analyst V. Chalupsky, M. Mala and J. Svec). Dissolution of the rock powder was carried out in Pt crucible with a HF-[H.sub.2]S[O.sub.4]-HN[O.sub.3] mixture. The contents of total Fe, MnO, MgO, [Na.sub.2]O and [K.sub.2]O were analysed by atomic absorption spectrometry (AAS) on the Perkin-Elmer spectrometer. FeO content was measured by titration, the contents of [H.sub.2][O.sup.+] and [H.sub.2][O.sup.-] were determined gravimetrically.
Minor elements were analysed by a simultaneous X-ray fluorescence (XRF) spectrometer Bruker S-4 Pioneer at the University of Salzburg (analyst G. Riegler). The samples were prepared by making pressed-rock powder pellets. REE analyses were made by ICP-MS method on the ICP mass-spectrometer Perkin Elmer Sciex ELAN 6000 in the Actlabs laboratory in Canada (analyst D. D'Anna). All XRF and ICP-MS analyses were calibrated against international standards. U and Th contents were determined by gamma-ray spectrometry using the NT-512 multi-channel gamma-ray spectrometer (Geofyzika Enterprise, analyst M. Skovierova). Precision of all analytical methods was tested by duplicate analyses.
Metatexites range from 60 to 75 wt.% Si[O.sub.2] (Table 1). The contents of Ti[O.sub.2], [Al.sub.2][O.sub.3], FeO, MgO (Fig. 2) and [K.sub.2]O (Fig. 3) decrease with increasing Si[O.sub.2]. The content of [Na.sub.2]O decreases only slightly with increasing Si[O.sub.2] (Fig. 4). The content of CaO increases systematically with increasing Si[O.sub.2] (Fig. 5). The content of [P.sub.2][O.sub.5] decreases slightly with increasing Si[O.sub.2]. Normative composition of metatexites from the Temelin area plotted in the Qz-Ab-Or ternary diagram fall close to the quartz-K-feldspar cotectic line either to the quartz field (Fig. 6). The content of some trace elements is also controlled by the behaviour of major elements. The content of Sr increases with increasing Si[O.sub.2]. A similar behaviour of CaO and Sr in metatexites is probable caused by binding of Sr to plagioclases in metatexites.
Compared to the composition of continental crust (Taylor and McLennan 1985) (Fig. 7), metatexites from the Temelin area enriched in Ba, Rb, Th, LREE and slightly to moderately depleted in Sr. The content of Th in metatexites only slightly varies around the average (10.2 ppm Th), being controlled by the content of Ce (Fig. 8) and probably by the content of monazite in these rocks. The fractionation of LREE/HREE ratio in metatexites of the Temelin area is only moderate ([La.sub.N]/[Yb.sub.N] = 6.4-9.6). Chondrite-normalized pattern of REE distribution in metatexites is characterized by a pronounced negative Eu anomaly (Eu/[Eu.sup.*] = 0.63-0.69) (Fig. 9).
Compared to metatexites, diatexites have higher Si[O.sub.2] and [Na.sub.2]O contents and lower FeO, MgO and [K.sub.2]O contents. The contents of CaO and Sr in diatexites decrease with increasing Si[O.sub.2]. This trend contrasts with the behaviour of both elements in metatexites and is probable connected with the fractionation of plagioclases in diatexites. The fractionation of REE in diatexites is more pronounced than in metatexites ([La.sub.N]/[Yb.sub.N] = 8.1-11.5). The same pattern shows also a more significant negative Eu anomaly (Eu/[Eu.sup.*] = 0.65-0.88) (Fig. 9). More significant fractionation of REE in diatexites is very probably caused by the decreasing content of HREE carriers in diatexites (zircon, xenotime?). The decreasing content of HREE-bearing minerals is also connected with Y depletion in diatexites relative to its content in metatexites (Fig. 7).
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Melt temperatures inferred from the zircon and monazite thermometers (Watson and Harrison 1983 and Montel 1993, respectively) were calculated according to the scheme of Montel (1993). As the composition of monazite is unknown, the value of [X.sub.REEPO4] = 0.83 was used following Montel (1993) (Table 3). The differences between the two thermometers are very probably connected with significant quantities of inherited zircon in metasedimentary protolith. On the other hand, the calculated melt temperatures are in good agreement with the position of diatexites in the Qz-Ab-Or diagram (Fig. 6).
