Weinberg R.F.,Monash University |
Hasalova P.,Czech Geological Survey |
Hasalova P.,Academy of Sciences of the Czech Republic
Lithos | Year: 2015
Water-fluxed melting, also known as fluid- or water-present melting, is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20. years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases, in the absence of a separate aqueous phase. The presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process, from melt volumes, viscosity and ability to segregate from rock pores, to melt chemical and isotopic composition. A review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments. Active tectono-magmatic processes create conditions for the release of aqueous fluids and deformation-driven, transient high permeability channels, capable of fluxing high-temperature regions of the crust where they trigger voluminous melting. Water-fluxed melting can be either congruent in regions at the water-saturated solidus, or incongruent at suprasolidus, P-T conditions. Incongruent melting reactions can give rise to peritectic hornblende, or to nominally anhydrous minerals such as garnet, sillimanite or orthopyroxene. In this case, the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence. The relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered. Fluids tend to move upwards and down temperature. However, there are cases in which pressure gradients drive fluids up temperature, potentially fluxing suprasolidus terranes. Crustal regions at conditions equivalent to the water-saturated solidus represent a natural impediment to the up-temperature migration of aqueous fluids because they are consumed in melting reactions. In this case, continued migration into supra-solidus terranes take place through the migration of water-rich melts. Thus, melts become the transport agent of water into supra-solidus terranes and responsible for water-fluxed melting. Other processes, such as the relatively rapid fluid migration through fractures, also allow regional aqueous fluids to by-pass the water-saturated solidus fluid trap and trigger melting above solidus conditions. When aqueous fluids or hydrous melts flux rocks at supra-solidus conditions, they equilibrate with the surroundings through further melting, decreasing water activity and giving rise to undersaturated melts. It is in these conditions that hornblende or anhydrous peritectic phases are stabilized. Unlike dehydration melting, the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system. Unlike melting at the water-saturated solidus, these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies. © 2014 Elsevier B.V.
Kopackova V.,Czech Geological Survey |
Kopackova V.,Charles University
International Journal of Applied Earth Observation and Geoinformation | Year: 2014
The pH is one of the major chemical parameters affecting the results of remediation programs carried out at abandoned mines and dumps and one of the major parameters controlling heavy metal mobilization and speciation. This study is concerned with testing the feasibility of estimating surface pH on the basis of airborne hyperspectral (HS) data (HyMap). The work was carried on the Sokolov lignite mine, as it represents a site with extreme material heterogeneity and high pH gradients. First, a geochemical conceptual model of the site was defined. Pyrite, jarosite or lignite were the diagnostic minerals of very low pH (<3.0), jarosite in association with goethite indicated increased pH (3.0-6.5) and goethite alone characterized nearly neutral or higher pH (>6.5). It was found that these minerals have absorption feature parameters which are common for both forms, individual minerals as well as parts of the mixtures, while the shift to longer wavelengths of the absorption maximum centered between 0.90 and 1.00 μm is the main parameter that allows differentiation among the ferric minerals. The multi range spectral feature fitting (MRSFF) technique was employed to map the defined end-members indicating certain pH ranges in the HS image datasets. This technique was found to be sensitive enough to assess differences in the desired spectral parameters (e.g., absorption shape, depth and indirectly maximum absorption wavelength position). Furthermore, the regression model using the fit images, the results of MRSFF, as inputs was constructed (R2 = 0.61, Rv2 = 0.76) to estimate the surface pH. This study represents one of the few approaches employing image spectroscopy for quantitative pH modeling in a mining environment and the achieved results demonstrate the potential application of hyperspectral remote sensing as an efficient method for environmental monitoring. © 2013 Elsevier B.V.
