Research Items (22)
The possible presence of carbonatites in the Eger Rift (NW Bohemian Massif, Czech Republic) has been debated for several decades without any apparent resolution. Here, we document an almost 2 m thick dyke of a silicocarbonatite (23 wt. % SiO2, 27 wt. % CO2) in the R2 (Roztoky nad Labem) drilling at the depth of 152.9–154.8 m. Despite the fact that the silicocarbonatite is associated with alkaline intrusive complex, its content of alkalis is rather low (Na2O + K2O = 2.5 wt. %), as are REE (REE = 82.6 ppm). The stable-isotope signature (18O = 7.43 ‰, 13C = −2.46 ‰) of this rock is distinct from surrounding sedimentary rocks, while it can be compared with C–O isotope systematics of some carbonatites in the world which probably sourced carbonates from older subduction events. The Sr–Nd isotope composition (87Sr/86Sr30 ~ 0.7062; 143Nd/144Nd30 ~ 0.51205) points to an enriched reservoir without known counterparts among alkaline rocks from the Eger Rift, perhaps a lithospheric mantle modified in course of the Variscan subduction. The position of the R2 silicocarbonatite in the Sr–Nd space may indicate a continuum of enriched radiogenic isotope systematics in worldwide carbonatite occurrences.
The Altenberg–Teplice Volcanic Complex (ATVC) exposed on both sides of the German–Czech border in the Erzgebirge/Krušné hory Mts. is one of the earliest late-Variscan to post-Variscan volcanic centres in Europe. The ATVC features an early volcanosedimentary succession preserved in the Schönfeld–Altenberg Depression Complex (SADC), covered by voluminous ignimbrites and lavas of the Teplice Rhyolite (TR). Published radiometric age dating of ATVC rocks and associated mineralizations suggest a Lower Namurian (Serpukhovian) age for the SADC. The SADC (10×15 km) was subdivided into the Schönfeld-Pre-Eruptive Sediments (SPES), and the volcanosedimentary successions of the Lower Schönfeld Complex (LSC) and the Upper Schönfeld Complex (USC). The SPES (maximum thickness of 60 m) is deposited on metamorphic basement and consists of sandstones and conglomerates with variable types of metamorphic clasts; it also contains carbonaceous layers. The LSC sequence starts with widespread, fine-grained ignimbrites (maximum thickness of 153 m) of rhyolitic composition. The explosive phase of the LSC was followed by the formation of (trachy-)dacitic lava(s) and subvolcanic bodies. The USC sequence commences with coarse-grained talus deposits, consisting of metamorphic clasts, indicating a major tectonic activity. Lavas and pyroclastic rocks dominate the USC in the southern part, whereas in the Schönfeld area (northern part), lava dome explosion-related pyroclastic and sedimentary deposits, alternating with carbonaceous layers, prevail. Charcoal fragments and fine charcoal dust is present in all SADC units as layers, or in the matrix of volcanosedimentary deposits. Allochtonous anthracite seams in the USC that were subject to historic mining in the Schönfeld area consist of a bedded alternation of carbonaceous deposits with clays to siltstones. Presumably, formation of charcoal was related to explosive eruptions and/or wild fires, and redeposition by alluvial processes. The SADC volcanic rocks are classified as dacites, trachy-dacites and rhyolites, having unusually elevated concentrations of Ti and compatible elements like Cr and V. Compared to the LSC, the USC volcanics show a less alkaline affinity. The studied samples are isotopically homogeneous, with εNd325= –2.4 to –3.3 and 87Sr/86Sr325 = 0.70556–0.70626, pointing to a common source of magmas for both the LSC and the USC. The two-stage Nd model ages vary between 1.2 and 1.3 Ga, similar to coeval Saxothuringian granites from the Erzgebirge Mts. as well as volcanic rocks from the Intra-Sudetic Basin.
