Moldavites from the Cheb Basin, Czech Republic

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Geochimica et Cosmochimica Acta 73 (2009) 1145–1179 www.elsevier.com/locate/gca

Moldavites from the Cheb Basin, Czech Republic ˇ ada d Roman Ska´la a,b,*, Ladislav Strnad b, Catherine McCammon c, Miroslav C b

a Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojova´ 269 CZ-16500 Praha 6 – Lysolaje, Czech Republic Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University CZ-12843 Praha 2, Czech Republic c Bayerisches Geoinstitut, Universita¨t Bayreuth, D-95440 Bayreuth, Germany d Minera´ly Cˇada, B. Neˇmcove´ 386, CZ-351 01 Frantisˇkovy La´zneˇ, Czech Republic

Received 13 May 2008; accepted in revised form 4 November 2008; available online 11 November 2008

Abstract Between 1993 and 2007, an estimated 2500–3000 individual moldavite pieces have been found in the Tertiary Cheb Basin, Western Bohemia. This identifies the area as the third most prominent source of Central European tektites, next to the South Bohemian and West Moravian strewn subfields. Basic macroscopic physical properties (weight, shape, color and sculpture) were evaluated for over 350 individual finds of tektites from 4 different localities in the Cheb Basin. All these properties are similar to those observed for the South Bohemian moldavites, particularly with respect of color and weight distribution. In total, 24 tektites from the Cheb Basin have been characterized chemically using electron microprobe. For comparison, a set of 17 moldavites from the South-Bohemian and Moravian strewn subfields was measured as well. Contents of major elements overlap between the two sample sets; the largest variation was observed for iron. The trends observed in the Harker plots, however, seem to differentiate several partial subgroups, some of them characteristic for Cheb tektites only. These results are also substantiated by cluster analysis, which reveals a tight group for most of the tektites from the Cheb Basin, forming two partial clusters. The rest of the Cheb moldavites cluster with the South Bohemian samples. Minor and trace elements were measured with an LA-ICP-MS technique; CI-normalized REE patterns compare well with those for other moldavites. Many tektites, both from Cheb and South Bohemia or Moravia, display considerable heterogeneity: they frequently show schlieren and fluidal fabric. Two samples of this kind from the Cheb Basin showed considerable enrichment in volatile elements (e.g., Zn and Cu), which is typical for Muong Nong-type Australasian tektites. Mo¨ssbauer spectroscopy confirmed the highly reducing character of 5 studied moldavites. Discovery of a new moldavite strewn subfield around Cheb substantiates the theory that moldavites were ejected from the Ries impact structure in a fan-shaped jet, although it is not clear yet if it was continuous or composed of individual rays. In addition, the chemistry of the Cheb moldavites indicates significant precursor material heterogeneity. Ó 2008 Elsevier Ltd. All rights reserved.

1. INTRODUCTION Moldavites, also known as the Central European tektites, occur at many localities in Bohemia and Moravia (e.g., Bousˇka and Konta, 1986; Trnka and Houzar, 2002), near Dresden in Lusatia in Germany (Lange, 1995), and in Austria (Koeberl, 1986) (Fig. 1). Based on their occurrence, chemical composition and age, moldavites have been

*

Corresponding author. Fax: +420 220 922 670. E-mail address: [email protected] (R. Ska´la).

0016-7037/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.gca.2008.11.003

interpreted to be produced about 14–15 Ma ago as a result of the Ries–Steinheim impact event (Schnetzler et al., 1966; Gentner et al., 1967; Shaw and Wasserburg, 1982; Staudacher et al., 1982; Engelhardt et al., 1987, 2005; Bigazzi and de Michele, 1996; Mader et al., 2001; Schwarz and Lippolt, 2002; Buchner et al., 2003; Laurenzi et al., 2003; Aziz et al., 2008; Di Vincenzo and Ska´la, in press). In the Cheb Basin, the moldavites were first found on the beach of the Jesenice water reservoir near Okrouhla´ in 1993 (Bousˇka et al., 1995) (Fig. 2). These authors also provided the first information on the chemical composition ˇ ada (2003) analyzed of the local tektites. Later, Ska´la and C

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Fig. 1. Map of Central Europe illustrating the distribution of moldavite partial strewn fields. Classical strewn subfields are shown in light gray and the Cheb Basin in dark gray. The Ries and Steinheim impact structures are also shown. The apical angle of the ejecta fan corresponding to moldavite distribution is 60°. The fan is more or less axisymmetrical along a line connecting the Ries and Steinheim structures. B = Berlin, L = Leipzig, M = Mu¨nchen, N = Nu¨rnberg, P = Praha, W = Wien.

Fig. 2. Schematic map showing localities where moldavites were found in the Cheb Basin: (1) Okrouhla´, beach of the Jesenice dam (the place where moldavites were originally found); (2) Drˇenice, gravel pit; (3) Drˇenice, beach of the Jesenice water reservoir; (4) Obilna´, gravel pit; (5) Velky´ Luh, gravel pit; (6) Odrava, road cut; and (7) Trˇebenˇ.

three more moldavites found in the gravel pit near Drˇenice, about 3 km NW of the place of the original finds. These data showed a much wider compositional range. Additional chemical data on the Cheb moldavites have been recently

ˇ anda et al. (2008). From 1993 to 2007 about published by R 2500 to 3000 individual pieces of moldavites were found in the region of the Cheb Basin, which makes the area the third most prolific source of Central European tektites next

Moldavites from the Cheb Basin

to the South Bohemian and West Moravian strewn subfields (Trnka and Houzar, 2002). Because of this large number of moldavites discovered it is important to determine whether the Cheb Basin represents a new, separate strewn subfield and whether there are some specific properties which differentiate Cheb moldavites from those from South Bohemia and Moravia. If the Cheb Basin did correspond to a new strewn subfield, it would support the hypothesis of a fan-shaped moldavite strewn field of Artemieva et al. (2002) and Sto¨ffler et al. (2002). In addition, Cheb tektites represent the part of the moldavite strewn field closest to the Ries crater (Fig. 1). The objectives of the present study included: (1) determination of macroscopic physical properties and study of the microscopic appearance of Cheb moldavites, in particular weight, color, internal fabric, and presence of inclusions; (2) acquisition of microchemical compositional data and evaluation of inter- and intra-sample variations for tektites from the Cheb Basin as well as those from the South Bohemian and Moravian strewn subfields; (3) in-situ determination of minor and trace element data on a microscale to identify possible local compositional variations and correlate them with texture and major element heterogeneities; (4) evaluation of the oxidation state of iron in selected tektites to assess the degree of tektite melt oxidation; (5) statistical evaluation of major element data using factor and cluster analysis; and (6) comparison of the properties for the tektites of the Cheb Basin and those from the South Bohemian and Moravian strewn subfields to define possible discrimination parameters. A novel approach has been adopted to process the individual spot analyses acquired within each of the samples analyzed. Instead of simple averaging, the analyses were separated into chemically different groups. These groups were further considered to represent separate chemical domains. 2. LOCAL GEOLOGICAL SETTINGS AND MOLDAVITE LOCALITIES The Cheb (Eger) Basin represents the westernmost of the Tertiary shallow sedimentary basins situated at the SSE foot of the Krusˇne´ hory mountains (Erzgebirge). At present, the Cheb Basin is geographically delineated approximately by the cities Cheb, Frantisˇkovy La´zneˇ, Plesna´, Kacˇerov and Kynsˇperk and Ohrˇ´ı, and occupies an area of about 300 km2 (Fig. 2). The Cheb Basin represents a short-lived, intracontinental basin. It is located at the intersection of the NE-striking Ohrˇe Rift (Eger Graben) and the NW-trending Cheb-Domazˇlice Graben. Its longer axis is oriented in a NNW–SSE direction. The maximum subsidence of the Cheb Basin is estimated not to exceed 400 m in the deepest part at the eastern tectonic rim. The maximum thickness of the Neogene sediments attains 300 m in this region (Mı´sarˇ et al., 1983). The sedimentary fill of the Cheb Basin has been traditionally divided into 5 units of Upper Eocene to Upper Pliocene age (Shrbeny´ et al., 1994; Kvacˇek et al., 2006). In addition, Middle Eocene volcano-sediments are reported from the area close to Velky´ Luh (Suhr, 2003). At the base of the stratigraphic sequence, there are relics of Upper Eocene clastics, which uncomformably overlie weathered crystalline rocks of the basement. They consist of sandstones and conglomerates and resemble the Stare´ Sedlo Formation of the nearby Sokolov Basin (Sˇpicˇa´kova´ et al., 2000;

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Kvacˇek et al., 2006). The overlying uppermost Oligocene to lowermost Miocene Lower Clay and Sand Formation is formed by fluvial and lacustrine clays, sands and gravels. At the top of it occurs the coal-bearing Main Seam Formation. It is composed of clays and sands with a coal seam and subordinate volcanics and volcanoclastics. The Early to Middle Miocene Cypris Formation was deposited in an anoxic lacustrine environment. The dominant sediments include bitumen clays and claystones laterally replaced by sands and carbonates representing litoral facies. Deposition of the Cypris Formation was, according to Shrbeny´ et al. (1994) and Kvacˇek et al. (2006), most probably terminated at the boundary between the Karpatian and the Badenian (or Burdigalian and Langhian using ICS IUGS terminology). The upper surface of the formation is erosional. The youngest preserved sediments were paleomagnetically dated as 17 Ma old; however Sˇpicˇa´kova´ et al. (2000) assumed that the sedimentation continued until 12 Ma. This would agree with the hypothesis of Kopecky´ and Va´cl (1999), who assumed that moldavites were deposited in the area of the Cheb Basin at the time of the sedimentation of the Cypris Formation. The overlying Vildsˇtejn Formation of Late Pliocene (to lowermost Quaternary?) age was deposited after a major hiatus and consists of kaolinite-rich clays and sands. At the top occur locally also rustybrown to yellowish-brown gravels and sandy gravels. According to ˇ ada et al. (1998), these gravels represent Bousˇka et al. (1995) and C moldavite-bearing sediments of the Cheb Basin, although they are certainly not coeval with them. The upper surface of the Vildsˇtejn Formation is either the recent erosional surface or the base of Quaternary deposits (gravels, loesses, loams). Up to now the moldavites have been reported from 7 different places in the area of the Cheb Basin: beaches of the Jesenice water reservoir (localities Drˇenice and Okrouhla´), gravel pits Drˇenice, Obilna´, and Velky´Luh, from a road cut near Odrava, and from the village of Trˇebenˇ (Fig. 2). The number of collected samples varies with time – for example, in the second half of 2004 and beginning of 2005 the amount of moldavites recovered from sediments exploited at the gravel pit Drˇenice, the most productive locality, decreased considerably, indicating inhomogeneous distribution of moldavites within the local sediments. Close to Okrouhla´ (#1; Fig. 2), the moldavite-bearing sediments are exposed on a narrow beach of the Jesenice water reservoir. This is the locality where moldavites were found for the first time in 1993. Local moldavites are deeply sculptured, have dull surfaces and occur in sandy gravels. The sediments which host the moldavites resemble those of Upper Miocene age occurring near Besednice in South Bohemia (the so-called Vra´bcˇe Member). There, these sands are considered to indicate the proximity of the original strewn field sediments (e.g., Trnka and Houzar, 2002). The finds on a beach near Drˇenice (#3), which are situated just on the opposite side of the water reservoir, are of the same type as those found near Okrouhla´. The coarsegrained yellow- and red-colored sands and sandy gravels of the Vildsˇtejn Formation represent moldavite-bearing sediments in the gravel pit near Drˇenice (#2). Features such as cross-bedding and wash-outs, as well as reappearing and nosing-out of layers indicate fluvial or fluviolacustrine sedimentation. Moldavite-bearing sediments crop out also in the area delimited by the villages Obilna´, Vrbova´ and Nebanice (#4). They are of Mindel and younger age and cover sediments of the Vildsˇtejn Formation. Several gravel pits are operated in this region. In the gravel pit near Velky´ Luh (#5), gravels and sands represent moldavite-bearing sediments. They overlie rusty colored sandy gravels incrusted with limonite. Both sands and gravels probably correspond to the Vildsˇtejn Formation. The original stratigraphic position of moldavite finds is uncertain, however, because all came from alluvial fans. In the course of highway construction an irregular moldavite fragment of glassy luster was found near Odrava village (#6) in sediments equivalent to those exploited in the gravel pit Drˇenice. Near the village Trˇebenˇ

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NE of Cheb (#7) a single oval moldavite with dull surface and abraded sculpture was found when a pond was dug on a private property.

3. SAMPLES AND EXPERIMENTAL METHODS Macroscopic physical properties were studied on 357 samples collected in the region of the Cheb Basin between 1997 and 2007 ˇ ada. and held in the private collection of Miroslav C Twenty-four samples from the gravel pit Drˇenice were selected for the present analytical study. They are referred as ‘‘D-X”, where X is the number of the sample. Five of them were deep green, five olive green, eleven bottle green, two light green, and one was pale green (using the color scale of Bousˇka and Povondra, 1964). Eighteen of the studied pieces were irregular or flattened fragments, five moldavites were oval- or disc-shaped full-forms, and one represented a flattened highly elongated rectangular rod-shaped fullform. The majority of the samples displayed pitted sculpture with round pits of variable diameter and depth. A few pieces showed deeper sculpture with relatively deep narrow straight or curvilinear grooves. Some of the samples also displayed fine linear striations. The luster of the studied pieces was either dull or glassy. The weight of the studied moldavites varied between 0.5 and 3.3 g. For direct comparison a set of samples from ‘‘classical” localities in the South Bohemia and Moravia was also studied. The samples came from the South Bohemian localities Besednice (Bs, 1 piece), Chlum (Ch, 7 pcs.), Jankov (J, 3 pcs.), and Slavcˇe (Sl, 2 psc.) and Moravian sites Slavice (Sv, 1 pc), Sˇteˇpa´novice (Sp, 1 pc.), and Vı´denˇsky´ rybnı´k (VR, 1 pc). The data collected for specimens from this reference set allowed the building up of a self-consistent database free of any bias due to instrument-specific systematic errors. This fact is important for mutual comparison and statistical processing of chemical and physical data. Secondary electron images for two moldavites from the Drˇenice gravel pit (D-1, D-4) were recorded with a CAMECA SX-100 microprobe (Institute of Geology, Academy of Sciences of the Czech Republic, Praha) at 20 kV accelerating voltage and 10 nA sample current on gold-sputtered chips. A JEOL JXA-8200 (Bayerisches Geoinstitut, University of Bayreuth, Bayreuth) and the CAMECA SX-100 (Institute of Geology, Academy of Sciences of the Czech Republic, Praha) microprobes operated at 15 kV accelerating voltage and 10 nA sample current were used to image the carbon-coated polished (thin-)sections using back-scattered electrons. The major element compositions of all 24 moldavites from the Cheb Basin as well as 17 specimens from South Bohemia and Moravia were measured with the CAMECA SX-100 electron microprobe (Institute of Geology, Academy of Sciences of the Czech Republic, Praha). To avoid the loss of volatile elements but still retain a good resolution, the accelerating voltage was set to 15 kV, the sample current was 4 nA, and the electron beam was defocused to a nominal 2 lm spotsize. The following elements were analyzed using their Ka spectrum lines (standards, spectrometer crystals, and detection limits, respectively, are given in parentheses): Si (quartz, TAP, 105 ppm), Ti (rutile, LPET, 65 ppm), Al (leucite, TAP, 74 ppm), Fe (magnetite, (L)LIF, 416 ppm), Mg (MgO, LTAP, 44 ppm), Ca (diopside, LPET, 54 ppm), Na (jadeite, LTAP, 55 ppm), K (leucite, LPET, 55 ppm). Counting time was 10 s at the peak and 5 s on each side of the peak for the background measurement. A fixed sequence of elements was set up in the measuring procedure with most volatile elements measured in the first spectrometer run, again to prevent any major experimental artifacts during the data acquisition. CAMECA proprietary software employing a ZAF correction procedure was used for spectra processing. Several samples displayed considerable heterogeneity on back-scattered-electron images. Consequently, these samples

were analyzed with maximum care and special attention was paid to assess the chemistry of individual compositional domains. Precision and accuracy of analyses were repeatedly monitored with the kaersutite standard (by SPI Supplies/Structure Probe, Inc.). Precision was better than 1 rel.% and accuracy was as good as 1–2 rel. %. Minor and trace element concentrations (incl. REEs) were measured with a quadrupole-based ICP-MS VG Elemental PQ3 instrument coupled to a modified NewWave UP 213 laser microprobe (Faculty of Science, Charles University, Praha) on polished thin sections of 11 samples (D-1, 2, 5, 6, 7, 13, 17, 19, Ch-6, Sl-2, and Sp-1). The spatial resolution of analyses was 40–80 lm. External calibration of the laser ablation analyses was done using Standard Reference Materials NIST (National Institute of Standards and Technology, USA) 612 and 610. For internal standardization 29Si concentrations based on electron microprobe measurements were applied. The concentration values for the NIST standards were taken from Pearce et al. (1997). The isotopes used were selected with respect to their most abundant species, free from isobaric overlap, and according to minimum interferences (Table 1). Formation of oxides (MO+/M+) was monitored using U in NIST 612 directly from ablation and the measured (254UO+/238U+) ratios varied less than 0.007. The overall instrumental analytical condition and data collection parameters are given in Table 2. Data reduction included correction for the gas blank, the internal standard and a calibration check, and the data were processed off-line in a MS Excel spreadsheet-based program. For details on analytical protocol and correction strategy see Strnad et al. (2005). The external reproducibility of this method was monitored with USGS BCR-2G glass as reference material (e.g., Norman et al., 1998; Tiepolo et al., 2003). Detection limits for all elements were calculated at the 3r level of the gas blank (Table 1). Mo¨ssbauer spectra of five powdered samples (D-9, D-13, D-15, J-3, Sp-1) were recorded at room temperature (293 K) in transmission mode on a constant acceleration Mo¨ssbauer spectrometer with a nominal 1.85 GBq 57Co source in a 6 lm Rh matrix (at the Bayerisches Geoinstitut, University of Bayreuth, Germany). The velocity scale was calibrated relative to a 25 lm a-Fe foil using the positions certified for (former) National Bureau of Standards standard reference material No. 1541; line widths of 0.28 mm/s for the outer lines of a-Fe were obtained at room temperature. Collection times for Mo¨ssbauer spectra were 1–3 days each for all samples. The spectra were processed using the extended Voigtbased fitting method (Lagarec and Rancourt, 1997) implemented in the commercially available fitting program RECOIL (distributed by Intelligent Scientific Applications Inc., Canada). Such a model was able to account for all absorption within experimental error and has previously been successfully applied to the analysis of silicate glass spectra (Alberto et al., 1996). Statistical evaluation of the major element compositional data was carried out with the program suite SYSTAT (Systat Software Inc., San Jose, CA, USA). Some statistical computations were performed also with a statistical system R (R Development Core Team, 2006).

