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Various marbles from historic quarries of the Czech Republic were examined by means of cathodoluminescence (CL) spectroscopy (quantitative data) to determine the possible inclusion of the method in marble provenance studies. The methodology used was based on a combination of electron microprobe analysis (Ca, Mg, Fe and Mn composition) and CL spectroscopy (intensity) of calcite and dolomite grains of the marbles studied. Several statistical techniques were applied to the CL-spectra to find the most effective way of characterization of the CL-spectra for provenance discrimination. The combination of Mg-admixture of calcite and position of the maximum (i.e., centre) of a single Gaussian curve was revealed to be the most discriminative dependence of the marbles studied. [ABSTRACT FROM AUTHOR]

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Frequency-dependent magnetic susceptibility, its anisotropy (AMS), its temperature variation, natural remanent magnetization and time-dependent isothermal remanent magnetization as well as Mössbauer spectroscopy of a small collection of Celtic and Mediaeval graphitic pottery from Southern Bohemia were investigated. The mineral composition of the pottery is dominated by fragments of quartz, accompanied mainly by various silicates from granitoids and paragneisses, or by calcite, within the plastic component being probably illite but also graphite. No ferrimagnetic minerals were found in optical microscope, among Fe-oxides only limonite was observed, even though the bulk susceptibility of the pottery varies in the orders of 10 to 10 [SI]. This may indicate presence of ferromagnetic particles in the ultrafine (superparamagnetic, SP) state, which is confirmed by frequency-dependent susceptibility ranging from 3% to almost 16%. The low temperature susceptibility vs. temperature curves are only moderately sloped, showing the Verwey transition only in one case. The high temperature curves mostly show presence of two magnetic phases, maghemite and magnetite. Cooling curves show distinctly lower susceptibilities than the heating curves indicating instability of the assemblage of ferrimagnetic minerals, particularly in temperatures slightly under 700 °C. Mössbauer spectroscopy confirmed the results of the frequency-dependent susceptibility, showing the increase of ferrimagnetic sextets in the spectra measured at 4.2K, likely indicating maghemite as the distinct ferrimagnetic phase. The frequency-dependent AMS indicates preferred orientation of SP1,16 particles, coaxiality between SP grain AMS and whole specimen AMS indicate that all grains, ultrafine and coarser ones, were oriented by the same process, i.e. copying the pottery structure created during wheel-turning. [ABSTRACT FROM AUTHOR]

We present a numerical model of the main phase (370-335 Ma) of the Variscan orogeny in the central part of the Bohemian Massif. The crustal deformation in our model is driven by radiogenic heating in the felsic lower crust, the lateral contraction of the Moldanubian domain due to convergence with the Saxothuringian plate (in the early stage of orogeny), and the indentation of the Brunovistulian basement into the weakened orogenic root (in the late stage). Our model explains the main geological events inferred from the geological record in the Moldanubian domain: formation of the orogenic plateau and onset of sedimentation at about 345 Ma, rapid exhumation of the orogenic lower crust at about 340 Ma and subsurface flow of crustal material (∼ 335 Ma and later). The results of our modeling suggest that delamination of the lithosphere, often invoked to explain the high temperature metamorphism in the orogenic lower crust of the Bohemian Massif, is not the only physical mechanism which can transfer a sufficient amount of heat to the crust to trigger its overturn. [ABSTRACT FROM AUTHOR]

The Štěnovice and Čistá granodiorite-tonalite plutons are small (~27 and ~38 km, respectively) intrusions that are largely discordant to regional ductile structures in the center of the upper-crustal Teplá-Barrandian unit, Bohemian Massif. Their whole-rock and trace-element compositions are consistent with medium-K calc-alkaline magma, generated above a subducted slab in a continental margin arc setting. The U-Pb zircon age of the Štěnovice pluton, newly determined at 375 ± 2 Ma using the laser ablation ICP-MS technique, is within the error of the previously published Pb-Pb age of 373 ± 1 Ma for the Čistá pluton. The two plutons also share other characteristics that are typical of concentrically expanded plutons (CEPs), such as elliptical cross-section in plan view, steep contacts, inferred downward-narrowing conical shape, faint normal zoning, and margin-parallel magmatic foliation decoupled from the regional host-rock structures. We interpret the Štěnovice and Čistá plutons as representing the initial Late Devonian stage of much more voluminous early Carboniferous arc-related plutonism (represented most typically by the Central Bohemian Plutonic Complex) in the upper crust of the central Bohemian Massif. These two plutons are important tectonic elements in that they indicate an overall shift of the arc-related plutonic activity from the ~NW to the ~SE, accompanied with a general compositional trend of the magmas from medium-K calc-alkaline to shoshonitic/ultrapotassic. Such a pattern is compatible with SE-directed subduction of the Saxothuringian Ocean beneath the Teplá-Barrandian overriding plate as a cause of arc-related magmatism in this part of the Bohemian Massif. [ABSTRACT FROM AUTHOR]

Exsolution lamellae of garnet in clinopyroxene and orthopyroxene porphyroclasts from garnet pyroxenites in the Moldanubian zone were studied to elucidate the pressure–temperature conditions of the exsolution process and to reconstruct the burial and exhumation path of ultramafic rocks in the Variscan orogen. The porphyroclasts occur in a fine-grained matrix with metamorphic fabrics, which consists of clinopyroxene and small amounts of garnet, orthopyroxene and amphibole. The clinopyroxene porphyroclasts contain garnet + orthopyroxene lamellae as well as ilmenite rods that have orientation parallel to (100) planes of the porphyroclasts. Orthopyroxene porphyroclasts host garnet and clinopyroxene lamellae, which show the same lattice preferred orientation. In both cases, lamellar orthopyroxene, clinopyroxene and garnet were partially replaced by secondary amphibole. Composition of exsolution phases and that of host pyroxene were reintegrated according to measured modal proportions and demonstrate that the primary pyroxene was enriched in Al and contained 8–11 mol.% Tschermak components. Conventional thermobarometry and thermodynamic modelling on the reintegrated pyroxene indicate that primary clinopyroxene and orthopyroxene megacrysts crystallized at 1300–1400 °C and 2.2–2.5 GPa. Unmixing and exsolution of garnet and a second pyroxene phase occurred in response to cooling and pressure increase before the peak pressure of 4.5–5.0 GPa was reached at ∼1100 °C. This scenario is consistent with a burial of hot upper-mantle ultramafics into a cold subcratonic environment and subsequent exhumation through 900 °C and 2.2–3.3 GPa, when the pyroxenites would have partially recrystallized during tectonic incorporation into eclogites and felsic granulites. [ABSTRACT FROM AUTHOR]

Strain patterns within mantle rocks and surrounding coarse-grained felsic granulites from the Kutná Hora Crystalline Complex in the Variscan Bohemian Massif have been studied in order to assess their strain coupling. The studied rock association occurs within low-strain domains surrounded by fine-grained granulite and migmatite. The Doubrava peridotite contains closely spaced and steeply dipping layers of garnet clinopyroxenite, which are parallel to the NE–SW-striking, high-temperature foliation in nearby granulites, while the Úhrov peridotite lacks such layering. The Spačice eclogite is not associated with peridotite and shows upright folds of alternating coarse- and fine-grained varieties bearing NE–SW-striking axial planes. Electron back-scattered diffraction measurements revealed full strain coupling between clinopyroxenites and coarse-grained granulites in the S1 fabric that is superposed on the S0 fabric preserved in peridotites. The B-type olivine lattice preferred orientation (LPO) characterizes the S0 fabric in peridotites and its reworking is strongly controlled by the presence of macroscopic clinopyroxenite layering. The S1 in clinopyroxenites and coarse-grained granulites is associated with the LS-type clinopyroxene LPO and prism < c> slip in quartz respectively. While the S1 fabric in these rock types is accompanied invariably by a sub-vertical stretching lineation, the S1 fabric developed in reworked Úhrov peridotite is associated with strongly planar axial (010) type of olivine LPO. The peridotites with the S0 fabric are interpreted to be relicts of a fore-arc mantle wedge hydrated to a various extent above the Saxothuringian subduction zone. The prograde metamorphism recorded in peridotites and eclogites occurred presumably during mantle wedge flow and was reaching UHP conditions. Strain coupling in the S1 fabric between clinopyroxenites and granulites at Doubrava and upright folding of eclogites at Spačice document a link between tectonic and magmatic processes during orogenic thickening, coeval with intrusions of the arc-related calcalkaline suites of the Central Bohemian Plutonic Complex ( c. 360–345 Ma). Juxtaposition of peridotites and granulites could be explained by a rheological heterogeneity connected to the development of clinopyroxenite layering in the upper mantle and a previously published model of a lithospheric-scale transpressional arc system. It invokes vertical shearing along NE–SW trending, sub-vertical foliations in the upper mantle that could have led to an emplacement of mantle bodies into the granulitized, orogenic root in the sub-arc region. Clearly, such a transpressional arc system could represent an important pathway for an emplacement of deep-seated rocks in the orogenic lower crust. [ABSTRACT FROM AUTHOR]

