Characteristics and origins of diverse Variscan peridotites in the Gföhl Nappe, Bohemian Massif, Czech Republic

Lithos 82 (2005) 1 – 23 www.elsevier.com/locate/lithos

Characteristics and origins of diverse Variscan peridotites in the Gfo¨hl Nappe, Bohemian Massif, Czech Republic Gordon Medaris Jr.a,*, Herb Wanga, Emil Jelı´nekb, Martin Mihaljevicˇb, Petr Jakesˇb a Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USA Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Praha, Czech Republic

b

Received 19 October 2003; accepted 25 October 2004 Available online 8 February 2005

Abstract In the Variscan Orogen, the Gfo¨hl terrane in the Moldanubian zone of the Bohemian Massif appears to be unusual among members of high-pressure collisional belts in containing diverse types of mantle-derived peridotite. Three groups of peridotite have been identified in the Czech part of the Gfo¨hl Nappe, based on major and trace element compositions, pressure–temperature (P–T) conditions, and cooling rates. Type I consists of spinel and garnet peridotite, is devoid of garnet pyroxenite or eclogite layers, has depleted major element and REE compositions, yields P–T estimates that lie in a low P/T regime, and experienced very rapid cooling. Type II is distinguished by relatively high Fe contents and an abundance of garnet pyroxenite layers. Type III consists of garnet peridotite, contains garnet pyroxenite and eclogite layers, shows a range of LREE depletion to enrichment, yields P–T estimates in a medium P/T regime, and cooled more slowly than Type I. Such a diversity of peridotite types in the Gfo¨hl Nappe is ascribed to derivation from different mantle sites between and beneath Bohemia and Moldanubia during their Early Carboniferous collision. Type I is likely suboceanic lithosphere and asthenosphere that originated in a pre-collision ocean basin between Bohemia and Moldanubia, Type II appears to be a disrupted mafic–ultramafic cumulate complex, and Type III probably represents subcontinental lithosphere that was derived from the mantle wedge beneath Bohemia. D 2005 Elsevier B.V. All rights reserved. Keywords: Peridotite; Geochemistry; Thermobarometry; Gfo¨hl Nappe; Bohemian Massif; Variscan

1. Introduction Mantle-derived peridotite is a significant and widely distributed lithologic feature of the Middle

* Corresponding author. E-mail address: [email protected] (G. Medaris). 0024-4937/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.lithos.2004.12.004

to Late Paleozoic Variscan Orogen in Europe (Medaris and Carswell, 1990; Medaris, 1999). Although such peridotite is volumetrically minor, it provides important insights into the processes that resulted in juxtaposition of mantle and crust during the collision of Laurussia, Gondwana, and intervening amalgamated microplates. In this paper we describe three types of peridotite in the Czech part

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of the Gfo¨hl Nappe, Bohemian Massif, and discuss their origins in the context of Variscan tectonics. Such information should provide a useful basis for comparison with mantle-derived peridotites in other segments of the Variscan Orogen and in highpressure/ultrahigh-pressure belts worldwide. The European Variscides have long been divided into the Rhenohercynian, Saxothuringian, and Moldanubian zones (Kossmatt, 1927), among which the Moldanubian zone is the most southerly one in the arcuate fold belt. In the Bohemian Massif, spinel peridotite occurs in the Monotonous and Varied units of the Moldanubian zone, in the Saxothuringian zone, and in the Tepla Barrandian block (Bohemia), which is a fragment of the Cadomian Orogen (Franke, 2000), but garnet peridotite occurs only in the Gfo¨hl Nappe (Machart, 1984), which is the uppermost tectonic unit in the Moldanubian zone, and in the Saxothuringian zone (Schma¨dicke and Evans, 1997). Elsewhere in the Variscan Orogen, garnet peridotite occurs in the Moldanubian zone in the Schwarzwald (Kalt et al., 1995; Kalt and Altherr, 1996), Vosges (Altherr and Kalt, 1996), and Massif Central (Lasnier, 1971; Gardien et al., 1990). It has previously been demonstrated that two contrasting types of peridotite occur in the Gfo¨hl Nappe in the Czech Republic (Medaris et al., 1990). One type, represented by the Nove´ Dvory body, consists of garnet peridotite, contains eclogite lenses, equilibrated in a medium pressure/temperature (P/T) regime, and has discordant contacts with surrounding migmatitic orthogneiss. The other type, represented by the Mohelno body, consists of spinel peridotite, with garnet appearing only at its margins, is devoid of eclogite, equilibrated in a low P/T regime, and has concordant contacts with surrounding high-pressure quartzofeldspathic granulite. This dichotomy has subsequently been recognized in other peridotite bodies in the Czech portion of the Gfo¨hl Nappe (Medaris, 1999) and is further supported by a contrast in major and trace element rock compositions. In addition, a third type of peridotite has been identified, based on the coexistence of garnet, spinel, and ilmenite, and relatively Fe-rich mineral and rock compositions (Mı´sarˇ and Jelı´nek, 1981; Mı´sarˇ et al., 1984). It now appears that the Gfo¨hl Nappe in the Czech Republic hosts a variety of peridotites that originated

from different sources, including subcontinental lithosphere, suboceanic asthenosphere, and an ultramafic– mafic layered intrusive complex. Derivation of peridotites from such a diversity of sources is a consequence of the complex interactions between the Armorican Terrane Assemblage and Moldanubia during Carboniferous collision.

2. Peridotite localities in the Gfo¨hl Nappe The Gfo¨hl Nappe, which is the uppermost tectonic level in the Moldanubian zone of the Bohemian Massif, consists of a lower unit of migmatitic, granitic orthogneiss, with subordinate paragneiss and amphibolite, and an upper unit of quartzofeldspathic high-pressure granulite, both of which contain bodies of poorly exposed peridotite. All the peridotites are polymetamorphic and have complex mineral parageneses, due in large part to extensive recrystallization and hydration associated with exhumation and cooling (e.g., six recrystallization stages have been inferred for peridotites in the Austrian part of the Gfo¨hl Nappe, Carswell, 1991). In this study we focus on the earliest discernible mineral assemblages and those associated with high-pressure stabilization of garnet, in an effort to determine the sources of peridotite and to evaluate the conditions of high-pressure (HP) Variscan metamorphism. In addition, for the sake of brevity the Czech ultramafic rocks are referred to collectively as peridotite (except where necessary for clarification), when in fact a range of rock types exists, including lherzolite, harzburgite, and dunite. The Czech peridotites (Table 1, Fig. 1) have been divided into three groups according to peridotite chemical compositions, identity and relations of the aluminous phases, orthopyroxene compositions, and estimated P/T conditions. Type I peridotites comprise both spinel- and garnet-bearing varieties, contain high-Al2O3 orthopyroxene, and equilibrated in a low P/T regime. The Type II peridotites are characterized by generally lower Mg#’s than those of Type I, association with abundant pyroxenite, the local coexistence of garnet and spinel, low-Al2O3 orthopyroxene, and a range of P/T regimes. Type III peridotites have the most uniform characteristics among the three

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Table 1 Summary of important features of Czech peridotites in the Gfo¨hl Nappe Locality (map #)

Type

Lithology

Bulk Mg#

Aluminous phase(s)

Al2O3 in Opx (wt.%)

P/T regime

Host rock

Mohelno (1)

I I

spl pd grt pd

90.0–90.5 88.7–89.7

5.6–6.3 3.7–4.8

Low Low

Granulite Granulite

Biskoupky (2)

I I

spl pd grt pd

89.6–90.6 89.4

5.0–5.7 4.5–4.9

Low Low

Granulite Granulite

Lom pod Libı´nem (3) Bory (4)

I

grt pd

88.9

2.3–3.3

Low

Granulite

II-Mg

grt pd

88.8–90.6

0.7–1.0

Medium

Granulite

II-Fe

grt pd

80.3–88.8

spl grt with spl inclusions spl grt with spl inclusions grt with spl inclusions grt with spl inclusions grt+spl

1.1–2.1

Granulite

II-Mg III III III III III

grt pd grt pd grt pd grt pd spl pd grt pd

88.3 86.5–89.7 88.6–90.3 (Fo 89.5)a (Fo 91.8)a (Fo 90.0)a

grt grt grt grt spl grt

Low to medium Medium Medium Medium Medium Medium(?) Medium

Sklenne´ (5) Nove´ Dvory (6) ´ hrov (7) U Becˇva´ry (8) Hamry (9) a b

1.0–1.1 0.6–0.9 1.1–1.3 0.4–0.5 n.a.b 1.7–1.9

Granulite Gneiss Gneiss Gneiss Granulite Granulite

Mg# for olivine. Not analyzed.