- Mar 2016
Peridotite xenoliths brought to the surface by basaltic lavas attest to a variety of mantle processes, including partial melting, melt percolation or refertilization. The whole rock Re–Os concentrations and Os isotopic compositions were determined for 30 xenoliths collected from 11 localities across the northern Bohemian Massif in order to evaluate the Os model ages and attempt to relate the results to major crustal tectonic events during the history. Most samples were affected by variable extent of metasomatic overprint, which is commonly paralleled by very low Os concentrations (< 1 ppb). Rhenium concentrations in the whole suite are below the primitive mantle value. A subset of samples shows evidence for Re addition from host basaltic rocks, consistent with the presence of abundant melt pockets with secondary sulphides. The 187Os/188Os ratios range from 0.1162 to 0.1330 and cannot be directly related to individual mantle domains, implying the inability of more recent tectonic events to reset the original Os isotopic systematics. The calculated mantle extraction ages (TMA) range from < 0.1 to 2.1 Ga, whereas future ages obtained for nine samples indicate metasomatic overprints. The Re depletion ages (TRD) vary between < 0.1 and ~ 1.6 Ga. However, the TRD is not well suited for direct comparison with crustal ages because it represents a minimum age limit rather than specific age estimate. Therefore, a modified model age (TRDII) was calculated assuming a non-zero Re content during the pre-metasomatic stage and using a composition of the most depleted sample in our suite. A prominent peak in the calculated TRDII ages ranges between 0.5 and 0.6 Ga which corresponds to the Cadomian orogenic cycle.
Two Neoproterozoic carbonatite suites of spatially related carbonatites and associated silicate alkaline rocks from Sevattur and Samalpatti, south India, have been investigated in terms of petrography, chemistry and radiogenic–stable isotopic compositions in order to provide further constraints on their genesis. The cumulative evidence indicates that the Sevattur suite is derived from an enriched mantle source without significant post-emplacement modifications through crustal contamination and hydrothermal overprint. The stable (C, O) isotopic compositions confirm mantle origin of Sevattur carbonatites with only a modest difference to Paleoproterozoic Hogenakal carbonatite, emplaced in the same tectonic setting. On the contrary, multiple processes have shaped the petrography, chemistry and isotopic systematics of the Samalpatti suite. These include pre-emplacement interaction with the ambient crustal materials with more pronounced signatures of such a process in silicocarbonatites. Calc-silicate marbles present in the Samalpatti area could represent a possible evolved end member due to the inability of common silicate rocks (pyroxenites, granites, diorites) to comply with radiogenic isotopic constraints. In addition, Samalpatti carbonatites show a range of C–O isotopic compositions, and δ¹³CV-PDB values between + 1.8 and + 4.1‰ found for a sub-suite of Samalpatti carbonatites belong to the highest values ever reported for magmatic carbonates. These heavy C–O isotopic signatures in Samalpatti carbonatites could be indicative of massive hydrothermal interaction with carbonated fluids. Unusual high-Cr silicocarbonatites, discovered at Samalpatti, seek their origin in the reaction of pyroxenites with enriched mantle-derived alkali-CO2-rich melts, as also evidenced by mantle-like O isotopic compositions. Field and petrographic observations as well as isotopic constraints must, however, be combined with the complex chemistry of incompatible trace elements as indicated from their non-uniform systematics in carbonatites and their individual fractions. We emphasise that, beside common carriers of REE like apatite, other phases may be important for incompatible element budgets, such as mckelveyite–(Nd) and kosmochlor, found in these carbonatites. Future targeted studies, including in-situ techniques, could help further constrain temporal and petrologic conditions of formation of Sevattur and Samalpatti carbonatite bodies.
