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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]

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]

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]

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]

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]