Abstract  We examined the shape of the Late Variscan Karlovy Vary granite massif located south of the Ohre/Eger graben in Northern Bohemia by reinterpretation of existing gravity data on two perpendicular profiles. The granite body of about 360 km2 total outcrop size has the elongation ratio 0.35 with the major axis trending NE-SW. The SW part of the body was crossed in the nineties by the seismic profile 9HR which localized the bottom of granites in a depth of about 10 km. We used this value as a reference datum in our gravity profiles. We positioned one of our profiles along the seismic profile 9HR and the other one perpendicularly, i.e. parallel with the elongation of the outcrop surface. We interpret the shape of the main granite body in the vicinity of Karlovy Vary as a continuous desk whose floor is horizontal (or subhorizontal) and varies along its whole extension about a depth of 10 km. This thickness is approximately identical with that of the Saxothuringian nappes imaged by seismic reflection. The near surface upper contact of the granite body is mildly inclined, and outward dipping. It changes to steep sides or inward inclined contacts in deeper levels. The Lesný-Lysina (Kynžvart) massif is a separate granite body about 324 km thick, not continuously connected with the main Karlovy Vary massif. The gravity curve suggests that granites often enclose in their endocontact large blocks of country metasediments or metabasites the existence of which is partly evidenced by their outcrops outside the line of the profile. The granite body is found density-homogenous. Minor density differences between granite varieties are caused mainly by more intense hydrothermal alterations in younger suite granites. We interpret vertical conduits for the ascent of granitic magmas to be parallel to the Jáchymov-Gera and Ohře (Eger) lineaments or the Mariánské Lázně fault zone as indicated by the elongation of some outcrops. However, they are not clearly imaged from the gravity data. The effect of the depression of the Sokolov basin along the faults parallel with the Ohře (Eger) lineament is shallow and it is not indicated by any change in the floor depth of the granite body. Comparison of the seismicity distribution suggests that the hypocenters occur mostly outside of the granite bodies or near their contact with the country rock. [ABSTRACT FROM AUTHOR]

Lenses and pods of mafic rocks from the Monotonous Unit near Svetlik are characterized by eclogite facies mineral assemblages; however some inclusion patterns (oriented quartz rods in clinopyroxene and cuboids of disordered graphite in garnet) that are usually known from ultra-high pressure rocks were also observed in one sample. Conventional thermobarometry yielded maximum P– T conditions of 2.0–2.5 GPa and 750 °C. Decompression and heating at amphibolite and granulite facies conditions resulted in the formation of at least five distinct types of symplectites. These include symplectitic intergrowth of ilmenite and clinopyroxene after titanite, described here for the first time from the Moldanubian Zone. In addition, symplectites of plagioclase and biotite with accessory amounts of spinel after tabular pseudomorphs (after phengite?) are also reported here. Mass balance relations indicate that symplectites of diopside + plagioclase after omphacite and plagioclase + spinel (sapphirine) after kyanite + garnet, formed by nearly isochemical reactions. All other symplectite-forming reactions were allochemical and were accelerated by the presence of fluid in the primary phases. Preserved zoning pattern in garnet with high compositional gradient in some samples suggests that the rocks were affected briefly by granulite facies overprint. [ABSTRACT FROM AUTHOR]

The exhumation of eclogite facies granulites (Omp–Plg–Grt–Qtz–Rt) in the Rychleby Mts, eastern Czech Republic, was a localised process initiated by buckling of crustal layers in a thickened orogenic root. Folding and post-buckle flattening was followed by the main stage of exhumation that is characterized by vertical ductile extrusion. This process is documented by structural data, and the vertical ascent of rocks from a depth of c. 70 to c. 35 km is documented by metamorphic petrology. SHRIMP 206Pb/238U and 207Pb/206Pb evaporation zircon ages of 342 ± 5 and 341.4 ± 0.7 Ma date peak metamorphic conditions. The next stage of exhumation was associated with sideways flat thrusting associated with lateral viscous spreading of granulites and surrounding rocks over indenting adjacent continental crust at a depth of c. 35–30 km. This stage was associated with syntectonic intrusion of a granodiorite sill at 345–339 Ma, emplaced at a crustal depth of c. 25 km. The time required for cooling of the sill as well as for heating of the country rocks brackets this event to a maximum of 250 000 years. Therefore, similar ages of crystallization for the granodiorite magma and the peak of eclogite facies metamorphism of the granulite suggest a very short period of exhumation, limited by the analytical errors of the dating methods. Our calculations suggest that the initial exhumation rate during vertical extrusion was 3–15 mm yr−1, followed by an exhumation rate of 24–40 mm yr−1 during further uplift along a magma-lubricated shear zone. The extrusion stage of exhumation was associated with a high cooling rate, which decreased during the stage of lateral spreading. [ABSTRACT FROM AUTHOR]

Significant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poličany, Kutná Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry of more than twenty silver minerals are studied here. Selenium mineralization is evidenced by a) the occurrence of selenium minerals, and b) significantly increased selenium contents in sulfosalts. Identified selenium minerals include aguilarite and selenides naumannite and clausthalite. The previously unknown sulfosalts from Kutná Hora are identified: Ag-excess fizélyite, fizélyite, andorite IV, andorite VI, unnamed Ag-poor Ag-Pb-Sb sulfosalts, semseyite, stephanite, polybasite, unnamed Ag-Cu-S mineral phases and uytenbogaardtite. Among the newly identified sulfides is argyrodite; germanium is a new chemical element in geochemistry of Kutná Hora. Three types of ore were recognized in the vein assemblage: the Pb-rich black ore (i) in quartz; the Ag-rich red ore (ii) in kutnohorite-quartz gangue; and the Ag-rich ore (iii) in milky quartz without sulfides. The general succession scheme runs for the Pb-rich black ore (i) as follows: galena – boulangerite (– jamesonite) – owyheeite – fizélyite – Ag-exces fizélyite – andorite IV – andorite VI – freieslebenite – diaphorite – miargyrite – freibergite. For the Ag-rich red ore (ii) and ore (iii) the most prominent pattern is: galena – diaphorite – freibergite – miargyrite – pyragyrite – stephanite – polybasite – acanthite. The parallel succession scheme progresses from Se-poor to Se-rich phases, i.e., galena – members of galena – clausthalite solid solution – clausthalite; miargyrite – Se-rich miargyrite; acanthite – aguilarite – naumannite. A likely source of selenium is in the serpentinized ultrabasic bodies, known in the area of "silver" lodes in the South of the ore district, which may enable to pre-concentrate selenium, released into hydrothermal fluids during tectonic events. The origin of the studied ore mineralization is primarily bound to the youngest stage of mineralization of the whole ore district, corresponding to the Ag-Sb sequence of the 'eb' ore type of the Freiberg ore district in Saxony (Germany) and shows mineralogical and geochemical similarities to low-sulfidation epithermal-style Ag-Au mineralization. [ABSTRACT FROM AUTHOR]

A comprehensive anatomical and mineralogical study of fossil wood fragments from fields in the vicinity of Bečov and Břvany villages (NW Bohemia, Czech Republic) indicates that Taxodioxylon gypsaceum (Cupressaceae s.l.) predominates, but also identifies another coniferous wood: Pinuxylon parryoides (Pinaceae) and three angiosperms Quercoxylon böckhianum , Castanoxylon bavaricum and Lithocarpoxylon sp. (all Fagaceae). This paper therefore presents the first occurrence of Pinaceae and Fagaceae fossil wood in the volcanic rocks of the České Středohoří Mts. as well as its youngest palaeobotanical record in general, late Oligocene in age (26.56 ± 0.38 Ma). The samples were buried by alkaline pyroclastic deposits and were mineralized by carbonates. Two distinct depositional processes burying the fossil woods were identified. Closer to the vent, the woods occur in a near-vent pyroclastic fall deposits of the former pyroclastic cone, whereas more distant sites consist of pyroclastic flow deposits. Carbonate mineralization mostly consists of dolomite, but subordinate amounts of magnesite (likely the first time this is documented in fossil wood) as well as calcite and siderite are present. Only one sample collected in the same area, bearing clear signs of riverbed transport (Lithocarpoxylon sp.), was perfectly silicified, but its origin remains unclear. • Consideration of individual and interspecific variability in fossil wood anatomy. • Whole-plant concept and its application when defining new fossil plant taxa. • Unique mineralization of fossil wood with magnesite. [ABSTRACT FROM AUTHOR]

Exsolution lamellae of baryte, Fe sulfides, Cu sulfides and Fe oxides were observed in apatite enclosed in garnet and omphacite and their intergranular spaces in ultrahigh-pressure eclogite in the Moldanubian Zone, Czech Republic. Micro-textural relations and compositional mapping of the apatite indicates a close relationship between the density of the exsolution lamellae and compositional domains that are rich in sulfur and iron. No relation between compositional domains and fluorine or chlorine content or any evidence of apatite metasomatisation was observed. On the basis of cathodoluminescence images, the compositional domains reflect sector zoning in apatite crystals by preferential uptake of elements due to differences in surface charge and morphology on the growth plane. It is concluded that the lamellae are products of exsolution in a closed system resulting from temperature decrease during metamorphism. [ABSTRACT FROM AUTHOR]