Weakly differentiated rocks such as basaltic trachyandesites occur rather rarely in the Cenozoic České Středohoří Volcanic Complex (Central Europe, Czech Republic). We present mineralogical, petrological and geochemical data for a basaltic trachyandesite sill located at the southern margin of the České Středohoří Volcanic Complex, where several smaller hills form a quasi-continuous belt between villages of Zahořany and Chotiněves. Uniform petrography and chemical composition provide compelling evidence that all individual outcrops belong to a single large sill, probably with the exception of the westernmost occurrence at the Křemín Hill. The sill is almost 5 km long (SW-NE) and likely up to 3 km wide (NW-SE). The elongated shape of the sill and its position suggest that the basaltic trachyandesite magma ascended along the Litoměřice Fault forming the southeastern edge of the NE-SW trending Ohře (Eger) Rift. The studied rocks are basic and alkali-rich (49.5-50.3 wt. % SiO 2 , sum K 2 O + Na 2 O = 7.8-8.1 wt. %), but their silica contents (volatile-free) approach the boundary of the intermediate domain. This correlates with low concentrations of compatible trace elements such as Cr (15-23 ppm). The limited degree of differentiation is reflected by smooth chon-drite-normalized REE patterns (La N /Yb N = 18.2-19.3) with the absence of any significant Eu and/or MREE anomaly. The incompatible trace-element contents (Sr = 920-1080 ppm, Ba = 840-950 ppm, ƩREE = 280-330 ppm) typify weakly differentiated alkaline volcanic rocks within the Ohře Rift. Based on the chemical composition we suggest that these basaltic trachyandesites belong to the České Středohoří Volcanic Complex rather than to MgO-poor foidites of the Central Bohemia Volcanic Field. The intrusive age of the sill has been determined using conventional whole-rock K-Ar method at 29.12 ± 0.63 Ma (1σ). The initial Sr-Nd isotope compositions (87 Sr/ 86 Sr i = 0.7048, 143 Nd/ 144 Nd i = 0.51270), compare well with existing data for the České Středohoří trachybasalts and attest to their common origin. The single large Zahořany-Chotiněves sill partly fills the apparent gap in the differentiation trend between basanites to trachybasalts and trachyandesites to phonolites reported for the alkaline volcanism of the České Středohoří Mts.
An assemblage of ancient Egyptian metalwork from the Early Dynastic and Old Kingdom periods, currently in the Egyptian Museum of Leipzig University (Germany), has been studied using a wide range of available archaeometallurgical methods. The 3rd millennium BC Egyptian copper metallurgy is known only superficially until now. The data are interpreted in the framework of the known and reconstructed distribution networks of ancient Egyptian society. The production technology of the objects has been examined. The lead isotope analyses have made it possible to discuss the origin of the ore used for the production of Old Kingdom metalwork for the first time. A rather surprising presence in the Early Dynastic assemblage of object similar in isotopic ratios to Anatolian Early Bronze Age metalwork is discussed. © 2018 Elsevier Ltd https://authors.elsevier.com/c/1XWHG_6yUMAj23
Early efforts at remediation of contaminated soils involve overturn or removal of the uppermost soil horizons. We find that such disruption is counterproductive, as it actually increases the mobility of the heavy metals involved. In our study, we sought to replicate in a controlled manner this commonly used remediation strategy and measure Pb, Zn, Cu and As concentrations in all soil horizons—both prior to and 1 year after disruption by trenching. BCR analyses (sequential leaching) indicate that Pb is affected to the greatest degree and is most highly mobile; however, Zn and As remain insoluble, thus partially ameliorating the detrimental effect. Differences in vegetation cover (i.e. spruce vs. beech forest) have little influence on overall element mobility patterns. The Krušné hory (Ore Mts., Czech Republic) study area is one of the more heavily contaminated areas in Central Europe, and thus the results reported here are applicable to areas affected by brown-coal-burning power plants. Full text is available here http://rdcu.be/wQ86
The first Sr isotopes from Bohemian Cretaceous Basin (Czech Republic).
- Jul 2017
- Old Kingdom Art and Archaeology 7
The research of Old Kingdom copper metallurgy is hindered by several problems. The number of archaeometallurgical analytical methods available in Egypt is limited, and it is almost impossible to export samples, although only about 50 milligrams of material would suffice for reasonable results. Old Kingdom artefacts abroad are in many cases unique objects and not all of them can be subjected to methods that provide accurate results because samples are needed for this purpose. Non-destructive methods are preferred, but their results are less accurate. Additionally, a vast number of small metal artefacts from the Old Kingdom are completely corroded without any metal core preserved, which renders any analysis meaningless. The issues of more precise typological definition of Old Kingdom artefact classes and distinguishing between full-size tools and model tools have been addressed recently in the monograph “Old Kingdom Copper Tools and Model Tools” by Martin Odler. Based also on these results, two projects have recently been examining archaeometallurgical questions connected with the production of Old Kingdom copper alloy artefacts. In the Egyptian Museum of the Leipzig University, selected Old Kingdom artefacts from Giza have been sampled by drilling and sawing and the samples were submitted to a wide array of contemporary methods in the Czech Republic, examining the chemical composition (X-ray fluorescence, neutron activation analysis), ore sources (lead isotope analysis), and technology (metallography, micro-hardness testing). Another set of artefacts from Giza, deposited in the Kunsthistorisches Museum Wien, has been submitted to X-ray fluorescence to find out the chemical composition of the objects. Moreover, a previously unknown inscription has been discovered on a spouted bowl (ÄS 7441). The paper informs about the results of the analyses, answering the questions of the ore sources, chemical composition and technologies applied to produce the artefacts. We also address the question of the use of alloys in Old Kingdom Egypt anew, as it appears that arsenical copper was used more widely and in different contexts than was previously thought.