Metatexites and diatexites of the Temelin area are products of regional metamorphism and the subsequent partial melting of sediments of the Monotonous group of the Moldanubian Zone. Their origin is connected with several stages of deformation. The older deformation is very probably connected with migmatization. The younger deformation, which is connected with the origin of muscovite, is probably cogenetic with the emplacement of post-tectonic granites of the Moldanubian batholith. The origin of metatexites was governed by partial melting of the original metasediments. Metatexites underwent only a partial segregation of quartz- and plagioclase-rich melt, and the characteristic banding of these rocks originated with distinctly separated bands of newly formed leucosome and restitic mesosome. The complete separation of newly formed granitic melt occurs in diatexites only. Migmatization and partial melting was connected with variable fractionation of Si[O.sub.2], FeO, MgO, CaO, [Na.sub.2]O, and [K.sub.2]O and also by the fractionation of some trace elements (Ba, Sr, Rb, HREE, Eu). The separation of granitic melt in diatexites resulted in its depletion in [K.sub.2]O, Ba and Rb and enrichment in CaO, partly also in Sr (Figs. 5, 7).
The calculated temperatures with using of the zircon an monazite thermometers are in agreement with the temperatures of partial melting suggested by other geothermometers in migmatites of the Bayerische Wald (Kalt et al. 1999). Kalt et al. (1999) assumed that high-temperature metamorphism in the Moldanubian Zone was induced by anomalously high heat flux to shallow crustal levels of 15-20 km depth subsequent to Variscan collision and crustal thickening. The origin of late muscovite was probably connected with the formation of ductile-brittle shear zones (e.g., the Vodnany zone) in the cooling stage of migmatites. In the Bayerische Wald, this cooling stage was dated by K-Ar biotite ages at 325-315 Ma (Kreuzer et al. 1989). On the northeastern margin of the Moldanubian Zone, the cooling stage, or, more precisely, the stage of the ductile shear zones formation was dated by K-Ar muscovite ages at 304-307 Ma (Kribek et al. 2002). The temperature of this cooling stage was calculated by using of chlorite thermometers (263-311[degrees]C) (Kribek et al. 2002). Cooling temperatures in the central part of the Moldanubian Zone were probably higher and were determined by the stability of biotite newly formed in the younger deformation stage.
Metatexites and diatexites in the Temelin area are part of the Monotonous group of the Moldanubian Zone. The structural borehole drilled on the northern margin of area of the Temelin nuclear power plant, provided a good section of migmatized series of the Monotonous group in the central part of the Moldanubian Zone. Modal composition of these rock series is very monotonous, being represented by migmatized biotite gneisses and sillimanite-biotite gneisses to metatexites (stromatitic migmatites) with relatively rare intercalations of diatexites (leucocratic migmatites). Metatexites are characterized by a prominent interlayering of mesosome with leucosome. The metatexites typically show stromatitic or less evolved phlebite-stromatitic structure. The proportion of mesosome and leucosome in the examined metatexites is highly variable. Mesosome is characterised by the occurrence of two deformation phases, the younger being characterized by the formation of muscovite and sillimanite. Diatexites typically show massive structure. Patchy light areas formed by quartz and feldspar can be only vaguely distinguished from dark areas with high amount of biotite. Diatexites, unlike metatexites, also show a poorly visible foliation. The content of K-feldspar in diatexites is significantly lower than in metatexites.
Compared to the composition of continental crust, metatexites of the Temelin area are enriched in Ba, Rb, Th, and LREE and slightly to moderately depleted in Sr. Compared to metatexites, the diatexites of the Temelin area have higher Si[O.sub.2] and [Na.sub.2]O contents and lower FeO, MgO and [K.sub.2]O contents. CaO and Sr contents in diatexites, as opposed to metatexites, decreases with increasing Si[O.sub.2]. This contrasting behaviour of the two elements is probably connected with the fractionation of plagioclases during intensive partial melting of these rocks. Fractionation of REE and depletion in Y also are controlled by the more intensive partial melting of diatexites.
The origin of metatexites and diatexites in the Temelin area is controlled by partial melting of the original metasediments rich in biotite. Metatexites underwent only a partial segregation of quartz- and plagioclase-rich melt giving rise to characteristic banding with distinctly separated bands of leucosome and mesosome. The complete separation of newly formed granitic melt occurs in diatexites only. Migmatization and partial melting were connected with variable fractionation of Si[O.sub.2], FeO, MgO, CaO and [K.sub.2]O and also accompanied by the fractionation of some trace elements (Ba, Sr, Rb, HREE and Eu). Calculated melt temperatures (808-867[degrees]C) agree with the peak metamorphic conditions of other parts of the Moldanubian Zone of the Bohemian Massif. The younger ductile-brittle stage of deformation was controlled by the common occurrence of muscovite and biotite and corresponded to the temperature of the cooling stage of migmatites. The cooling stage very probably corresponded with the incipient Variscan extension in the central part of the Bohemian Massif, which was connected with the opening of the Late Carboniferous (Late Stephanian) and Permian pull-apart sedimentary basins (see also Kribek et al. 2002).