4. RESULTS 4.1. Physical properties Weight, color, and shape distributions were evaluated based on the inspection of 357 pieces of Cheb moldavites from the following localities: Drˇenice (gravel pit, 317 pcs.), Obilna´ (gravel pit, 26 pcs.), Okrouhla´ (beach of the Jesenice water reservoir, 7 pcs.), and Velky´ Luh (gravel pit, 7 pcs.). Taking into account the estimated number of

Moldavites from the Cheb Basin Table 1 Monitored isotopes and detection limits (DL) for LA-ICP-MS analysis.

V Cr Mn Co Ni Cu Zn As Rb Sr Y Zr Nb Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U Sia a

Isotope (m/z)

DL (lg g 1)

51 52 55 59 60 65 66 75 85 88 89 90 93 121 133 137 139 140 141 146 147 151 157 159 163 165 166 169 172 175 178 181 208 232 238 29

0.081 1.4 0.85 0.095 1.5 0.92 1.6 1.0 0.41 0.096 0.045 0.54 0.053 0.075 0.049 0.25 0.067 0.033 0.021 0.095 0.086 0.029 0.062 0.013 0.065 0.012 0.057 0.004 0.069 0.008 0.095 0.049 0.33 0.078 0.069

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Table 2 LA-ICP-MS instrumental settings and data acquisition parameters. Instrument Plasma RF power Reflected power Plasma gas flow rate Auxiliary gas flow rate Nebulizer gas flow rate Carrier gas flow rate Cones Scanning mode Points per peak Data collecting Dwell time Acquisition time Detector Voltage Laser instrument Wavelength Laser energy Repetition rate Crater diameter Raster pattern Overall sensitivity (LA)

VG Elemental PQ3 1370 W <1 W 13.5 l/min (Ar) 0.85 l/min (Ar) 0.50 l/min (Ar) 1.05 l/min (He) Nickel peak jumping 1 TRA (Time Resolved Analysis) 10.24 ms 180 s (40 s gas blank + 120 s ablation) 2995 V (pulse count) 1650 V (analog) New Wave UP 213 213 nm (Nd:YAG 5th harmonic) 0.95 mJ 10 40–80 lm linear (approx. 400 lm) 1.5  105 cps per 140Ce in NIST 612 (40 lg g 1)

Internal standard.

moldavites found in the territory of the Cheb Basin so far (2500–3000 pcs.), this set represents a statistically significant amount – between 10% and 13% of the entire population – and, consequently, may be considered representative. Internal fabric and surface details of the Cheb Basin moldavites were studied optically on 12 selected samples from the Drˇenice gravel pit. 4.1.1. Weight and density The hitherto largest moldavite known from the Cheb Basin weighs 36 g and was found in the gravel pit near Drˇenice. It is held in the collection of the company TEKAZ, Ltd., which operates this gravel pit. The weight distribution for moldavites from the Drˇenice gravel pit is shown in Fig. 3; it is strongly skewed with 84% of all pieces weighing less than 6 g. Such a weight distribution agrees fairly well with the curve observed for the locality Chlum n. Malsˇ´ı in South Bohemia (Bousˇka and Rost, 1968; Turnovec and Kveˇtonˇ, 1975). Bulk density was measured by applying the liquid suspension method for 6 moldavites from Drˇenice (D-1, 2, 4,

Fig. 3. Weight distribution of moldavites found at the locality Drˇenice sand pit.

6–8) also used later for microprobe analysis. For each sample three to five small splinters of glass were measured at the same time in the liquid column. This method showed that the density is not invariant within individual samples: while some fragments floated, others sank. This variation is due to inhomogeneous distribution of bubbles and lechatelierite inclusions. Measured densities vary between 2.352 and 2.369 g cm 3, a range also observed for other moldavites (Bousˇka and Konta, 1986). 4.1.2. Color The majority of the moldavites from the region are transparent or translucent. Bottle and olive green molda-

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vites are most abundant among the evaluated samples. Other tones of green are less common. No brown-colored pieces were found. The quantitative distribution of colors in the Drˇenice samples is comparable to that for moldavites from the South Bohemian localities Habrˇ´ı or Slavcˇe (cf. Fig. 9 in Bousˇka, 1994). 4.1.3. Shape and surface features The diversity of appearance of Cheb moldavites is shown in Fig. 4. All these moldavites represent splash-form tektites; no other megascopically clearly different primary shapes (e.g., Muong Nong-types, ablated types) were found. The shapes observed include spheroids, ellipsoids, discs, half-discs, dumbbell- or rod-shaped pieces, droplets, triangular samples, and their fragments. Besides fragments, the most frequently found shapes are ellipsoids and spheroids. In contrast, the dumbbell- or rod-shaped forms are rarest. Surface sculpture is not a primary feature and reflects – in addition to the original internal fabric of individual moldavites – post-depositional conditions, particularly the type of corrosion agents and permeability of the host sediments. On a megascopic scale we found that several types of sculpture may be distinguished among the tektites found at the four localities studied. Most of the pieces (if we ignore mechanically damaged ones) have a sculptured surface and have either a dull or a glassy luster. Also, a considerable number of finds has surfaces decorated with more or less hemispherical pits. At the locality Okrouhla´, several moldavites with very deep sculpture were found; this sculpture resembles that known from the South Bohemian locality Besednice. Several pieces also show large and deep elliptical pits, which clearly represent former bubbles that were etched open in the course of weathering. Under a bin-

ocular lens the so-called ‘‘pit” sculpture (see Bousˇka and Konta, 1986) is seen to dominate. Specimens investigated by SEM showed what Konta (1988) described as a ‘‘pit sculpture”. This type of sculpture indicates that the surface of a specimen was shaped primarily by acid etching (by groundwater-dissolved CO2 and humic acids) in sediments with relatively high permeability (gravels or sands). Details of the sculpture are illustrated in Figs. 5a and b. 4.1.4. Internal fabric All samples investigated contain bubbles. Their size and frequency varies not only among individual pieces but also among different parts of the samples. The sizes of the bubbles vary from less than 1 lm to several millimeters. The bubbles are either elongated – occasionally strongly – or more or less spherical. Elongated bubbles are usually oriented with their long axis parallel to the fluidal structure, although some were found to be inclined with respect to the fluidal structure. Lechatelierite inclusions (Fig. 5c; confirmed by EPMA; SiO2 content exceeding 98 wt.%) are ubiquitous and their amount in the samples varies considerably. Moldavites with well developed fluidal structure or highly heterogeneous samples contain large numbers of lechatelierite schlieren. The shapes of lechatelierite inclusions are diverse: next to linear needle-, disc-, or lens-like features, lechatelierite forms various bent inclusions or meander-shaped flat stripes [‘‘thread- or ribbon-like shapes” of Barnes (1969) or ‘‘thin horse-shoe hairpins” and ‘‘hairpins” of Knobloch et al. (1988)]. The size of the inclusions is extremely variable – there are, occasionally side-by-side, tiny particles less than 2 lm in diameter and a few tens of lm in length and large inclusions up to 0.5 mm across and with lengths of several

Fig. 4. Typical shapes and sculpture types found among the Cheb moldavites. Scale bars represent 1 cm.

Moldavites from the Cheb Basin

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Fig. 5. (a and b) Secondary electron images of the ‘‘pit sculpture” on the surface of moldavites from Drˇenice. The fine pits on the surface are typical for etching in an acidic, highly permeable environment. (c and d) Back-scattered electron images of dark-colored lechatelierite inclusions in light-colored, heterogeneous moldavite and a schlieren-rich heterogeneous moldavite.

millimeters. The lechatelierite schlieren are also revealed in back-scattered electron (BSE) images (e.g., Fig. 5c). Overall, the shape, sculpture (incl. microsculpture) and surface characteristics resemble closely, similar to color distribution, moldavites from the South Bohemian partial strewn field. Like other moldavites those from the Cheb Basin are internally inhomogeneous as demonstrated by optical microscopy and BSE images (Fig. 5d). There are numerous schlieren which are best visible between crossed polarizers as the change in glass properties induces stress which causes weak anomalous birefringence. Stress also developed at the boundaries of lechatelierite inclusions or close to bubbles. Schlieren are usually parallel to the fluidal structure and, often also elongated lechatelierite inclusions highlight such flow directions. In some cases the presence, amount and appearance of inhomogeneities on the microscale resemble features found in layered tektites (e.g., samples D-5 and D-17). 4.2. Major element composition In total 728 electron microprobe analyses were collected for moldavites from the Cheb Basin covering a wide compositional range (in wt.%): SiO2 73.9–85.1; TiO2 0.16– 0.56; Al2O3 6.5–13.3; FeO 0.51–2.34; MgO 1.09–3.22; CaO 1.60–5.05; Na2O 0.16–0.65 and K2O 2.22–4.13. In addition, 448 analyses for South Bohemian moldavites and 103 for Moravian samples were acquired. Moldavites from Moravia have considerably lower contents of MgO (at max. 1.42 wt.%) and CaO (at max. 1.84 wt.%) compared to both Cheb and South Bohemian samples. Overall, our data agree well with previously published values (Delano

and Lindsley, 1982; Bousˇka and Konta, 1986; Delano et al., 1988, 1992; Bousˇka et al., 1990; Meisel et al., 1997; Engelhardt et al., 2005). The microprobe data reveal substantial scatter in chemical composition, not only between individual samples, but also on the micrometer scale within individual specimens (Harker diagrams in Fig. 6). This is the case not only for the Cheb moldavites but also for those from the traditional partial strewn fields. Linescans best illustrate these heterogeneities [cf. Fig. 2b in Engelhardt et al. (2005) or Fig. 2 ˇ ada (2006)]. The largest variation was noted in Ska´la and C for sample Bs-1; the relative standard deviations (in %) in a set of over 80 analyses are as follows: SiO2: 2.5; TiO2: 24.6; Al2O3: 10.4; FeO: 25.1; MgO: 32.6; CaO: 43.3; Na2O: 14.9; K2O: 2.7. Among the Cheb moldavites the most pronounced variation was observed in samples D-5, D-17, D-19, D-20, and D-21 where relative standard uncertainties for FeO exceeded 20 rel.% and those for CaO and MgO range from 15 rel.% to 20 rel.%. Variations for silicon and potassium do not exceed 3 rel.%, on average, in these samples. Similarly to the heterogeneous Cheb tektites, several moldavite samples from South Bohemia (Ch-1, Jankov samples, Sl-1) and virtually all Moravian samples reveal heterogeneity, following the same general trends. On the contrary, samples D-6, D-7, and D-9 (Cheb Basin) and Ch-4, Ch-6, and Sl-2 (S. Bohemia) show very small variation in chemical composition, yet relative standard uncertainties for FeO exceeded 10 rel.% even in these materials. It should also be noted that the overall distribution of the analytical data for TiO2, CaO, MgO, Na2O, and K2O in Cheb moldavites is far from normal; instead an obvious bimodal distribution is observed. On the other hand, FeO content follows an almost perfect normal distribution.

R. Ska´la et al. / Geochimica et Cosmochimica Acta 73 (2009) 1145–1179

K2O (wt. %)

Na2O (wt. %)

0.7

0.5

0.5

0.4

0.4

0.3

0.3

0.2

0.2

0.1

0.1

14

14

12

12

10

10

8

8

6

6

3.0 2.5 2.0 1.5 1.0 0.5 0.0

3.0 2.5 2.0 1.5 1.0 0.5 0.0

3.5 3.0 2.5 2.0 1.5 1.0 0.5

3.5 3.0 2.5 2.0 1.5 1.0 0.5

5

5

4

4

3

3

2

2

1

1

0

0

0.7 0.6 0.5 0.4 0.3 0.2 0.1

0.7 0.6 0.5 0.4 0.3 0.2 0.1

4.0

4.0

3.5

3.5

3.0

3.0

2.5

2.5

Cheb Basin : TiO2 (wt. %)

0.6

D1 D2 D3 D4 D5 D6

D7 D8 D9 D10 D11 D12

D13 D14 D15 D16 D17 D18

D19 D20 D21 D22 D23 D24

S. Bohemia & Moravia : Al2O3 (wt. %)

S. Bohemia & Moravia :

Bs1 Ch1 Ch2 Ch3 Ch4

Ch5 Ch6 Ch7 Hb1

J1 J2 J3 Sl1

Sl2 Sp1 Sv1 Vr1

FeO (wt.%)

Cheb Basin :

MgO (wt.%)

0.6

CaO (wt.%)

CaO (wt.%)

MgO (wt.%)

FeO (wt.%)

Al2O3 (wt. %)

TiO2 (wt. %)

0.7

SiO2 (wt.%) 72 74 76 78 80 82 84 86

Na2O (wt. %)

SiO2 (wt.%) 72 74 76 78 80 82 84

K2O (wt. %)

1152

2.0

2.0 72 74 76 78 80 82 84 SiO2 (wt.%)

72 74 76 78 80 82 84 86 SiO2 (wt.%)

Fig. 6. Harker diagrams of major element oxide versus silica contents for moldavites analyzed in this study. In most cases the compositional trends observed for the moldavites from the Cheb Basin (left column) differ from compositions determined for the South Bohemian or Moravian moldavites (right column).

Table 3 Major element compositions (wt.%) of the studied moldavites from the Cheb Basin and localities in the South Bohemia and Moravia with outliers excluded. Range, and statistical measures of position and scale, are shown together with number of analyses involved in the calculation of these variables (n). Sample

n

SiO2

TiO2

FeO

MgO

CaO

Na2O

K2O

CaO/MgO

K2O/Na2O

8.16 ± 0.23 9.98 ± 0.33 9.74 ± 0.52 8.31 ± 0.19 7.80 ± 0.20 7.30 ± 0.06 6.95 ± 0.19 7.64 ± 0.32 10.42 ± 0.18 9.43 ± 0.24 8.46 ± 0.16 10.80 ± 0.24 8.32 ± 0.14 8.15 ± 0.13 7.98 ± 0.15 8.58 ± 0.09 9.94 ± 0.48 10.81 ± 0.34 9.56 ± 0.16 8.26 ± 0.10 9.80 ± 0.61 8.48 ± 0.51 9.61 ± 0.20 10.20 ± 0.42 9.39 ± 0.23 9.92 ± 0.61 12.01 ± 0.73 8.83 ± 0.39 7.91 ± 0.37 10.75 ± 0.95 9.32 ± 0.84 8.83 ± 0.19 8.80 ± 0.16 8.51 ± 0.19 8.87 ± 0.08

1.32 ± 0.18 1.72 ± 0.22 1.87 ± 0.13 1.34 ± 0.20 1.17 ± 0.22 1.04 ± 0.12 0.94 ± 0.23 1.00 ± 0.22 1.77 ± 0.21 1.65 ± 0.21 1.35 ± 0.29 1.82 ± 0.16 1.42 ± 0.27 1.12 ± 0.17 1.10 ± 0.22 1.32 ± 0.21 1.79 ± 0.30 2.04 ± 0.15 1.57 ± 0.25 1.33 ± 0.27 1.65 ± 0.30 1.20 ± 0.21 1.43 ± 0.21 1.73 ± 0.45 1.26 ± 0.05 1.59 ± 0.28 1.75 ± 0.28 1.53 ± 0.22 1.30 ± 0.19 2.15 ± 0.10 1.69 ± 0.30 1.30 ± 0.18 1.31 ± 0.20 1.31 ± 0.18 1.36 ± 0.22

2.68 ± 0.06 1.80 ± 0.05 1.70 ± 0.07 2.58 ± 0.09 2.79 ± 0.06 2.54 ± 0.11 1.91 ± 0.10 2.58 ± 0.27 1.74 ± 0.05 1.96 ± 0.05 2.14 ± 0.05 1.84 ± 0.09 2.87 ± 0.04 3.09 ± 0.11 2.39 ± 0.04 2.72 ± 0.04 1.85 ± 0.10 2.24 ± 0.06 2.45 ± 0.08 2.56 ± 0.05 1.58 ± 0.16 1.13 ± 0.03 1.87 ± 0.05 2.16 ± 0.14 1.77 ± 0.07 1.90 ± 0.19 2.65 ± 0.21 1.86 ± 0.11 1.46 ± 0.11 2.31 ± 0.24 1.90 ± 0.24 2.17 ± 0.07 2.57 ± 0.05 2.27 ± 0.14 2.85 ± 0.18

4.70 ± 0.17 2.48 ± 0.10 2.36 ± 0.08 4.43 ± 0.14 4.18 ± 0.08 3.68 ± 0.06 2.65 ± 0.12 3.51 ± 0.37 2.60 ± 0.08 2.90 ± 0.10 4.46 ± 0.12 2.75 ± 0.12 4.77 ± 0.13 4.72 ± 0.17 3.66 ± 0.13 4.86 ± 0.08 2.56 ± 0.16 3.14 ± 0.17 3.90 ± 0.08 4.46 ± 0.09 2.38 ± 0.24 1.75 ± 0.09 2.60 ± 0.07 2.99 ± 0.18 2.40 ± 0.03 2.95 ± 0.27 3.99 ± 0.35 2.74 ± 0.17 2.19 ± 0.18 3.52 ± 0.43 2.80 ± 0.37 3.68 ± 0.14 4.19 ± 0.19 3.53 ± 0.23 4.30 ± 0.28

0.30 ± 0.03 0.54 ± 0.04 0.58 ± 0.03 0.29 ± 0.02 0.26 ± 0.03 0.23 ± 0.01 0.23 ± 0.03 0.24 ± 0.03 0.54 ± 0.04 0.47 ± 0.05 0.33 ± 0.04 0.51 ± 0.05 0.28 ± 0.03 0.26 ± 0.04 0.28 ± 0.02 0.34 ± 0.04 0.52 ± 0.05 0.52 ± 0.05 0.57 ± 0.04 0.27 ± 0.03 0.55 ± 0.04 0.54 ± 0.03 0.50 ± 0.04 0.50 ± 0.03 0.47 ± 0.03 0.40 ± 0.05 0.39 ± 0.02 0.50 ± 0.03 0.46 ± 0.09 0.54 ± 0.06 0.51 ± 0.04 0.38 ± 0.04 0.27 ± 0.03 0.26 ± 0.02 0.24 ± 0.02

3.73 ± 0.08 2.77 ± 0.07 2.82 ± 0.06 3.54 ± 0.08 3.42 ± 0.06 3.38 ± 0.04 3.35 ± 0.10 3.27 ± 0.07 2.47 ± 0.07 3.36 ± 0.09 3.98 ± 0.07 2.51 ± 0.07 3.86 ± 0.07 3.53 ± 0.11 3.29 ± 0.09 3.78 ± 0.09 3.12 ± 0.08 3.11 ± 0.06 3.35 ± 0.08 3.48 ± 0.09 2.88 ± 0.09 2.89 ± 0.20 3.32 ± 0.10 3.25 ± 0.08 3.27 ± 0.08 2.51 ± 0.06 2.33 ± 0.11 2.70 ± 0.06 2.70 ± 0.06 2.63 ± 0.01 2.69 ± 0.10 3.84 ± 0.08 3.30 ± 0.08 3.35 ± 0.08 3.23 ± 0.05