The mineralogical composition of mining wastes and contaminated soils is the key factor that controls the retention and release of pollutants. Herein, we used bulk analyses, selective extractions, X-ray diffraction, electron microprobe, and Raman microspectrometry to determine the distribution and speciation of As as a function of depth in four slightly acidic to near-neutral soil and mining waste profiles at the Smolotely-Líšnice historical Au district (Czech Republic). The soils there, which have developed from long-term weathering, exhibit As levels as high as 1.87 wt% in the richest area; the 80–90 year old mining waste contains up to 0.87 wt% As. In the soils and mining waste, the primary As ore (arsenopyrite) has almost completely oxidized to secondary As minerals such as arseniosiderite, bariopharmacosiderite, yukonite, and Fe (hydr)oxides (ferrihydrite, goethite, and hematite), with variable As 2 O 5 and CaO concentrations (up to 27.5 and 3.8 wt%, respectively). Arsenic distribution and speciation were found to vary with depth and soil type. Whereas the presence of multiple As-hosting phases that occurred in the mining waste and cambisol developed over a granodiorite, bariopharmacosiderite was absent in the cambisol overlying gabbrodiorite. Poorly-crystalline phases such as yukonite and As-bearing ferrihydrite were not detected in the gleysol. These differences in the secondary As mineralogy were attributed to the different redox conditions and variations in the prevailing chemical systems in the saprolites/soils. The variable solubility of the secondary As-bearing phases influences the mobility of As in shallow soils and near-surface mining wastes. [ABSTRACT FROM AUTHOR]

Garnet and other rock-forming minerals from A-type granite dikes in the Pre-Variscan Brno Batholith were analyzed to determine relative contributions of individual minerals to whole-rock Y and REE budget and to assess incorporation mechanisms of these elements in garnet. Minor to accessory garnet (<2 vol%) is the essential reservoir for Y+REE in the Hlína granite accounting ~84% Y and 61% REE of the total whole-rock budget. Zircon is another important carrier of REE with ~13% Y and ~11% REE. At least ~21% REE and 1% Y were probably hosted by Th- and U-rich monazite that has been completely altered to a mixture of secondary REE-bearing phases. The contribution of major rockforming minerals (quartz and feldspars) is low (~1% Y; 10% LREE; ~1% HREE) excluding Eu, which is hosted predominantly by feldspars (~90%). Minor to accessory muscovite and magnetite incorporate ~1% Y and ~2% REE of the whole-rock budget. Magmatic garnet Sps41-46Alm28-44And0-13 Grs6-12Prp0-1 is Y- and HREE-rich (up 1.54 wt% Y; up ~1 wt% ΣREE), and the Y+REE enter the garnet structure via the menzerite-(Y) substitution. The Y and REE show complex zoning patterns and represent sensitive indicator of garnet evolution, in contrast to a homogeneous distribution of major divalent cations. General outward decrease of Y+REE is a common feature due to the strong partitioning of Y+HREE in the garnet relative to the other phases. REE underwent significant fractionation during growth of early garnet I; the YbN/NdN ratio generally decreases from the core to rim of garnet I. Higher Mn and Al, lower Ca, and Y+REE contents, as well as higher YbN/NdN ratio and more negative Eu anomaly in garnet II overgrowths indicate its crystallization from a more evolved melt. Application of zircon saturation geothermometry provides upper temperature limit of 734 ± 14 °C for the closed-system crystallization. Mineral equilibria reveal that crystallization started at QFM + 1.2, and preferential sequestration of Fe3+ into garnet and magnetite was responsible for progressively reducing conditions. Equilibrium between magnetite, garnet, quartz, and plagioclase, representing the final crystallization stage of the granitic magma, occurred at 658-663 °C and QFM 0 to + 0.8, hence at undercooling of ~75 °C. [ABSTRACT FROM AUTHOR]

Chitinozoans are most commonly known to occur as isolated vesicles, and less commonly (but still regularly) in chains i.e. linear catenary structures. Chitinozoan clusters have been little studied, but are critical to the question of the biological affinity of chitinozoans. Bedding-plane assemblages and acid-digestion residues from Ordovician rocks of the Welsh Basin (Llanfawr, UK) and the Prague Basin (Beroun, Czech Republic) have yielded exceptionally preserved chitinozoan clusters of the family Conochitinidae arranged as parallel vesicles, with apertures either facing in the same direction or in opposite directions. Three genera (Belonechitina , Eremochitina ?, and Conochitina) occur in the clusters, with each cluster being monospecific. This remarkable cluster arrangement is herein termed the P-cluster, in new terminology. Figured clusters available in the literature were analysed, and P-clusters are confirmed to occur in all three chitinozoan families. Modelling simulations of the relative abundances of different cluster morphologies suggest that P-clusters originated from a hypothetical, large cluster, functionally comparable with the already well-known Desmochitina clusters and interpreted as an egg mass. Our findings support the interpretation of all chitinozoans as metazoan eggs. • Ordovician chitinozoan clusters discovered in Wales and the Czech Republic. • Cocoon-like clusters described for the first time outside the family Desmochitinidae. • New classification of chitinozoan clusters proposed. • Cluster morphology supports metazoan egg interpretation. • Chitinozoophorans exhibited a diversity of egg-laying strategies. [ABSTRACT FROM AUTHOR]

Blueschist facies rocks, exposed within consolidated continental blocks, provide some of the best evidence for the existence of previous suture(s). They usually occur as lenses or layers embedded within greenschist or amphibolite facies rocks and indicate reequilibration at medium- to low-pressure conditions. In the Bohemian Massif, a few occurrences of blueschists have been reported, and here, new evidence of high-pressure (HP) metamorphism in various lithologies is presented that suggests a larger extent of blueschist facies rocks along the northern border of this Massif. An earlier blueschist facies metamorphism is documented by inclusions of glaucophane in garnet, epidote and titanite from metabasites along with zoned white mica having a phengitic core and a muscovite rim in metapelites and orthogneisses. The estimated P-T conditions, obtained using pseudosections and mineral isopleths, correspond to blueschist and low-temperature eclogite facies conditions (1.1-2.0 GPa at 350-550 °C). Together with medium-temperature eclogites from different units in the Bohemian Massif they indicate a geothermal gradient of 8-10 °C km−1, which is typical for cool subduction. Radiometric dating on phengite from metapelites confirms an early Palaeozoic cooling age of c. 360 Ma for this HP metamorphic event. The presence of blueschist facies rocks, their P-T relations and age constraint together with those from eclogite facies rocks allows us to locate the Variscan suture, which straddles the SE margin of Saxothuringian Zone from Erzgebirge to Sudetes, and its possible continuation to the Moldanubian Zone, where eclogite facies and UHPM rocks are abundant. [ABSTRACT FROM AUTHOR]

The Karlovy Vary Massif (KVM) in northern Bohemia is a composite granite body built up of Late Variscan biotite, two-mica and lithium mica granites. We summarize the available whole-rock geochemical and petrological data and correlate them with similar information from three boreholes in the northern and southwestern parts of the Massif. The aim of the study was to determine whether various types of granites differ in their physical and chemical properties, and whether any differences in physical characteristics affect the accuracy of geophysical interpretation. In accord with the earlier studies, we distinguish two geochemically and petrophysically contrasting granite suites - the Older Intrusive Complex (OIC) and Younger Intrusive Complex (YIC). The geochemical data show that the OIC and YIC granites differ significantly in the content of most major-element oxides (like SiO2, TiO2, FeO, Fe203tot, MgO and CaO). As to physical parameters, the granites differ markedly in magnetic susceptibilities and in the contents of radioactive elements (U and Th). From gravity and magnetic data we compiled a 22 km long geophysical profile, which crosses two of the three studied boreholes. For the construction of geological model along this profile, we used the data on the petrophysical properties measured on samples from the boreholes. Densities of the individual granite types are very similar to each other and thus the distinction of the OIC and YIC granites based on gravity data is not possible. Magnetic susceptibility differs markedly for the OIC and YIC granites in the drill logs, but absolute values of magnetic susceptibilities are very low. Modelling showed that neither gravimetry nor magnetometry are suitable methods for distinguishing between the different types of granites. On the other hand, it proved that the spatial distribution of individual granite intrusions does not affect the overall interpretation of the shape, size and depth of the whole granite body. [ABSTRACT FROM AUTHOR]