groups, consisting solely of garnet peridotite (except for the Hamry peridotite) with low-Al2O3 orthopyroxene and a medium P/T regime. As summarized in Table 1, Type I and II peridotites are enclosed by felsic HP granulite, and Type III peridotites are surrounded by Gfo¨hl gneiss (the Hamry peridotite again being an exception). However, the apparent correlation between peridotite type and host rock may not be a reliable means of discrimination among all peridotites throughout the Gfo¨hl Nappe and in the Moldanubian zone elsewhere, because Gfo¨hl gneiss is thought to be the retrograde equivalent of HP granulite (Matejovska´, 1975; Cooke and O’Brien, 2001). Thus, it may simply be fortuitous that the investigated Type III peridotite bodies lie in portions of the granulite terrane that have been retrograded to gneiss. Nevertheless, in many parts of the Gfo¨hl Nappe, gneiss structurally underlies granulite, and the association of Type III peridotites with gneiss suggests that such bodies are generally situated in the lower level of the nappe complex. Occurrences and mineralogical characteristics of the investigated Czech peridotites are summarized in the following sections, and references to detailed descriptions of the individual localities

may be found in Machart (1984) and Medaris (1999). 2.1. Czech peridotite bodies in granulite 2.1.1. Mohelno (Type I, Locality 1 in Fig. 1) The Mohelno peridotite, which is a folded tabular body approximately 300 m thick and 4 km long, is composed almost entirely of spinel peridotite with subordinate lenses of spinel pyroxenite, and garnet peridotite occurs only within a few meters of the contact with surrounding Na´me˘sˇt’ granulite. Spinel peridotite has a porphyroclastic texture, in which large, strained pyroxene clasts are set in a fine-grained, recrystallized groundmass of olivine, pyroxene, and spinel (Fig. 2A). Garnet peridotite has an inequigranular texture, in which large spheroidal grains of garnet and pyroxene occur in a fine-grained groundmass of olivine, pyroxene, and spinel. Garnet has formed at the expense of spinel, as indicated by the common presence of spinel inclusions in garnet (Fig. 2B). Garnet is surrounded by an inner, fine-grained pyroxene-spinel kelyphite and an outer, fibrous amphibole-spinel kelyphite. Foliation in garnet peridotite is parallel to that in adjacent granulite,

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and the retrograde kelyphite assemblages in garnet peridotite are isofacial with retrograde assemblages in associated granulite. 2.1.2. Biskoupky (Type I, Locality 2 in Fig. 1) The Biskoupky body, which lies 2 km east of the Mohelno body, is identical to it in every respect, except for being larger, about 6 km in length. It is likely that the Mohelno, Biskoupky, and smaller similar peridotite lenses in the Na´me˘sˇt’ granulite represent disrupted fragments of an initially larger, continuous body. 2.1.3. Lom pod Libı´nem (Type I, Locality 3 in Fig. 1) Peridotite boudins and lenses, measuring 310 m to 1030 m, are enclosed by granulite in a quarry about 2 km SSE of the town of Prachatice. Garnet is

rarely preserved in the Lom pod Libı´nem peridotite, having been largely replaced by several stages of kelyphite. Locally, spinel grains are found in kelyphite domains after garnet (Fig. 2C), indicating that spinel was the earliest aluminous phase in peridotite at this locality. Thus, the sequence of assemblages in the Lom pod Libı´nem peridotite is similar to that at Mohelno and Biskoupky: first, ol+opx+cpx+spl; second, ol+opx+cpx+grt; followed by several retrograde assemblages. 2.1.4. Bory (Type II-Mg and Type II-Fe, Locality 4 in Fig. 1) At the Hornı´ Bory quarry, ultramafic and mafic boudins, ranging in size from decimeters to meters, are concentrated along several horizons in the Bory granulite. The boudins consist of a variety of

Fig. 1. Terrane map of the southern part of the Bohemian Massif (after Fusa´n et al., 1967; Mı´sarˇ et al., 1983; Franke, 1989; Matte et al., 1990). Numbers refer to peridotite localities listed in Table 1; symbols for different types of peridotite are designated in the inset.

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Fig. 2. Photomicrographs of selected Czech peridotites: (A) Type I spinel peridotite, Biskoupky; (B) Type I garnet peridotite, Mohelno; (C) Type I garnet peridotite, Lom pod Libı´nem; (D) Type II-Mg garnet peridotite, Bory; (E) Type II-Fe garnet+spinel peridotite, Bory; (F) Type III garnet peridotite, Nove´ Dvory. Abbreviations: ilm, ilmenite; kely, kelyphite; grt, garnet; opx, orthopyroxene; spl, spinel. Panel (A) partly crossed polarizers; all others, plane polarized light; scale bar is 1 mm in each panel.

lithologies, including dunite, harzburgite, lherzolite, olivine pyroxenite, pyroxenite, and eclogite, some of which are garnetiferous. Textures of the boudins range from massive to foliated, and some boudins have a pronounced mineralogical layering. As summarized in Table 1, some peridotite samples have relatively high bulk Mg#’s that are typical for mantle-derived peridotite and are designated here as Type II-Mg. However, most peridotite samples have lower Mg#’s and are designated as Type II-Fe. In Type II-Mg, spinel inclusions occur in garnet (or kelyphite after garnet, Fig. 2D), and in Type II-Fe, garnet, spinel, and ilmenite appear to coexist stably (Fig. 2E). The ultramafic and mafic boudins have been extensively recrystallized under low-pressure granulite and amphibolite facies conditions, as has the surrounding granulite. Garnet in peridotite, pyroxenite, and eclogite has been partly to completely replaced by kelyphite, omphacite in eclogite has been largely replaced by symplectite, and growth of hydrous phases, including amphibole, biotite, chlorite, and serpentine, is widespread. A conspicuous feature of many boudins, especially peridotite, is the presence of a biotite-rich reaction rim, which reflects the

incompatibility and reaction of olivine in the boudins with minerals in the surrounding granulite under retrograde conditions. 2.1.5. Sklenne´ (Locality 5 in Fig. 1) The Sklenne´ garnet peridotite is a single, 0.71.0 m boudin, which is enclosed by granulite that appears to be an extension of the Bory granulite, the main body of which lies 4 km to the south. Because of its position, occurrence, and major element composition, the Sklenne´ peridotite is thought to be related to the Bory peridotite suite and is designated Type II-Mg. Spheroidal grains of garnet, about 5 mm in diameter, are distributed uniformly in a fine-grained, equigranular polygonal groundmass of olivine, orthopyroxene, and clinopyroxene. Garnet is surrounded by an inner, fibrous kelyphite of amphibole and spinel and a thin, outer zone of fine-grained amphibole. 2.2. Czech peridotite bodies in gneiss (Type III) 2.2.1. Nove´ Dvory (Locality 6 in Fig. 1) The Nove´ Dvory peridotite (0.82.0 km) is allochthonous and allofacial with respect to sur-

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rounding Gfo¨hl migmatitic orthogneiss. The body consists largely of garnet peridotite, which contains layers of garnet pyroxenite and eclogite, and there is no evidence for the existence of spinel prior to the stabilization of garnet. The peridotite has an inequigranular texture, in which large garnet grains occur in a fine-grained, equigranular polygonal groundmass of olivine, orthopyroxene, clinopyroxene, and garnet (Fig. 2F). Aside from serpentinization, postgarnet recrystallization is minimal, except for thin rims of fibrous amphibole-spinel kelyphite around garnet. 2.2.2. U´hrov (Locality 7 in Fig. 1) ´ hrov peridotite is a poorly exposed body The U  (200 600 m) in the Bestvina Formation, which is a fragment of the Gfo¨hl Nappe in the Kutna Hora complex (Synek and Oliveriova´, 1993). Scattered small outcrops and boulders of garnet peridotite, garnet pyroxenite, and eclogite show all the same mineralogical and textural features as those in comparable rock types at Nove´ Dvory. 2.2.3. Becˇva´ry (Locality 8 in Fig. 1) The Becˇva´ry peridotite is another poorly exposed body (0.81.0 km) in a fragment of the Gfo¨hl Nappe farther west in the Kutna Hora Complex. A single excellent outcrop in an abandoned quarry reveals garnet peridotite like that at Nove´ Dvory, which contains three, 5 to 10 cm-thick garnet pyroxenite layers and one, 5-cm thick eclogite layer. 2.2.4. Hamry (Type III, Locality 9 in Fig. 1) The Hamry peridotite is poorly exposed in an overgrown roadcut about 20 m long, surrounded by the Blansky Les granulite. It is reported that four, steeply dipping, alternating spinel peridotite and garnet peridotite layers, each about 5 m thick, were revealed in the fresh roadcut 30 years ago (Jelı´nek, personal communication). Spinel peridotite contains olivine, orthopyroxene, clinopyroxene, and Cr-rich spinel in a medium-grained, equigranular polygonal texture, and garnet peridotite consists of large (5 mm) spheroidal to lobate garnet grains in a fine- to medium-grained, inequigranular polygonal groundmass of olivine, orthopyroxene, and clinopyroxene.

2.3. Austrian peridotite bodies in granulite Peridotite is also an important constituent of granulite complexes (Dunkelsteiner Wald, St. Leonhard, Po¨chlarn-Wieselburg, Go¨ pfritz-Blumau) in lower Austria (Carswell, 1991; Becker, 1996a, 1997a,b). Like their Czech counterparts, peridotite bodies in Austria contain a variety of lithologies, including garnet lherzolite, garnet harzburgite, spinel harzburgite, garnet pyroxenite, and eclogite. In rare cases, Cr-rich spinel inclusions are found in kelyphite domains after garnet (Fig. 1a in Becker, 1997b), indicating the existence of spinel prior to the stabilization of garnet in some peridotite samples.