1.76 ± 0.06 1.37 ± 0.04 1.39 ± 0.05 1.72 ± 0.05 1.50 ± 0.03 1.46 ± 0.13 1.39 ± 0.05 1.36 ± 0.04 1.50 ± 0.06 1.48 ± 0.06 2.09 ± 0.06 1.49 ± 0.05 1.66 ± 0.05 1.53 ± 0.04 1.53 ± 0.06 1.79 ± 0.04 1.38 ± 0.06 1.39 ± 0.05 1.60 ± 0.05 1.74 ± 0.05 1.50 ± 0.06 1.54 ± 0.09 1.39 ± 0.04 1.40 ± 0.04 1.36 ± 0.06 1.56 ± 0.05 1.51 ± 0.04 1.48 ± 0.05 1.50 ± 0.01 1.54 ± 0.02 1.48 ± 0.06 1.70 ± 0.07 1.63 ± 0.06 1.55 ± 0.04 1.51 ± 0.04

12.7 ± 1.4 5.1 ± 0.3 4.9 ± 0.3 12.4 ± 1.2 13.4 ± 1.4 14.8 ± 0.7 14.8 ± 2.6 13.7 ± 1.8 4.6 ± 0.4 7.2 ± 0.7 12.2 ± 1.3 5.0 ± 0.5 13.7 ± 1.5 14.0 ± 2.4 11.7 ± 1.1 11.4 ± 1.5 6.0 ± 0.6 6.0 ± 0.4 5.9 ± 0.5 13.3 ± 1.3 5.3 ± 0.4 5.4 ± 0.7 6.7 ± 0.5 6.4 ± 0.9 7.0 ± 0.5 6.4 ± 0.8 5.9 ± 0.7 5.5 ± 0.3 5.9 ± 1.0 4.9 ± 0.5 5.3 ± 0.4 10.1 ± 0.9 12.6 ± 1.4 12.9 ± 1.2 13.5 ± 1.8 (continued

K2O/CaO 0.79 ± 0.03 1.12 ± 0.04 1.19 ± 0.04 0.80 ± 0.03 0.82 ± 0.02 0.92 ± 0.03 1.27 ± 0.07 0.94 ± 0.11 0.95 ± 0.04 1.16 ± 0.05 0.89 ± 0.03 0.92 ± 0.05 0.81 ± 0.03 0.75 ± 0.04 0.90 ± 0.03 0.78 ± 0.02 1.22 ± 0.07 0.99 ± 0.08 0.86 ± 0.03 0.78 ± 0.02 1.22 ± 0.11 1.67 ± 0.08 1.28 ± 0.05 1.08 ± 0.07 1.36 ± 0.04 0.86 ± 0.08 0.59 ± 0.08 0.99 ± 0.07 1.23 ± 0.11 0.74 ± 0.03 0.98 ± 0.13 1.04 ± 0.05 0.79 ± 0.04 0.95 ± 0.07 0.75 ± 0.04 on next page)

Moldavites from the Cheb Basin

Cheb Basin Substrewn-field–position ± scale D-1 28 78.4 ± 0.4 0.22 ± 0.02 D-2a 23 79.6 ± 0.5 0.40 ± 0.03 D-2b 9 80.2 ± 0.4 0.40 ± 0.02 D-3 30 78.4 ± 0.3 0.23 ± 0.02 D-4a 23 79.3 ± 0.2 0.22 ± 0.02 D-4b 6 80.8 ± 0.5 0.20 ± 0.04 D-5a 15 82.9 ± 0.3 0.20 ± 0.02 D-5b 25 80.5 ± 1.1 0.22 ± 0.03 D-6 29 79.4 ± 0.4 0.42 ± 0.03 D-7 25 79.2 ± 0.5 0.34 ± 0.03 D-8 24 78.7 ± 0.5 0.23 ± 0.03 D-9 30 78.9 ± 0.6 0.43 ± 0.03 D-10 26 77.6 ± 0.6 0.24 ± 0.03 D-11 27 78.2 ± 0.6 0.22 ± 0.03 D-12 29 81.0 ± 0.5 0.21 ± 0.03 D-13 24 78.3 ± 0.4 0.22 ± 0.03 D-14a 35 79.6 ± 0.7 0.40 ± 0.04 D-14b 4 77.6 ± 0.5 0.43 ± 0.02 D-15 25 77.8 ± 0.2 0.35 ± 0.04 D-16 28 79.5 ± 0.4 0.22 ± 0.03 D-17a 33 80.7 ± 1.3 0.34 ± 0.05 D-17b 4 83.9 ± 0.9 0.29 ± 0.03 D-18a 28 80.2 ± 0.4 0.32 ± 0.04 D-18b 7 78.7 ± 1.2 0.36 ± 0.01 D-18c 5 81.3 ± 0.9 0.29 ± 0.02 D-19a 31 80.2 ± 1.2 0.37 ± 0.03 D-19b 8 76.1 ± 1.4 0.42 ± 0.06 D-20a 25 80.8 ± 0.9 0.35 ± 0.04 D-20b 6 83.5 ± 1.5 0.29 ± 0.04 D-20c 5 77.2 ± 1.8 0.46 ± 0.09 D-21 23 80.0 ± 1.8 0.37 ± 0.06 D-22 25 79.2 ± 0.4 0.22 ± 0.03 D-23 27 79.3 ± 0.5 0.24 ± 0.03 D-24a 29 80.9 ± 0.7 0.24 ± 0.03 D-24b 7 79.2 ± 0.4 0.23 ± 0.04

Al2O3

1153

1154

Sample

n

SiO2

TiO2

Al2O3

South Bohemian and Moravian Substrewn-fields–position ± scale Bs-1a 1 75.1 0.65 14.56 Bs-1b 9 79.3 ± 1.6 0.44 ± 0.10 12.11 ± 0.65 Bs-1c 78 82.3 ± 1.8 0.31 ± 0.06 9.95 ± 0.71 Ch-1 28 78.5 ± 0.6 0.34 ± 0.03 10.58 ± 0.20 Ch-2 27 80.1 ± 0.3 0.27 ± 0.02 9.18 ± 0.16 Ch-3 25 80.6 ± 0.5 0.27 ± 0.03 9.37 ± 0.18 Ch-4 27 78.1 ± 0.4 0.24 ± 0.02 8.83 ± 0.12 Ch-5a 24 79.6 ± 0.5 0.28 ± 0.03 9.39 ± 0.14 Ch-5b 5 78.7 ± 0.5 0.28 ± 0.00 9.54 ± 0.28 Ch-6 28 79.7 ± 0.4 0.29 ± 0.02 9.43 ± 0.18 Ch-7a 16 76.2 ± 0.5 0.41 ± 0.04 11.67 ± 0.37 Ch-7b 19 77.7 ± 0.6 0.36 ± 0.03 10.77 ± 0.21 Hb-1 20 78.7 ± 0.9 0.27 ± 0.03 9.61 ± 0.24 J-1 28 78.9 ± 0.5 0.30 ± 0.03 9.65 ± 0.28 J-2a 23 76.1 ± 0.6 0.44 ± 0.03 11.79 ± 0.32 J-2b 6 74.2 ± 0.6 0.52 ± 0.04 13.13 ± 0.32 J-3 29 78.6 ± 0.5 0.30 ± 0.04 9.61 ± 0.36 Sl-1a 20 80.3 ± 0.5 0.27 ± 0.02 9.52 ± 0.16 Sl-1b 6 79.1 ± 0.7 0.27 ± 0.02 9.87 ± 0.46 Sl-1c 4 76.9 ± 0.4 0.27 ± 0.02 9.83 ± 0.10 Sl-2 25 79.4 ± 0.5 0.30 ± 0.03 9.73 ± 0.13 Sp-1a 1 78.7 0.33 11.38 Sp-1b 3 78.9 ± 0.2 0.45 ± 0.00 11.29 ± 0.16 Sp-1c 1 77.7 0.40 11.87 Sp-1d 5 77.3 ± 0.2 0.44 ± 0.05 11.55 ± 0.23 Sp-1e 20 78.1 ± 0.2 0.42 ± 0.04 11.63 ± 0.18 Sv-1a 3 82.1 ± 0.1 0.30 ± 0.01 10.06 ± 0.07 Sv-1b 15 80.4 ± 0.4 0.34 ± 0.04 10.43 ± 0.37 Sv-1c 17 80.3 ± 0.5 0.35 ± 0.03 10.46 ± 0.25 Vr-1a 30 81.4 ± 0.5 0.32 ± 0.04 10.14 ± 0.21 Vr-1b 8 81.2 ± 0.2 0.31 ± 0.01 10.20 ± 0.11

Line missing

FeO

MgO

CaO

Na2O

K2O

CaO/MgO

K2O/Na2O

K2O/CaO

3.73 2.47 ± 0.34 1.63 ± 0.29 1.89 ± 0.31 1.36 ± 0.26 1.43 ± 0.22 1.38 ± 0.15 1.48 ± 0.23 1.41 ± 0.06 1.58 ± 0.20 2.46 ± 0.39 2.09 ± 0.41 1.62 ± 0.19 1.48 ± 0.30 2.36 ± 0.32 2.94 ± 0.37 1.47 ± 0.24 1.46 ± 0.21 1.43 ± 0.42 1.65 ± 0.32 1.59 ± 0.19 2.23 2.26 ± 0.14 2.71 2.47 ± 0.15 2.44 ± 0.29 1.87 ± 0.22 1.49 ± 0.27 1.93 ± 0.19 1.68 ± 0.28 1.73 ± 0.42

1.02 0.68 ± 0.16 0.70 ± 0.24 1.87 ± 0.14 1.95 ± 0.09 1.48 ± 0.07 2.32 ± 0.08 2.15 ± 0.06 2.53 ± 0.11 1.94 ± 0.05 1.94 ± 0.09 1.93 ± 0.08 2.29 ± 0.32 2.43 ± 0.38 2.04 ± 0.11 2.09 ± 0.19 2.62 ± 0.40 1.86 ± 0.10 2.50 ± 0.31 3.68 ± 0.12 2.11 ± 0.04 1.32 1.17 ± 0.02 1.17 1.29 ± 0.06 1.34 ± 0.04 1.12 ± 0.01 1.16 ± 0.06 1.24 ± 0.05 1.11 ± 0.06 1.26 ± 0.03

0.62 0.47 ± 0.10 0.59 ± 0.26 2.39 ± 0.20 2.73 ± 0.14 2.26 ± 0.11 4.66 ± 0.06 2.79 ± 0.10 3.34 ± 0.41 2.55 ± 0.07 2.32 ± 0.12 2.26 ± 0.10 3.24 ± 0.32 3.33 ± 0.48 2.31 ± 0.18 2.15 ± 0.28 3.55 ± 0.47 2.52 ± 0.10 3.29 ± 0.26 4.56 ± 0.22 2.67 ± 0.05 0.81 0.84 ± 0.04 0.88 1.10 ± 0.02 1.11 ± 0.07 1.30 ± 0.02 1.52 ± 0.10 1.66 ± 0.11 1.45 ± 0.09 1.56 ± 0.03

0.65 0.53 ± 0.02 0.50 ± 0.08 0.40 ± 0.04 0.34 ± 0.04 0.48 ± 0.04 0.36 ± 0.03 0.37 ± 0.03 0.35 ± 0.04 0.44 ± 0.04 0.61 ± 0.03 0.54 ± 0.04 0.44 ± 0.06 0.30 ± 0.04 0.66 ± 0.05 0.72 ± 0.04 0.31 ± 0.03 0.30 ± 0.03 0.31 ± 0.03 0.27 ± 0.04 0.39 ± 0.03 0.63 0.66 ± 0.01 0.64 0.59 ± 0.05 0.62 ± 0.05 0.37 ± 0.02 0.38 ± 0.03 0.38 ± 0.03 0.32 ± 0.03 0.33 ± 0.01

4.20 4.13 ± 0.10 4.00 ± 0.10 3.64 ± 0.09 3.44 ± 0.08 3.73 ± 0.08 3.75 ± 0.07 3.57 ± 0.11 3.35 ± 0.08 3.72 ± 0.10 3.84 ± 0.08 3.73 ± 0.08 3.53 ± 0.15 3.26 ± 0.23 4.04 ± 0.09 4.17 ± 0.24 3.22 ± 0.24 3.61 ± 0.08 3.30 ± 0.02 2.85 ± 0.09 3.61 ± 0.09 2.94 4.02 ± 0.04 4.17 4.01 ± 0.05 3.96 ± 0.09 3.35 ± 0.01 3.39 ± 0.13 3.38 ± 0.08 3.36 ± 0.08 3.25 ± 0.07

0.61 0.70 ± 0.12 0.82 ± 0.14 1.28 ± 0.06 1.40 ± 0.05 1.53 ± 0.07 2.01 ± 0.07 1.29 ± 0.04 1.32 ± 0.08 1.31 ± 0.04 1.20 ± 0.05 1.17 ± 0.05 1.42 ± 0.08 1.37 ± 0.09 1.13 ± 0.06 1.04 ± 0.10 1.36 ± 0.10 1.35 ± 0.07 1.31 ± 0.04 1.24 ± 0.02 1.27 ± 0.03 0.61 0.71 ± 0.02 0.76 0.85 ± 0.02 0.83 ± 0.06 1.17 ± 0.04 1.32 ± 0.06 1.34 ± 0.10 1.31 ± 0.06 1.26 ± 0.07

6.5 8.0 ± 0.7 8.2 ± 1.3 9.3 ± 1.1 10.4 ± 1.3 7.8 ± 0.7 10.5 ± 1.0 9.6 ± 0.9 9.8 ± 1.1 8.5 ± 0.7 6.3 ± 0.4 6.9 ± 0.5 8.2 ± 1.3 10.9 ± 1.2 6.1 ± 0.5 5.8 ± 0.3 10.3 ± 0.7 12.2 ± 1.1 10.8 ± 1.0 10.7 ± 1.5 9.4 ± 0.7 4.6 6.2 ± 0.3 6.5 6.9 ± 0.7 6.4 ± 0.5 9.2 ± 0.4 9.1 ± 0.5 9.1 ± 0.7 10.7 ± 0.9 9.9 ± 0.3

6.74 9.00 ± 2.56 8.07 ± 3.09 1.53 ± 0.16 1.26 ± 0.07 1.66 ± 0.09 0.80 ± 0.02 1.28 ± 0.07 1.01 ± 0.12 1.46 ± 0.07 1.66 ± 0.09 1.65 ± 0.09 1.10 ± 0.14 1.01 ± 0.21 1.76 ± 0.17 2.03 ± 0.23 0.93 ± 0.18 1.44 ± 0.08 1.01 ± 0.11 0.63 ± 0.05 1.35 ± 0.04 3.65 4.78 ± 0.37 4.72 3.63 ± 0.04 3.60 ± 0.26 2.60 ± 0.02 2.24 ± 0.20 2.05 ± 0.17 2.33 ± 0.18 2.06 ± 0.10

R. Ska´la et al. / Geochimica et Cosmochimica Acta 73 (2009) 1145–1179

Table 3 (continued)

0.18–0.26 0.36–0.45 0.33–0.42 0.19–0.27 0.18–0.25 0.16–0.23 0.16–0.23 0.18–0.28 0.36–0.48 0.30–0.41 0.19–0.28 0.37–0.48 0.19–0.30 0.17–0.29 0.17–0.27 0.18–0.29 0.31–0.49 0.42–0.48 0.28–0.44 0.16–0.29 0.25–0.44 0.26–0.31 0.24–0.42 0.30–0.41 0.25–0.40 0.29–0.44 0.35–0.50 0.26–0.43 0.26–0.33 0.38–0.56 0.25–0.48 0.18–0.27 0.18–0.29 0.17–0.29 0.18–0.30

7.72–8.53 9.36–10.65 9.26–10.45 7.98–8.66 7.45–8.19 7.22–7.56 6.48–7.30 6.99–8.20 10.09–10.80 9.10–10.11 7.99–8.68 10.35–11.28 8.04–8.60 7.85–8.35 7.71–8.28 8.34–8.77 9.24–10.78 10.47–11.12 9.13–9.83 8.10–8.46 8.79–11.22 8.08–8.87 9.36–10.17 9.74–10.90 9.13–9.60 8.96–11.31 11.22–13.34 8.05–9.65 7.26–8.35 9.25–11.62 7.95–11.06 8.40–9.16 8.50–9.10 8.15–8.93 8.77–9.04

1.05–1.69 1.24–2.11 1.50–2.16 0.83–1.72 0.64–1.50 0.70–1.18 0.51–1.43 0.67–1.43 1.39–2.16 1.08–2.00 0.89–1.97 1.56–2.23 0.92–1.99 0.83–1.44 0.61–1.47 0.83–1.76 1.11–2.22 1.68–2.16 1.05–2.09 0.79–1.96 0.95–2.29 1.00–1.37 1.08–1.97 1.12–2.22 1.08–1.34 1.07–2.20 1.32–2.05 1.11–1.93 1.15–1.84 1.52–2.34 1.26–2.29 1.02–1.66 0.96–1.69 1.02–1.65 1.17–1.96

2.58–2.81 1.71–1.92 1.59–1.77 2.42–2.74 2.68–2.90 2.41–2.68 1.73–2.05 2.19–3.09 1.62–1.81 1.83–2.07 2.07–2.25 1.71–2.03 2.80–2.95 2.85–3.22 2.31–2.50 2.65–2.78 1.65–2.04 2.19–2.36 2.28–2.59 2.48–2.67 1.33–1.98 1.10–1.15 1.78–1.95 2.00–2.30 1.73–1.83 1.59–2.26 2.42–3.01 1.68–2.08 1.27–1.55 2.06–2.53 1.42–2.38 2.06–2.30 2.43–2.66 2.03–2.52 2.69–3.00

4.46–5.01 2.32–2.63 2.24–2.57 4.11–4.68 4.07–4.31 3.60–3.89 2.43–2.81 2.94–4.21 2.47–2.84 2.70–3.12 4.27–4.73 2.56–3.06 4.49–5.05 4.38–5.03 3.38–3.92 4.61–5.03 2.32–2.97 2.95–3.28 3.78–4.08 4.32–4.69 1.94–2.90 1.60–1.81 2.47–2.73 2.78–3.36 2.35–2.48 2.52–3.49 3.49–4.67 2.35–3.01 1.91–2.39 3.17–3.89 2.16–3.44 3.41–3.91 3.94–4.73 3.17–3.94 4.09–4.56

0.24–0.35 0.48–0.62 0.53–0.65 0.24–0.33 0.22–0.29 0.22–0.28 0.16–0.28 0.18–0.29 0.48–0.63 0.41–0.58 0.26–0.43 0.43–0.61 0.23–0.33 0.16–0.33 0.23–0.33 0.25–0.40 0.42–0.64 0.48–0.56 0.49–0.63 0.22–0.32 0.47–0.64 0.51–0.56 0.44–0.59 0.46–0.58 0.44–0.49 0.31–0.51 0.37–0.46 0.45–0.56 0.37–0.54 0.30–0.58 0.43–0.60 0.33–0.47 0.22–0.32 0.22–0.32 0.22–0.28