- Apr 2016
Peridotite xenoliths brought to the surface by basaltic lavas attest to a variety of mantle processes, including partial melting, melt percolation or refertilization. The whole rock Re–Os concentrations and Os isotopic compositions were determined for 30 xenoliths collected from 11 localities across the northern Bohemian Massif in order to evaluate the Os model ages and attempt to relate the results to major crustal tectonic events during the history. Most samples were affected by variable extent of metasomatic overprint, which is commonly paralleled by very low Os concentrations (b 1 ppb). Rhenium concentrations in the whole suite are below the primitive mantle value. A subset of samples shows evidence for Re addition from host basaltic rocks, consistent with the presence of abundant melt pockets with secondary sulphides. The 187 Os/ 188 Os ratios range from 0.1162 to 0.1330 and cannot be directly related to individual mantle domains, implying the inability of more recent tec-tonic events to reset the original Os isotopic systematics. The calculated mantle extraction ages (T MA) range from b 0.1 to 2.1 Ga, whereas future ages obtained for nine samples indicate metasomatic overprints. The Re depletion ages (T RD) vary between b 0.1 and ~1.6 Ga. However, the T RD is not well suited for direct comparison with crustal ages because it represents a minimum age limit rather than specific age estimate. Therefore, a modified model age (T RDII) was calculated assuming a non-zero Re content during the pre-metasomatic stage and using a composition of the most depleted sample in our suite. A prominent peak in the calculated T RDII ages ranges between 0.5 and 0.6 Ga which corresponds to the Cadomian orogenic cycle.
- Apr 2012
Keywords: Načetín, fly ash, lead, zinc, antimony, barium, soils, hazardous elements, contamination, BCR sequential extraction The release of hazardous elements from anomalous geomaterials represents risk for the environment. In our research, we focused on exogenic alteration of fly ash (FA) originating from glass-works in Svetla nad Sazavou (Czech Republic). This factory produces glass with high amounts of PbO. Fly ash from electrostatic filter contains elevated concentrations of Pb (800 ppm), Zn (13 500 ppm), Sb (31 500 ppm) and Ba (67 000 ppm). In present history, small amount of FA may be emitted from factory and can settle in the surrounding environment (soil). To assess possible risk for the environment we placed samples (0.5 g) of the FA in small nylon bags into soils with different vegetation cover (spruce, beech and unforested area) situated near village Načetín in the Krušné hory Mts. (Ore Mts.), northwest Czech Republic. This locality was selected as a representative example of contaminated place; it neighbours industrial cities and thermal power plants and this area was severally polluted in the past (several decades till early 1990s) mainly by sulphur compounds. The individual sites have the same geological background, climatic conditions and also the same pollution input levels. The distances between sites are about 500 meters. Bags with samples of the FA was placed into individual soil horizons (litter (A0), A, B and C horizons for spruce; litter (A0), A, B and C horizons for beech and A, B and C horizons for unforested area). The pH of all horizons did not exceed value 4.6 and the lowest pH values were observed in upper horizons. Samples of the FA were exposed in soils for a period of one year (October 2010 - October 2011), and then were removed together with samples of soils, which immediately surrounded the bags with the FA. Concentrations of studied elements in the FA and concentrations of these elements in the soil samples (initial and after exposition) were determined by inductively coupled plasma mass spectrometry (ICP-MS), after a total decomposition in a mixture of HF and HClO4. The speciation of studied elements was determined by BCR sequential extraction procedure. We determined concentrations of elements bounded in extractable, reducible, oxidizable and residual fraction. We observed changes in concentrations of monitored elements in several forms in all monitored sites and in individual horizons and also changes in total concentrations of these elements throughout the sites and horizons.