3. Peridotite chemistry Forty-two samples of Czech peridotite were analyzed for major and minor elements by XRF techniques at XRAL Laboratories (Ontario) and by wet chemical methods at Charles University (Praha). The results are summarized in Appendix A, where the analyses have been recalculated on an anhydrous basis and all Fe is taken to be FeO, because of extensive serpentinization and associated formation of magnetite in most samples. It has been previously demonstrated that serpentinization does not significantly affect bulk rock variations in major elements (Frey et al., 1985; Becker, 1996a). The rare earth elements, Sc, Cr, Co, and Ni were obtained for 24 of the Czech samples by instrumental neutron activation analysis (INAA) at Washington University (St. Louis), following the procedures described by Korotev (1987), and by ICP-MS at the Department of Geochemistry and Mineralogy, Charles University (Praha), following the methods of Weiss et al. (1990) and using PCC1 (peridotite) and DTS1 (dunite) as standards. The results are summarized in Appendix B, and REE data in subsequent figures are normalized to the primitive mantle values given by McDonough and Sun (1995). 3.1. Major and minor elements Variations for selected elements in Czech peridotites are illustrated in Fig. 3, where SiO2, Al2O3,

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Fig. 3. Oxide variation diagrams for Czech peridotites in the Gfo¨hl Nappe. The compositions of primitive mantle (McDonough and Sun, 1995) and Austrian peridotites (Becker, 1996a) and the Ronda variation trend (Frey et al., 1985) are shown for comparison.

FeO, and CaO are plotted against MgO. The compositions of primitive mantle (McDonough and Sun, 1995) and Austrian peridotites (Becker, 1996a) and the variation trend for the well documented Ronda massif, Spain (Frey et al., 1985), are included for comparison. Taken as a whole, the Czech data present a rather chaotic array, but patterns emerge when each of the three peridotite types is considered separately. Czech Type I peridotites show a slight decrease in SiO2 and FeO, and a larger decrease in Al2O3 and CaO with an increase in MgO (Fig. 3). TiO2 and Na2O (not shown) also decrease with an increase in MgO. Such negative correlations are comparable to those for Austrian peridotites and the Ronda massif, although the Austrian and Ronda suites include samples with higher MgO contents. Among the Czech Type I samples analyzed so far, garnet peridotites have lower MgO contents than do related spinel peridotites. Type II-Fe peridotites from Bory are distinctive, showing considerable scatter in the data and having consistently higher FeO and lower SiO2 contents

than those of the Czech Type I, Austrian, and Ronda peridotites (Fig. 3). The apparent positive correlation of FeO with MgO may reflect the influence of cumulate processes involving relatively Fe-rich olivine, as considered in the Discussion section. Type II-Fe peridotites are also characteristically higher in TiO2 and lower in Cr2O3 and NiO for a given level of MgO, compared to Type I. In contrast to Type II-Fe peridotites, major and minor element compositions of the Type II-Mg peridotite samples from Bory and Sklenne´ are comparable to those of the Type I suite. Variation trends in the Czech Type III peridotites are generally similar to those in the Type I suite, although there is a greater degree of scatter in the data (Fig. 3). In detail, MgO contents in the Type III suite extend to lower contents than do those in Type I, and Type III samples contain lower CaO contents for a given MgO value. Type III garnet peridotites are characterized by relatively abundant veins and layers of garnet pyroxenite and eclogite, and the scatter in the peridotite compositional variations may be due in part to cryptic metasomatism by the melts from which pyroxenite and eclogite crystallized.

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3.2. Rare earth elements Among the Czech peridotites, Type I from the Mohelno and Biskoupky bodies shows the most consistent REE pattern, having a flat distribution of HREE at a level of 0.3 to 1.0 times that for primitive mantle and being uniformly depleted in LREE (Fig. 4). Many samples show a slight negative Eu anomaly. The total REE concentrations for samples from the Mohelno and Biskoupky bodies overlap, but garnet peridotites from the two bodies contain higher REE concentrations than do spinel peridotites. In contrast, Type I peridotite from Lom pod Libı´nem shows a marked enrichment in LREE (Fig. 4), although it contains a level of HREE comparable to that in the Mohelno and Biskoupky garnet peridotites. Among Type I peridotites, the sample from Lom pod Libı´nem shows the most pronounced negative Eu anomaly. Two samples of Type II-Mg garnet peridotite from Bory have relatively flat REE patterns at 0.3 to 0.6 times that of primitive mantle (Fig. 4). Type IIMg peridotite from Sklenne´ has a similar level of REE depletion, but shows a pronounced, convexupward REE pattern. Two samples of Type II-Fe

garnet peridotite from Bory also show a pronounced, convex upward REE pattern, similar to that at Sklenne´, but at higher REE concentrations (Fig. 4). A third sample of Type II-Fe peridotite from Bory has an overall REE depletion, with a pattern that shows an increase from the HREE to Sm and a flat distribution of the LREE. Type III garnet peridotites display a range of REE patterns, which are related to the proximity of garnet pyroxenites (Fig. 4). Samples of Nove´ Dvory garnet peridotite, whose outcrops are free of pyroxenite, are LREE depleted, and samples of peridotite from Nove´ ´ hrov, and Becˇva´ry, which are adjacent to Dvory, U pyroxenite veins, have flat to LREE enriched patterns. Four samples have negative Eu anomalies, and one, a positive anomaly. Europium anomalies are common in pyroxenites and eclogites associated with Czech Type III peridotites (Medaris et al., 1995) and Austrian peridotites (Becker, 1996a,b). A plot of Ce/Sm vs. Sm/Yb, normalized to primitive mantle, provides an effective means for comparing REE patterns among the various samples of Czech peridotites. The four quadrants of such a plot discriminate among REE patterns that are LREE depleted, LREE enriched, convex downward, and

Fig. 4. REE abundances in Czech peridotites from the Gfo¨hl Nappe, normalized to primitive mantle (McDonough and Sun, 1995).

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Fig. 5. Ce/Sm vs. Sm/Yb ratios (normalized) for Czech, Austrian, and Ronda peridotites. Note the separation of different REE patterns into four quadrants, as illustrated by the inset figures.

convex upward, as shown schematically by the insets in Fig. 5. Ratios that lie near the center (origin) of the diagram would represent a flat pattern, relative to primitive mantle. Type I peridotites from Mohelno and Biskoupky plot in the LREE depleted quadrant of Fig. 5, as do peridotites from the Ronda massif and abyssal peridotites (not shown). Note that spinel peridotites are displaced farther from the origin than are garnet peridotites. The Type I Lom pod Libı´nem peridotite lies in the LREE enriched quadrant, as does one sample of Type II-Mg peridotite from Bory. Type IIFe peridotite from Bory is separate from most other Czech peridotites, plotting well within the convex upward quadrant, although the Sklenne´ peridotite also has a convex upward pattern. Ratios for the Type III peridotites generally trend from LREE depleted to LREE enriched. Interestingly, many Austrian peridotites plot in the convex downward quadrant, from which Czech peridotites are absent. Such a convex downward pattern for some Austrian peridotites may be due to a combination of extreme depletion in incompatible elements (cf. high MgO and low Al2O3 and CaO contents for some Austrian samples in Fig. 3) and subsequent enrichment in LREE’s.

4. Mineral chemistry Olivine, orthopyroxene, clinopyroxene, garnet, and spinel were analyzed by wavelength-dispersion spectrometry (WDS) with a Cameca SX51 instrument at the University of Wisconsin, using a 15 kV accelerating voltage, a 20 nA beam current (Faraday cup), a beam diameter of 1 Am, Probe for Windows software utilizing the matrix correction of Armstrong (1988), and a combination of natural and synthetic minerals as standards. Analyses of representative minerals in 21 samples from the nine investigated peridotite bodies, including those used in subsequent thermobarometric calculations, are summarized in Appendix C. Silicate minerals in Czech Type I, II-Mg, and III peridotites are similar in composition to those in Mg–Cr, mantle-derived peridotites elsewhere. In terms of Ca, Mg, and Fe, compositions overlap among individual mineral species from Type I, IIMg, and III peridotites (Fig. 6). Olivine is magnesian (Fo 91.1–89.3), as is orthopyroxene (En 91.4–89.5), garnet is pyrope-rich, with a mean composition of Prp 72.2F2.8 (2j), Alm 15.5F2.2, Sps 0.6F0.2, Grs 11.6F1.8, and clinopyroxene is Cr-diopside (0.7–1.4

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Fig. 6. Compositions of coexisting olivine, orthopyroxene, clinopyroxene, and garnet in Czech peridotites, projected into the plane, Ca–Mg–Fe. Coexisting phases are designated by dashed lines.