3.55–3.87 2.64–2.94 2.74–2.90 3.40–3.65 3.31–3.56 3.35–3.47 3.17–3.54 3.16–3.37 2.31–2.58 3.18–3.49 3.86–4.13 2.42–2.65 3.75–4.00 3.28–3.74 3.09–3.41 3.64–3.98 2.95–3.30 3.02–3.16 3.17–3.49 3.30–3.70 2.71–3.06 2.73–3.13 3.09–3.55 3.12–3.37 3.17–3.35 2.38–2.63 2.22–2.42 2.57–2.82 2.53–2.78 2.53–2.75 2.51–2.88 3.68–3.99 3.10–3.49 3.21–3.55 3.15–3.33

1.68–1.89 1.31–1.46 1.34–1.47 1.64–1.81 1.45–1.57 1.38–1.55 1.33–1.51 1.30–1.47 1.40–1.67 1.37–1.66 2.01–2.23 1.39–1.59 1.56–1.75 1.46–1.61 1.43–1.63 1.72–1.90 1.29–1.55 1.34–1.45 1.53–1.69 1.66–1.83 1.38–1.61 1.46–1.59 1.32–1.45 1.32–1.46 1.31–1.43 1.48–1.67 1.38–1.56 1.40–1.64 1.50–1.56 1.44–1.56 1.36–1.57 1.53–1.79 1.51–1.79 1.46–1.61 1.47–1.55

10.3–15.7 4.6–5.6 4.3–5.1 10.8–15.0 11.6–16.2 12.6–15.6 11.3–21.5 10.9–19.0 3.8–5.3 5.9–8.5 9.1–15.0 4.1–5.9 12.0–16.9 10.2–22.9 9.5–14.9 9.4–14.6 4.9–7.4 5.7–6.4 5.2–7.1 10.7–15.7 4.6–6.2 4.8–5.8 5.8–7.8 5.7–7.2 6.5–7.5 5.0–8.2 5.1–6.4 4.8–6.1 5.0–7.4 4.5–8.3 4.6–6.0 8.4–11.8 10.2–15.0 10.4–15.2 11.5–15.0 (continued

0.72–0.84 1.04–1.20 1.13–1.27 0.74–0.88 0.78–0.86 0.86–0.95 1.15–1.38 0.77–1.13 0.88–1.02 1.02–1.25 0.83–0.93 0.79–1.00 0.75–0.87 0.68–0.82 0.81–0.97 0.74–0.82 1.08–1.35 0.93–1.05 0.82–0.91 0.75–0.83 0.98–1.47 1.62–1.73 1.19–1.37 1.00–1.14 1.32–1.43 0.73–1.02 0.49–0.69 0.89–1.16 1.13–1.33 0.71–0.83 0.76–1.22 0.94–1.14 0.67–0.86 0.84–1.08 0.71–0.81 on next page)

Moldavites from the Cheb Basin

Cheb Basin Substrewn-field–range D-1 28 77.7–79.4 D-2a 23 78.5–80.9 D-2b 9 78.9–80.7 D-3 30 77.8–79.1 D-4a 23 78.9–79.8 D-4b 6 80.4–81.4 D-5a 15 82.2–83.3 D-5b 25 79.0–82.4 D-6 29 78.4–80.1 D-7 25 78.4–80.0 D-8 24 77.7–79.6 D-9 30 77.6–79.8 D-10 26 76.4–78.7 D-11 27 77.1–79.9 D-12 29 80.3–82.3 D-13 24 77.6–79.0 D-14a 35 77.9–80.6 D-14b 4 77.2–78.3 D-15 25 77.4–78.3 D-16 28 78.7–80.3 D-17a 33 78.3–83.1 D-17b 4 83.1–85.1 D-18a 28 79.3–81.2 D-18b 7 77.0–80.2 D-18c 5 80.6–82.0 D-19a 31 77.7–81.8 D-19b 8 73.9–77.7 D-20a 25 79.0–82.1 D-20b 6 82.5–85.0 D-20c 5 75.6–79.3 D-21 23 76.9–83.2 D-22 25 78.5–80.0 D-23 27 78.4–80.0 D-24a 29 79.6–82.1 D-24b 7 78.7–79.7

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1156

Table 3 (continued) Sample

n

SiO2

TiO2

a

Not available.

FeO

MgO

CaO

Na2O

K2O

CaO/MgO

K2O/Na2O

K2O/CaO

N/A 11.27–13.20 8.77–11.64 10.09–10.97 8.90–9.48 8.95–9.81 8.59–9.06 9.05–9.61 9.36–9.84 9.06–9.84 11.01–12.28 10.31–11.21 9.25–10.07 9.01–10.01 11.22–12.45 12.81–13.77 9.00–10.31 9.19–9.90 9.39–10.61 9.72–9.90 9.47–9.93 N/A 11.17–11.40 N/A 11.38–11.69 11.28–12.05 9.68–10.10 9.81–11.16 9.92–10.95 9.55–10.51 9.93–10.36

N/A 2.13–2.91 1.12–2.30 1.15–2.64 0.93–1.79 0.96–1.88 1.02–1.75 1.02–2.01 1.28–1.53 1.22–1.98 1.72–3.14 1.28–2.65 1.29–1.91 0.99–2.01 1.79–2.92 2.69–3.19 0.92–1.85 1.02–1.82 0.96–1.88 1.34–1.84 1.25–1.95 N/A 2.17–2.42 N/A 2.33–2.61 2.01–3.01 1.72–2.10 1.11–1.91 1.59–2.25 0.86–2.19 1.37–2.16

N/A 0.52–0.89 0.43–1.27 1.57–2.16 1.81–2.12 1.35–1.59 2.16–2.44 2.07–2.27 2.45–2.63 1.88–2.06 1.81–2.06 1.81–2.08 1.70–2.85 1.89–3.34 1.84–2.26 1.89–2.35 1.98–3.47 1.69–2.06 2.23–2.78 3.55–3.77 2.02–2.16 N/A 1.15–1.22 N/A 1.23–1.34 1.28–1.42 1.06–1.12 1.04–1.27 1.16–1.35 0.99–1.21 1.23–1.33

N/A 0.36–0.69 0.24–1.24 1.94–2.74 2.48–2.99 2.02–2.46 4.51–4.75 2.60–2.98 3.03–3.67 2.44–2.70 2.10–2.55 2.07–2.49 2.70–3.83 2.38–4.35 1.88–2.59 1.87–2.77 2.77–4.41 2.34–2.71 3.09–3.64 4.43–4.74 2.58–2.77 N/A 0.81–0.89 N/A 1.09–1.12 0.95–1.24 1.29–1.32 1.38–1.72 1.43–1.84 1.26–1.61 1.52–1.77

N/A 0.40–0.57 0.36–0.73 0.31–0.49 0.24–0.42 0.41–0.54 0.30–0.43 0.32–0.44 0.32–0.39 0.37–0.52 0.54–0.64 0.48–0.63 0.31–0.52 0.24–0.38 0.57–0.73 0.69–0.78 0.25–0.39 0.24–0.34 0.26–0.35 0.24–0.31 0.34–0.45 N/A 0.62–0.67 N/A 0.55–0.63 0.54–0.71 0.36–0.41 0.34–0.45 0.32–0.43 0.26–0.37 0.30–0.34

N/A 3.99–4.26 3.77–4.29 3.49–3.84 3.32–3.58 3.58–3.85 3.60–3.91 3.41–3.81 3.30–3.42 3.52–3.92 3.70–3.97 3.54–3.93 3.21–3.75 2.70–3.66 3.90–4.20 3.94–4.44 2.70–3.60 3.43–3.75 3.28–3.49 2.78–2.94 3.45–3.81 N/A 4.00–4.09 N/A 3.97–4.08 3.76–4.12 3.34–3.41 3.21–3.63 3.23–3.52 3.18–3.49 3.14–3.33

N/A 0.56–0.80 0.50–1.14 1.18–1.40 1.30–1.49 1.38–1.63 1.92–2.16 1.23–1.39 1.19–1.40 1.22–1.37 1.13–1.28 1.07–1.30 1.32–1.59 1.23–1.54 0.95–1.23 0.92–1.18 1.16–1.52 1.25–1.51 1.28–1.41 1.22–1.26 1.23–1.32 N/A 0.69–0.76 N/A 0.83–0.91 0.70–0.96 1.15–1.25 1.22–1.40 1.13–1.46 1.17–1.43 1.14–1.38

N/A 7.2–10.6 5.5–10.9 7.7–11.8 7.9–13.9 6.6–9.4 8.6–12.7 8.1–11.0 8.8–10.5 7.2–10.3 5.8–7.4 6.0–7.7 6.4–11.2 9.0–13.8 5.4–7.0 5.0–6.2 8.9–11.8 10.6–14.7 9.5–12.8 9.5–11.9 7.9–10.5 N/A 6.0–6.4 N/A 6.3–7.4 5.6–7.5 8.1–9.4 8.1–9.8 8.0–10.4 9.2–12.5 9.5–10.7

N/A 5.83–11.89 3.19–16.81 1.29–1.97 1.11–1.41 1.48–1.84 0.76–0.84 1.15–1.38 0.90–1.12 1.32–1.60 1.51–1.85 1.52–1.87 0.84–1.39 0.62–1.46 1.52–2.23 1.42–2.28 0.61–1.26 1.31–1.57 0.90–1.11 0.59–0.66 1.28–1.45 N/A 4.52–5.03 N/A 3.59–3.76 3.22–4.27 2.53–2.61 1.89–2.56 1.80–2.41 2.05–2.71 1.83–2.16

R. Ska´la et al. / Geochimica et Cosmochimica Acta 73 (2009) 1145–1179

South Bohemian and Moravian Substrewn-fields – range Bs-1a 1 N/Aa N/A Bs-1b 9 77.3–80.9 0.31–0.55 Bs-1c 78 77.9–85.3 0.20–0.48 Ch-1 28 77.3–79.9 0.29–0.38 Ch-2 27 79.5–80.6 0.21–0.32 Ch-3 25 79.9–81.5 0.23–0.32 Ch-4 27 77.2–78.7 0.20–0.29 Ch-5a 24 78.8–80.8 0.24–0.34 Ch-5b 5 78.2–79.1 0.24–0.28 Ch-6 28 78.6–80.6 0.25–0.34 Ch-7a 16 75.3–77.0 0.35–0.49 Ch-7b 19 77.0–78.7 0.33–0.42 Hb-1 20 76.9–80.3 0.21–0.33 J-1 28 78.0–79.7 0.24–0.34 J-2a 23 75.1–77.1 0.39–0.51 J-2b 6 73.5–75.1 0.48–0.55 J-3 29 77.7–79.9 0.21–0.36 Sl-1a 20 79.5–81.7 0.24–0.33 Sl-1b 6 78.2–80.4 0.25–0.30 Sl-1c 4 76.5–77.3 0.26–0.29 Sl-2 25 78.6–80.4 0.25–0.36 Sp-1a 1 N/A N/A Sp-1b 3 78.7–79.2 0.40–0.45 Sp-1c 1 N/A N/A Sp-1d 5 77.1–77.5 0.39–0.49 Sp-1e 20 77.8–78.4 0.34–0.48 Sv-1a 3 82.0–82.8 0.25–0.31 Sv-1b 15 79.3–80.9 0.27–0.42 Sv-1c 17 79.1–81.0 0.30–0.40 Vr-1a 30 80.4–82.4 0.25–0.38 Vr-1b 8 80.7–81.3 0.29–0.37

Al2O3

Moldavites from the Cheb Basin

1157

Fig. 7. Alkali element and alkali element ratio plot for analyzed moldavites. The data for moldavites from Cheb (left panels) and those from the South Bohemian and Moravian strewn subfields (right panels) can easily be discriminated.

Fig. 8. Variation of CaO and MgO versus K2O contents (in wt.%) in the Cheb moldavites (left panels) compared to trends for South Bohemian and Moravian tektites (right panels).

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Distributions for SiO2 and Al2O3 are positively skewed. For South Bohemian moldavites the distribution of the data is different. A bimodal curve was observed for MgO, and the calcium distribution displays 3 maxima. Other elements follow either skewed normal distributions or they have more complex distribution curves (SiO2 and FeO). Samples from Moravia show bimodal distribution curves for SiO2, Al2O3, Na2O, and K2O, whereas the remaining elements are distributed more or less normally. The compositional variability encountered within individual moldavite pieces required the development of a procedure that would allow grouping of individual analyses from a single sample to more or less homogeneous subsets. We used BSE images and multivariate statistical and graphic methods for that purpose. In particular, scatter-plot matrix (SPLOM) and hierarchical clustering diagrams as implemented in SYSTAT were found very useful. These graphs allowed separation of partial compositional sets (‘‘domains” or ‘‘lithologies”) as well as elimination of outliers (e.g., due to the presence of lechatelierite inclusions close to an analyzed spot). From the data divided in this way into separate subgroups and with the outliers eliminated, the basic statistical moments were calculated for these individual subpopulations. Table 3 summarizes the minimum and maximum values, measures of position and scale (i.e., usually arithmetic mean and standard deviation) and number of individual point measurements used to calculate these statistical moments. For the small data sets, instead of mean and standard uncertainty, appropriately chosen modified statistical moments describing the data variation were used following the suggestions of Rousseeuw and Verboven (2002). Some subgroups consist of a single analytical point which was not classified as an outlier because there was no physical or chemical reason to do so. Such analyses simply reflect a greater heterogeneity of the moldavites studied and reveal the entire spread of the chemical composition. In these cases, obviously, no statistical moments can be given to characterize these glassy domains. The data obtained (Table 3) substantially widen the compositional range reported for both Cheb and South Bohemian moldavites (sample Bs-1). Taking into account solely the range of element contents, it appears that the Cheb tektites are close to the South Bohemian moldavites, albeit a part of them resembles rather the composition reported for the Moravian samples in the literature (Delano and Lindsley, 1982; Koeberl, 1986, 1990). Compositional trends plotted in scatter diagrams, however, are much more useful than only the comparison of element contents. The plots show, for many element combinations, completely different trends or groupings for the Cheb tektites compared to the South Bohemian or Moravian moldavites. Marked differences are found in the MgO vs. SiO2 and CaO vs. SiO2, K2O (and Na2O/K2O) vs. Na2O, CaO vs. K2O diagrams (Figs. 6–8). The most obvious difference between moldavites from the Cheb Basin and those from the South Bohemian and Moravian partial strewn fields is found in the CaO vs. K2O diagram (Fig. 8; similar variation is found also in MgO vs. K2O plot). Analyses of Cheb tektites cluster in

an S-shaped trend with only sample D-22 located off the trend. In contrast, most moldavites from the South Bohemian strewn subfield form a linear trend exhibiting a negative correlation for both elements and intersect the trend defined by the Cheb Basin moldavites only partially. Only South Bohemian sample Ch-4 shares the trend with the Cheb moldavites. This sample represents the so-called HCa/Mg-type (see below). At the intersection of the Sshaped and linear trends, there are several analyses from samples Ch-2, 5, Hb-1, J-1, 3, and Sl-1. The Moravian samples Sp-1, Sv-1, and VR-1 and that from Besednice display the lowest CaO contents and form two distinct clusters below that defined by the South Bohemian moldavites. Similar to the CaO vs. K2O plot, the data for the Cheb moldavites and those from the South Bohemian and Moravian strewn subfields can easily be discriminated with alkali and alkali ratio diagrams (Fig. 7). In the K2O vs. Na2O plot, the Cheb moldavites form two well separated groups, with South Bohemian and Moravian moldavites plotting just between these two clusters. The Cheb moldavites define several, more or less, linear trends in the alkali ratio plot.

Fig. 9. Variation of MgO versus CaO content for the Cheb moldavites compared to the data observed for moldavites from classical localities. Fields of so-called normal and HCa/Mg types are indicated by white and gray shading, respectively. Moldavites from the Cheb Basin (top) display a transitional composition not observed in samples from the South Bohemia and Moravia (bottom).

Moldavites from the Cheb Basin

other major element oxides except Na2O and K2O. Meisel et al. (1997) pointed out similar trends for their analyses of moldavites, yet the Harker diagrams (Fig. 6) constructed from our dataset show no such correlations. Instead, we found only several partial trends for element pairs involving SiO2; these trends cover only several moldavite pieces but are not shared by the analyses of the remaining samples. Whereas CaO and MgO reveal two correlation trends with

5

CaO / TiO2 10 15 20

25

30

200

200

150

150

100

100

50

50

0

0

20

20

15

15

10

10

5

5

0

0

4

4

3

3

2

2

1

1

0

0

8

8

6

6

4

4

2

2

0

0

1.25

1.25

1.00

1.00

0.75

0.75

0.50

0.50

0.25

0.25

0.00

0.00 0

5

10 15 20 CaO / TiO2

0

25

D7 D8 D9 D10 D11 D12

10 15 20 CaO / TiO2

25

30

S. Bohemia & Moravia :

Cheb Basin : D1 D2 D3 D4 D5 D6

5

SiO2 / MgO

30 0

Al2O3 / MgO

25

FeO / MgO

CaO / TiO2 10 15 20

K2O / MgO

SiO2 / MgO Al2O3 / MgO

FeO / MgO K2O / MgO Na2O / MgO

5

Na2O / MgO

Only one of these trends, however, is shared by South Bohemian and Moravian moldavites. Also, no substantial deviation from linearity of the trends in the alkali ratio plot was noticed. Several authors (e.g., O’Keefe, 1976; Koeberl, 1988, 1990) claimed in review papers that specific correlations exist between certain elements. In particular, it was repeatedly demonstrated that silica is negatively correlated with most

0

1159

D13 D14 D15 D16 D17 D18

D19 D20 D21 D22 D23 D24

Bs1 Ch1 Ch2 Ch3 Ch4

Ch5 Ch6 Ch7 Hb1

J1 J2 J3 Sl1

Sl2 Sp1 Sv1 Vr1

Fig. 10. Oxide ratio plots for analyzed moldavites. Analyses of the moldavites from the Cheb Basin (left column) form two slightly separated clusters; one of them shows affinity to Moravian moldavites, whereas the second compares better with the South Bohemian moldavites (right column). Data follow the hyperbolic trends observed by Delano and Lindsley (1982).

