Abstract The West Sudetes (NE margin of the Bohemian Massif) consist of a complex mosaic of several tectonometamorphic units juxtaposed during the Variscan orogeny. The polyphase Variscan tectonothermal development of the West Sudetes was determined by 40 Ar/ 39 Ar ages of single grains and mineral concentrates. Late Famennian (359 Ma) mica ages from the high-grade Góry Sowie Block suggest continuous uplift after a Late Devonian high temperature-low pressure (HT-LP) event contemporaneous with the end of subduction-related high pressure-low temperature (HP-LT) metamorphism in the East Krkonoše Complex. Mid-Late Devonian high pressure events in the Krkonoše-Jizera Terrane and Orlica-Śnieżnik Dome are followed by coeval high temperature events between 345 and 335 Ma (Viséan). The latter are interpreted as consequence of uplift, and decompression during overthrusting of both complexes on their forelands. Subsequent small- to large-scale shear movements dated at around 325–320 Ma (early Namurian) affected the Orlica-Śnieżnik Dome, Krkonoše-Jizera Terrane, including the Intra-Sudetic Fault, and also the eastern Lusatian Granitoid Complex. They were accompanied by contemporaneous emplacement of the Krkonoše-Jizera pluton. The upper limit of the tectonometamorphic and magmatic activity is dated at 314–312 Ma (Namurian/Westphalian boundary). The final juxtaposition of the diversified tectonometamorphic units, which constitute the West Sudetes, took place in early Namurian times.

Abstract New single zircon ages enable us to provide an evolutionary scenario for the Neoproterozoic to Cambro-Ordovician tectonic history of part of the easternmost Sudetes along the northeastern margin of the Bohemian Massif. The easternmost crustal segment (Brunia) yields Neoproterozoic ages from both autochthonous and allochthonous Variscan units; these ages document a Cadomian (Pan-African) history that may be linked with the northern margin of Gondwana. A Cambro-Ordovician magmatic–thermal event in Brunia is represented by granitic to pegmatitic dykes intruding Neoproterozoic crust and by localized partial anatexis. Farther west a narrow zone of Cambro-Ordovician rifting is identified (Staré Městro belt), marked by gabbroic magmatism, bimodal volcanism and medium-pressure granulite facies metamorphism. The westernmost crustal domain (Orlica–Sniezník dome) is represented by Neoproterozoic crust intruded by Cambro-Ordovician plutons consisting of calk-alkaline granitoid rocks and affected by widespread Cambro–Ordovician anatexis. The geodynamic setting of the Neoproterozoic and Cambro-Ordovician domains is similar to that of the Western Sudetes, where both Cambro-Ordovician rifting and calc-alkaline magmatism were identified. We discuss the rifting mechanics in terms of sequential crustal thinning along the northern margin of Gondwana. The calc-alkaline magmatism, in conjunction with crustal rifting, is related to a back-arc geometry in front of a retreating south-dipping subduction zone during progressive closure of the Tornquist Ocean southeast of Avalonia.

Abstract This chapter summarizes the style, timing, composition and tectonic setting of the main occurrences of Cambrian to early Permian magmatic rocks in central Europe, which are here described within the framework of the Cadomian and Variscan Orogenies. In general terms, the Variscan Orogeny may be considered to be the result of Silurian to early Carboniferous accretion onto the southern margin of Laurussia of various Gondwana-derived terranes or microplates of predominantly Neoproterozoic (Cadomian/Pan-African) crust, together with their passive margin sequences and accreted island arcs ( Franke 1989 ; Matte 1991 ; Ziegler 1993 ). These microplates originated from various parts along the northern margin of Gondwana in the Early Palaeozoic, and moved northward towards Laurentia and Baltica (see Krawczyk et al. 2008 ). These rifting, spreading, subduction, accretion and collision events occurred over a long period and were associated with magmatic activity of varying styles, compositions and volumes, of which the variously deformed and metamorphosed equivalents are found throughout Variscan Europe. Another important, late to post-Variscan phase of magmatism which occurred throughout Europe was of late Carboniferous to early Permian age. The magmatic rocks and their metamorphosed equivalents are exposed in basement uplifts (the Variscan massifs), such as the Bohemian Massif, Odenwald, Spessart, Black Forest, Vosges, Massif Central, Iberia and the Rhenohercynian Zone (Fig. 12.1 ). In these internal parts of the Variscan Orogen, magmatic rocks are ubiquitous but are predominantly plutonic rocks and their metamorphosed equivalents, since mainly deep crustal levels are exposed. To the south, von Raumer (1998 )

Abstract Sm-Nd garnet geochronology is often hampered by the presence of submicroscopic inclusions of rare earth element-rich phosphates, which lower age precision, lead to inaccurate ages or make dating impossible. We propose a single-step sulphuric acid leaching technique as a very efficient tool in eliminating phosphate inclusions, which helps to achieve more precise and more accurate Sm-Nd garnet dates. Examples from silimanite grade metapelites demonstrate the much higher efficiency of this method in comparison with previously proposed techniques based on HF and HCl. 147 Sm/ 144 Nd ratios obtained on garnets leached by sulphuric acid were twice as high as those obtained by HF and HCl leaching. This led to age precision better than 3% for Tertiary samples. Comparison of leached and unleached nearly inclusion-free garnets from high pressure granulites, demonstrates that there is no Sm/Nd fractionation induced by H 2 SO 4 leaching. Our new technique eliminates phosphates, but does not attack garnet. This considerably reduces the necessity for hand-picking and lowers the amount of sample required for analysis making Sm-Nd garnet dating a more easily applied geochronometer.

Abstract The central European Bohemian Massif has undergone over two centuries of scientific investigation which has made it a pivotal area for the development and testing of modern geological theories. The discovery of melt inclusions in high-grade rocks, either crystallized as nanogranitoids or as glassy inclusions, prompted the re-evaluation of the area with an ‘inclusionist’ eye. Melt inclusions have been identified in a wide range of rocks, including felsic/perpotassic granulites, migmatites, eclogites and garnet clinopyroxenites, all the result of melting events albeit over a wide range of pressure/temperature conditions (800–1000°C/0.5–5 GPa). This contribution provides an overview of such inclusions and discusses the qualitative and quantitative constraints they provide for melting processes, and the nature of melts and fluids involved in these processes. In particular, data on trace-element signatures of melt inclusions trapped at mantle depths are presented and discussed. Moreover, experimental re-homogenization of nanogranitoids provided microstructural criteria allowing assessment of the conditions at which melt and host are mutually stable during melting. Overall this work aims to provide guidelines and suggestions for petrologists wishing to explore the fascinating field of melt inclusions in metamorphic terranes worldwide, based on the newest discoveries from the still-enigmatic Bohemian Massif.