Eclogite, felsic orthogneiss and garnet-staurolite metapelite occur in a 5 km long profile in the area of Międzygórze in the Orlica-Śnieżnik dome (Bohemian Massif). Petrographic observations and mineral equilibria modelling, in the context of detailed structural work, are used to document the close juxtaposition of high-pressure and medium-pressure rocks. The structural succession in all lithologies shows an early shallow-dipping fabric, S1, that is folded by upright folds and overprinted by a heterogeneously developed subvertical foliation, S2. Late recumbent folds associated with a weak shallow-dipping axial-plane cleavage, S3, occur locally. The S1 fabric in the eclogite is defined by alternation of garnet-rich (grs = 22-29 mol.%) and omphacite-rich (jd = 33-36 mol.%) layers with oriented muscovite (Si = 3.26-3.31 p.f.u.) and accessory kyanite, zoisite, rutile and quartz, indicating conditions of ∼19-22 kbar and ∼700-750 °C. The assemblage in the retrograde S2 fabric is formed by amphibole, plagioclase, biotite and relict rutile surrounded by ilmenite and sphene that is compatible with decompression and cooling from ∼9 kbar and ∼730 °C to 5-6 kbar and 600-650 °C. The S3 fabric contains in addition domains with albite, chlorite, K-feldspar and magnetite indicating cooling to greenschist facies conditions. The metapelites are composed of garnet, staurolite, muscovite, biotite, quartz, ilmenite and chlorite. Chemical zoning of garnet cores that contain straight ilmenite and staurolite inclusion trails oriented perpendicular to the external S2 fabric indicates prograde growth, from ∼5 kbar and ∼520 °C to ∼7 kbar and ∼610 °C, during the formation of the S1 fabric. Inclusion trails parallel with the S2 fabric at garnet and staurolite rims are interpreted to be a continuation of the prograde path to ∼7.5 and ∼630 °C in the S2 fabric. Matrix chlorite parallel to the S2 foliation indicates that the subvertical fabric was still active below 550 °C. The axial planar S2 fabrics developed during upright folding are associated with retrogression of the eclogite under amphibolite facies conditions, and with prograde evolution in the metapelites, associated with their juxtaposition. The shared part of the eclogite and metapelite P- T paths during the development of the subvertical fabric reflects their exhumation together. [ABSTRACT FROM AUTHOR]

The calc-alkaline Miřetín Pluton (newly dated at 346 Ma ± 5 Ma; an U-Pb age obtained by laser-ablation ICP MS method on zircons) is a NNE-SSW elongated intrusive body emplaced into the upper- to mid- crustal rocks of the Polička Unit (eastern Teplá-Barrandian Zone; Bohemian Massif). Its composition reveals similarities to other calc-alkaline granitoids, which are mostly interpreted as products of magma mixing between the basic magmas derived from mantle wedge above a subduction zone with crustally-derived acid melts. The conditions of magma crystallization estimated at 653-681 °C and 0.29-0.43 GPa roughly correspond to peak metamorphic evolution of the host volcano-sedimentary rocks of the northwestern part of the Polička and Hlinsko units. The Miřetín Pluton was emplaced into a NNE-SSW oriented transpressional domain, well recognized on a regional scale along the eastern margin of the Teplá-Barrandian Zone. During, or shortly after the magma emplacement, the Miřetín Pluton was affected by pervasive submagmatic to high-T solid-state deformation, reflecting an additional strain increment of regional transpression in a narrow zone of thermal softening. Sharply superimposed low-T solid-state fabric preserved along the western part of the Pluton was connected with normal shearing between the Polička Unit at the bottom and the overlying Hlinsko Unit after 335 Ma. [ABSTRACT FROM AUTHOR]

A detailed airborne magnetic and gamma-ray spectrometric as well as ground gravity survey in the south-western part of the Moldanubian Zone (Bohemian Massif) provided detailed geophysical characteristics of the principal geological units and large-scale tectonic features. The Knížecí Stolec durbachitic pluton with high contents of natural radioactive elements (Th, U and K) represents a body with no magnetically anomalous response but a pronounced positive gravity anomaly. The Křišt'anov granulite massif, which is a host rock of the Knížec&iacute Stolec pluton, exhibits low concentrations of Th and U, high abundances of K, slight magnetic and a negative gravity anomalies. The Plechý, composite pluton is characterized by strikingly low gravity and an extremely monotonous magnetic field. One of its petrographic varieties (the Tristolicnik granite) is enriched in natural radioactive elements, especially in Th and U. Metamorphic complexes of the Monotonous and Varied groups contain multiple magnetic anomalies mostly related to the intercalated metabasic rocks; they also cause positive gravity anomalies. The Linsser density boundaries at a depth of 0.5 km clearly delimit the Plechý, composite pluton and the Lhenice zone and indicate several structurally and/or lithologically different domains within the Křišt'anov granulite massif and in the Knížecí Stolec pluton. The 2.5D gravity model indicates an asymmetric shape of the Knížecí Stolec pluton, which is deepest in its SE part (at least 4 km). The joint interpretation of the geophysical and structural data revealed that the maximum depth of the pluton is c. 4.5 km, with gently to moderately dipping intrusive contacts in the north and subvertical orientation in the south. The asymmetric shape of the pluton is consistent with its inferred syntectonic emplacement coeval with the regional subvertical contraction and development of regional flat-lying fabric. The gravity model combined with structural analyses also implies a considerable depth of the south Bohemian granulite massifs. This indicates their steep exhumation path and is at variance with the model of the Moldanubian Zone as a sequence of flat-lying nappes. The south-western part of the studied area is reworked by the NE-directed compression, referred to as the 'Bavarian' deformation phase. [ABSTRACT FROM AUTHOR]

Abstract: Felsic granulites from the Kutná Hora complex in the Moldanubian zone of central Europe preserve mineral assemblage that records transition from early eclogite to granulite facies conditions, and exhibits leucocratic banding, which is interpreted as an evidence for melt loss during the decompression path. The granulites are layered and consist of variable proportions of quartz, ternary feldspar, garnet, biotite, kyanite, and rutile. In the mesocratic layers, garnet grains show relatively high Ca contents corresponding to 28–41mol% grossular end member. They have remarkably flat compositional profiles in their cores but their rims exhibit an increase in pyrope and a decrease in grossular and almandine components. In contrast, garnets from the leucocratic layers have relatively low Ca contents (15–26mol% grossular) that further decrease towards the rims. In addition to modeling of pressure–temperature pseudosections, compositions of garnet core composition, garnet rim-ternary feldspar–kyanite–quartz equilibrium, ternary feldspar composition, and the garnet–biotite equilibrium provide five constraints that were used to reconstruct the pressure–temperature path from eclogite through the granulite and amphibolite facies. In both layers, garnet cores grew during omphacite breakdown and phengite dehydration melting at 940°C and 2.6GPa. Subsequent decompression heating to 1020°C and 2.1GPa produced Ca- and Fe-poor garnet rims due to the formation of Ca-bearing ternary feldspar and partial melt. In both the mesocratic and leucocratic layer, the maximum melt productivity was 26 and 18vol.%, respectively, at peak temperature constrained by the maximum whole-rock H2O budget, ~1.05–0.75wt.%, prior to the melting. The preservation of prograde garnet-rich assemblages required nearly complete melt loss (15–25vol.%), interpreted to have occurred at 1000–1020°C and 2.2–2.4GPa by garnet mode isopleths, followed by crystallization of small amounts of residual melt at 760°C and 1.0GPa. Phase formation and melt productivity were independently determined by experiments in the piston-cylinder apparatus at 850–1100°C and 1.7–2.1GPa. Both the thermodynamic calculations and phase equilibrium experiments suggest that the partial melt was produced by the dehydration melting: muscovite+quartz=melt+K-feldspar+kyanite. The presence of partial melt facilitated attainment of mineral equilibria at peak temperature thus eliminating any potential relics of early high-pressure phases such as phengite or omphacite. By contrast, adjacent mafic granulites and eclogites, which apparently share the same metamorphic path but have not undergone partial melting commonly preserve relics or inclusions of eclogite-facies mineral assemblages. [Copyright &y& Elsevier]

In the Orlica-Śnieżnik Dome (NE Bohemian massif), alternating belts of orthogneiss with high-pressure rocks and belts of mid-crustal metasedimentary-metavolcanic rocks commonly display a dominant subvertical fabric deformed into a subhorizontal foliation. The first macroscopic foliation is subvertical, strikes NE-SW and is heterogeneously folded by open to isoclinal folds with subhorizontal axial planes parallel to the heterogeneously developed flat-lying foliation. The metamorphic evolution of the mid-crustal metasedimentary rocks involved successive crystallization of chlorite-muscovite-ilmenite-plagioclase-garnet, followed by staurolite-bearing and then kyanite-bearing assemblages in the subvertical fabric. This was followed by garnet retrogression, with syntectonic crystallization of sillimanite and andalusite parallel to the shallow-dipping foliation. Elsewhere, andalusite and cordierite statically overgrew the flat-lying fabric. With reference to a P-T pseudosection for a representative sample, the prograde succession of mineral assemblages and the garnet zoning pattern with decreasing grossular, spessartine and X are compatible with a P- T path from 3.5-5 kbar/490-520 °C to peak conditions of 6-7 kbar/∼630 °C suggesting burial from 12 to 25 km with increasing temperature. Using the same pseudosection, the retrograde succession of minerals shows decompression to sillimanite stability at ∼4 kbar/∼630 °C and to andalusite-cordierite stability at 2-3 kbar indicating exhumation from 25 km to around 9-12 km. Subsequent exhumation to ∼6 km occurred without apparent formation of a deformation fabric. The structure and petrology together with the spatial distribution of the metasedimentary-metavolcanic rocks, and gneissic and high-pressure belts are compatible with a model of burial of limited parts of the upper and middle crust in narrow cusp-like synclines, synchronous with the exhumation of orogenic lower crust represented by the gneissic and high-pressure rocks in lobe-shaped and volumetrically more important anticlines. Converging P- T- D paths for the metasedimentary rocks and the adjacent high-pressure rocks are due to vertical exchanges between cold and hot vertically moving masses. Finally, the retrograde shallow-dipping fabric affects both the metasedimentary-metavolcanic rocks and the gneissic and high-pressure rocks, and indicates that the ∼15-km exhumation was mostly accommodated by heterogeneous ductile thinning associated with unroofing of a buoyant crustal root. [ABSTRACT FROM AUTHOR]