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silica for Cheb moldavites, there is virtually no correlation between SiO2 and FeO or K2O. In the Al2O3 vs. SiO2 plot, three separate trends displaying negative correlations may be defined, although the correlation is much weaker than in the case of MgO or CaO. In K2O and Na2O vs. SiO2 diagrams, two separate clusters were found. Identifying correlations for the data for South Bohemian and Moravian moldavite samples is even more complicated. As data scatter substantially, it is occasionally possible to delineate the trend only for analyses from a single sample. Inspecting the correlation matrix calculated from the entire dataset for Cheb moldavites, we identify positive correlations between CaO and MgO (Pearson correlation coefficient: 0.918), TiO2 and Al2O3 (0.837) TiO2 and Na2O (0.783), Al2O3 and Na2O (0.735), and CaO and K2O (0.713). Cheb moldavites also display a negative correlation between TiO2 and K2O ( 0.728). No other element pairs show absolute values of Pearson correlation coefficients higher than 0.7. Pearson correlation coefficients higher than 0.7 were observed among the South Bohemian moldavites for the TiO2 and Al2O3, TiO2 and FeO, Al2O3 and FeO, MgO and CaO, and Na2O and K2O (positive correlations). The correlation matrix calculated for Moravian moldavites illustrates good negative correlations between SiO2 and TiO2, SiO2 and Al2O3, SiO2 and MgO, SiO2 and Na2O, SiO2 and K2O, CaO and Na2O, and CaO and K2O, whereas TiO2 and

Al2O3, TiO2 and Na2O, TiO2 and K2O, Al2O3 and FeO, Al2O3 and MgO, Al2O3 and Na2O, Al2O3 and K2O, FeO and Na2O, FeO and K2O, and Na2O and K2O are positively correlated. In the CaO vs. MgO plot, two moldavites, D-8 from the Cheb Basin and Ch-4 from the South Bohemian locality Chlum, corresponding to the so-called HCa/Mg-type (Fig. 9; CaO/MgO ratio  2.0), were identified. Both these samples are relatively homogeneous. The entire compositional range covered by the Cheb moldavites is less than that defined in the literature for moldavites from classical localities, but there are analyses plotting between the field of normal and HCa/Mg moldavites (samples D-1, 3, 10, 11, 13, 16, 22, 23 and partly also D-15 and D-24b; CaO/ MgO ratio  1.6–1.7). Though transitional compositions have not yet been encountered among South Bohemian nor Moravian moldavites, their presence among the samples from the Cheb Basin makes a further separation of moldavites into the ‘‘normal” and ‘high Ca/Mg” groups, respectively, rather questionable. The oxide-ratio graphs [X/MgO (where X = SiO2, Al2O3, FeO, Na2O, K2O or Sr) vs. CaO/TiO2] shown in Fig. 10 have been used as a tool to distinguish between moldavites from different partial strewn fields in the past (e.g., Delano and Lindsley, 1982). Our data, similar to those for Austrian moldavites (Koeberl et al., 1988), do not seem to

Fig. 11. Two-way cluster analysis of major element chemical composition for the samples from the Cheb Basin. Two clearly differentiated clusters (A and B) are highly dissimilar. Samples belonging to cluster A are characterized by elevated contents of Ca, Mg, and K whereas those from cluster B are enriched in Ti, Al, Fe, and Na. Variable shading illustrates the element contents on the zero mean (m) and unit variance (s) standardized scale.

Moldavites from the Cheb Basin

substantiate the use of these plots for this purpose. For example, the lowest value of the CaO/TiO2 ratio was observed for the sample from the South Bohemian locality Besednice, although generally low values of this ratio are found in Moravian moldavites. Analyses of the Cheb moldavites form two separated clusters in these diagrams; one shows affinity to Moravian moldavites, the second one compares better with South Bohemian moldavites, although its CaO/TiO2 values attain even higher values than those of South Bohemian samples. In general, the data acquired follow the hyperbolic trends observed by Delano and Lindsley (1982). According to them these trends corroborate the hypothesis that moldavites formed by incomplete mixing of at least two components and that fractional vaporization played no significant role in the moldavite formation process. All the differences in trends or grouping of elements between the set of analyses for Cheb moldavites and moldavites from the classical localities seem to indicate that the composition of the tektites from the Cheb Basin is influenced, besides previously identified components (sand-, clay-, and carbonate-dominated sediments), by not yet well constrained material, which possesses K/Ca, K/Mg, and K/ Na ratios different from precursors of moldavites from the classical localities (Figs. 7 and 8). 4.3. Statistical assessment of major element compositions The major element data were further processed by statistical methods: two-way hierarchical clustering and factor analysis. Prior to the analysis, however, the data had to be transformed because the range of variation of contents among individual elements was high. Following Reimann et al. (2002), the data were first log-transformed to obtain a more homogeneous ranges. However, this emphasized the influence of variables with a large variation – in particular the FeO content. Therefore, we standardized the logtransformed data to a zero mean and unit variance. The two-way hierarchical cluster analysis was used to evaluate links among different samples (i.e., cases) and their compositions (i.e., variables). This method clusters variables and cases at the same time. Both cases and variables are permuted to bring similar values next to one another and produce a matrix. Dendrograms showing results of one-dimensional hierarchical cluster analysis separately for variables and cases are displayed at the matrix edges. To measure the similarity between individual data points the Euclidean distances metric (root-mean-squared distances) was chosen. This metric is simply the geometric distance in multidimensional space. Ward’s method was used to amalgamate clusters. It calculates the sum of squared Euclidean distances from each case in a cluster to the mean of all variables. The cluster to be merged is the one which will increase the sum by the least amount. This is an analysis-of-variance (ANOVA) type approach and has become a popular method for this reason. Fig. 11 shows the permuted matrix after two-way cluster analysis and reveals the compositional characteristics of the Cheb moldavites on the zero mean (m) and unit variance (s) scale. The dendrogram, amalgamating individually defined

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chemical domains, separates these domains into 2 clearly defined clusters (labeled A and B) with very high degree of dissimilarity. The cluster tree, aggregating chemical species, reveals 3 groups, which separate at about 50% of maximum linkage distance. Cluster A consists of the following samples: D-1, 3, 4(a, b), 5(a, b), 8, 10, 11, 12, 13, 16, 22, 23, 24(a, b). Cluster B comprises the remaining specimens: D-2(a, b), 6, 7, 9, 14(a, b), 15, 17(a, b), 18(a, b, c), 19(a, b), 20(a, b, c), 21. There is no sample consisting of ‘‘lithologies” that belong to two different clusters. The structure of clusters clearly substantiates the separation of certain samples into several chemical domains: individual lithologies of samples D-4, 14, 17, 20 or 24 are located in different branches of the cluster tree with relatively high linkage distances. Group A is characterized, in general, by elevated contents of MgO, CaO and K2O, and depletion in TiO2, Al2O3, FeO and Na2O compared to the samples of cluster B. The SiO2 content is more or less comparable in all materials, although, on average, it is higher in the samples of cluster B; domains D-17b and D-20b show the highest SiO2 contents of all. Also, it is obvious that cluster A contains fewer heterogeneous samples than cluster B. The three clusters agglomerating the chemical species reveal an interesting structure. Though one would expect tight clustering of K2O with Na2O, no such feature is present. Instead, K2O is closely associated to CaO and MgO. In order to compare the major element compositions of the Cheb, South Bohemian and Moravian moldavites, the same procedure was applied to the combined dataset. The dataset splits into 5 clusters at about 30% of maximum linkage distance. Two of them contain – with the exception of HCa/Mg sample Ch-4 – exclusively compositional domains from the Cheb samples. The first cluster (I) is identical to group A (Fig. 11) obtained from the analysis of the Cheb materials plus sample Ch-4. The second cluster (II) comprises most of the samples from cluster B (Fig. 11) as defined from analysis of only the Cheb moldavites. Only samples D-7, 15, 18(a, b, c) (first grouplet) and D-17b, 20b (second grouplet) could not be linked to other Cheb samples. The first of the grouplets was amalgamated into a cluster containing South Bohemian samples with the exception of all compositional domains of moldavites Bs1 and J-2 and the lithology Ch-7a (III). The second of the grouplets of Cheb tektites defined above then aggregated to a cluster with Moravian samples Sv-1 and Vr-1 (IV). The third Moravian sample from Sˇteˇpa´novice (Sp-1) clustered with moldavites Bs-1 and J-2 and the compositional domain Ch-7a (V). Major element clustering for all samples displays a pattern similar to that observed for the separately processed Cheb moldavites. The only exception is that, instead of CaO and MgO, potassium agglomerates first with SiO2 and only then these two clusters fuse together at about 60% of the maximum linkage distance. The permuted matrix resulting from the two-way hierarchical clustering reveals how the elements were distributed among individual samples within the clusters. The characteristic feature of the cluster comprising, besides D-17b and D-20b lithologies, the Moravian samples Sv-1 and

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Fig. 12. Component loading plots show results of the principal component analysis for moldavites from the Cheb Basin (left) and those from South Bohemian and Moravian partial strewn fields (right). Both component loadings and standardized scores are plotted. The structure of component loadings differs between both graphs. Standardized scores indicate two source materials which did not mutually mix in the case of the Cheb moldavites; whereas samples from the South Bohemian and Moravian partial fields display a multicomponent origin.

Vr-1 (cluster IV), are low MgO and, in part, also CaO contents and increased SiO2 concentration. The cluster containing most of the South Bohemian samples (and Cheb samples D-7, 15, 18; cluster III) is, in general, similar to cluster A of Fig. 11, except that enrichments in MgO, CaO, and K2O, and depletions in FeO, Al2O3, TiO2, and Na2O are less pronounced. Completely different attributes are observed for the last of the five clusters. The samples Bs-1, J-2, Sp-1, and lithology Ch-7a (cluster V) are strongly enriched in FeO, Al2O3, TiO2, Na2O, and K2O, whereas MgO, CaO and, to some extent, also SiO2 are significantly depleted. Principal component analysis (PCA) with subsequent Varimax rotation was carried out separately for the Cheb moldavites, and for South Bohemian and Moravian moldavites. Both groups of moldavites, applying the Keiser criterion (i.e., extracting the factors with eigenvalues higher than 1.0 only), produced two-dimensional factor loading plots with three more or less distinct groups of elements (Fig. 12). The two extracted principal components accounted for 83% of the total variance in the case of the Cheb moldavites and for 81% in the case of the South Bohemian and Moravian moldavites. Individual groups of the elements in the plot of the samples from the South Bohemian and Moravian partial strewn fields consist of: (1) SiO2, (2) CaO and MgO, and (3) TiO2, Al2O3, FeO, K2O, and Na2O. The first two contribute mainly to principal component 2, whereas principal component 1 separates the latter. Such a pattern agrees perfectly with results published by Delano et al. (1988) for factor analysis carried out on 114 moldavite samples from South Bohemia and Moravia. For samples from the Cheb Basin, however, the re-

sults of PCA significantly differ: the loading due to K2O is no longer associated with Na2O but instead it projects to a segment of the plot delimited by SiO2; a group consisting of CaO and MgO is closer to the latter and, in fact, is almost in an inverse position compared to the plot showing the results of PCA for the samples from Southern Bohemia and Moravia (Fig. 12). Standardized scores, superimposed onto the component loading plots, show how individual samples are influenced by the given principal-component trends. Moldavites from the Cheb Basin are grouped into two subparallel linear trends and a small grouplet embodying analyses of sample D-15. The two trends are parallel to the SiO2 loading and a cluster corresponding to D-15 lies between them in negative continuation of the SiO2 loading vector (Fig. 12). This structure is in agreement with the results of the cluster analysis. The samples to the left of the loading due to SiO2 correspond to the members of cluster A, whereas samples belonging to cluster B are found to the right of this loading. The structure observed for the South Bohemian and Moravian samples is completely different. There is a large cluster slightly off-center to the left of the plot which contains most of the data points; the only obvious exceptions are samples Bs-1, J-2, Sp-1, and possibly also Ch-7. This observation is fully consistent with the results of the cluster analysis given above, where these samples form a separate cluster. 4.4. Minor and trace element composition LA-ICP-MS results for 33 minor and trace elements in eight Cheb samples (D-1, 2, 5, 6, 7, 13, 17, 19), two moldavites from South Bohemia (Ch-6, Sl-2), and one from Mor-

Table 4 Minor and trace element compositions (ppm) of the studied moldavites from the Cheb Basin and localities in the South Bohemia and Moravia with outliers excluded. Range and statistical measures of position and scale, are shown together with the number of analyses involved in the calculation of these variables (n). Sample

n

Cr

Mn

Co

Ni

Cu

Zn

Rb

Sr

Y

Position ± scale D-l 6 D-2a 2 D-2b 4 D-5a 3 D-5b 4 D-6 5 D-7 6 D-13 5 D-17a 3 D-17b 3 D-19a 2 D-19b 4 Ch-6 4 Sl-2 5 Sp-la 1 Sp-ld 2 Sp-le 2

23.1 ± 0.8 23.5 24.9 ± 2.0 20.1 ± 3.6 22.6 ± 2.5 29.5 ± 2.1 25.0 ± 1.3 26.8 ± 0.9 22.5 ± 0.3 16.8 ± 1.8 24.3 23.7 ± 0.5 27.3 ± 0.7 25.8 ± 0.4 35.6 35.7 39.6

18.3 ± 0.8 20.1 21.9 ± 1.4 16.5 ± 2.6 19.0 ± 2.2 25.1 ± 1.5 21.2 ± 0.6 20.9 ± 1.1 20.8 ± 1.7 13.8 ± 1.1 18.9 17.9 ± 0.7 25.1 ± 0.3 23.2 ± 0.2 34.4 35.2 38.1

888 ± 43 537 584 ± 14 907 ± 1 860 ± 5 580 ± 36 756 ± 27 805 ± 11 521 ± 58 231 ± 88 756 719 ± 46 746 ± 19 535 ± 10 270 263 243

4.35 ± 0.12 4.17 4.50 ± 0.43 4.87 ± 0.60 5.43 ± 0.11 5.42 ± 0.25 4.67 ± 0.11 4.65 ± 0.09 5.17 ± 0.84 3.89 ± 0.05 7.06 4.29 ± 0.13 5.13 ± 0.15 4.97 ± 0.21 6.08 6.56 6.87

7.3 ± 0.7 4.0 4.9 ± 0.9 8.7 ± 0.1 9.1 ± 0.9 5.8 ± 0.7 4.9 ± 0.2 8.8 ± 0.6 5.7 ± 0.6 3.0 ± 1.1 4.8 4.2 ± 0.7 17.0 ± 0.7 10.9 ± 0.4 13.3 13.2 16.0

1.63 ± 0.18 1.59 1.70 ± 0.34 4.66 ± 0.28 4.43 ± 0.67 2.53 ± 0.64 1.60 ± 0.20 1.92 ± 0.25 1.70 ± 0.05 1.46 ± 0.05 3.00 1.90 ± 0.07 1.55 ± 0.47 1.14 ± 0.13 0.94 1.10 1.94

31 ± 4 39 46 ± 10 202 ± 13 274 ± 9 57 ± 5 14 ± 2 16 ± 2 68 ± 5 126 ± 25 46 50 ± 9 24 ± 1 9±2 9 12 17

121 ± 4 86 88 ± 4 108 ± 6 112 ± 2 89 ± 5 107 ± 1 127 ± 2 93 ± 4 74 ± 5 85 83 ± 2 133 ± 2 127 ± 5 152 156 156

131 ± 10 202 209 ± 25 112 ± 2 111 ± 17 251 ± 19 202 ± 8 129 ± 2 192 ± 13 102 ± 13 258 239 ± 14 155 ± 6 131 ± 12 126 109 98

15.63 ± 1.65 18.22 18.21 ± 2.95 13.71 ± 0.07 13.44 ± 1.97 19.60 ± 1.94 21.14 ± 1.42 13.16 ± 0.65 15.72 ± 0.66 11.70 ± 0.62 21.58 20.25 ± 1.24 16.89 ± 0.50 17.75 ± 0.10 25.71 20.93 18.16

Range D-l D-2a D-2b D-5a D-5b D-6 D-7 D-13 D-17a D-17b D-19a D-19b Ch-6 Sl-2 Sp-la Sp-ld Sp-le

22.0–23.8 23.2–23.8 22.5–26.7 17.7–23.0 21.0–23.9 27.4–31.6 23.3–26.7 25.8–27.6 22.3–25.1 15.6–18.1 24.0–24.6 23.2–24.1 26.7–28.0 25.4–26.7 N/Aa 35.7–35.8 38.1–41.1

17.3–19.1 19.8–20.4 18.9–23.1 14.3–18.2 17.6–20.4 22.6–26.8 20.3–23.8 19.9–22.0 19.6–21.9 13.1–15.6 18.9–19.0 17.4–18.6 24.8–25.3 22.9–24.3 N/A 35.1–35.2 36.6–39.6

846–913 530–544 509–593 881–907 857–872 545–611 704–788 783–818 482–623 172–304 742–769 664–766 731–762 524–588 N/A 260–266 243–243

4.19–4.51 3.90–4.43 3.99–4.91 4.23–5.27 5.30–5.50 5.15–5.61 4.01–4.83 4.56–4.77 4.60–5.74 3.85–4.34 6.31–7.81 4.18–4.48 5.02–5.26 4.61–5.12 N/A 6.34–6.78 6.76–6.98

6.5–7.9 3.6–4.5 4.2–5.6 7.9–8.8 7.8–9.9 5.0–6.3 4.7–5.6 8.2–9.4 5.1–6.1 2.2–3.8 4.7–4.9 3.6–4.9 16.6–18.4 9.8–11.2 N/A 12.2–14.2 15.6–16.4

1.21–1.88 1.41–1.77 1.27–2.13 4.47–4.94 3.58–5.23 0.96–3.55 0.99–1.81 1.70–2.18 1.67–1.89 1.43–3.00 2.73–3.28 1.86–2.18 1.34–1.78 0.97–1.49 N/A 1.01–1.18 1.64–2.24

26–37 36–43 36–57 193–217 268–283 47–66 12–16 14–21 65–106 107–143 46–46 44–61 23–25 7–11 N/A 11–12 16–18

118–125 85–88 84–93 103–112 110–113 85–92 105–108 125–131 86–95 71–79 85–85 81–85 131–135 124–132 N/A 153–158 155–158

121–140 189–214 182–236 95–113 101–120 223–281 193–214 128–145 184–215 93–126 257–258 221–257 148–159 124–153 N/A 108–110 97–99

6 2 4 3 4 5 6 5 3 3 2 4 4 5 1 2 2

14.06–17.24 16.28–20.16 15.87–21.47 12.62–13.76 12.21–14.56 16.91–23.06 19.70–23.94 12.74–14.98 15.27–18.28 11.28–12.70 21.36–21.80 19.18–21.52 16.53–17.49 17.66–21.05 N/A 20.83–21.03 17.64–18.68 (continued on next page)

Moldavites from the Cheb Basin

V

1163

1164

Table 4 (continued) Sample

n

Nb

Cs

Ba

La

Ce

Pr

Nd

Sm

Eu

Position ± scale D-l 6 D-2a 2 D-2b 4 D-5a 3 D-5b 4 D-6 5 D-7 6 D-13 5 D-17a 3 D-17b 3 D-19a 2 D-19b 4 Ch-6 4 Sl-2 5 Sp-la 1 Sp-ld 2 Sp-le 2

184 ± 20 216 213 ± 20 190 ± 4 189 ± 18 256 ± 23 261 ± 21 149 ± 7 195 ± 1 178 ± 2 268 252 ± 10 179 ± 5 205 ± 4 290 237 206