This study was supported by the Ministry of Education, Youth and Sports of the Czech Republic (Project No. ME-555). Author is also very grateful for critical comments two anonymous reviewers.
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Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, V Holesovickach 41, CZ-182 09 Praha 8, Czech Republic, E-mail: firstname.lastname@example.org
Table 1 Chemical analyses of migmatites from the Temelin area (wt.%). R-1405 R-1406 R-1407 R-1408 R-1409 Si[O.sub.2] 63.34 59.87 61.99 60.26 75.14 Ti[O.sub.2] 0.73 0.78 0.72 0.74 0.50 [A.sub.2][O.sub.3] 16.55 17.59 17.11 17.91 12.07 [Fe.sub.2][O.sub.3] 1.16 1.33 1.33 1.34 0.92 FeO 4.70 5.36 5.19 5.00 2.34 MnO 0.07 0.07 0.13 0.06 0.04 MgO 2.59 3.00 2.40 2.77 1.21 CaO 1.40 1.64 1.20 1.45 1.35 [Na.sub.2]O 2.48 2.33 1.80 2.35 2.87 [K.sub.2]O 3.07 3.06 4.22 3.28 1.85 [H.sub.2][O.sup.+] 2.66 3.33 2.61 3.34 1.17 [H.sub.2][O.sup.-] 0.38 0.37 0.34 0.45 0.17 [P.sub.2][O.sub.5] 0.20 0.20 0.23 0.22 0.11 Total 99.33 98.93 99.27 99.17 99.74 Ba (ppm) 721 651 1057 751 657 Rb (ppm) 122 128 154 131 67 Sr (ppm) 152 162 122 190 199 Zr (ppm) 203 189 162 173 208 U (ppm) 1.3 2.3 5.2 5.6 1.4 Th (ppm) 9.9 11.5 9.3 9.3 8.5 R-1410 R-1411 R-1412 R-1413 R-1414 Si[O.sub.2] 74.56 71.15 63.60 60.28 68.44 Ti[O.sub.2] 0.50 0.66 0.82 0.75 0.53 [A.sub.2][O.sub.3] 12.57 13.43 16.22 17.91 14.17 [Fe.sub.2][O.sub.3] 0.93 1.02 0.84 1.57 0.53 FeO 2.43 3.14 4.65 4.20 3.75 MnO 0.04 0.06 0.04 0.03 0.04 MgO 1.28 1.65 2.17 2.17 1.90 CaO 1.41 2.04 2.64 2.12 3.08 [Na.sub.2]O 3.10 3.24 2.51 3.40 1.92 [K.sub.2]O 1.98 1.89 2.85 4.71 3.13 [H.sub.2][O.sup.+] 1.16 1.20 1.98 1.55 1.39 [H.sub.2][O.sup.-] 0.18 0.15 0.29 0.21 0.19 [P.sub.2][O.sub.5] 0.10 0.11 0.21 0.15 0.17 Total 100.24 99.74 98.82 99.05 99.24 Ba (ppm) 546 614 723 1133 937 Rb (ppm) 79 72 120 156 125 Sr (ppm) 202 225 262 225 296 Zr (ppm) 181 323 186 193 215 U (ppm) 2.2 4.5 3.1 5.7 3.2 Th (ppm) 7.7 13.0 9.8 10.7 12.9 R-1415 R-1418 Si[O.sub.2] 66.90 65.29 Ti[O.sub.2] 0.59 0.72 [A.sub.2][O.sub.3] 14.72 15.98 [Fe.sub.2][O.sub.3] 1.13 0.46 FeO 3.75 4.15 MnO 0.03 0.03 MgO 1.76 1.88 CaO 2.67 2.41 [Na.sub.2]O 2.55 2.75 [K.sub.2]O 3.20 3.50 [H.sub.2][O.sup.+] 1.52 1.36 [H.sub.2][O.sup.-] 0.12 0.15 [P.sub.2][O.sub.5] 0.19 0.19 Total 99.13 98.87 Ba (ppm) 805 1083 Rb (ppm) 117 124 Sr (ppm) 265 280 Zr (ppm) 186 202 U (ppm) 1.0 3.8 Th (ppm) 8.5 10.0 R-1405--muscovite-biotite metatexite, Krtenov, borehole Js-799, 211.0-211.4 m, R-1406--drab banded muscovite-biotite metatexite, Krtenov, borehole Js-799, 263.0-263.4 m, R-1407--drab banded muscovite-biotite metatexite, Krtenov, borehole Js-799, 337.0-337.4 m, R-1408--massive metatexite, Krtenov, borehole Js-799, 429.0-429.3 m, R-1409--biotite diatexite, Krtenov, borehole Js-799, 459.0-459.4 m, R-1410--sillimanite-biotite diatexite, Krtenov, borehole Js-799, 460.0-460.4 m, R-1411--garnet-biotite diatexite, Krtenov, borehole Js-799. 