Abstract: A new model of the structure and composition of the Variscan crust in the Bohemian Massif is proposed based on 3D gravity modelling, geological data, seismic refraction (CEL09) and reflection (9HR) sections. The Bohemian Massif crust is characterized by a succession of positive and negative anomalies of about 60–80km wavelength for nearly constant Moho depths. The south-western part of the Bohemian Massif displays a large negative Bouguer anomaly corresponding to high grade rocks (granulites and migmatites) of the Palaeozoic crustal root represented by the Moldanubian domain. The adjacent Neo-Proterozoic Bruno-Vistulian microcontinent displays an important gravity high reflecting mafic and intermediate medium grade metamorphic and magmatic rocks. The deep crustal boundary between the root domain and the Bruno-Vistulian microcontinent is represented by a strong gradient located 50 to 70km westwards from the surface boundary between these units indicating that the high density basement rocks are covered by a thin sheet of low density granulites and migmatites. North-west from the Moldanubian domain occurs an important gravity high corresponding to the Neo-Proterozoic basement of the Teplá-Barrandian Unit limited in the north by southeast dipping reflectors of the Teplá suture which is characterized by high density eclogites and ultramafics. The footwall of the suture corresponds to low density felsic crust of the Saxothuringian basement. The reflection and refraction seismics and gravity modelling suggest a complex lithological structure of the Moldanubian domain marked by a low density 5–10km thick lower crustal layer located above the Moho, a 5–10km thick heavy mafic layer, a 10km thick mid-crustal layer of intermediate density and a locally developed 2–5km thick low density layer at the surface. The low density lower crust correlates well with low P-wave velocities in the range 6.0–6.4kms−1 in the CEL09 section. This complex geophysical structure and surface geology are interpreted as a result of Carboniferous partial overturn of low density lower crust and high and intermediate density crust in the area of central root and by viscous extrusion of low density orogenic lower crust over the high density Bruno-Vistulian continent. Comparison of these data with geophysical profiling of the Andean and the Tibetan plateaus suggests that modern orogenic systems reveal comparable deep crustal geophysical pattern. Based on these similarities we propose that the Variscan root represents a deep crustal section of above mentioned plateaus, which may have develop by the same orogenic process. [Copyright &y& Elsevier]

Abstract: Emplacement mode and original shape and dimensions of a well exposed phonolite body in the České středohoří Mountains (Czech Republic) were reconstructed using combined techniques of structural analysis of magmatic fabrics and columnar jointing together with analogue and thermal mathematical modeling of cooling for different shapes of experimental bodies. Phreatomagmatic rocks in the vicinity of some phonolite stocks in the area of interest suggest that the phonolite bodies were likely emplaced into maar-diatremes. Our modeling revealed that intrusion of magma into phreatomagmatic maar-diatreme craters can result in cryptodomes, extrusive domes, lava lakes or branched intrusions. The fabric and columnar jointing pattern of the selected phonolite body reveals best fit with an asymmetric extrusive dome emplaced into the maar crater. The scaling analysis and thermal modeling also suggest that the phonolite extrusion could have formed within 6–66days and cooled to the background temperature after 10,000years. Combined analogue and thermal modeling also revealed that the phonolite extrusions into maar-diatreme craters are marked by upper tier (collonade) of vertical columns and lower tier of curved and outward flaring columns. Both tiers in the phonolite extrusions are divided by a subhorizontal suture. [Copyright &y& Elsevier]

The boundary between the Saxothuringian and the Teplá-Barrandian zones at the western margin of the Bohemian Massif represents an important tectonic suture of the Central European Variscides. However, most of this boundary is covered by Late Carboniferous and younger sedimentary and volcanic rocks, which prevent direct observation of particular geological units. We present a compilation of geological and depth measurement data from 12,134 exploration boreholes that reached the basement of the volcanic and sedimentary infill in the area of the Eger Graben in the north-western Bohemia, and correlate covered geological units with those exposed on the present-day surface. The resulting compilation reveals the relief of the sedimentary basins basement and interprets the real extent of the basement geological units in the western part of the Bohemian Massif. It also shows the position of the contact between units with the Saxothuringian and the Teplá-Barrandian affinities and suggests the boundary between rocks with Devonian metamorphic record and those metamorphosed during the Early Carboniferous period of the Variscan tectonometamorphic cycle. [ABSTRACT FROM AUTHOR]

The metamorphic evolution of micaschists in the north-eastern part of the Saxothuringian Domain in the Central European Variscides is characterized by the early high-pressure M1 assemblage with chloritoid in cores of large garnet porphyroblasts and a Grt–Chl–Phe–Qtz ± Pg M2 assemblage in the matrix. Minerals of the M1–M2 stage were overprinted by the low-pressure M3 assemblage Ab–Chl–Ms–Qtz ± Ep. Samples with the best-preserved M1–M2 mineralogy mostly appear in domains dominated by the earlier D1 deformation phase and are only weakly affected by subsequent D2 overprint. Thermodynamic modelling suggests that mineral assemblages record peak-pressure conditions of ≥18–19 kbar at 460–520 °C (M1) followed by isothermal decompression 10.5–13.5 kbar (M2) and final decompression to <8.5 kbar and <480 °C (M3). The calculated peak P–T conditions indicate a high-pressure/low-temperature apparent thermal gradient of ∼7–7.5 °C km−1. Laser ablation inductively coupled plasma mass spectrometry isotopic dating and electron microprobe chemical dating of monazite from the M1–M2 mineral assemblages give ages of 330 ± 10 and 328 ± 6 Ma, respectively, which are interpreted as the timing of a peak pressure to early decompression stage. The observed metamorphic record and timing of metamorphism in the studied metapelites show striking similarities with the evolution of the central and south-western parts of the Saxothuringian Domain and suggest a common tectonic evolution along the entire eastern flank of the Saxothuringian Domain during the Devonian–Carboniferous periods. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropy of magnetic susceptibility (AMS) and Electron back-scattered diffraction (EBSD) of magnetite and sanidine fabrics throughout an eroded trachyte lava dome in Tertiary volcanic province of the NW Czech Republic revealed two fabric types. The high degree of AMS fabric is associated with sanidine textural domains similar to normal kink bands (Type I fabric) and occupies the whole body except the SW margin. Folded fabric and low anisotropy of AMS also in the SW margin reveals sanidine alignment domains resembling reverse kink-bands (Type II fabric). The flow of trachyte lava occurred via simultaneous slip of sanidine crystals along their (010) planes and also by readjustment of the textural domain boundaries according to the fibre-slip theory. This microfabric study suggests that the Type II fabrics resulted from collapse of vertically anisotropic trachyte crystal mush above the feeding conduit. Type I fabric is interpreted to originate from Type II fabrics by further stretching of highly attenuated fold limbs. Asymmetric Type I fabrics along margins of the dome are related to outflow of trachyte lava away from the conduit region due to divergent flow. The trachyte fabric zonality is interpreted to reflect the process of successive emplacement of progressively rotated trachyte lava lobes within a lava dome that locally preserves the collapsed and folded vertical fabrics. [Copyright &y& Elsevier]

Abstract: Serpentinized peridotite–clinopyroxenite, approximately 11×5 m in size, enclosed in high-pressure felsic granulite, occurs in a quarry near the village of Bory (Gföhl Unit of the Moldanubian Zone of Western Moravia, Czech Republic). The anisotropy of magnetic susceptibility (AMS) was used to investigate the fabrics of both the ultramafic body and the host granulite. The granulite shows a PT path from above 2 GPa/850–900 °C following nearly isothermal decompression to sillimanite stability field with subsequent cooling. Two foliations (S1-preserved only in isoclinal folds and the dominant S2 foliation parallel to leucocratic bands) are visible in granulite. Through investigating low-field variation of the AMS, one could resolve the AMS into the field-independent and field-dependent components. In the ultramafic body, the former component is due to mafic silicates and pure magnetite, while in the host granulite it is due to mafic silicates. The latter component is due to pyrrhotite in both the ultramafic body and granulite. The field-independent and field-dependent components are coaxial within ultramafic body and within granulite, but show different orientations between the ultramafic body and granulite. Consequently, the magnetic fabric in the ultramafic body is different from that in the host granulite even though they experienced common structural history during granulite facies metamorphism. The componental movements forming the granulite fabric were evidently not strong enough to strongly overprint the magnetic fabric of ultramafic rocks. The ultramafic rocks have therefore sufficient mechanical strength to maintain their pre-granulite facies metamorphic fabric even at such high temperatures and high pressure that are characteristic of granulite facies metamorphism. [Copyright &y& Elsevier]