5.63 ± 0.29 7.62 8.14 ± 0.50 5.67 ± 0.06 5.67 ± 0.48 9.02 ± 0.49 7.80 ± 0.14 5.40 ± 0.24 7.10 ± 0.23 4.79 ± 0.52 8.55 8.11 ± 0.53 6.54 ± 0.24 7.64 ± 0.48 10.03 9.84 9.24

12.74 ± 0.60 13.90 14.25 ± 0.86 13.84 ± 0.82 14.51 ± 0.43 13.56 ± 0.33 16.68 ± 0.96 12.83 ± 0.40 15.65 ± 0.49 12.17 ± 1.14 12.51 12.29 ± 0.14 14.90 ± 0.36 13.90 ± 0.06 17.54 17.78 17.88

563 ± 33 889 928 ± 102 417 ± 12 411 ± 18 994 ± 106 816 ± 30 229 ± 5 772 ± 84 383 ± 89 1030 970 ± 76 695 ± 25 309 ± 3 689 614 586

23.2 ± 2.2 32.4 33.2 ± 4.1 22.1 ± 0.7 22.0 ± 1.6 38.8 ± 6.5 35.2 ± 1.4 20.6 ± 0.6 29.2 ± 0.5 21.1 ± 1.8 39.0 36.5 ± 2.3 26.0 ± 0.8 28.4 ± 1.1 36.3 30.3 28.1

45.0 ± 2.2 59.6 63.6 ± 4.9 47.2 ± 3.0 48.0 ± 0.8 77.6 ± 4.7 67.4 ± 1.5 43.3 ± 1.1 61.8 ± 2.0 50.5 ± 2.8 83.8 74.4 ± 6.4 42.8 ± 1.2 50.4 ± 2.1 67.1 61.5 59.1

5.29 ± 0.34 7.27 7.51 ± 0.86 5.11 ± 0.31 5.20 ± 0.25 9.03 ± 1.56 8.10 ± 0.28 4.99 ± 0.23 6.93 ± 0.10 4.98 ± 0.08 8.99 8.42 ± 0.50 5.82 ± 0.19 6.61 ± 0.30 8.16 6.91 6.56

21.7 ± 2.1 31.5 31.5 ± 3.9 21.1 ± 0.1 21.1 ± 1.3 37.5 ± 6.4 34.4 ± 1.5 19.8 ± 0.3 28.4 ± 0.9 20.6 ± 1.2 37.7 34.6 ± 2.4 24.5 ± 0.8 27.3 ± 1.9 34.1 27.9 26.9

4.0 ± 0.3 5.3 5.3 ± 0.6 3.6 ± 0.3 3.7 ± 0.2 6.2 ± 0.9 6.0 ± 0.2 3.6 ± 0.4 4.9 ± 0.2 3.4 ± 0.1 6.4 6.1 ± 0.4 4.2 ± 0.1 4.8 ± 0.5 6.0 5.1 4.7

0.81 ± 0.07 0.98 1.00 ± 0.13 0.69 ± 0.04 0.73 ± 0.04 1.14 ± 0.12 1.12 ± 0.08 0.76 ± 0.04 0.99 ± 0.06 0.60 ± 0.12 1.20 1.13 ± 0.09 0.92 ± 0.02 0.97 ± 0.06 1.08 0.95 0.93

Range D-l D-2a D-2b D-5a D-5b D-6 D-7 D-13 D-17a D-17b D-19a D-19b Ch-6 Sl-2 Sp-la Sp-ld Sp-le

167–202 194–237 198–248 182–193 177–204 217–299 234–300 145–172 194–211 165–180 265–270 244–265 174–184 202–248 N/A 236–238 203–209

5.19–5.95 7.43–7.82 7.17–8.50 4.61–5.71 5.26–6.09 8.36–9.61 7.62–8.36 5.22–5.61 6.95–7.56 4.44–5.28 8.45–8.64 7.68–8.57 6.41–6.71 7.30–8.34 N/A 9.82–9.85 9.07–9.41

12.13–13.21 13.27–14.53 13.40–15.08 12.77–14.40 14.18–14.77 12.45–13.96 16.07–17.46 12.43–13.18 14.51–15.98 11.01–12.93 12.33–12.69 12.18–12.39 14.67–15.08 13.83–14.13 N/A 18.38 17.41–18.34

523–598 837–942 820–1001 384–425 396–432 877–1083 774–838 224–241 715–865 323–477 1009–1050 890–1053 666–719 293–347 N/A 612–616 576–595

20.8–25.4 29.4–35.3 29.0–37.7 19.7–22.5 20.8–23.6 32.9–43.6 33.7–38.3 20.0–23.1 28.8–32.8 19.8–22.8 38.9–39.2 34.5–39.7 25.3–26.9 27.3–32.6 N/A 30.1–30.4 27.3–28.9

41.9–47.3 57.2–62.0 55.5–66.7 43.1–49.2 47.4–49.5 69.6–82.7 65.6–69.7 42.2–44.5 60.4–66.5 48.7–62.0 82.1–85.4 69.3–80.3 41.5–44.1 48.5–54.1 N/A 61.0–61.9 57.7–60.5

4.80–5.66 6.71–7.82 6.65–8.43 4.64–5.31 5.03–5.50 7.69–10.17 7.83–8.61 4.79–5.29 6.87–7.64 4.93–5.52 8.91–9.06 8.01–9.18 5.59–6.07 6.36–7.35 N/A 6.85–6.97 6.42–6.70

19.8–23.9 28.8–34.2 27.7–35.5 18.8–21.2 20.3–22.6 31.3–42.1 32.9–37.3 19.4–22.6 27.7–31.2 19.8–22.4 37.7–37.7 32.8–37.4 24.0–25.6 25.3–30.8 N/A 27.9–28.0 25.5–28.3

3.7–4.3 4.8–5.8 4.8–5.9 3.2–3.8 3.5–3.8 5.4–7.1 5.7–6.7 3.3–3.9 4.7–5.3 3.3–3.8 6.4–6.5 5.8–6.5 4.2–4.4 4.3–5.6 N/A 5.0–5.3 4.6–4.8

0.72–0.90 0.92–1.05 0.86–1.12 0.61–0.72 0.70–0.78 1.02–1.27 1.06–1.21 0.73–0.80 0.90–1.03 0.52–0.70 1.17–1.23 1.05–1.19 0.87–0.93 0.91–1.05 N/A 0.95–0.95 0.89–0.97

6 2 4 3 4 5 6 5 3 3 2 4 4 5 1 2 2

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R. Ska´la et al. / Geochimica et Cosmochimica Acta 73 (2009) 1145–1179

Zr

Position ± scale D-l 6 D-2a 2 D-2b 4 D-5a 3 D-5b 4 D-6 5 D-7 6 D-13 5 D-17a 3 D-17b 3 D-19a 2 D-19b 4 Ch-6 4 Sl-2 5 Sp-la 1 Sp-ld 2 Sp-le 2

3.25 ± 0.41 4.15 4.09 ± 0.56 2.76 ± 0.07 2.95 ± 0.16 5.11 ± 1.33 4.75 ± 0.23 2.93 ± 0.23 3.50 ± 0.26 2.51 ± 0.05 5.09 4.58 ± 0.16 3.78 ± 0.13 3.99 ± 0.14 5.46 4.21 4.27

0.473 ± 0.043 0.581 0.583 ± 0.062 0.409 ± 0.033 0.419 ± 0.044 0.697 ± 0.089 0.665 ± 0.026 0.436 ± 0.060 0.535 ± 0.008 0.362 ± 0.013 0.682 0.690 ± 0.032 0.531 ± 0.034 0.565 ± 0.017 0.846 0.633 0.624

2.811 ± 0.355 3.489 3.428 ± 0.520 2.574 ± 0.002 2.528 ± 0.249 3.991 ± 0.940 4.000 ± 0.309 2.490 ± 0.146 2.956 ± 0.036 2.216 ± 0.138 4.039 3.770 ± 0.129 3.170 ± 0.120 3.524 ± 0.315 4.471 3.662 3.827

0.59 ± 0.03 0.63 0.63 ± 0.07 0.49 ± 0.01 0.49 ± 0.05 0.78 ± 0.20 0.77 ± 0.08 0.48 ± 0.02 0.57 ± 0.01 0.44 ± 0.01 0.77 0.73 ± 0.04 0.62 ± 0.04 0.69 ± 0.04 0.87 0.72 0.69

1.62 ± 0.12 1.79 1.77 ± 0.31 1.37 ± 0.04 1.36 ± 0.07 2.09 ± 0.61 2.07 ± 0.14 1.35 ± 0.22 1.57 ± 0.08 1.15 ± 0.04 2.14 2.01 ± 0.12 1.66 ± 0.07 1.90 ± 0.09 2.53 2.05 1.93

0.227 ± 0.019 0.239 0.251 ± 0.011 0.197 ± 0.006 0.199 ± 0.011 0.307 ± 0.049 0.297 ± 0.020 0.201 ± 0.027 0.221 ± 0.007 0.174 ± 0.025 0.314 0.296 ± 0.030 0.231 ± 0.008 0.294 ± 0.026 0.373 0.297 0.288

1.50 ± 0.15 1.66 1.66 ± 0.17 1.32 ± 0.06 1.34 ± 0.14 2.02 ± 0.58 2.01 ± 0.08 1.35 ± 0.13 1.55 ± 0.05 1.22 ± 0.07 1.97 1.89 ± 0.08 1.59 ± 0.05 1.86 ± 0.03 2.54 2.02 1.90

0.252 ± 0.018 0.275 0.275 ± 0.025 0.216 ± 0.007 0.217 ± 0.023 0.338 ± 0.088 0.339 ± 0.032 0.217 ± 0.021 0.252 ± 0.002 0.196 ± 0.008 0.331 0.316 ± 0.015 0.267 ± 0.013 0.305 ± 0.012 0.398 0.325 0.308

4.953 ± 0.694 5.613 5.650 ± 0.427 4.896 ± 0.315 5.044 ± 0.243 7.204 ± 1.741 6.930 ± 0.593 4.140 ± 0.349 5.263 ± 0.008 4.736 ± 0.284 7.344 6.949 ± 0.282 4.946 ± 0.184 5.933 ± 0.652 7.378 6.335 5.877

Range D-l D-2a D-2b D-5a D-5b D-6 D-7 D-13 D-17a D-17b D-19a D-19b Ch-6 Sl-2 Sp-la Sp-ld Sp-le

2.91–3.62 3.73–4.56 3.65–4.89 2.55–2.81 2.83–3.08 3.96–6.33 4.49–5.45 2.71–3.14 3.33–3.95 2.48–2.81 5.02–5.16 4.45–4.93 3.63–3.92 3.83–4.66 N/A 4.05–4.38 4.10–4.44

0.406–0.548 0.520–0.642 0.519–0.656 0.378–0.431 0.392–0.454 0.597–0.896 0.637–0.752 0.373–0.496 0.530–0.570 0.353–0.406 0.671–0.693 0.610–0.718 0.475–0.558 0.545–0.684 N/A 0.614–0.651 0.595–0.653

2.428–3.188 3.161–3.817 3.025–3.942 2.201–2.575 2.393–2.682 3.158–4.746 3.724–4.407 2.310–2.870 2.932–3.433 2.123–2.352 3.914–4.163 3.658–3.862 3.036–3.288 3.151–4.090 N/A 3.595–3.728 3.628–4.027

0.48–0.62 0.58–0.68 0.58–0.72 0.44–0.50 0.46–0.51 0.60–0.91 0.70–0.83 0.46–0.53 0.57–0.65 0.42–0.44 0.76–0.78 0.69–0.77 0.57–0.65 0.64–0.78 N/A 0.69–0.76 0.66–0.73

1.37–1.71 1.58–2.01 1.53–2.08 1.20–1.40 1.30–1.41 1.63–2.47 1.94–2.27 1.20–1.59 1.51–1.75 1.12–1.24 2.06–2.22 1.82–2.10 1.60–1.74 1.78–2.14 N/A 2.04–2.06 1.77–2.10

0.201–0.245 0.225–0.253 0.241–0.285 0.180–0.201 0.188–0.209 0.244–0.375 0.279–0.355 0.181–0.223 0.216–0.278 0.157–0.204 0.295–0.333 0.265–0.319 0.225–0.256 0.260–0.330 N/A 0.294–0.300 0.281–0.296

1.35–1.65 1.51–1.81 1.52–1.92 1.13–1.35 1.20–1.46 1.55–2.41 1.92–2.38 1.19–1.47 1.52–1.79 1.17–1.27 1.91–2.03 1.81–1.97 1.56–1.64 1.82–2.05 N/A 2.02–2.02 1.76–2.05

0.217–0.273 0.252–0.299 0.254–0.316 0.189–0.221 0.201–0.231 0.260–0.396 0.314–0.379 0.201–0.232 0.251–0.289 0.188–0.201 0.324–0.337 0.300–0.332 0.257–0.275 0.290–0.341 N/A 0.317–0.333 0.289–0.327

4.284–5.702 0.45–0.54 5.006–6.221 0.60–0.71 5.292–6.511 0.61–0.73 4.684–5.196 0.40–0.48 4.837–5.295 0.46–0.51 5.726–8.336 0.59–0.86 6.124–7.848 0.59–0.69 3.819–4.513 0.42–0.50 5.257–5.794 0.54–0.61 4.459–4.927 0.39–0.46 7.338–7.349 0.71–0.75 6.684–7.195 0.65–0.73 4.599–5.091 0.54–0.63 5.271–6.724 0.65–0.77 N/A N/A 6.264–6.407 0.79–0.80 5.618–6.136 0.70–0.86 (continued on next page)

Moldavites from the Cheb Basin

6 2 4 3 4 5 6 5 3 3 2 4 4 5 1 2 2

0.49 ± 0.06 0.65 0.67 ± 0.08 0.47 ± 0.02 0.49 ± 0.05 0.73 ± 0.13 0.65 ± 0.04 0.46 ± 0.06 0.56 ± 0.02 0.40 ± 0.01 0.73 0.71 ± 0.03 0.59 ± 0.05 0.67 ± 0.02 0.87 0.80 0.78

1165

1166

Table 4 (continued) Th

U

K/U

Th/U

La/Th

Zr/Hf

Rb/Sr

LaN/YbN

Eu/Eu*

Position ± scale D-l 6 D-2a 2 D-2b 4 D-5a 3 D-5b 4 D-6 5 D-7 6 D-13 5 D-17a 3 D-17b 3 D-19a 2 D-19b 4 Ch-6 4 Sl-2 5 Sp-la 1 Sp-ld 2 Sp-le 2

7.9 ± 0.8 19.2 21.3 ± 4.0 37.5 ± 4.3 51.7 ± 1.7 16.6 ± 1.4 15.4 ± 1.2 4.3 ± 0.4 20.4 ± 2.9 29.1 ± 2.4 12.5 13.5 ± 2.4 6.2 ± 0.3 3.6 ± 0.3 3.5 3.7 6.3

9.05 ± 0.86 14.48 14.74 ± 1.33 8.53 ± 0.20 8.76 ± 0.41 16.96 ± 3.50 15.66 ± 1.04 8.17 ± 0.58 11.96 ± 0.09 7.47 ± 0.18 16.71 15.81 ± 1.19 10.05 ± 0.48 11.28 ± 0.41 14.18 12.10 11.57

2.77 ± 0.20 2.69 2.85 ± 0.17 3.84 ± 0.25 4.42 ± 0.22 3.91 ± 0.73 3.50 ± 0.50 2.71 ± 0.11 3.39 ± 0.02 3.68 ± 0.04 3.06 3.20 ± 0.27 2.26 ± 0.08 2.46 ± 0.14 2.57 2.55 3.02

11188 8558 8208 7238 6146 5248 7979 11593 7057 6513 6813 6044 13629 12204 9480 13069 10895

3.28 ± 0.32 5.38 4.97 ± 0.10 2.17 ± 0.07 1.98 ± 0.19 4.31 ± 0.19 4.46 ± 0.48 2.87 ± 0.09 3.54 ± 0.12 2.01 ± 0.06 5.47 4.97 ± 0.60 4.39 ± 0.10 4.70 ± 0.32 5.51 4.75 3.85

2.568 ± 0.064 2.235 2.246 ± 0.063 2.590 ± 0.016 2.519 ± 0.093 2.302 ± 0.071 2.267 ± 0.042 2.556 ± 0.157 2.415 ± 0.006 2.655 ± 0.140 2.336 2.322 ± 0.033 2.574 ± 0.022 2.517 ± 0.069 2.562 2.501 2.432

37.3 ± 1.8 38.5 37.6 ± 0.8 38.8 ± 0.2 37.5 ± 1.8 35.9 ± 4.3 37.9 ± 0.3 37.3 ± 1.4 37.0 ± 0.2 37.0 ± 0.8 36.5 36.4 ± 0.5 36.4 ± 1.2 36.2 ± 4.0 39.3 37.4 35.1

0.93 ± 0.05 0.43 0.43 ± 0.05 1.00 ± 0.07 1.01 ± 0.14 0.35 ± 0.03 0.53 ± 0.03 0.98 ± 0.06 0.47 ± 0.02 0.73 ± 0.05 0.33 0.35 ± 0.02 0.86 ± 0.02 0.97 ± 0.08 1.21 1.43 1.59

10.7 ± 0.1 13.5 13.5 ± 0.4 11.6 ± 0.1 11.4 ± 0.7 13.5 ± 1.7 12.0 ± 0.6 10.8 ± 0.9 13.0 ± 0.2 11.9 ± 0.3 13.7 13.3 ± 0.1 11.3 ± 0.3 10.5 ± 0.5 9.9 10.4 10.3

0.681 ± 0.016 0.640 0.633 ± 0.009 0.659 ± 0.017 0.676 ± 0.017 0.625 ± 0.080 0.633 ± 0.034 0.703 ± 0.007 0.691 ± 0.013 0.635 ± 0.012 0.637 0.635 ± 0.005 0.697 ± 0.021 0.655 ± 0.026 0.573 0.622 0.626

Range D-l D-2a D-2b D-5a D-5b D-6 D-7 D-13 D-17a D-17b D-19a D-19b Ch-6 Sl-2 Sp-la Sp-ld Sp-le

6.8–9.2 18.2–20.2 19.1–24.1 34.6–41.4 50.1–53.3 15.0–18.7 14.3–16.4 3.8–5.9 18.4–26.2 25.7–30.7 12.4–12.5 12.0–16.6 6.0–6.5 3.1–3.8 N/A 3.4–4.0 5.7–6.9

7.99–9.99 13.17–15.79 13.20–16.35 7.79–8.67 8.36–9.08 13.66–19.31 14.49–16.81 7.55–9.21 11.90–13.60 7.35–8.90 16.62–16.80 14.77–16.96 9.68–10.54 10.77–13.22 N/A 12.10–12.10 10.92–12.23

2.50–2.95 2.63–2.75 2.70–3.08 3.59–4.01 4.22–4.74 3.24–4.59 2.99–3.84 2.52–3.11 3.37–3.44 3.65–3.79 3.05–3.07 2.98–3.41 2.20–2.44 2.32–2.69 N/A 2.52–2.58 2.75–3.28

N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

2.97–3.65 5.02–5.75 4.88–5.79 2.13–2.26 1.82–2.13 4.10–4.75 3.77–5.62 2.77–3.65 3.46–4.01 1.97–2.42 5.46–5.48 4.33–5.69 4.32–4.49 4.38–5.56 N/A 4.69–4.81 3.73–3.97

2.499–2.693 2.234–2.236 2.197–2.307 2.524–2.600 2.409–2.599 2.175–2.407 2.183–2.325 2.409–2.695 2.410–2.453 2.560–2.865 2.313–2.359 2.299–2.339 2.556–2.675 2.202–2.594 N/A 2.488–2.514 2.360–2.505

35.5–39.0 38.1–38.9 36.7–38.1 37.1–38.9 36.6–38.5 32.0–38.6 36.8–38.2 33.0–38.7 36.5–37.1 36.5–37.6 36.1–36.8 35.9–36.8 35.4–37.8 30.4–38.8 N/A 37.1–37.7 33.0–37.2

0.87–0.98 0.41–0.45 0.36–0.48 0.95–1.09 0.93–1.11 0.33–0.38 0.50–0.56 0.87–1.02 0.45–0.48 0.63–0.77 0.33–0.33 0.32–0.37 0.85–0.88 0.87–1.03 N/A 1.41–1.44 1.56–1.62

10.6–11.1 13.5–13.5 13.2–14.5 11.5–12.1 10.7–12.0 12.4–14.7 11.1–12.6 10.0–11.7 12.7–13.1 11.8–12.4 13.3–14.2 13.2–14.0 11.0–11.6 10.0–11.0 N/A 10.3–10.4 9.8 -10.8

0.665–0.696 0.618–0.661 0.625–0.675 0.648–0.671 0.659–0.687 0.550–0.676 0.607–0.653 0.695–0.765 0.682–0.728 0.540–0.643 0.617–0.658 0.631–0.676 0.650–0.710 0.621–0.700 N/A 0.617–0.627 0.616–0.636

a

n

6 2 4 3 4 5 6 5 3 3 2 4 4 5 1 2 2

Not available.