Kotkova J.,Czech Geological Survey |
Kotkova J.,Masaryk University |
Harley S.L.,University of Edinburgh
Journal of Petrology | Year: 2010
In situ mineral (garnet, zircon) trace element and garnet-rock REE distribution data obtained on leucogranulites from the Bohemian Massif are consistent with an origin of these now strongly deformed rocks as migmatitic leucogranites formed through dehydration-melting of muscovite-bearing protoliths at high pressures during the Variscan orogeny. Partial melting at P-T conditions of 900-940°C and 1·6-1·8 GPa consumed mica and feldspar to produce peritectic kyanite and high-Ca (20-24 mol % grossular), high-Eu garnet along with leucogranitic melt. DREE(Grt/rock) values calculated from this garnet and its host rock are consistent with garnet-melt equilibrium at these P-T conditions. Ternary feldspar and rutile (2000-3200 ppm Zr) crystallized from the leucogranite melts in the migmatites at minimum temperatures of >880-920°C. These formed along with apatite prior to and accompanying the crystallization of garnet rims and the majority of the garnet that occurs in the leucogranulites. This garnet is typified by strong depletion in Eu and DREE(Grt/rock) values consistent with garnet-melt equilibrium only after the fractionation of apatite (<0·3 wt %) and ternary feldspar (5-15 wt %). Zircons in one leucogranulite are dominated by oscillatory-zoned grains that yield pre-Variscan U-Pb ages (495 and 433 Ma) and crystallized, from Ti-in-zircon thermometry, at 700-810°C in their original host magmas. These xenocrystic grains are potentially preserved because of the short timespan of the high P-T Variscan event at 340 Ma and the moderate amounts of leucogranitic partial melt present in the rocks, estimated as at least 30 wt % melt from Zr mass balance. The production of new zircon associated with the Variscan event in this leucogranulite is limited to weakly zoned zircon rims characterized by flat heavy REE patterns that approach REE equilibrium with garnet rims. This post-peak zircon was formed at minimum P-T conditions of 840°C and 0·8-1·0 GPa along the decompression-cooling path defined by previous work for the Bohemian Massif granulites. The garnet-whole-rock REE relationships, observation of Eu depletion between early and later garnet growth phases, and Zr-Ti thermometric estimates indicating temperatures of >840°C for this evolution cannot be explained by the alternative interpretation of the leucogranulites as reworked and recrystallized pre-Variscan low-P granitoids, but support a model in which the Bohemian leucogranulites were high-P Variscan-age migmatites containing significant amounts of melt. © The Author 2010. Published by Oxford University Press. All rights reserved.
Barnet I.,Czech Geological Survey
Environmental Earth Sciences | Year: 2012
The construction of the European Geogenic Radon Map in a proposed grid system 10 × 10 km requires the data test to derive the probability of exceeding the indoor action level 200 Bq m -3 from the geologically based data. The Czech Republic disposes both indoor and soil gas data sets to test the real probability to exceed 200 Bq m -3 from indoor radon measurements and to compare it with the probability calculated from soil gas radon concentrations. Comparison of real and calculated probability enables to delineate the areas, where under- or overestimation can be expected. The results of data processing show minor differences between processing the raw data in generalised polygons of geological units and in a grid net, when using the generalised geological characteristics of grid cells. © 2011 Springer-Verlag.
Kriz J.,Czech Geological Survey
Bulletin of Geosciences | Year: 2010
Silurian Spanila Barrande, 1881 (Nepiomorphia Kříž, 2007) of Perunica and the European peri-Gondwana contains two species, Spanila gracilis (Münster in Goldfuss, 1837) and Spanila discipulus Barrande, 1881. It represents an important taxon-range-zone in the middle Ludfordian to the earliest Pr̈ídolí cephalopod limestone facies and may be correlated with the interval from the Neocucullograptus kozlowskii Biozone to the early Monograptus parultimus Biozone. Semi-infaunal Tetinka Barrande, 1881 from the Gorstian of Perunica was most probably the ancestor of Spanila, adapted to the specific semi-infaunal or infaunal mode of life. The assumption of semi-infaunal mode of life is supported by the cyrtiid brachiopod epibionts attached by their triangular ventral interarea to the posterior part of the shell, presumably above the level of the sediment. Spanila occupied narrow spaces between the crowded current-oriented cylindrical cephalopod shells and is commonly preserved with conjoined valves, often in the living position, i.e. with the frontal face down and parallel with bedding plane.