wt.% Cr2O3). The relatively large variation in Ca/ (Mg+Fe) ratio in clinopyroxene reflects the range in blocking temperatures recorded by clinopyroxene grains, depending on the different thermal histories of the various Czech peridotite bodies, as discussed below. Minerals in Type II-Fe peridotite, as the designation implies, are more Fe-rich than those in Types I, II-Mg, and III. In two analyzed samples (Fig. 6), olivine is Fo 86.8 and 80.7, orthopyroxene is En 86.9 and 82.8, garnet has Prp–Alm–Sps–Grs contents of 60.6–23.1–1.5–14.7 and 55.0–27.8–1.0–16.2, and clinopyroxene has a Mg# of 89.1 and contains 0.32 wt.% Cr2O3. In contrast to the relative uniformity of orthopyroxene composition with respect to Ca, Mg, and Fe, contents of Al2O3 and Cr2O3 vary widely in orthopyroxene from different types of Czech peridotite (Fig. 7). The range of Al2O3 and Cr2O3 contents reflects different equilibration conditions, and the variation in Al2O3/Cr2O3 ratio is largely due to the effect of bulk composition. Orthopyroxene from the Type I Mohelno and Biskoupky bodies contains the highest contents of Al2O3 and Cr2O3 (higher in spinel peridotite than in garnet peridotite) and shows a relatively wide range in Al2O3/Cr2O3 ratio. Orthopyroxene from the Type I Lom pod Libı´nem peridotite contains significantly lower amounts of Al2O3 and Cr2O3. Based on the presently available analyses, there is little difference between

orthopyroxene in Type II-Mg and Type II-Fe peridotites, both having low contents of Al2O3 and Cr2O3 and a wide range in Al2O3/Cr2O3. Orthopyroxene from Type III peridotite has a relatively constant Al 2O 3/Cr 2O 3 ratio and generally low Al2O3 and Cr2O3 contents, with those from Hamry being the highest among this group. The composition of primary spinel in the Czech peridotites (Fig. 8) is controlled largely by bulk rock Cr/Al and Mg/Fe ratios and, to a lesser extent, by equilibration conditions. Spinel in Type I spinel peridotite from Mohelno and Biskoupky is Al- and Mg-rich, similar to disseminated spinel in spinel peridotite massifs elsewhere. In garnet peridotite from Mohelno and Biskoupky the composition of matrix spinel is similar to that in spinel peridotite, but spinel inclusions in garnet are higher in Cr/(Cr+Al) and slightly lower in Mg/ (Mg+Fe2+). In the Lom pod Libı´nem peridotite, the compositions of matrix spinel and inclusions in garnet are similar to each other, although both are higher in Cr/(Cr+Al) and lower in Mg/(Mg+Fe2+) than those from Mohelno and Biskoupky. Spinel in kelyphite is consistently Cr-poor [Cr/(Cr+Al) b0.1], which reflects its inheritance of Cr/Al ratio from garnet during its formation by the reaction, grt+ol=spl+opx+cpx.

Fig. 7. Al2O3 and Cr2O3 contents (wt.%) of orthopyroxene in Czech peridotites.

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Fig. 8. Compositions of spinel in Czech peridotites, projected onto the plane, Mg–Fe–Al–Cr.

In Type II-Fe peridotite from Bory, spinel appears to be in textural equilibrium with garnet and ilmenite. Spinel in Type II-Fe peridotite is more Fe-rich than that in Type I (Fig. 8), and some spinel grains in sample 99BY3A are strongly zoned, with core to rim values of Cr/(Cr+Al) ranging from 0.42 to 0.25, and values of Mg/(Mg+Fe2+), from 0.45 to 0.60. The only primary spinel recognized so far in Type III peridotite occurs in the spinel peridotite layers in the Hamry body. This spinel is the most Cr-rich of any analyzed in this study, having a value for Cr/(Cr+Al) of ~0.60 and a range in Mg/(Mg+Fe2+) of 0.50–0.55 (Fig. 8).

5. Geothermobarometry Several geothermometers and geobarometers have been calibrated for garnet peridotites, but the determination of meaningful P–T values for

11

such rocks is not a trivial task, because of common polymetamorphism, compositional zoning in minerals, and the inherent problem of using a combination of exchange and net transfer reactions, which may have quenched at different times under different P–T conditions. As recommended by Brenker and Brey (1997), the preferred method for calculating bpeakQ P–T values for garnet peridotites is to apply the olivine–garnet Fe–Mg exchange geothermometer and Al-in-orthopyroxene geobarometer to the core compositions of garnet and orthopyroxene and the composition of matrix olivine, because Fe and Mg diffusion is relatively slow in garnet compared to that in olivine and pyroxene, Al diffusion is slow in orthopyroxene, and olivine, which is the predominant phase, will undergo the least compositional change during cooling. Accordingly, we have followed this approach for the Czech garnet peridotites, applying the O’Neill and Wood calibration (1979; O’Neill, 1980) of the olivine–garnet geothermometer and the Brey and Ko¨hler calibration (1990) of the Alin-orthopyroxene geobarometer to phases that were judged from textural relations to be in equilibrium at the garnet stage. Mineral compositions used in the thermobarometric calculations are summarized

Table 2 Summary of P–T estimates for Czech garnet peridotites Type

Locality

Sample

T, 8C

P, kbar

I I I I I I II-Mg II-Mg II-Fe II-Fe III III III III III III III III

Mohelno Mohelno Mohelno Biskoupky Biskoupky Lom pod Libı´nem Bory Sklenne´ Bory Bory Nove´ Dvory Nove´ Dvory Nove´ Dvory Nove´ Dvory Nove´ Dvory ´ hrov U Becˇvary Hamry

CZ3A CZ3B CM14 CS-BS-1A CS-BS-1B CS-LL-1B 97CZ3C CS-SK-1 99BY3A 85GM8B CZ2A CZ2B CZ2C M1 NM2 CZ9A Fiala CZ21A

1275 1270 1120 1310 1335 1015 910 1195 870 960 1175 875 1105 1180 985 1170 845 1245

27.6 27.1 22.4 29.1 29.6 25.4 38.3 50.3 25.6 24.6 54.5 33.4 44.8 60.1 43.1 43.8 40.6 44.3

12

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Fig. 9. Pressure–temperature estimates for Czech garnet peridotites, based on the Al-in-orthopyroxene geobarometer (Brey and Ko¨hler, 1990) and the olivine–garnet Fe–Mg exchange geothermometer (O’Neill and Wood, 1979; O’Neill, 1980). P–T estimates for garnet peridotites in other Eurasian terranes ( ) are shown for comparison. The high, medium, and low P/T regimes recognized by Medaris (1999) are indicated by the gray fields. P–T estimates for Gfo¨hl granulite ( G) and eclogite (E) are from Carswell and O’Brien (1993), Cooke et al. (2000), and Medaris et al. (1998).

.

in Appendix C and the results are summarized in Table 2. A survey of garnet peridotites in 11 Eurasian HP/ UHP terranes (Medaris, 1999) revealed that such rocks record an enormous range of P–T conditions, but that results for different terranes fall into three P/T regimes (regardless of the combination of geothermometers and geobarometers used), which are designated high P/ T, medium P/T, and low P/T (Fig. 9). It should be emphasized that the three P/T regimes do not represent geotherms, but should be regarded as the equivalent of metamorphic field gradients (England and Thompson, 1984). The Czech garnet peridotites also yield a wide range of P–T values, but there is a good correspondence between the P–T results for Czech peridotite Types I and III and the previously established P/T regimes for other Eurasian HP/UHP terranes. Type I garnet peridotites from Mohelno, Biskoupky, and Lom pod Libı´nem yield relatively low pressures and high temperatures within the low P/T regime (Fig. 9). P–T estimates for high-pressure granulite and eclogite from the Gfo¨hl granulite

terrane (Carswell and O’Brien, 1993; Cooke et al., 2000; Medaris et al., 1998) also lie within the low P/ T array. Spinel peridotites from Mohelno and Biskoupky could have been stable up to pressures of 21–22 kbar within the low P/T field (based on their spinel compositions; O’Neill, 1981), but their equilibration temperature at ~1100 8C (derived from two-pyroxene geothermometry; Taylor, 1998), is significantly less than that of garnet peridotite at ~1300 8C. Type II garnet peridotites from Bory and Sklenne´ yield scattered results (Fig. 9). Both Type II-Mg samples lie within the medium P/T field, and Type II-Fe samples plot at lower pressures, one being located on the edge of the low P/T field, and the other, between the medium and low P/T regions. Type III garnet peridotites yield relatively high pressures for a given temperature, all plotting within the medium P/T region (Fig. 9). The wide range of temperatures along the P/T array may represent quenching of samples at different times during the P–T evolution of this otherwise coherent suite of peridotites. Spinel peridotite interlayered with garnet peridotite at Hamry contains Cr-rich spinel, which has a maximum pressure stability of ~40 kbar at 1250 8C (O’Neill, 1981), raising the possibility that spinel and garnet peridotite at Hamry may be isofacial. Although P–T estimates have been made for garnet peridotites in the Austrian part of the Gfo¨hl Nappe (Carswell, 1991; Becker, 1997a,b), the results cannot be directly compared to those for the Czech peridotites, because analyses of matrix olivine in the Austrian occurrences were not published. The best estimates for P–T conditions of the garnetiferous ultramafic assemblages in Austria, based on pyroxene geothermometry and geobarometry, were given as 1050F20 8C, 31F3 kbar by Carswell and 1100–1200 8C, 30–35 kbar by Becker.