476.0-477.3 m, R-1412--drab banded muscovite-biotite metatexite, Krtenov, borehole Js-799, 582.1-582.5 m, R-1413--sillimanite-muscovite-biotite metatexite, Krtenov, borehole Js-799, 599.5-599.8 m, R-1414 --drab banded biotite metatexite, Krtenov, borehole Js-799, 599.8-600.0 m, R-1415--banded biotite metatexite, Krtenov, borehole Js-799, 608.0-608.4 m, R-1418--banded sillimanite-biotite metatexite, Krtenov, borehole Js-799, 727.0-727.3 m. Major elements analysed by classical wet methods, laboratory of the IRSM AS CR (analyst V. Chalupsky, M. Mala, J. Svec), minor elements analysed by XRF method, laboratory of the University of Salzburg (analyst G. Riegler), U and Th analysed by gamma-ray spectrometry, laboratory of Geofyzika Brno (analyst M. Skovierova). Table 2 Content of rare earth elements in migmatites from the Temelin area (ppm). R-1406 R-1407 R-1409 R-1410 R-1411 La 40.10 36.90 33.10 27.10 41.80 Ce 79.50 72.50 64.20 53.10 83.80 Pr 9.04 8.33 6.95 5.80 8.97 Nd 36.00 32.80 26.40 22.40 33.70 Sm 7.07 6.50 4.92 4.22 6.23 Eu 1.51 1.26 0.971 1.16 1.30 Gd 6.28 5.74 4.13 3.80 5.15 Tb 1.01 0.88 0.62 0.62 0.80 Dy 5.88 5.12 3.53 3.70 4.63 Ho 1.21 1.00 0.70 0.79 0.93 Er 3.50 2.96 2.04 2.33 2.79 Tm 0.518 0.441 0.308 0.364 0.440 Yb 3.08 2.91 1.94 2.26 2.74 Lu 0.458 0.410 0.287 0.340 0.423 [La.sub.N]/ 8.80 8.57 11.53 8.10 10.31 [Yb.sub.N] Eu/[Eu.sup.*] 0.69 0.63 0.65 0.88 0.70 R-1406--drab banded muscovite-biotite metatexite, Krtenov, borehole Js-799, 263.0-263.4 m, R-1407--drab banded muscovite-biotite metatexite, Krtenov, borehole Js-799, 337.0-337.4 m, R-1409--biotite diatexite, Krtenov, borehole Js-799, 459.0-459.4 m, R-1410--sillimanite-biotite diatexite, Krtenov, borehole Js-799, 460.0-460.4 m, R-1411--garnet-biotite diatexite, Krtenov, borehole Js-799, 476.0-477.3 m. Rare earth elements analysed by ICP mass spectrometry in the Actlabs laboratory (analyst D. D'Anna). Table 3 Calculated melt temperatures inferred from the zircon ([T.sub.Zr]) (Watson and Harrison 1983) and monazite ([T.sub.REE]) (Montel 1993) geothermometers for diatexites from the Temelin area. [T.sub.Zr] [T.sub.REE] Sample [degrees]C [degrees]C R-1409 837 831 R-1410 820 808 R-1411 867 831 R-1409--biotite diatexite, Krtenov, borehole Js-799, 459.0-459.4 m, R-1410--sillimanite-biotite diatexite, Krtenov, borehole Js-799, 460.0-460.4 m, R-1411--garnet-biotite diatexite, Krtenov, borehole Js-799, 476.0-477.3 m.
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|Publication:||Acta Montana. Serie A: Geodynamics|
|Date:||Jul 1, 2003|
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