Metagranites and migmatites of the Svratka and the Orlice-Sněžnik units, northeastern Bohemian Massif, exhibit a number of similarities in their lithological, mineralogical and geochemical features. Both of these units were affected by intense migmatitization accompanied by intrusion of peraluminous granites during the Cambrian to Ordovician. The chemical composition and mineralogy of all the studied rocks correspond to crustal melts. From the geochemical point of view, both rock groups (migrnatites and metagranites) exhibit progressive geochemical fractionation (increase in the SiO2, Rb, XFeO, Wand Sn contents, accompanied by a decrease in the concentrations of Ba, Sr, Mg and Ca) as a result of varying degrees of partial melting and fractional crystallization. The main rock-forming minerals are influenced by metamorphic recrystallization under amphibolite-facies conditions during the Variscan orogeny. [ABSTRACT FROM AUTHOR]

New occurrences of high-pressure metabasites in the Kutná Hora Unit (KHC) are described. These HP rocks include eclogites (± Ky), Cpx-Grt amphibolites, metagabbros and Cpx-bearing granulites. All the eclogite samples studied are formed of well-preserved HP mineral assemblages with variable degree of subsequent metamorphic overprint. Eclogites from the inner part of the KHC (Roztěž, Bořetice) mostly had a Mg-rich tholeiitic protolith. Chemical, mineralogical and metamorphic data reveal that these eclogites are petrologically similar to the eclogite samples from the better known Běstvina Unit. Eclogites from Bořetice, Poličany and Roztě ž preserve relict mineral assemblage from a pre-eclogite stage, enclosed in garnet with prograde zoning pattern. They bear mineralogical evidence of a very high-pressure history, even substantially higher (maximum 8.4 wt. % of Na2O in Cpx, P~ 4.3 GPa) than the previously described eclogites from Spačice and Úhrov in the Běstvina Unit. A set of three eclogites from the northern margin of the Moldanubian Zone south of Chotěboř was used for comparison (Bída, Borovský Creek, Krátká Ves). They preserve also a peak pressure record that corresponds to minimum pressures above 2.0 GPa. Better understanding of regional relationships amongst the discussed units can, be achieved only using isotopic and geochronological data. [ABSTRACT FROM AUTHOR]

In this paper are reviewed structural, petrological and geochronological data from the main units at the NE periphery of the Moldanubian Zone, i.e. Kutná Hora Complex, Svratka Unit, Polička and Zábřeh units, as well as the Strážek Unit of the Moldanubian Zone. In this domain of the Bohemian Massif, the lower- and upper-crustal units are dominated by metamorphic fabrics produced during the Variscan orogeny. The mid- to upper-crustal Svratka, Polička and Zábřeh units are affected by -MP/MT "long-lived" (-350-339 Ma) tectonometamorphic event reflecting --WNW-ESE right-lateral strike-slip shearing (transpressional to transtensional tectonics). These regional fabrics are in the Polička and Zábřeh units related with syn-tectonic emplacement and crystallization of calc-alkaline intrusions (Zábřeh Intrusive Complex, Miřetín nad Budislav plutons). In the three structurally high units in the Kutná Hora Complex, Orlice-Sněžník and the Strářek units the strike-slip, "long-lived" tectonics is rather localized; the high-pressure, high-temperature events followed by heterogeneous and polyphase exhumation of deep-seated rocks to mid-crustal levels are preserved. Ultrapotassic rocks (durbachites) of the Sněžník Unit, dated at -339 Ma, intruded posttectonicaly. [ABSTRACT FROM AUTHOR]

Abstract: The Late Devonian subduction followed by the Early Carboniferous continental collision of the Saxothuringian and overriding upper-crustal Teplá–Barrandian units led to the growth of a large magmatic arc (the ∼354–337 Ma Central Bohemian Plutonic Complex) in the central part of the Bohemian Massif. Far-field tectonic forces resulting from the collision produced ∼WNW–ESE to ∼NW–SE regional shortening across the forearc upper crust above the subduction zone; the shortening was accommodated by predominantly top-to-the-ESE tectonic transport along the southeastern flank of the Teplá–Barrandian unit. Approaching the magmatic arc margin, the regional structural pattern changes and exhibits significant across- and along-strike variations interpreted as a result of strain partitioning, where the Saxothuringian/Teplá–Barrandian convergence interacted in different ways with the intruding magma pulses. Around the voluminous, northeasterly ∼354 Ma Sázava pluton the principal shortening was at high angle to the forearc-facing intrusive contact and the host rocks were significantly thermally softened. The regional top-to-the-ESE tectonic transport converted here into arc-parallel ductile flow within the structural aureole around and above the pluton. In contrast, a narrow to nonexistent ductile strain aureole is preserved in the host rocks around discordant sheet-like plutons (the southwesterly pre-354 (?) Ma Marginal granite and the Milín granodiorite of unknown radiometric age). Our AMS study of the Marginal granite and Milín granodiorite, and mapping of mesoscopic magmatic foliations and lineations in another neighboring sheet-like pluton (the ∼346 Ma Kozárovice granodiorite), reveals sigmoidal map-scale fabric patterns consistent with dextral transpression. We thus suggest that the thin sheet-like plutons were oriented obliquely to the principal shortening and were rheologically weaker than the host rocks prior to final crystallization, producing dextral transpression recorded by the internal fabrics of these plutons. Our study shows that the far-field plate kinematics during pluton emplacement is not the only factor that controls strain partitioning in continental magmatic arcs. The two contrasting styles of pluton emplacement documented here indicate that the pluton shape, orientation of intrusive contacts with respect to the background plate convergence vector, and heat budget of intrusions (magma volume, composition, and proportion of hot mantle component) may also govern strain partitioning. [Copyright &y& Elsevier]

Abstract: A highly unusual fabric pattern and inferred flow mechanism was discovered in the shallow-level Říčany granite pluton, Bohemian Massif, using an integrated structural and anisotropy of magnetic susceptibility (AMS) study. The pluton consists of an outer strongly porphyritic and an inner weakly porphyritic biotite granite separated by a wide gradational contact. Both varieties share a steep margin-parallel magmatic foliation (defined by K-feldspar phenocrysts and biotite) and magnetic (AMS) foliation carried by biotite. The steep foliation bears a shallowly-plunging magnetic lineation arranged parallel to the circumference of the pluton margin and a steep magnetic lineation in the weakly porphyritic pluton center. We propose a new mechanism of magma flow, in which the bulk ascent along a steep-sided, cylindrical conduit was partitioned into a high-viscosity, phenocryst-rich outer margin flowing helically and a low-viscosity, phenocryst-poor center flowing vertically. This interpretation is supported quantitatively by a simple model of magma flow within a cylindrical pipe, in which the linear decrease in phenocryst content from the pluton margin inwards causes a power-law decrease in the effective viscosity of the magma. According to the Poiseuille equation, such a power-law viscosity distribution across the conduit produces a central zone of high magma ascent velocity. The magnetic (AMS) fabric pattern in the Říčany pluton may thus preserve a record of helical magma ascent driven by viscosity partitioning in a steep-sided conduit, which presumably linked an underlying magma chamber with a volcanic feeder at the surface. Except for one deep-seated granite–migmatite complex, no such helical fabric pattern has been documented in a granite pluton as of yet. We propose that the viscosity-partitioned helical flow may be a more common magma ascent mechanism in shallow-level volcano-plutonic systems than previously envisaged. [Copyright &y& Elsevier]

Abstract: A large ultramafic body (garnet clinopyroxenite and garnet peridotite) embedded in felsic granulite at Bory (Moldanubian Zone of Western Moravia, Czech Republic) contains multiple carrier of susceptibility. Low-field variation of anisotropy of magnetic susceptibility (AMS) enables the separation of the field independent and low-field dependent AMS components to be made. In granulite, the former is carried by paramagnetic minerals and a subordinate admixture of magnetite, while the latter is due to pyrrhotite. In the ultramafite, the field-independent component is carried by pure magnetite formed by serpentinization, while the field-dependent component is due to pyrrhotite and subordinate paramagnetic minerals. Despite small differences, all AMS components are roughly coaxial both within granulite and within ultramafite, but very different between granulite and ultramafite. The difference indicates that the forces that imposed the later granulite fabric were not strong enough to obliterate the original magnetic fabric of the ultramafites. [Copyright &y& Elsevier]