6. Cooling rates Compositional zoning is prevalent in garnet in the Czech peridotites. Typically, garnet has compositionally uniform cores, but shows an increase

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

in Fe and concomitant decrease in Mg at contacts with olivine and pyroxene. Such zoning is the result of arrested Fe–Mg exchange between garnet and adjacent ferromagnesian silicates during cooling, and can be modeled by using the diffusion equation and appropriate diffusion coefficients (e.g. Wilson and Smith, 1985; Medaris and Wang, 1986). Previously, cooling rates were calculated for samples from the Mohelno and Nove´ Dvory peridotites by using finite differences to solve the diffusion equation for measured zoning profiles in garnet against olivine inclusions (Medaris et al., 1990). Although excellent agreement was achieved between the measured and model compositional profiles, the cooling rates required for such agreement were unreasonably fast, because appropriate diffusion coefficients for Fe and Mg in pyrope–almandine garnet were unavailable at that time. Subsequently, Ganguly et al. (1998) experimentally determined the self-diffusion coefficients

13

for Fe and Mg in pyrope and almandine garnets, cast in the form of the Arrhenius relation, D=D 0exp{ [ Q(1 bar)+PDV +]/RT}, with the following parameters: Fe: Q (1 bar)=65,532(F10,111) cal/mol, D 0=3.50(F2.30) 10 5 cm2/s, DV +=5.6(F2.9) cm3/mol M g: Q ( 1 b a r ) = 6 0, 76 0 (F8 ,2 57 ) c al / m o l , D 0=4.66(F2.48) 10 5 cm2/s, DV +=5.3(F3.0) cm3/mol We have used these diffusion parameters to recalculate cooling rates for previously analyzed Mohelno and Nove´ Dvory garnet peridotites, following the same procedures and boundary conditions as those described in detail by Medaris et al. (1990). In two samples of Mohelno peridotite, compositional profiles in garnet grains against olivine inclusions have larger amplitudes and shorter decay distances than do those from the Nove´ Dvory

Fig. 10. Variation of almandine content in garnet grains adjacent to olivine inclusions. Symbols, measured compositions; continuous curves, compositional profiles calculated from diffusion modelling. Bilinear cooling rate estimates are given in the insets.

14

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

peridotite (Fig. 10). As found previously, diffusion models using a single cooling rate, either linear or exponential, fail to match both core and rim compositions of zoned garnet grains, but models using a bilinear cooling rate yield an acceptable fit. For the Mohelno samples, an extremely rapid initial cooling rate, 5000 8C/m.y., is necessary to preserve the garnet core compositions, and slower secondstage cooling rates, 50 to 1 8C/m.y., are required to reach the garnet rim compositions (see Fig. 10 for specific temperature intervals and bilinear cooling rates). In contrast, for the two Nove´ Dvory samples, a much slower initial cooling rate, 10 8C/m.y., and a second-stage rate of 1 8C/m.y., are sufficient to provide good fits to the compositional profiles (Fig. 10). Such different model cooling rates for the Mohelno and Nove´ Dvory peridotites further enhance the distinction between these two types of Czech peridotite.

7. Discussion Peridotites in the Czech part of the Gfo¨hl Nappe have been assigned to three groups, according to their bulk major element compositions, mineral compositions, and P/T regimes. The major and trace element compositions of the Type I Mohelno and Biskoupky peridotites are typical of depleted mantle, similar to those of abyssal peridotites in oceanic settings, and their unusually high temperatures (~1300 8C) in the low P/T field suggest an asthenospheric connection. In contrast, the Type III Nove´ ´ hrov, and Becˇva´ry bodies have major and Dvory, U trace element compositions and a P/T regime consistent with derivation from subcontinental lithosphere. The Type II-Fe peridotite boudins at Bory may represent fragments of a disrupted mafic–ultramafic cumulate complex, based on their relatively Fe-rich compositions, scatter in major element variation diagrams, layered aspect, and association with abundant pyroxenite. However, not all the investigated peridotites are completely consistent with respect to the characteristics of a designated type. The Type I Lom pod Libı´nem peridotite shows LREE enrichment, rather than the LREE depletion found in the Mohelno and Biskoupky peridotites. The Type II-Mg Sklenne´

peridotite is the most problematic, having a major element composition like that of Type I, a convexupward REE pattern like that of some Type II-Fe boudins, and a P–T value lying in the medium P/T field. Among four samples of Czech peridotite analyzed for radiogenic isotopes (Beard, 1992), Mohelno is the most depleted, with an e Nd (335 Ma) value of 9.8, ´ hrov, and 6.6 and 4.0 for Nove´ compared to 7.4 for U Dvory. These values lie within the ranges determined for Austrian peridotites, which are 9.2 to 12.5 for samples distant from pyroxenite layers and 0.2 to 7.1 for those proximal to such layers (Becker, 1996a). Nd and Sr isotopes for garnet peridotites and associated garnet pyroxenites in the Gfo¨hl Nappe define an array of decreasing e Nd with increasing initial 87Sr/86Sr from peridotite to pyroxenite (Becker, 1996a; Brueckner and Medaris, 1998). The garnet pyroxenite and eclogite layers in Czech Type III peridotites and in Austrian peridotites are thought to represent high-pressure crystal cumulates from melts that migrated through lithospheric mantle (Medaris et al., 1995; Becker, 1996b). Nd, Sr, and O isotope analyses and negative Eu anomalies indicate that subducted oceanic crust contributed to the melts from which the garnet pyroxenites and eclogites crystallized. Sm–Nd mineral isochron ages for Gfo¨hl garnet peridotites range from 329 to 354 Ma (mean=339F10 Ma, n=7), although the Mohelno garnet peridotite gives a significantly older age, 371 Ma (Beard, 1992; Becker, 1997a). Garnet pyroxenite and eclogite layers yield Sm–Nd ages similar to those in the host garnet peridotites, ranging from 324 to 344 Ma (mean=336F7 Ma, n=9), although older Sm–Nd ages of 370, 373, and 377 Ma were obtained from garnet pyroxenites at Mitterbachgraben, Nı´hov, and Becˇva´ry, respectively (Beard et al., 1992; Becker, 1997a; Brueckner et al., 1991; Carswell and Jamtveit, 1990). The mean Sm–Nd ages of 336 and 339 Ma for Gfo¨hl garnetiferous ultramafic rocks are comparable to the U–Pb ages for metamorphic zircon from Gfo¨hl granulite, which range from 338 to 347 Ma and are taken to represent the time of high pressure–high temperature Variscan metamorphism (Kro¨ner et al., 2000, and citations therein). Several features indicate that Early Carboniferous high pressure–high temperature metamorphism at

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

~10008C, 16 kbar (Carswell and O’Brien, 1993) in the Gfo¨hl granulite unit was a relatively short-lived event. Small garnet grains in Gfo¨hl eclogite and clinopyroxene granulite preserve prograde compositional zoning in a few rare instances (Medaris et al., 1998; Cooke et al., 2000). Applying the relation, x 2fDt (x, distance; D, diffusion coefficient; t, time), and the diffusion coefficients of Ganguly et al. (1998) to garnet grains with a 1 mm radius indicates that such grains would homogenize in 1.2 to 2.8 million years at 1000 8C, depending on composition, and in 11 to 27 million years at 900 8C. Evidently, heating of Gfo¨hl granulite and

15

residence at the maximum P–T conditions were not of protracted duration. Cooling and exhumation of the Gfo¨hl granulite unit were also rapid, judging from the fast cooling rates calculated for the Mohelno peridotite, 40Ar/39Ar ages of 341–329 Ma for hornblende and 329–326 Ma for muscovite in units overridden by the Gfo¨hl Nappe at the eastern margin of the Bohemian Massif (Dallmeyer et al., 1992), and Vise´an deposition of granulite debris in the Moravian foreland basin (Dvorˇak, 1982). The provenance of the two predominant groups of Czech Gfo¨hl peridotites, Types I and III, can be

Fig. 11. Hypothetical tectonic scenario to account for the origin and evolution of Types I and III peridotite in the Gfo¨hl Nappe. Black, oceanic crust; light gray, continental crust; hatch pattern, lithosphere; dark gray, asthenosphere. I and III, positions of Types I and III peridotites.

16

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

interpreted in the context of the tectonic scenario presented by Franke (2000). During Frasnian time, bilateral subduction was occurring beneath Bohemia (Fig. 11, upper panel). Moldanubia, which was either a member of the Armorican Terrane Assemblage or a fragment of northern Gondwana, was separated from Bohemia by a small ocean basin and spreading center, which allowed shallow rise of asthenospheric mantle. With closure of the ocean basin and collision of Moldanubia and Bohemia (Fig. 11, middle panel), imbrication of asthenospheric mantle (Type I peridotite), oceanic crust, and continental crust may have occurred in the vicinity of the subducted spreading center, giving rise to the lithologic association of the Gfo¨hl granulite unit and elevating temperatures in the crustal rocks. Might the 371 Ma Sm–Nd age for the Mohelno garnet peridotite reflect such juxtaposition of hot mantle and cooler crust? Deeper in the subduction zone, fluids originating from the subducted oceanic crust and slab interface infiltrated the overlying subcontinental lithosphere (Type III peridotite), producing the garnet pyroxenite and eclogite layers in peridotite and causing cryptic metasomatism. Perhaps this event has been recorded in the few Sm–Nd ages of ~375 Ma in some garnet pyroxenites. With further subduction (Fig. 11, lower panel), perhaps accompanied by incipient detachment of the Gfo¨hl granulite unit, peridotite from the overlying lithospheric wedge (Type III peridotite) may have settled into subducted Gfo¨hl crust, as in the sinking intrusion model of Brueckner (1998). The numerous U–Pb and Sm–Nd ages in the range, 340–335 Ma, record the high pressure–high temperature conditions in the Gfo¨hl complex at this stage in its tectonic evolution. Slab breakoff then released the subducted Moldanubian block and allowed for its rapid exhumation and cooling, providing an additional opportunity for material from the overlying mantle wedge to be incorporated into the ascending complex. Two interesting implications for the Czech peridotites arise from the tectonic scenario presented here. First, the retrograde compositional zoning in garnet grains in peridotite may have been initiated during juxtaposition of hot mantle with cooler crust, reflecting local thermal gradients rather than cooling