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Pb

Sample

Moldavites from the Cheb Basin

1167

Fig. 13. Variation of Nb versus Sr (a), Rb versus Cs (b), and La versus Lu (in ppm) illustrating compositional heterogeneity between individual samples or intra-sample inhomogeneities. In general, splitting of data into different groups or trends is consistent with the results of cluster analysis.

avia (Sp-1) are presented in Table 4. The resolution of 40– 80 lm allowed mutual correlation of minor/trace and major elements, the relationships of which in the past were occasionally obscured when using bulk analytical approaches. Contents of the analyzed elements are more or less conˇ anda, 1976; sistent with published data (e.g., Bousˇka and R Bousˇka and Konta, 1986; Bousˇka et al., 1990; Meisel et al., 1997; Engelhardt et al., 2005). A substantial scatter of the analytical data has been noted not only among individual samples (e.g., content of Mn ranges from less than 200 to more than 900 ppm, Ba from 230 to 1100 ppm, and the largest relative variation was found for Zn which ranges between 10 and 300 ppm), but also for some samples among separate analyses of one sample. This confirms the significant intra-sample heterogeneity observed already for major elements (D-5, 17, 19, Sp-1) with EMP analyses. Also, similar to major element data, the distribution curves for individual minor and trace elements often display bimodal (Rb, Sr, Y, Zr, Nb, Ba, REE, Hf, Ta and Th) or highly skewed (Mn, Co, Ni, Cu, Zn, Cs, Pb and U) shapes. This justifies splitting the analyses acquired for highly heterogeneous samples into two (or three in the case of sample Sp-1) different lithologies which correspond to those defined by major element data. There are four Cheb samples that require such a division: D-2, 5, 17, and 19. Variations in the concentrations of individual elements are not systematic. For most elements the distribution curves corresponding to samples of the three geographic regions overlap only

partially or they do not overlap at all. When a distribution of a particular element for the Cheb moldavites is bimodal, the distribution curves corresponding to South Bohemian moldavites frequently plot between the two maxima of the curves for Cheb moldavites (for Co, Sr, Y, Nb, La, Nd, Sm, Eu, Gd, Th). Application of multivariate statistical and graphic procedures, similar to those adopted for major element data, revealed tight overall correlations between pairs of minor and/or trace elements (e.g., V vs. Cr, Zn vs. Pb, Y vs. Nb, Zr vs. LREE’s, LREE’s vs. HREE’s, Th vs. LREE’s, Ta vs. HREE’s). Pearson correlation coefficients exceeded 0.85 for these element pairs, which quantitatively confirms close linking observed qualitatively in SPLOM diagrams. In addition to tight linear trends, several pairs of elements display clustering of individual analyses into groups, often showing rather straight semiparallel trends, illustrating compositional heterogeneity in some of the samples, intersample or regional compositional differences (Fig. 13). To evaluate possible correlation of minor, trace and major elements, it is necessary to use estimates of position (mean, Huber moment or median) for the two elements under consideration. This is a complicated task because each of these estimates is computed from different numbers of individual analyses with different dispersion, and consequently possesses different weight. Nevertheless, accepting this statistical drawback, important information may be obtained from the plots relating minor/trace elements to

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Fig. 15. Variation of Sr versus Zn and Pb. Volatile elements are substantially enriched in samples D-5 and D-17 from the Cheb Basin.

Fig. 14. Variation of Ca, Mg, and Fe (wt.%) versus Mn (ppm). Calcium and magnesium are positively correlated; iron is negatively correlated.

major elements. In addition to strong linear correlations expected a priori (Rb–K; Y–Ti, Al, Fe; Nb–Ti, Al, Fe; Ta–Ti, Al, Fe, etc.), several other linear trends are observed including V and Cr vs. Fe, Mn vs. Na, Ni vs. K. Similar to the minor and/or trace element correlations, certain major and minor/trace elements pairs are useful to differentiate between different compositional lithologies or regions (e.g., Ti–Sr, HREEs; Al–Mn, Rb, Sr, Ba, LREEs, Th; Fe–Rb, Sr, Ba, REEs, Th). Because of its importance as a suggested moldavite coloring agent (Bousˇka and Konta, 1986), the role of manganese was inspected in more detail. Data by Delano et al. (1988) demonstrate a strong positive correlation of manganese with magnesium (0.966) and calcium (0.957), yet our Pearson correlation coefficients are considerably lower at 0.857 (MgO) and 0.845 (CaO). In contrast to the results

of these authors, who showed that iron is not correlated with manganese (correlation coefficient of 0.424), we found a negative correlation between these two elements with a Pearson correlation coefficient of 0.706. Lower values of the correlation coefficients for relationships involving manganese with MgO and CaO are due mainly to a splitting of the dataset into two separate, quite distant clusters, where one includes analyses corresponding to Moravian moldavite Sp-1 and one to the lithology of sample D-17; all other data points fall into the second group, which displays quite poor correlations (Fig. 14). These results do not necessarily contradict the hypothesis that a major amount of Mn was incorporated into carbonates rather than being associated with iron in silicates. No correlation of strontium with other ions in carbonate, as proposed by Meisel et al. (1997), was found in our study. In addition, the observed general correlation of Mn and Fe does not follow the findings of Delano et al. (1988), who related the lack of an Mn vs. Fe correlation to a reduction of iron during moldavite formation. An interesting feature was found for samples D-5 and D-17 from the Cheb Basin. Both specimens display considerable chemical heterogeneity. In addition, however, we observed substantial relative enrichment in volatile elements – zinc, lead, and copper, although the latter occurs at concentrations close to the detection limit. Nevertheless,

Moldavites from the Cheb Basin

1169

Fig. 16. (a) Distribution of Eu/Eu* values for studied moldavites approaches a normal distribution; the values are close to UCC. (b) The Rb/ Cs ratio displays a non-normal distribution and departs from values normally reported for juvenile upper continental crust. UCC data from Rudnick and Gao (2003).

the contents of Zn and Pb are between about 20 and almost 15 times higher than the minimum concentrations in all other samples (Fig. 15). In addition, Zn and Pb are positively correlated with a Pearson correlation coefficient of 0.95. It should be noted that volatile elements are enriched also in three other Cheb moldavites (D-2, D-6, and D-19), which contain about twice as much Zn and Pb than other Cheb, South Bohemian or Moravian moldavites. As the process of moldavite formation is still an open question, we inspected also selected element ratios, some of which are used as petrogenetic indicators. In principle, the distribution of these diagnostic ratios follows trends

observed for individual element concentrations, i.e., there is no systematic behavior, and the distribution curves often depart from an ideal normal distribution, being substantially skewed or even displaying a bimodal shape. Among the distributions approaching a normal shape and resulting in values close to upper continental crust (UCC) are Eu/ Eu* [0.6–0.7 vs. 0.72; Fig. 16a; values for UCC from Rudnick and Gao (2003)], Sm/Nd (0.16–0.19 vs. 0.174 for UCC), and Lu/Hf (0.04–0.055 vs. 0.058 for UCC). Ratios generally close to UCC values but showing highly skewed distributions include, for example, Ba/Rb (UCC = 7.5) or Th/Sm (UCC = 2.23). Zirconium vs. hafnium ratios,

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Fig. 17. Chondrite-normalized rare earth element patterns for moldavites: (a) comparison of ranges of measured REE contents for Cheb (gray-shaded region), South Bohemian (solid black lines) and Moravian moldavites (solid gray lines); (b) Chondrite-normalized REE patterns for two different glass lithologies of the sample D-17. Average CI chondrite REE abundances from McDonough and Sun (1995).

traditionally assumed to be chondritic [Zr/Hf = 34.3 for chondrites (Mu¨nker et al., 2003)], were observed to vary between 32 and 39 for the samples from the Cheb Basin and between 30.4 and 38.8 for specimens from traditional localities, respectively. Most of the values were about 36–37, which is identical to 36.7 reported for UCC by Rudnick and Gao (2003). Such an observation is consistent with the data of David et al. (2000), who reported close to chondritic Zr/Hf ratios for most continental crust materials, except for several anomalous values in evolved granites (granitic rocks are known to occur in the Ries crater basement). Niobium vs. tantalum ratios vary between 10 and 14; these values agree with those given for loess and shales by Barth et al. (2000) and Kamber et al. (2005). In contrast to the ratios above, there are several others which depart substantially from values normally reported for juvenile upper continental crust. These include, e.g., Rb/Cs (6– 10 in studied moldavites vs. 20 for UCC, Fig. 16b), Rb/Sr (0.4–1.6 vs. 0.26 for UCC), La/Nb (3–5 vs. 2.6 for UCC), and Sr/Nd (3–7 vs. 11.9 for UCC). Chondrite-normalized REE patterns (Fig. 17a) are typical for mature Phanerozoic crust sediments with LREE considerably enriched over HREE (LaN/YbN  10–14; CeN/ YbN  7–11) and negative europium anomalies (Eu/Eu*

Fig. 18. Room temperature 57Fe Mo¨ssbauer spectra for the studied moldavites. The velocity scale is calibrated according to room temperature a-Fe. Diamonds show the measured data. The black line is the total fit, the light-gray-shaded doublet is the fit for site 1 and the dark-gray-shaded doublet is the fit for site 2. Fitted parameters are given in Table 5.

typically about 0.65–0.70). The patterns for Cheb, South Bohemian and Moravian moldavites overlap. Local intra-

Area

0.16 0.11 0.31 0.47 0.19

q

0.57 1.00 0.68 0.68 0.68

Moldavites from the Cheb Basin

1171

sample heterogeneity is demonstrated in Fig. 17b where CInormalized REE distribution patterns are given for sample D-17: two different trends are present and are clearly separated from each other by a factor of 1.2–1.6.

0.39 0.11 0.50 0.51 0.36 1.20 0.78 1.27 1.42 1.04 160 260 260 75 260

The parameters listed: CS: center shift (relative to a-Fe); QS: quadruple splitting; r: Gaussian line width; q: correlation.

0.11 0.06 0.22 0.29 0.15 0.78 0.87 0.93 0.99 0.88 0.84 0.89 0.69 0.53 0.81 0.57 0.99 0.83 0.71 0.80 0.62 0.46 0.52 0.53 0.54 1.882 1.830 1.900 1.930 2.010 0.03 0.05 0.04 0.03 0.04 1.073 1.030 1.032 1.020 1.069

q r (mm/s) QS (mm/s) r (mm/s)

D-9 D-13 D-15 J-3 SP-1

1 2 1 3 1

CS (mm/s)

r (mm/s) Site 2

CS (mm/s)

Area Site 1 Time (days) Wt (mg) Sample

Table 5 Mo¨ssbauer

57

Fe hyperfine parameters for the studied moldavites obtained from fits using the x-VBF method (Lagarec and Rancourt, 1997).

QS (mm/s)

r (mm/s)

4.5. Ferrous-to-ferric iron ratios and iron coordination Ferric–ferrous iron ratio for moldavites have has been determined by numerous authors in the past. Most of the studies are based on wet chemical analyses. The values reported, however, vary considerably. Bousˇka and Povondra (1964) analyzed 7 moldavites and determined Fe3+/Fetot ratios of 0.04–0.16. They also quoted analyses of samples from Dukovany (Moravia) by another analyst, who reported a much wider variation of Fe3+/Fetot ratios between 0.02 and 0.32. Philpotts and Pinson (1966) gave Fe3+/Fetot values between 0.07 and 0.15. Konta and Mra´z (1969) reported Fe3+/Fetot values for 13 moldavites to be between 0.01 and 0.82. Fudali et al. (1987) critically reviewed these data as well as those for other tektites and measured ferric–ferrous iron ratios from 5 randomly selected splashform Australasian tektites. They applied wet chemical analytical procedures, electron-spin-resonance and Mo¨ssbauer spectroscopic methods. They obtained reproducibly low Fe3+/Fetot values between 0.02 and 0.10 and considered values for splash-form tektites outside of these limits erroneous. More recently, Dunlap et al. (1998) and Rossano et al. (1999a) studied the ferric–ferrous iron ratios in moldavites and Australasian tektites based on Mo¨ssbauer spectroscopic data. Dunlap et al. (1998) fitted a small peak in their moldavite spectra which they attributed to Fe3+ and concluded 6% of the total iron was ferric. In contrast, Rossano et al. (1999a) found no indication of trivalent iron in their moldavite. However, they admitted that they could not exclude a Fe3+ content up to 5%, which was the noise level in their spectra. Mo¨ssbauer spectra acquired here for 3 Cheb, 1 South Bohemian, and 1 Moravian tektite are similar, with only one asymmetric doublet (Fig. 18), and resemble those collected from other tektites (Dunlap, 1997; Dunlap et al., 1998; Rossano et al., 1999a; Dunlap and Sibley, 2004), impact glasses (Dunlap and McGraw, 2007), and reduced silicate glass (see, for example, Alberto et al., 1996; McCammon, 2004). An obvious shoulder may be noted between the two main components, which indicate the presence of at least two components. We processed our spectra with the extended Voigt-based fitting (x-VBF) approach of Lagarec and Rancourt (1997) and were able to distinguish two separate distributions contributing to the spectra. The addition of a third component due to ferric iron did not result in an improvement of the fit. Actually, as results of the fitting procedure were highly model dependent, we conclude that there is no evidence for Fe3+ in any of the collected spectra, with an estimated detection limit of ca. 3% (i.e., Fe3+/Fetot = 0.00 ± 0.03). Consequently, the final fit comprised an x-VBF analytic line shape assuming a two-dimensional (2D) Gaussian distribution for Fe2+ absorption only. The variable parameters included center shift (CS), Gaussian distribution width (rCS), quadrupole splitting (QS), Gaussian distribution width

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(rQS), and correlation between the CS and QS distributions (q). The Lorentzian line width was constrained to be equal for all distributions. The observed values of the weighted mean values of center shift and quadrupole splitting vary within a narrow range of 1.00–1.01 and 1.7–1.8 mm/s, respectively. Thus, our data coincide with those given for moldavites both by Dunlap et al. (1998) and Rossano et al. (1999a). The complete summary of the fitted hyperfine parameters is given in Table 5. The two doublets resolved in the spectra provide information on probable local coordination of iron in the moldavite samples. Subordinate distribution may be interpreted unambiguously, in agreement with Dunlap (1997), Dunlap et al. (1998), Rossano et al. (1999a,b), Dunlap and Sibley (2004), and Dunlap and McGraw (2007) as a minor amount of tetrahedrally coordinated ferrous iron. However, the assignment of the coordination number to the second, dominant, distribution is equivocal. Dunlap et al. (1998) favored a traditional interpretation: an octahedral coordination. Rossano et al. (1999a,b) argued that 5-fold coordination might better explain deviations in hyperfine parameters observed for tektites from those for other reduced glasses. Giuli et al. (2002), based on the results of a Fe K-edge extended X-ray absorption fine structure (EXAFS) and high-resolution X-ray absorption near edge structure (XANES) spectroscopic study, concluded that tektites (including a moldavite) have an average coordination number close to 4.5, which they interpreted to relate to either coexisting 4- and 5-fold-coordinated or 4- and 6-fold-coordinated iron. In addition, five-fold or a transitional coordination of iron has been inferred for various minerals and glasses from interpretation of spectroscopic and diffraction data (Brown et al., 1995; Rossano et al., 1999a,b; Galoisy et al., 2001; Rossman and Taran, 2001; Wilke et al., 2001; Giuli et al., 2002; Farges et al., 2004; Jackson et al., 2005). However, our data do not follow the trend described by Rossano et al. (1999a), particularly the narrower CS distribution for the minor contribution. Instead, the CS distribution for the minor component in our spectra is 2–10 times wider than that for the dominant component. Consequently, we cannot confirm their observation, although relatively wide distributions in CS most probably result from a range of different local Fe2+ coordination environments in the samples. The broad distribution of QS values, on the other hand, may be indicative of local distortion of individual iron sites irrespective of their coordination environment. 5. DISCUSSION 5.1. Appearance The macroscopic physical properties of the Cheb moldavites studied resemble those of moldavites from the South Bohemian partial strewn field. Size and weight of the Cheb moldavites fit the overall pattern observed over the territory of the Czech Republic, i.e., the smallest samples come, in general, from the places closest to the source structure (the Ries impact crater). In contrast, larger pieces are found at more distal locations (Moravia). Such a distribution does

not follow the usual radial size trend observed among ordinary proximal and distal ejecta (Melosh, 1989, and references therein). Yet, as pointed out by Buchner et al. (2007), moldavites were not ejected and transported in a solid phase but as a vapor–melt mixture with extreme ejection velocities. Indeed, Artemieva et al. (2002) and Sto¨ffler et al. (2002) were able to numerically model not only the melt formation and ejection process during and shortly after the Ries-forming impact, but also the ballistic trajectories for molten moldavites, which reflect the actual observed size distribution over the entire strewn field. Yet, it should be noted that the size of droplets used for the model are too small considering the size of moldavites and their rate of corrosion (see Trnka and Houzar, 2002); tektites were necessarily much larger when formed, and, consequently some parameters of the numerical model may require revision, rendering the current results rather qualitative. Also interesting is a moldavite find from Besednice (Bs1, South Bohemia), which possesses all the macroscopic and microscopic features of the Muong Nong-type tektites. This piece is layered and contains relatively more compact and more porous layers; the latter display numerous bubbles and lechatelierite inclusions under the microscope. Its find in South Bohemia is consistent with the general distribution scheme of the Muong Nong-type tektites within the framework of the Australasian strewn field, i.e., these layered tektites occur closest to the source crater. It also confirms earlier finds of this type of moldavites reported by Rost (1966), Glass et al. (1990) and Sˇvardalova´ (2007). 5.2. Chemical composition Major, minor and trace element abundances suggest unequivocally that there are two different groups among the moldavites from the Cheb Basin. This result is strongly supported by cluster and factor analysis. Actually, most of the Cheb moldavites form a distinct group compared to other Central European tektites. The chemistry of Cheb moldavites is unrelated to any chemical trends observed for South Bohemian or Moravian moldavites we determined in this study. The trend is most influenced by the mutual relationships of K2O with CaO and MgO in terms of the major element composition. The distinction is also obvious for certain minor and trace elements (e.g., Co, Ni, Sr, Y, LREE’s, Hf). In addition, it was found that Muong Nong-type-like material from Besednice, besides its extreme heterogeneity, possesses the compositional characteristics of moldavites otherwise occurring in the Moravian partial strewn field. This is in accordance with Koeberl et al. (1988), who found a limited applicability of oxide-ratio plots in separating South Bohemian and Moravian moldavites. And, even more importantly, it indicates that there is a certain degree of heterogeneity within individual partial strewn fields, either due to different precursor materials or spatial mixing of melts. Our observations also demonstrate that moldavites represent highly reduced glasses with ferric iron contents not exceeding about 3% total iron, which is much less than has been determined in some previous studies. In addition,