Abstract: The geological inventory of the Variscan Bohemian Massif can be summarized as a result of Early Devonian subduction of the Saxothuringian ocean of unknown size underneath the eastern continental plate represented by the present-day Teplá-Barrandian and Moldanubian domains. During mid-Devonian, the Saxothuringian passive margin sequences and relics of Ordovician oceanic crust have been obducted over the Saxothuringian basement in conjunction with extrusion of the Teplá-Barrandian middle crust along the so-called Teplá suture zone. This event was connected with the development of the magmatic arc further east, together with a fore-arc basin on the Teplá-Barrandian crust. The back-arc region – the future Moldanubian zone – was affected by lithospheric thinning which marginally affected also the eastern Brunia continental crust. The subduction stage was followed by a collisional event caused by the arrival of the Saxothuringian continental crust that was associated with crustal thickening and the development of the orogenic root system in the magmatic arc and back-arc region of the orogen. The thickening was associated with depression of the Moho and the flux of the Saxothuringian felsic crust into the root area. Originally subhorizontal anisotropy in the root zone was subsequently folded by crustal-scale cusp folds in front of the Brunia backstop. During the Visean, the Brunia continent indented the thickened crustal root, resulting in the root''s massive shortening causing vertical extrusion of the orogenic lower crust, which changed to a horizontal viscous channel flow of extruded lower crustal material in the mid- to supra-crustal levels. Hot orogenic lower crustal rocks were extruded: (1) in a narrow channel parallel to the former Teplá suture surface; (2) in the central part of the root zone in the form of large scale antiformal structure; and (3) in form of hot fold nappe over the Brunia promontory, where it produced Barrovian metamorphism and subsequent imbrications of its upper part. The extruded deeper parts of the orogenic root reached the surface, which soon thereafter resulted in the sedimentation of lower-crustal rocks pebbles in the thick foreland Culm basin on the stable part of the Brunia continent. Finally, during the Westfalian, the foreland Culm wedge was involved into imbricated nappe stack together with basement and orogenic channel flow nappes. [Copyright &y& Elsevier]

Metabasic rocks form an important constituent of the Chýnov and Český Krumlov units belonging to the Varied Group (Moldanubian Zone, south Bohemia). The amphibolites are dominated by amphibolite-facies mineral assemblages of mainly tschermakitic amphibole and plagioclase. Hornblendes show compositional variation with Si~ 6.5 apfu, Mg/(Mg + Fe) ~ 0.5 and (Na + K)^ ~ 0.5 apfu. Garnet with clinopyroxene are subordinate and occur in a few samples only. No relics of previous greenschist- or granulite-facies assemblages have been observed, most likely due tothe relatively simple metamorphic history. The petrology indicates rather close correlation of the Chýnov and Český Krumlov units. The similarities include presence of dolomite in carbonate bodies, graphite schists, rocks with marialitic scapolite, locally also Ti-andradite (± magnetite, epidote) oxidic assemblages and thin layers of Mn-rich garnet-quartz rocks. However, there is a major difference in the oxidation state. Most Chýnov amphibolites have Fe2O3/FeO = 0.70-1.00 and their protolith probably experienced an early incipient oxidation. Great deal of the parental basalts thus could have been effusive. The Český Krumlov amphibolites have Fe2O3/FeO ⩽0.4, perhaps because they show much closer association with graphite schists that could have been responsible for the reduction of the adjacent rock units. The dataset is dominated by EMORB-like tholeiite basalts interpreted as having been derived by Early Palaeozoic melting of a strongly depleted mantle source (ϵϵ500Nd = +8.6 to +9.4; TDMMd= 0.43-0.50 Ga). This argues stoutly against Precambrian age of the Varied Group in south Bohemia. The composition of the remaining samples reflects contamination by upper continental crust (ϵ500Nd = +3.1 to +1.3, progressive enrichment in Th, development of a significant negative Nb, and lesser P and Ti anomalies on the NMORB-normalized spiderplots). A much smaller group of amphibolites is characterised by steep REE patterns (LaN/YbN = 5.5-11) and high contents of HFSE (Nb, Ta, Zr and P). It is of a clear OlB affinity, with parental alkali basalt (Nb/Y = 0.7-1.6) generated by a low degree of partial melting of a deep, garnet-bearing asthenospheric mantle source (ϵ500Nd = +4.5 to +6.1; TDMNd= 0.75-0.83 Ga). Metamorphosed doleritic/gabbroic dykes cutting the Palaeoproterozoic SvëtlIk orthogneiss show rather unradiogenic Nd isotopic composition (ϵ500Nd = +0.1 and -3.6; TDMNd= 1.34 and 2.03 Ga). This precludes closed-system crystallization from depleted mantle derived melts in Phanerozoic times. The exact age and nature of their parental magma remain enigmatic but any genetic link with the amphibolites in the structurally overlying Český Krumlov Varied Unit seems ruled out. Overall, the most likely tectonic setting of the magmatism was attenuated lithosphere, subjected to an Early Palaeozoic extension, leading eventually to fragmentation of the northern Gondwana margin. The minor OlB component preserved as alkali basalts as well as some contribution to the EMOR-like basaltic magmas was probably added by a rising mantle plume. [ABSTRACT FROM AUTHOR]

Garnet–clinopyroxene intermediate granulites occur as thin layers within garnet–kyanite–K–feldspar felsic granulites of the St. Leonhard granulite body in the Bohemian Massif. They consist of several domains. One domain consists of coarser-grained coexisting ternary feldspar, clinopyroxene, garnet, quartz and accessory rutile and zircon. The garnet has 16–20% grossular, and the clinopyroxene has 9% jadeite and contains orthopyroxene exsolution lamellae. Reintegrated ternary feldspar and the Zr-in-rutile thermometer give temperatures higher than 950 °C. Mineral equilibria modelling suggests crystallization at 14 kbar. The occurrence and preservation of this mineral assemblage is consistent with crystallization from hot dry melt. Between these domains is a finer-grained deformed matrix made up of diopsidic clinopyroxene, orthopyroxene, plagioclase and K-feldspar, apparently produced by reworking of the coarser-grained domains. Embedded in this matrix, and pre-dating the reworking deformation, are garnet porphyroblasts that contain clinopyroxene, feldspar, quartz, rutile and zircon inclusions. In contrast with the garnet in the coarser-grained domains, the garnet generally has >30% grossular, the included clinopyroxene has 7–27% jadeite and the Zr content of rutile indicates much lower temperatures. Some of these high-grossular garnet show zoning in Fe/(Fe + Mg), decreasing from 0.7 in the core to 0.6 and then increasing to 0.7 at the rim. These garnet are enigmatic, but with reference to appropriate pseudosections are consistent with localized new mineral growth from 650 to 850 °C and 10 to 17 kbar, or with equilibration at 20 kbar and 770 °C, modified by two-stage diffusional re-equilibration of rims, at 10–15 and 8 kbar. The strong pervasive deformation has obscured relationships that might have aided the interpretation of the origin of these porphyroblasts. The evolution of these rocks is consistent with formation by igneous crystallization and subsequent metamorphism to high- T and high- P, rather than an origin by ultrahigh- T metamorphism. Regarding the petrographic complexity, combination of the high grossular garnet with the ternary feldspar to infer ultrahigh- T metamorphism at high pressure is not justified. [ABSTRACT FROM AUTHOR]

A large database of structural, geochronological and petrological data combined with a Bouguer anomaly map is used to develop a two-stage exhumation model of deep-seated rocks in the eastern sector of the Variscan belt. An early sub-vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks. These events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18−20 kbar to depths equivalent to 8−10 kbar, and for coeval burial of upper crustal rocks to depths equivalent to 8–9 kbar. Following the folding and vertical extrusion event, sub-horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening. Fabrics that record the early vertical extrusion originated between 350 and 340 Ma, during building of an orogenic root in response to SE-directed Saxothuringian continental subduction. Fabrics that record the later sub-horizontal exhumation event relate to an eastern promontory of the Brunia continent indenting into the rheologically weaker rocks of the orogenic root. Indentation initiated thrusting or flow of the orogenic crust over the Brunia continent in a north-directed sub-horizontal channel. This sub-horizontal flow operated between 330 and 325 Ma, and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re-equilibration. The erosion depth as well as the degree of reworking decreases from south to north, pointing to an outflow of lower crustal material to the surface, which was subsequently eroded and deposited in a foreland basin. Indentation by the Brunia continental promontory was highly noncoaxial with respect to the SE-oriented Saxothuringian continental subduction in the Early Visean, suggesting a major switch of plate configuration during the Middle to Late Visean. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we present structural and AMS data from the ∼335Ma ultrapotassic Jihlava syenitoid pluton, which intruded the lower- to mid-crustal orogenic root (Moldanubian Unit) in the Bohemian Massif, Central European Variscides. The emplacement of the pluton was accommodated by multiple processes, such as ductile host-rock shortening, formation of sheeted zones by magma wedging, magmatic stoping, and possibly host-rock displacement within a wide transtensional zone. Magmatic fabrics preserved in the pluton reflect both intrusive processes and regional strain. Margin-parallel and ∼ENE–WSW foliations, which probably formed by strain during emplacement of inner magma pulses, were overprinted by tectonic strain within a zone of distributed wrench-dominated dextral transtension. This zone probably accommodated exhumation of different segments in the eastern part of the Moldanubian Unit during pluton emplacement. In contrast to existing models, we emphasize that the Jihlava pluton, as well as other ultrapotassic plutons widespread in the Moldanubian Unit, are structurally highly variable bodies emplaced by multiple intrusive processes. Our case study illustrates how careful documentation of structural relations around these ultrapotassic plutons may constrain the kinematic framework and local exhumation histories in different segments of the orogenic root during and shortly after the ∼340Ma mechanical event in the Central European Variscides. [Copyright &y& Elsevier]