associated with exhumation. The calculated initial cooling rates for the garnet peridotites may thus have more bearing on rates of mantle and crust intermingling than on exhumation rates for the Gfo¨hl Nappe. However, garnet grains in the Czech peridotites eventually should have recorded the cooling effects due to exhumation, which are perhaps seen in the calculated second stage cooling rates. Second, with respect to separation age from convecting mantle, the Type I suboceanic mantle is predicted to be younger than the Type III subcontinental mantle. Further investigation utilizing Lu–Hf and Rh–Os isotopes should allow this prediction to be tested. Although the Type II peridotites appear to represent fragments of a disrupted mafic–ultramafic cumulate complex, the provenance of such a complex is unclear in the context of the proposed tectonic scenario. Isotopic data, which are currently lacking, are needed to evaluate the oceanic or continental affinity of this ultramafic suite. A characteristic feature of the Type II peridotites is their occurrence as small, widely scattered bodies in granulite at the Hornı´ Bory quarry, which we have described as boudins. Intriguingly, some Gfo¨hl granulite has been interpreted as having originated from high-pressure felsic melts (Vra´na, 1989; Jakesˇ, 1997; Kotkova´ and Harley, 1999). If so, the small peridotite bodies in the Hornı´ Bory quarry may represent xenoliths from the upper mantle or lower crust that were incorporated in such high-pressure melts, all of which were subsequently deformed and recrystallized to varying degrees. The existence of such high-pressure melts would enhance the buoyancy of the Gfo¨hl complex and contribute to its rapid exhumation.

Acknowledgments Financial support was provided to Emil Jelı´nek by grants from the Ministry of Education, Czech Republic (Nr. J13/98:113100005) and the Granting Agency of the Czech Academy of Science ( Nr. IAA3013403). We thank Tony Carswell, Angelika Kalt, and Jana Kotkova´ for their perceptive and constructive reviews.

Appendix A. Major element analyses of Czech peridotites

Mohelno

Sample

MH 2

CZ3A

CZ 3B1

CZ3B2

CM 14

CZ3C1

CZ3C2

02CZ4

Biskoupky 02CZ5

CB3A

CB4C

CS-BS1A

CS-LL-1B

Lithology

grt pd

grt pd

grt pd

grt pd

grt pd

spl pd

spl pd

spl pd

spl pd

spl pd

spl pd

grt pd

grt pd

Map #

1

1

1

1

1

1

1

2

2

2

2

2

3

Method

wet

XRF

XRF

wet

wet

XRF

wet

wet

wet

wet

wet

wet

wet

45.34 0.20 3.18 0.41 0.27 8.75 0.13 38.42 2.95 0.27 0.02 0.04 100.00 88.7

44.79 0.13 3.70 0.33 0.25 7.99 0.15 39.02 3.40 0.20 0.02 0.01 100.00 89.7

42.55 0.10 2.72 0.36 0.28 8.00 0.15 42.72 2.94 0.15 0.01 0.01 100.00 90.5

45.77 0.10 2.62 0.42 0.30 7.88 0.13 39.78 2.82 0.13 0.01 0.03 100.00 90.0

45.23 0.11 2.25 0.42 0.30 8.43 0.11 41.56 1.46 0.09 0.01 0.03 100.00 89.8

44.53 0.11 2.89 0.33 0.24 7.76 0.12 40.93 2.85 0.18 0.01 0.03 100.00 90.4

45.73 0.09 2.91 0.39 0.28 7.57 0.12 40.93 1.82 0.11 0.01 0.03 100.00 90.6

44.92 0.18 3.62 0.35 0.25 8.11 0.12 39.29 2.87 0.24 0.02 0.03 100.00 89.6

46.16 0.18 3.18 0.36 0.27 8.14 0.12 38.52 2.75 0.28 0.01 0.03 100.00 89.4

44.62 0.15 2.78 0.34 0.24 8.74 0.13 39.23 3.29 0.21 0.22 0.04 100.00 88.9

Anhydrous; all Fe as FeO; oxides in wt.% SiO2 45.49 44.84 45.24 TiO2 0.15 0.19 0.17 Al2O3 3.76 4.95 3.41 Cr2O3 n.d. 0.42 0.43 NiO n.d. 0.23 0.25 FeO 8.26 8.07 8.17 MnO 0.14 0.15 0.14 MgO 38.87 37.64 39.09 CaO 3.05 3.23 2.84 Na2O 0.24 0.25 0.24 K2O 0.01 0.01 0.01 P2O5 0.02 0.02 0.01 Total 100.00 100.00 100.00 Mg # 89.4 89.3 89.5

Lom pod Libı´nem

Locality

Bory

Sample

HB8

HB2

HB81

HB72

HB14

HB9

HB75

HB19

HB11

HB13

HB64a

HB7

HB1

97CZ3C

99BY3A

99BY1B

85GM8B

Lithology

dun

pd

grt pd

pd

pd

dun

pd

dun-pd

pd-px

pd

dun

pd

pd, kely

grt pd

grt dun

grt pd

grt pd

Map #

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

Method

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

41.94 0.13 1.54 0.16 0.18 10.22 0.08

41.02 0.17 1.33 2.24 0.02 10.43 0.09

42.11 0.06 2.35 n.d. n.d. 10.92 0.22

40.56 0.14 2.63 n.d. n.d. 11.15 0.21

41.17 0.13 1.45 0.26 0.14 11.24 0.09

40.28 0.14 1.46 0.18 0.01 12.22 0.06

39.02 0.07 0.36 n.d. n.d. 13.89 0.26

40.38 0.13 1.15 0.56 0.05 13.11 0.08

44.55 0.25 2.66 0.64 0.21 10.66 0.98

44.86 0.09 1.91 0.37 0.30 7.88 0.11

40.78 0.18 1.74 0.66 0.34 12.16 0.14

46.03 0.14 1.35 0.43 0.30 8.00 0.13

40.88 0.32 5.41 0.46 0.21 14.48 0.18

Anhydrous; all Fe as FeO; oxides in SiO2 43.62 44.84 52.61 TiO2 0.06 0.03 0.06 Al2O3 1.73 1.82 1.25 Cr2O3 0.14 0.16 n.d. NiO 0.22 0.21 n.d. FeO 8.89 9.02 8.25 MnO 0.17 0.08 0.19

wt.% 43.93 0.11 2.53 n.d. n.d. 9.34 0.17

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Locality

(continued on next page)

17

18

Appendix A (continued) Bory

Sample

HB8

HB2

HB81

HB72

HB14

HB9

HB75

HB19

HB11

HB13

HB64a

HB7

HB1

97CZ3C

99BY3A

99BY1B

85GM8B

Lithology

dun

pd

grt pd

pd

pd

dun

pd

dun-pd

pd-px

pd

dun

pd

pd, kely

grt pd

grt dun

grt pd

grt pd

Map #

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

Method

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

wet

Anhydrous; MgO CaO Na2O K2O P2O5 Total Mg #

all Fe as FeO; oxides in wt.% 43.31 41.44 36.66 41.56 1.76 2.30 0.88 2.26 0.03 0.05 0.00 0.00 0.04 0.04 0.02 0.06 0.03 0.00 0.06 0.03 100.00 100.00 100.00 100.00 89.7 89.1 88.8 88.8