Kriz J.,Czech Geological Survey
Bulletin of Geosciences | Year: 2010
The genus Kenzieana Liljedahl, 1989 (Nepiomorphia Kříž, 2007) from Perunica, the European peri-Gondwana and Baltica is the oldest known, very long ranging Silurian (late Wenlock to late Přídolí) genus of Spanilidae Kříž, 2007, and was most probably the ancestor of the Gorstian Algerina Kříž, 2008, and the Ludfordian Spanila Barrande, 1881. Kenzieana is represented by K. bellula (Barrande, 1881) from the Homerian (late Wenlock), and K. cardiopsis (Barrande, 1881) from the late Wenlock to the late Přídolí. K. angusta Liljedahl, 1989, and K. lata Liljedahl, 1989 from Gotland are the junior synonyms. Distinctly inflated, foreshortened shells of Kenzieana with almost flat and circular frontal face show adaptive convergence with the Silurian Slavinka plicata (Barrande, 1881), Recent Corculum Röding, 1798, Fragum Röding, 1798, and Hippopus Lamarck, 1799. Kenzieana was very shallow and slow burrower resting in the sediment on its anterior, almost subcircular or widely elliptical and flat frontal face with a few byssal threads attached to loose detritus.
Simunek Z.,Czech Geological Survey
Palaeontographica Abteilung B: Palaeophytologie | Year: 2014
Two species from the Stephanian B of the Krkonoše Piedmont Basin, Czech Republic are described. Only the adaxial cuticle of one sample has been preserved and therefore this sample was determined as Cordaites sp. A. The cuticle of the second species was very well preserved including the adaxial and abaxial cuticles. Namely the abaxial cuticle is important for specific determination. It shows wide stomatiferous and narrow non-stomatiferous bands. Stomatiferous bands are formed by up to 19 stomatal rows. Such a large number °f stomatal rows in a single stomatiferous band have not yet been observed in other species. Based on this sample, the new species Cordaites barthelii ŠIMŮNEK sp. nov. was erected. © 2014 E. Schweizerbartsche Verlagsbuchhandlung, Stuttgart, Germany.
Zitt J.,Academy of Sciences of the Czech Republic |
Vodrazka R.,Czech Geological Survey
Cretaceous Research | Year: 2013
The polychaete worm Terebella phosphatica Leriche occurs at the locality of Plaňany (Bohemian Cretaceous Basin) together with remains of the Atreta- Bdelloidina community, attached to the crystalline cobbles and boulders at the base of the Bílá Hora Formation, Whiteinella archaeocretacea Zone, the Lower Turonian. Terebella formed tubes with agglutinated phosphatic particles, mostly faecal pellets, firmly attached to the substrate. The surrounding phosphatic lag containing not only faecal pellets, but also coprolites, various indeterminate phosphatic particles and remains of phosphatized and unphosphatized macrofauna (ichthyolites, bivalves, sponges, crinoids) served as a source of phosphatic particles for the construction of the worm tubes. Formation of the phosphatic lag and the production and phosphatization of its components have been evaluated in relation to repeated phosphogenic episodes during which the phosphatic crusts covering the substrates encrusted by epifauna were formed. Three phosphogenic episodes alternated with episodes of substrate and crust colonization. The tube construction of Terebella shows size- and shape- selective use of particles both during growth and in relation to position in the tube wall. Orientation of faecal pellets normal to the tube axis was found at the bases of the tube walls. High juvenile mortality found in some areas of the substrate was probably due to stress caused by turbulent sedimentation nearby. All the phenomena described probably are part of the unique sequence of short-term events that characterizes the condensed sedimentation of the basal Lower Turonian in the Bohemian Cretaceous Basin. The tubes of the polychaete worm Terebella phosphatica described here are not only the first find of this species in the Bohemian Cretaceous Basin, but also the oldest so far known from any part of the world. © 2012 Elsevier Ltd.