Abstract: The progressive deformation recorded in the magnetic fabric of sedimentary rocks was studied in the SE Rhenohercynian Zone (RHZ), eastern margin of the Bohemian Massif, Czech Republic. Almost 800 oriented samples of the Lower Carboniferous mudstones and graywackes were collected from the SSE part of the Czech RHZ, so-called the Drahany Upland. The anisotropy of magnetic susceptibility (AMS) is predominantly controlled by the preferred orientation of paramagnetic phyllosilicates, mainly iron-bearing chlorites. A regional distribution of the magnetic fabric within the Drahany Upland revealed an increasing deformation from the SSE to the NNW. In the SE, the magnetic fabric is bedding-parallel with magnetic lineation scattered in the bedding plane or trending N–S to NNE–SSW. Further to the NW, the magnetic foliation rotates from the bedding-parallel orientation to the orientation parallel to the evolving cleavage. This rotation is accompanied by a decrease of the anisotropy degree and the prolate nature of the anisotropy ellipsoids. The magnetic lineation is parallel to the strike of the bedding, bedding/cleavage intersection, pencil structure or the fold axes on a regional scale. In the NW part of the Drahany Upland, the magnetic foliation becomes parallel to the cleavage accompanied by an increase of the anisotropy degree and the oblate nature of the anisotropy ellipsoids. The increasing trend of deformation corresponds to the SSE–NNW increase in the degree of anchimetamorphism; both trends being oblique to the main lithostratigraphic formations as typically observed in the sedimentary rocks of the accretionary wedges. The SSE–NNW increase in deformation and anchimetamorphism continues to the Nízký Jeseník Mts., representing the northern part of the same accretionary wedge. The kinematics of deformation could not be unambiguously assessed. The observed magnetic fabric may reflect either lateral shortening or horizontal simple shear or a combination of both mechanisms. Regarding the subduction process, it seems that the sedimentary sequences of the Drahany Upland were subducted, partly offscraped and accreted frontally or partly underplated as opposed to the Nízký Jeseník Mts. where some return flow must have occurred. [Copyright &y& Elsevier]

A mid-ocean ridge basalt (MORB)-type eclogite from the Moldanubian domain in the Bohemian Massif retains evidence of its prograde path in the form of inclusions of hornblende, plagioclase, clinopyroxene, titanite, ilmenite and rutile preserved in zoned garnet. Prograde zoning involves a flat grossular core followed by a grossular spike and decrease at the rim, whereas Fe/(Fe + Mg) is also flat in the core and then decreases at the rim. In a pseudosection for H2O-saturated conditions, garnet with such a zoning grows along an isothermal burial path at c. 750 °C from 10 kbar in the assemblage plagioclase-hornblende-diopsidic clinopyroxene-quartz, then in hornblende-diopsidic clinopyroxene-quartz, and ends its growth at 17–18 kbar. From this point, there is no pseudosection-based information on further increase in pressure or temperature. Then, with garnet-clinopyroxene thermometry, the focus is on the dependence on, and the uncertainties stemming from the unknown Fe3+ content in clinopyroxene. Assuming no Fe3+ in the clinopyroxene gives a serious and unwarranted upward bias to calculated temperatures. A Fe3+-contributed uncertainty of ±40 °C combined with a calibration and other uncertainties gives a peak temperature of 760 ± 90 °C at 18 kbar, consistent with no further heating following burial to eclogite facies conditions. Further pseudosection modelling suggests that decompression to c. 12 kbar occurred essentially isothermally from the metamorphic peak under H2O-undersaturated conditions ( c. 1.3 mol.% H2O) that allowed the preservation of the majority of garnet with symplectitic as well as relict clinopyroxene. The modelling also shows that a MORB-type eclogite decompressed to c. 8 kbar ends as an amphibolite if it is H2O saturated, but if it is H2O-undersaturated it contains assemblages with orthopyroxene. Increasing H2O undersaturation causes an earlier transition to SiO2 undersaturation on decompression, leading to the appearance of spinel-bearing assemblages. Granulite facies-looking overprints of eclogites may develop at amphibolite facies conditions. [ABSTRACT FROM AUTHOR]

Key lithological units of the high-grade eastern margin of the Bohemian Massif were dated using the U-Pb and Pb-Pb methods on zircons in order to establish a chronological framework for the geodynamic evolution of the Variscan orogenic root. The protolith ages for metagranitoids, orthogneisses and granulites of thickened lower and middle crust reveal the existence of magmatic activity that occurred over a 100 million year time interval from Cambro-Ordovician to early Devonian times, probably related to discontinuous intracontinental rifting of Neoproterozoic crust. Our geochronological data suggest that the eastern part of the orogenic root represents thermally softened and rifted Neoproterozoic crust, preserved farther to the east as the Brunia microcontinent. Zircon ages for felsic granulites, high-grade gneisses of the lower crust and of a syn-convergence granodioritic intrusion in the upper crust indicate that thickening and exhumation of the crust occurred during a narrow time interval between 370 and 340 Ma. Exhumation of the lower crust to mid-crustal levels was a localized process that occurred at ∼340 Ma and was associated with crustal-scale folding in the internal part of the root as well as orogenic channel flow along the eastern collisional margin. Both types of exhumation mechanisms were driven by deep-level wedging (indentation) of the easterly Brunia continent, followed by deposition of heavy minerals and pebbles derived from high-pressure rocks in the adjacent foreland basin. Final orogenic development was characterized by NE-SW dextral transpressive shearing parallel to the Brunia margin as well as dextral transtension associated with activity along the Elbe lithospheric fault. These processes affected the marginal parts of the orogenic root and were accompanied by 330 to 325 Ma old syntectonic granitoid intrusions along reactivated lithotectonic boundaries. Rotation of the assembled orogenic belt, accompanied by lithospheric faulting driven by westerly subduction roll-back, may be the most plausible model to explain late deformation of the orogenic root. [ABSTRACT FROM AUTHOR]

Vertical variations in magnetic fabric and paragenesis of the ferrimagnetic minerals for a virtually upright dyke of the Altenberg syenogranite porphyry were investigated using profile data of borehole E-16 to a depth of 922.7 m (Eastern Krusˇne´ hory Mts., NW Bohemia). It was revealed that this dyke likely consists of two magma pulses indicated both by magnetic fabric and by opaque mineralogy. In most of the profile, the magnetite grains are oriented parallel to the sub-vertical dyke. Only at the base of the upper magma pulse, in a depth interval of 200–400 m, are these grains oriented sub-horizontally being thus perpendicular to the dyke walls. This pattern can be interpreted as a consequence of a static vertical compaction of the magma of the basal portions of the upper pulse due to the pressure of the ascending lower pulse. The large planes of the ferrimagnetic minerals are oriented perpendicular to the shortening direction. [Copyright &y& Elsevier]

High concentrations of airborne asbestos in the ambient air are still a serious problem of air quality in numerous localities around the world. Since 2002, elevated concentrations of asbestos minerals of unknown origin have been detected in the ambient air of Pilsen, Czech Republic. To determine the asbestos fibre sources in this urban air, a systematic study was conducted. First, 14 bulk dust samples were collected in Pilsen at nine localities, and 6 bulk samples of construction aggregates for gravel production were collected in a quarry in the Pilsen-Litice district. The quarry is the largest quarry in the Pilsen region and the closest quarry to the built-up urban area. X-ray diffraction of the asbestos minerals revealed that monoclinic amphibole (MA, namely actinolite based on subsequent SEM-EDX analysis) in the bulk samples accounted for < 1-33% of the mass and that the highest values were found in the bulk dust samples from the railway platform of the Pilsen main railway station. Simultaneously, 24-h samples of airborne particulate matter (PM) at three localities in Pilsen were collected. Actinolite was identified in 40% of the PM samples. The relationship between the meteorology and presence of actinolite in the 24 PM 10 samples was not proven, probably due to the long sampling integration time. Therefore, highly time-and-size-resolved PM sampling was performed. Second, sampling of size-segregated aerosols and measurements of the wind speed (WS), wind direction (WD), precipitation (P) and hourly PM 10 , PM 2.5 and PM 1 were conducted in a suburban locality near the quarry in two monthly highly time-resolved periods (30, 60, 120 min). Three/eight PM size fractions were sampled by a Davis Rotating-drum Uniform-size-cut Monitor (3/8DRUM) and analysed for the presences of asbestos fibres by scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX). Asbestos fibre detection in highly time-resolved PM samples and current WD and WS determination allows the apportionment directionality of asbestos fibre sources. The number of critical actinolite asbestos fibres (length ≥ 5 μm and width < 3 μm, 3:1) increased with the PM 1-10 /PM 10 and PM 2.5-10 /PM 10 ratios, WS > 2 m s -1 and precipitation < 1 mm. Additionally, the number of critical actinolite asbestos fibres was not related to a specific WD. Therefore, we conclude that the sources of airborne critical actinolite asbestos fibres in Pilsen's urban area are omnipresent. Frequent use of construction aggregates and gravel from the metamorphic spilite quarries in the Pilsen region and in many localities around the urban area is a plausible explanation for the omnipresence of the critical actinolite asbestos fibres concentration in Pilsen's ambient air. Mitigation strategies to reduce the concentrations of critical actinolite asbestos fibres must be developed. Continuous monitoring and performing SEM-EDX analysis of highly time-and-size-resolved PM samples, correlated with fast changing WS and WD, seems to be a strong tool for efficiently controlling the mitigation strategies of critical actinolite asbestos fibres.