42.88 2.75 0.05 0.07 0.00 100.00 88.2

42.10 2.23 0.10 0.25 0.00 100.00 87.8

42.35 1.95 0.00 0.00 0.03 100.00 87.4

42.48 2.77 0.00 0.02 0.04 100.00 87.2

41.33 4.09 0.02 0.08 0.00 100.00 86.8

43.34 2.18 0.05 0.06 0.00 100.00 86.3

45.87 0.46 0.00 0.04 0.03 100.00 85.5

43.22 1.17 0.06 0.07 0.00 100.00 85.5

35.10 4.65 0.24 0.07 0.00 100.00 85.4

42.72 1.50 0.08 0.15 0.04 100.00 90.6

42.47 1.39 0.06 0.01 0.05 100.00 86.2

40.31 3.13 0.11 0.04 0.03 100.00 90.0

33.14 4.51 0.15 0.19 0.06 100.00 80.3

´ hrov U

Locality

Sklenne´

Nove´ Dvory

Sample

CS-SK-1

M1

SP5

SP13

MSP2

CZ 2D

CZ 2H

CND 1D

CND 5B

CS-UR-5

CS-UR-6

CS-UR-7

Lithology

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt pd

Map #

5

6

6

6

6

6

6

6

6

7

7

7

Method

wet

wet

wet

wet

wet

XRF

XRF

XRF

XRF

XRF

XRF

XRF

45.71 0.32 4.83 0.39 0.38 8.63 0.11 34.64 4.67 0.29 0.03 0.00 100.00 87.7

45.69 0.33 2.22 0.18 0.38 8.60 0.12 39.88 2.48 0.09 0.05 0.00 100.00 89.2

45.54 0.40 5.57 0.29 0.06 8.43 0.15 36.31 3.03 0.22 0.00 0.00 100.00 88.5

43.94 0.25 2.90 0.58 0.26 10.90 0.10 39.11 1.20 0.74 0.01 0.01 100.00 86.5

44.87 0.19 3.06 0.34 0.34 10.30 0.11 38.70 1.82 0.24 0.01 0.01 100.00 87.0

46.49 0.05 2.15 0.37 0.30 8.26 0.13 40.31 1.72 0.15 0.03 0.01 100.00 89.7

47.33 0.12 2.54 0.36 0.28 9.19 0.15 37.45 2.37 0.16 0.02 0.02 100.00 87.9

46.23 0.06 1.59 n.d. n.d. 8.19 0.12 42.79 0.95 0.03 0.01 0.02 100.00 90.3

45.74 0.07 1.99 n.d. n.d. 8.53 0.14 42.48 0.95 0.08 0.01 0.02 100.00 89.9

48.46 0.21 4.02 n.d. n.d. 8.54 0.14 37.24 1.09 0.26 0.01 0.02 100.00 88.6

Anhydrous; all Fe as FeO; oxides in wt.% SiO2 45.07 46.81 TiO2 0.18 0.20 Al2O3 3.36 3.77 Cr2O3 0.45 0.35 NiO 0.30 0.18 FeO 9.08 9.17 MnO 0.13 0.15 MgO 38.30 35.84 CaO 2.78 3.16 Na2O 0.27 0.20 K2O 0.02 0.00 P2O5 0.05 0.18 Total 100.00 100.00 Mg # 88.3 87.4

Analytical methods: wet: wet chemical, Charles University, Praha; XRF: X-ray fluorescence, XRAL Laboratories, Ontario.

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Locality

Appendix B. Trace element analyses of Czech peridotites (ppm)

Mohelno

Sample

Biskoupky

Lom pod Libı´nem

Bory

´ hrov Becvary U

Sklenne´ Nove´ Dvory

CZ 3A CZ3B

CM 14 CZ3C CZ3C

CS-BS1D CB3A

02CZ5

CS-BS1A CB4C

02CZ4

Lithology grt pd grt pd

grt pd spl pd spl pd

grt pd

spl pd

spl pd

grt pd

spl pd

spl pd

grt pd

grt pd

grt pd

grt pd

grt pd

grt dun

grt pd

grt pd grt pd grt pd

grt pd

grt pd grt pd

Map #

1

1

2

2

2

2

2

2

3

4

4

4

4

4

5

6

6

7

Method

INAA ICP-MS INAA INAA ICP-MS ICP-MS

INAA

INAA INAA

Sc Cr Co Ni La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

18.9 2890 95.2 1780 0.208 0.80

0.306 0.132 0.109

0.553 0.085

1

2829 117 2153 0.263 0.677 0.122 0.728 0.281 0.106 0.468 0.072 0.478 0.111 0.329 0.051 0.336 0.052

1

13.8 2550 97.4 1920 0.257 0.98

12.5 2280 99.9 1990 0.094 0.24

0.249 0.096

0.150 0.060

0.081

0.046

0.365 0.055

0.268 0.041

1

2926 129 2393 0.074 0.216 0.037 0.285 0.139 0.051 0.253 0.040 0.273 0.067 0.198 0.033 0.213 0.037

2718 117 2192 0.410 1.040 0.121 0.876 0.340 0.115 0.470 0.080 0.580 0.132 0.414 0.057 0.439 0.063

CS-LL-1B BY3BB 85GM8B 99BY1B 97CZ3C 99BY3A CS-SK-1 CZ 2C CZ 2D CND 1D CND 5B CZ 9B CZ 6B

6

6

ICP-MS ICP-MS ICP-MS

ICP-MS ICP-MS ICP-MS

ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS ICP-MS INAA INAA INAA

2691 118 2207 0.111 0.241 0.040 0.241 0.119 0.045 0.220 0.038 0.270 0.065 0.197 0.031 0.212 0.035

2385 106 1991 0.082 0.325 0.063 0.444 0.207 0.081 0.347 0.060 0.411 0.097 0.289 0.045 0.306 0.048

5761 57 724 0.896 2.930 0.561 3.337 1.331 0.480 1.840 0.311 1.954 0.421 1.163 0.162 0.992 0.149

2298 99 1874 0.091 0.322 0.062 0.403 0.156 0.057 0.260 0.038 0.247 0.056 0.163 0.026 0.166 0.026

2454 112 2098 0.276 0.782 0.129 0.729 0.280 0.100 0.396 0.067 0.435 0.098 0.289 0.044 0.284 0.045

2911 125 2375 0.112 0.262 0.041 0.282 0.132 0.051 0.225 0.039 0.266 0.062 0.187 0.029 0.198 0.031

2373 104 1924 1.405 2.934 0.415 1.800 0.490 0.120 0.541 0.083 0.509 0.107 0.310 0.047 0.305 0.047

3181 154 1634 0.317 0.977 0.196 1.126 0.475 0.197 0.640 0.096 0.514 0.107 0.275 0.042 0.242 0.041

2975 128 2405 0.335 0.948 0.189 0.772 0.253 0.091 0.340 0.056 0.358 0.080 0.236 0.036 0.240 0.037

2526 120 2360 0.330 0.908 0.140 0.597 0.168 0.058 0.190 0.035 0.203 0.050 0.140 0.027 0.155 0.031

4573 164 2711 0.403 1.060 0.179 0.850 0.299 0.082 0.290 0.040 0.215 0.047 0.125 0.022 0.120 0.024

3119 131 2365 0.225 0.669 0.122 0.761 0.286 0.126 0.418 0.065 0.401 0.086 0.239 0.034 0.220 0.034

8

11.4 2330 101.4 1950 0.104 0.50

7.6 3980 125.9 2010 0.103 0.46

9.0 2560 107.5 2340 0.176 0.62

10.6 2430 107.5 2170 0.915 2.70

12.2 2330 98.1 1910 0.671 1.60

19 2140 85.3 1540 0.880 2.60

0.210 0.083

0.208 0.093

0.144 0.043

0.392 0.111

0.277 0.081

3.0 0.674 0.234

0.053

0.041

0.029

0.080

0.077

0.167

0.269 0.043

0.193 0.024

0.119 0.020

0.233 0.038

0.255 0.040

0.585 0.092

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Locality

19

20

Appendix C. Mineral compositions used in thermobarometric calculations (oxides in wt.%) OLIVINE Locality 1

1

1

1

2

2

2

2

3

4

4

4

5

6

6

6

6

6

Sample CZ3A CZ3B CM 14 CZ3C CS-BS-1A CS-BS-1D 02CZ4 02CZ5 CS-LL-1B 85GM8B 97CZ3C 99BY3A CS-SK-1 CZ2A CZ2B CZ2C M1 C2

F

E

7

9

D

Mean

Mean

Mean Mean Mean

Mean

Mean

Mean

Mean

Mean Mean Mean Mean Mean Mean

SiO2 FeO MnO MgO NiO Total

40.70 40.80 41.20 40.60 40.36 9.94 10.10 9.73 9.85 9.93 0.12 0.14 0.13 0.26 0.14 49.60 48.50 48.90 48.80 48.32 0.41 0.38 0.42 0.45 0.37 100.77 99.92 100.38 99.96 99.12

40.63 9.93 0.15 48.54 0.36 99.62

40.69 40.64 40.70 9.18 9.42 10.06 0.14 0.13 0.12 49.05 48.96 48.51 0.37 0.35 0.39 99.42 99.51 99.79

39.14 17.81 0.22 42.01 0.22 99.41

40.52 9.26 0.16 49.49 0.37 99.81

39.82 13.23 0.35 45.82 0.29 99.51

40.34 10.24 0.11 49.09 0.40 100.18

40.50 40.70 8.81 9.11 0.12 0.10 50.50 49.43 0.51 0.37 100.44 99.70

2

2

4

A

40.70 40.53 42.08 40.61 40.89 9.25 8.99 9.93 10.41 9.70 0.09 0.08 0.10 0.10 0.14 49.35 49.57 48.58 48.81 48.85 0.40 0.45 n.d. n.d. 0.42 99.79 99.62 100.69 99.93 99.99

ORTHOPYROXENE Locality 1

1

1

1

2

2

3

4

4

5

6

6

6

6

Sample CZ3A CZ3B Olga

CZ3C CS-BS-1A CS-BS-1D 02CZ4 02CZ5 CS-LL-1B 85GM8B 97CZ3C 99BY3A CS-SK-1 CZ2A CZ2B CZ2C M1

Grain

H

A

Mean

Mean

Mean Mean Mean

Mean

Mean

SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Na2O Total

54.40 54.10 54.90 53.80 54.33 0.00 0.13 0.00 0.00 0.16 4.32 4.56 4.04 5.63 4.64 0.48 0.38 0.54 0.59 0.48 6.62 6.88 6.18 6.58 6.50 0.14 0.14 0.11 0.07 0.14 33.70 32.90 33.10 33.00 32.76 0.60 0.65 1.02 0.59 0.74 0.02 0.00 0.13 0.00 0.06 100.28 99.74 100.02 100.26 99.80