Svabenicka L.,Czech Geological Survey
Geologica Carpathica | Year: 2012
Nannofossil biostratigraphy and mutual correlation was worked out for the Cenomanian-Coniacian deposits of the Bohemian Cretaceous Basin (BCB) and Outer Western Carpathians (OWC) in the territory of the Czech Republic. Similar assemblages of the BCB and from sediments deposited on the SE slopes of West European Platform, Waschbergždánice-Subsilesian Unit, OWC support the hypothesis that the two areas were connected by a sea way (nowadays the Blansko trough). The nannoflora of the Silesian Unit, OWC show more afinity to high latitudes as is documented by the presence of Marthasterites furcatus in the Lower Turonian, UC6b and UC7 Zones. Turonian and Coniacian deep-water flysch sediments of the Silesian Unit and Magura Group of Nappes provide nannofossils on rare occassions. Strongly atched nannofossils dominated by W. barnesiae from Cenomanian black shales of the BCB are comparable to those of the Silesian Unit and reflect a similar shallow nearshore sea. In the BCB, uppermost Cenomanian is marked by the last occurrence (LO) of Axopodorhabdus albianus and first occurrence (FO) of Quadrum intermedium (6 and 7 elements) and lowermost Turonian by a sudden quantitative rise in nannoflora and by the FO Eprolithus octopetalus. First Eiffellithus eximius and thus the base of the UC8 Zone was recorded in the upper part of ammonite Zone Collignoniceras woollgari in the lower Middle Turonian. Lithastrinus grillii is the stratigraphically youngest nannofossil species in this region and indicates the uppermost Coniacian. In the OWC, the Albian-Cenomanian boundary was recorded in the Silesian Unit and is marked by the LO Crucicribrum anglicum and FO Prediscosphaera cretacea and Corollithion kennedyi in the uppermost Albian. The Turonian-Coniacian boundary found both in the BCB and Waschberg-Ždánice-Subsilesian Unit, OWC is indicated by the FO Broinsonia parca expansa and by the base of the interval with common Marthasterites furcatus. In both areas, events were found closely below the FO inoceramid species Cremnoceramus waltersdorfensis. The Coniacian-Santonian boundary interval (Waschberg-Ždánice- Subsilesian and Foremagura Units, OWC) is indicated by Lithastrinus grillii occasionally accompanied by Lucianorhabdus ex gr. cayeuxii, Hexalithus sp. and Arkhangelskiella specillata.
Polechova M.,Czech Geological Survey
Bulletin of Geosciences | Year: 2013
A rich bivalve fauna from the Middle Ordovician (Šárka Formation, early and mid Darriwilian) of Bohemia shows close affinities to Middle Ordovician bivalves from Spain (Iberian Peninsula) and France (Armorican Massif). Twelve species and nine genera (one new) are described: Praenucula applanans (Barrande, 1881), Praenucula bohemica (Barrande, 1881), Praenucula dispar (Barrande, 1881), Concavodonta ponderata (Barrande, 1881), Pseudocyrtodonta ala (Barrande, 1881), Pseudocyrtodonta incola (Barrande, 1881), Tatula petula gen. et sp. nov., Redonia deshayesi Rouault, 1851, Babinka prima Barrande, 1881, Coxiconchia britannica (Rouault, 1851), and the oldest pteriomorphids in the Prague Basin Modiolopsis sp. and Cyrtodonta sp. Ctenodonta, widely used as cumulative name for all praenuculids, was not recorded in the Middle Ordovician of Bohemia. Remarks on the characters of the Protobranchia shell are discussed, the value of the orientation of the teeth to the umbo or out from the umbo for higher systematic has been overestimated in the past. Accessory muscle scars in the Protobranchia help to move with foot, not only by retraction and protraction but also by elevation; some of them hold a visceral sac. The Recent Protobranchia mostly show simpler type of taxodont teeth in comparison with the Ordovician Protobranchia. Palaeoecological aspects of all the species are shown, infaunal burrowers dominate in the lithofacies of the black shales of the Šárka Formation. The bivalve association is dominated numerically by heterodonts, subdominant are several species of protobranchs and two pteriomorphids. The palaeogeographic distribution of the Middle Ordovician bivalves is discussed. Some of the Middle Ordovician bivalves are widely distributed, they reach Baltica and also the Laurentian margins and probably had to have planktotrophic larvae. Clear preference of the heterodonts for high latitude is confirmed by the dominant heterodonts (six species) in the bivalve association of the Middle Ordovician Šárka Formation.