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found. This indicates that moldavites originated in a confined area where conditions remained invariant over the time of their formation. In addition to the iron valence state, our data suggest the presence of two coordination environments of ferrous iron in moldavites. It is important to take this fact into account as the local bonding requirements around the iron (among other cations) in silicate glasses and melts helps to explain differences in their physical properties, including color, density, or viscosity. The coordination geometries of ferrous iron in synthetic anhydrous silicate glasses are controversial, with some workers favoring distorted octahedral coordination for divalent Fe and others favoring 4- and 5coordinated sites (for a detailed discussion see Jackson et al., 2005). The bond expansion at elevated temperatures results in a decrease of bond valence sums around network modifiers, in contrast to network formers whose bond valence sums do not change much with increasing temperature, because they are tightly bonded to oxygen atoms. To maintain Pauling’s second rule, reorganization of the local coordination environment is obviously required upon heating. Since other cations such as Si or Na already occur in their lowest coordination numbers of 4 and 5 or 6, respectively, it is most likely that the coordination number of ferrous iron decreases (Jackson et al., 2005). Thus we expect, in agreement with divalent iron speciation data for tonalitic and rhyolitic melts (Jackson et al., 2005), that our Mo¨ssbauer spectroscopic data are consistent with iron being predominantly 4- or 5-coordinated. 5.3. Possible source material

Fig. 19. Major element contents normalized to upper continental crust. About 20 rel.% enrichment in silica and 30 to more than 80 percent depletion in titanium, aluminum, iron and sodium relative to UCC were observed in the studied moldavites. UCC data from Rudnick and Gao (2003).

no systematic regional variation in iron oxidation state, as mentioned by Trnka and Houzar (2002) for example, was

When constraining source materials for moldavites, both chemical composition and paleogeography should be considered. Based on numerous studies, Hercynian crystalline basement and Mesozoic sediments in the Ries target area have been excluded as potential source material, and currently only the Tertiary Upper Freshwater (Obere Su¨ßwasser) Molasse (OSM) sediments are considered to have contributed substantially to moldavite melt (e.g., Bousˇka et al., 1973; Horn et al., 1985; Engelhardt et al., 1987, 2005; Meisel et al., 1997; Trnka and Houzar, 2002, and references therein). A near-surface origin of the source material is also supported by results of a study of 10Be and 36 Cl distribution in moldavite (Serefiddin et al., 2006, 2007). This has also indicated that the precursor material was only loosely consolidated. The fact that the material was indeed rather loose is inferred also from data of the Deep Impact mission (Melosh, 2006): terrestrial analogs such as porous sand or loess are particularly susceptible to melting when shock-compressed, and, consequently, would represent suitable precursor material. Statistical assessment of the major element compositional data indicates that, in addition to a silica-dominated source, two major components have contributed to the composition of the Cheb moldavites. These two components display no significant mixing ratio. Existence of these two independent constituents is inferred from the separation of the samples into two clearly defined clusters (Fig. 11), as well as two subparallel linear trends defined

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Fig. 20. Minor and trace element contents normalized to upper continental crust. Among the minor and trace elements the most obvious feature is a 3-fold enrichment in cesium. In contrast, vanadium, chromium, cobalt, nickel, copper, niobium, strontium, and tantalum are depleted. UCC data from Rudnick and Gao (2003).

Moldavites from the Cheb Basin

in the standardized score plot produced by the principal component analysis (Fig. 12). In addition, two distinct sources for the Cheb moldavites are supported by the bimodal distribution of several minor and trace elements (Fig. 16). In the first component, besides silica, carbonate material with detrital mica dominates; the second one is characterized by K-depleted alumosilicate material, possibly clay- or marl-like material, supplemented with silica. Both trends are parallel to the loading due to SiO2 (Fig. 12). It is obvious that silica either represents just a diluting component for the other two independent constituents or it was fractionally vaporized. Results for South Bohemian and Moravian samples (with only a few exceptions) differ significantly, showing instead multicomponent source materials with mutual and variable mixing. Different source materials for the Cheb, South Bohemian and Moravian moldavites are also evident from some elemental ratios. The chondrite-normalized REE patterns (Fig. 17a) are fully consistent with an evolved crustal source for moldavites. Based on La/Th and La/Yb (McLennan et al., 1980; Plank, 2005), Sm/Nd (McLennan and Hemming, 1992), and La/Th, Cr/Th, Ni/Co (Condie, 1993) ratios, it is obvious that the source material of moldavites correspond to juvenile upper continental crust. Although most of the Zr/Hf ratio values are consistent with UCC data, some differ substantially. These outliers, considering behavior of Zr in recent weathering profiles (Nesbitt and Markovics, 1997), indicate that weathering of evolved granites known to display such values (David et al., 2000) must have contributed to the sedimentary precursor of the Cheb moldavites. The upper-continental-crust-normalized contents of major elements in the moldavites (Fig. 19) show about 20 rel.% enrichment in silica. Titanium, aluminum, iron and sodium, in contrast, are depleted relative to UCC by 30 to more than 80 percent. Contents of magnesium and calcium are usually lower than in the average upper continental crust, although several Cheb moldavites reveal either UCC or even higher values (e.g., CaO in sample D13 is enriched by a factor of 1.35 relative to UCC). Minor and trace elements (Fig. 20) display complex patterns. The most obvious feature is an approximately 3-fold enrichment in cesium in all samples. Some samples are also enriched in Rb. In contrast, vanadium, chromium, cobalt, nickel, copper, niobium, strontium, and tantalum are depleted. Such a pattern is, according to Barth et al. (2000), typical for post-Archean shales, and, to some extent, also for loesses. Rare earth element patterns follow a flat distribution close to the UCC pattern in moldavites from classical localities. Cheb moldavites, however, are separated into groups: one displays a relatively flat pattern of UCC-normalized REEs at about 0.7–0.8 UCC contents; the second group shows a two-step trend with enrichment in elements between La and Gd and depletion for the remaining REEs. We compared the UCC-normalized patterns for moldavites to those for OSM sediments occurring in the Ries area (Engelhardt et al., 2005). Taking into account only major elements, the closest match, except for the potassium con-

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tent, is observed for some sands (Fig. 19), particularly those from drill cores at Demmingen and Krumbach (cf. Table 13 in Engelhardt et al., 2005). The K2O content in moldavites would require incorporation of some micaceous material of about UCC potassium concentration. Marly sands display a completely different pattern with extreme calcium enrichment, which makes them a questionable precursor for moldavites. The comparison of minor and trace element contents in moldavites with those in OSM sediments complicates the situation even further – data for any of the sediments (Engelhardt et al., 2005) do not follow the trends in moldavites (Fig. 20). It is obvious that there is no direct counterpart to moldavites among OSM sediments sampled in or around the Ries crater and mentioned in the literature. Obviously, no single source could duplicate moldavite composition satisfactorily, and mixing of several components is required to yield suitable concentrations of elements. Most probably the remnants of the original source material(s) are no longer preserved in the area of the Ries crater, as already suggested by Meisel et al. (1997), being either completely vaporized during the impact at or very close to the impact site or eroded in more distal regions. Such a possibility is also supported by the most recent paleogeographic reconstructions (Becker-Haumann, 2001; Kuhlemann and Kempf, 2002; Kuhlemann, 2007) and estimated erosion rates (Kuhlemann et al., 2006). Whatever the actual precursors were, the question remains about their spatial distribution in the target area. Also, it is not clear whether this distribution may be related to properties of the moldavites within individual strewn subfields, including the moldavite size variation with radial distance from the impact site or regional differences in color and/or chemical composition. As summarized by Ho¨rz et al. (1983), the pre-impact geography of the Ries area at the time of impact was rather complex. The target was crosscut into mesa-like ridges separated by deep valleys, and the tops of these ridges were capped by OSM sediments. The OSM materials were deposited in a period of modest tectonic activity, which resulted in a great variability in facies and lithology over small vertical and horizontal distances (Ho¨rz et al., 1983). Consequently, a lithologically varied complex of sands, clays and carbonates formed. A considerable part of the OSM sediments was derived most probably from the Upper Marine Molasse (Obere Meeresmolasse, OMM) sediments, which were eroded, reworked and then incorporated into the OSM material. The OMM sediments are excluded as a potential moldavite source material, as their extent was limited by the cliff-line located to the south, well outside of the present crater rim. In addition, roughly at the center of the crater, there was an escarpment oriented in NE-SW direction at the time of impact; to the north, there were no Tertiary sediments at all [cf. Figs. 2 and 3 in Ho¨rz et al. (1983)]. The paleogeographic reconstructions by Ho¨rz et al. (1983) limit the thickness of potential precursor sediments to not more than a few tens of meters, in agreement with beryllium-10 isotopic data (Serefiddin et al., 2006, 2007). Also, the lateral distribution of potential source materials was limited considering the topography of the region. The variation of the observed moldavite properties over the entire moldavite strewn field

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thus reflects original facies changes, lithology variation, and constrained extent of the OSM. In conclusion, the most suitable candidates for moldavite source rocks are deltaic, fluviolacustrine and lacustrine sands with variable subordinate clay and carbonate admixtures formed in shallow basins. These basins were located most probably just along the shoreline of the Molasse Basin, and they might even have been intermittently closed and separated from the main basin located to the south. In addition to these shallow basin sediments, however, an incorporation of some subaerial materials cannot be excluded. 5.4. Notes on the moldavite formation process Although there is general consensus that moldavites were formed from surfacial sediments during the Ries impact event, details of this process are still unresolved. Some authors (Delano and Lindsley, 1982; Delano et al., 1988; Meisel et al., 1997) interpreted the chemistry of moldavites by melting and incomplete mixing of several components. Others (Engelhardt et al., 1987, 2005) favored fractional condensation from the plasma produced during the impact, followed by the coalescence of tektite droplets. The energy required for source rock melting was attributed to various processes including direct shock, jetting, bow shock, etc., by different researchers – for a review see Montanari and Koeberl (2000). Transport of melt particles from the impact site has been relatively satisfactorily, though rather qualitatively (see above), described by Artemieva et al. (2002), Sto¨ffler et al. (2002), and Artemieva (2008). Our results may help to shed light on some aspects of moldavite origin when combined with published data. Heterogeneities in moldavite glass support the hypothesis of Delano and Lindsley (1982) that the individual constituents (sand, clay, carbonate) of the precursor were mixed before the impact, and that moldavites reflect the chemical and spatial characteristics of the source material(s). The different subsets in oxide-ratio plots that are well separated seem to validate the hypothesis of Delano et al. (1988) about several components involved in the formation of the moldavite melt, rather than supporting the theory of fractional condensation from the ejection cloud by Engelhardt et al. (1987, 2005). The highly variable contents of volatile elements such as Zn or Pb in samples from the Cheb Basin as well as the presence of moderately volatile Cs and Rb at elevated concentrations in all studied moldavites also makes the fractional condensation scenario rather improbable. The highly reduced character of moldavites is consistent with melting of the source material under extremely high temperatures, which produced superheated melts. Such a melt, according to Sheffer and Melosh (2005), when cooled rapidly and accelerated away from the crater, reaches the blocking temperature below which the melt cannot equilibrate with the surrounding vapor that is high in oxygen, and the melt remains reduced. Rapid cooling of the melt is substantiated by the finding of baddeleyite by Glass et al. (1990) and Sˇvardalova´ (2007) from the Mung Nongtype moldavites, and thought to have formed due to thermal decomposition of zircon. Baddeleyite is present in the

form of granular aggregates. Individual sub-micrometer particles forming these aggregates are neither dispersed nor significantly assimilated by melt. Instead, there is a halo around the aggregates showing enrichment in silica. Though highly refractory, zircon would not convert to baddeleyite if vapor had been produced and dynamically scattered. All the observations appear to be consistent with an origin of moldavites by melting of an unconsolidated sedimentary precursor consisting predominantly of sand complemented by clays and carbonates. Thermal energy to melt the precursor was generated by a detached shock wave in front of a projectile where temperatures in excess of 40,000 K were generated considering the expected speed of a projectile (Nemtchinov et al., 1994). This explains the absence or very low concentration of a meteoritic component contamination in tektite melts (Koeberl, 2007). A fast spreading thermal layer associated with the radiation emitted due to the terminal phase of the flight of the projectile then may help to transport tektites from the impact site. Once formed, melt was subsequently transported on ballistic trajectories at high altitudes, where it was then solidified as inferred from low gas pressure in bubbles (Artemieva, 2008). 6. CONCLUSIONS The physical properties studied indicate that the tektites from the Cheb Basin are similar to those from the South Bohemian strewn subfield. The chemical analyses, however, show that the vast majority of the Cheb moldavites differs from both South Bohemian and Moravian samples; the main distinguishing parameter is the different trend in correlation of potassium with calcium or magnesium. It means that the Cheb Basin represents a new separate part of the Central European tektite strewn field. The chemical data indicate an origin of the Cheb moldavites from loose juvenile, near-surface and silica-rich sedimentary materials, most probably sand-dominated sediments of the Obere Su¨ßwasser Molasse. Inter-sample heterogeneity among the Cheb moldavites points to the existence of two separate and different precursors leading to the formation of two compositionally different groups. Intra-sample inhomogeneities such as schlieren or lechatelierite particles most probably reproduce, though only roughly, the original spatial and chemical characteristics of the source material. Elevated and variable contents of highly and moderately volatile species (Zn, Pb, Cs, Rb) seem to exclude significant partial fractionation as an important moldavite-forming process. The differences in chemical composition between the Cheb moldavites and those from the classical localities as demonstrated above reflect different precursor lithologies. However it should be noted that these precursors possibly differed only due to mixing of different proportions of sand, clay, and carbonate source materials. The sample from Besednice (South Bohemian partial strewn field) is the most chemically heterogeneous moldavite among those studied, and it possesses many features usually ascribed to the Muong Nong-type tektites (Glass

Moldavites from the Cheb Basin

et al., 1990). Two similar, compositionally heterogeneous samples from the Cheb Basin show considerable enrichment in volatile elements. This is also a feature typical of layered tektites, although in the case of Cheb moldavites the macro- and microscopic appearance does not convincingly correspond to that of the Muong Nong-like tektites. The Cheb Basin, as a new partial strewn field, apparently fits into a fan-shaped area with an apical angle of approximately 60 degrees covered by moldavites (Fig. 1). Moreover, it represents the most proximal occurrence of moldavites known within the entire Central European tektite strewn field. The strewn field is located axisymmetrically along the continuation of the Steinheim–Ries line. This substantiates the hypothesis that moldavites were ejected from the Ries impact structure as a fan-shaped jet. Today, individual finds of moldavites are confined to a few regions (South Bohemia, Moravia, northern Austria, Lusatia), together with several scattered finds over the territory close to the Vltava (Moldau) River. Such a pattern, however, does not necessarily follow the original distribution of moldavite ejecta: it is not yet clear whether the moldavites were ejected as separate ‘‘jets” to individual, currently known partial strewn fields, or whether they were transported as a continuous front, parts of which were not preserved due to geological processes following moldavite deposition. ACKNOWLEDGMENTS This work was funded by the grants of the Czech Science Founˇ R) No. 205/05/2593 and Ministry of Education MSM dation (GAC 0021620855 and falls within the research plan AV0 Z30130516 of the Institute of Geology AS CR. Suggestions by Alex Deutsch, Luigi Folco and an anonymous reviewer improved the original manuscript. We thank W.U. Reimold for editorial handling. Our thanks go also to A. Langrova´ (Inst. of Geology, AS CR, Prague) for analyzing the samples by EPMA and taking the majority of SEM photographs. Detlef Krauße (BGI, University Bayreuth) provided help with some BSE images. Macrographs of the moldavites were kindly provided by R. Rotter. Gravel pit Drˇenice was made accessible by T. Zuckermann (a property owner). He also provided part of the samples for the study. We are indebted to I. Dolezˇal and M. Trnka who provided the samples from localities Slavcˇe and those in Moravia, respectively. REFERENCES Alberto H. V., Pinoto da Cunha J. L., Mysen B. O., Gil J. M. and Ayres de Campos N. (1996) Analysis of Mo¨ssbauer spectra of silicate glasses using a two-dimensional Gaussian distribution of hyperfine parameters. J. Non-Cryst. Solids 194, 48–57. Artemieva N. (2008) High-velocity impact ejecta: tektites and martian meteorites. In Catastrophic Events Caused by Cosmic Objects (eds. V. V. Adushkin and I. V. Nemchinov). Springer, Dordrecht, pp. 267–289. Artemieva N., Pierazzo E. and Sto¨ffler D. (2002) Numerical modeling of tektite origin in oblique impacts: implication to Ries–Moldavites strewn field. Bull. Czech Geol. Survey 77, 303– 311. Aziz H. A., Bo¨hme M., Rocholl A., Zwing A., Prieto J., Wijbrans J. R., Heissig K. and Bachtadse V. (2008) Integrated stratigraphy and 40Ar/39Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in eastern Bavaria (Germany). Int. J. Earth Sci. 97, 115–134.

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