54.17 0.17 4.78 0.49 6.46 0.16 32.82 0.69 0.04 99.77

53.86 53.85 56.13 0.13 0.16 0.12 5.51 5.17 2.49 0.60 0.68 0.36 6.06 5.93 6.51 0.14 0.13 0.13 32.72 32.25 33.99 0.59 1.08 0.54 0.01 0.06 0.02 99.61 99.30 100.28

55.46 0.05 1.78 0.04 11.59 0.29 30.53 0.31 0.01 100.06

57.29 56.80 0.06 0.11 0.85 1.19 0.17 0.16 5.90 8.89 0.13 0.34 35.37 33.02 0.27 0.29 0.01 0.00 100.05 100.80

C1

H

E

6

7

8

9

NM2 CZ9A Fiala CZ21A

Mean

Mean Mean Mean Mean Mean A

56.94 0.10 1.03 0.10 6.40 0.09 35.30 0.36 0.03 100.35

56.67 0.00 0.69 0.18 5.97 0.13 35.77 0.30 0.11 99.81

A

56.70 56.25 57.30 57.45 56.48 57.99 56.18 0.00 0.00 0.08 0.03 0.00 0.04 0.12 0.81 0.91 0.66 0.61 1.27 0.42 1.86 0.16 0.19 0.12 0.11 0.26 0.07 0.33 6.07 6.29 6.12 6.12 6.32 6.33 6.66 0.11 0.16 0.11 0.09 0.14 0.14 0.19 35.57 35.85 35.56 35.45 34.98 34.88 34.42 0.11 0.30 0.05 0.16 0.19 0.16 0.40 0.00 0.10 0.00 0.03 0.00 0.04 0.01 99.52 100.03 99.99 100.05 99.63 100.08 100.16

CLINOPYROXENE Locality 1

1

1

1

2

2

2

2

3

4

4

5

6

6

6

6

Sample CZ3A CZ3B Olga CZ3C CS-BS-1A CS-BS-1D 02CZ4 02CZ5 CS-LL-1B 85GM8B 97CZ3C CS-SK-1 CZ2A CZ2B CZ2C M1 Grain

E

C1

E

F

Mean

SiO2 TiO2 Al2O3 Cr2O3

52.60 52.90 52.80 51.80 52.10 0.62 0.52 0.00 0.00 0.58 6.53 6.88 6.04 6.56 6.93 0.93 0.71 1.14 0.96 1.10

6

7

8

9

NM2 CZ9A Fiala CZ21A

C

G

Mean

Mean

Mean

Mean

Mean

Mean Mean Mean Mean Mean A

A

52.38 0.57 6.75 0.90

51.35 0.48 6.23 0.89

52.08 0.48 6.25 1.13

53.16 0.33 3.54 1.08

54.51 0.09 1.53 0.32

54.80 0.10 1.38 0.69

54.49 0.30 3.62 0.64

54.20 54.43 54.20 55.05 55.53 54.22 54.82 53.46 0.00 0.00 0.00 0.22 0.19 0.00 0.18 0.39 2.68 2.58 3.04 2.84 3.04 3.32 3.53 3.68 1.33 1.27 1.22 1.04 1.38 1.05 0.70 1.27

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

Grain

40.30 9.40 0.10 49.00 0.52 99.31

8

NM2 CZ9A Fiala CZ21A

FeO MnO MgO CaO Na2O Total

3.47 3.53 2.44 2.64 2.28 0.11 0.11 0.08 0.02 0.08 15.80 15.60 14.90 15.40 14.84 17.20 17.50 20.20 20.70 20.03 1.74 1.71 2.19 1.20 1.73 99.00 99.46 99.79 99.28 99.68

2.88 0.11 15.26 19.01 1.91 99.76

2.20 0.07 17.99 19.06 1.05 99.32

2.51 0.10 15.07 20.63 1.43 99.69

2.41 0.07 16.25 21.59 0.95 99.39

3.68 0.06 16.80 22.31 0.46 99.76

1.86 0.06 17.30 22.92 0.73 99.84

2.53 0.06 15.96 20.32 1.99 99.92

5

6

2.76 2.76 2.83 2.94 3.06 2.21 2.80 2.63 0.11 0.08 0.13 0.08 0.07 0.10 0.07 0.07 15.93 15.75 15.77 15.60 15.28 15.97 14.68 16.30 20.30 20.35 20.00 19.63 18.53 21.06 19.63 20.00 2.30 2.01 2.46 2.30 2.86 1.78 3.00 1.73 99.61 99.22 99.66 99.69 99.93 99.70 99.40 99.53

GARNET Locality 1

1

1

2

2

3

4

4

4

6

6

6

6

7

8

Sample

CZ3A CZ3B Olga

CS-BS-1A CS-BS-1D CS-LL-1B 85GM8B 97CZ3C 99BY3A CS-SK-1 CZ2A CZ2B CZ2C M1

NM2 CZ9A Fiala

Grain

F

C

F

C

A

Mean

Mean

Mean

Mean

A

C

A

F

A

SiO2 TiO2 Al2O3 Cr2O3 FeO MnO MgO CaO Total

41.10 0.00 22.10 1.68 7.51 0.28 21.90 4.77 99.34

41.40 42.00 0.00 0.00 22.50 22.30 1.27 1.52 7.69 7.84 0.28 0.34 21.80 21.30 4.68 4.70 99.62 100.00

42.08 0.44 22.66 1.13 7.23 0.28 20.98 4.49 99.31

41.58 0.23 23.01 1.22 7.17 0.31 21.09 4.78 99.39

42.32 0.16 22.59 1.58 8.48 0.39 20.01 5.01 100.55

41.30 0.03 22.93 0.39 13.76 0.50 15.46 6.10 100.46

42.14 0.05 23.37 0.38 8.96 0.47 19.92 4.55 99.83

41.06 0.04 21.37 2.28 11.44 0.75 16.81 5.69 99.46

42.48 0.52 22.30 0.91 8.53 0.31 21.50 4.02 100.57

41.70 0.00 21.60 2.28 7.53 0.27 21.40 5.00 99.78

41.20 0.00 21.80 1.63 9.14 0.34 20.40 4.72 99.23

41.50 41.50 0.00 0.24 22.30 22.20 1.50 1.50 8.28 8.16 0.29 0.32 21.10 21.50 4.72 4.69 99.69 100.11

40.80 0.26 21.00 2.79 8.61 0.38 20.50 5.28 99.62

41.34 0.00 21.77 1.60 8.34 0.33 21.38 4.48 99.23

F

G

9 CZ21A A 41.48 0.00 22.13 1.89 7.79 0.32 21.36 4.86 99.83

SPINEL Locality

1

2

2

4

4

4

9

9

9

9

9

9

9

9

Sample

CZ3C

02CZ4

02CZ5

85GM8B

99BY3A

99BY3A

CZ21F

CZ21F

CZ21F

CZ21F

CZ21F

CZ21F

CZ21F

CZ21F

Grain

E

Mean

Mean

Mean

Mean cores

Mean rims

C core

C rim

D core

D rim

G core

G rim

H core

H rim

TiO2 Al2O3 Cr2O3 V2 O3 FeO MnO MgO ZnO NiO Total

0.07 51.70 13.70 0.08 13.60 0.04 18.30 0.24 0.29 98.02

0.02 53.10 13.00 0.06 13.83 0.06 18.36 0.21 0.34 98.97

0.05 50.80 16.50 0.03 13.31 0.13 17.77 0.18 0.29 99.06

0.27 38.08 26.59 0.46 23.56 0.18 10.17 0.17 0.08 99.57

0.34 28.67 36.60 0.24 22.50 0.36 9.88 0.06 0.08 98.72

0.15 46.58 19.65 0.18 17.50 0.34 14.55 0.07 0.16 99.16

0.11 19.63 46.9 0.17 21.21 0.32 11.01 0.22 0.07 99.64

0.11 21.25 44.74 0.16 21.24 0.3 11.08 0.22 0.06 99.16

0.1 19.55 47.13 0.19 20.93 0.29 11.08 0.2 0.06 99.53

0.09 20.35 45.33 0.16 20.73 0.26 11.59 0.19 0.07 98.77

0.1 19.88 46.26 0.19 21.52 0.31 10.69 0.22 0.07 99.24

0.08 20.57 45.09 0.19 21.73 0.31 10.66 0.25 0.05 98.93

0.09 20.51 46.13 0.18 21.17 0.3 10.8 0.24 0.06 99.48

0.07 21.13 44.61 0.18 20.86 0.28 11.76 0.23 0.06 99.18

G. Medaris Jr. et al. / Lithos 82 (2005) 1–23

41.86 0.00 22.84 0.99 10.52 0.45 18.99 4.28 99.94

Localities; 1 Mohelno; 2 Biskoupky; 3 Lom pod Libinem; 4 Bory; 5 Sklenne; 6 Nove Dvory; 7 Uhrov; 8 Becvary; 9 Hamry.

21

22

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