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The gabbro-dioritoid rocks from Veľké Železné (Nízke Tatry Mts., Western Carpathians, Slovakia) were recently studied in order to better understand the age, origin, and evolution of the basic/intermediate magmas associated with Variscan granitic rocks. Their genesis was investigated from the points of view of petrology, whole-rock geochemistry (including Sr, Nd, and Pb isotopic characteristics), as well as U-Th-Pb zircon and apatite dating. The Famennian magmatic crystallization age of ca. 360 Ma (determined from zircon: 362.4 ± 2.9 Ma and apatite: 358.4 ± 2.8 Ma) is older than the Tournaisian-Visean ages for granite intrusions in the Tatric Unit. Geochemically, the studied rocks have an affinity to arc-related basalts, consisting of a metaluminous, magnesian, and high-potassium calc-alkaline character. Isotope data (i.e., (87Sr/86Sr)360 = 0.7035-0.7044 and εNd360 = +1.4 to +1.6) demonstrate that these gabbro-dioritoids were formed from the mantle-influenced, lower crustal and/or sub-continental lithospheric mantle (SCLM) sources, whereas the unsystematic increase of Pb isotope ratios indicate either the melting of an ancient Enriched mantle-II (EM-II) reservoir or the upper crustal assimilation and/or local fluid alteration. The data presented in this paper favour the origin of the studied gabbro-dioritoids at a continental arc, although we cannot rule out their genesis as a result of the subsequent slab break-off. [ABSTRACT FROM AUTHOR]

Metamorphic sole rocks at the base of the mantle tectonites of the Meydan ophiolite in South-East Anatolia, Turkey, are directly overlain by sheared serpentinites and cut by unmetamorphosed mafic dikes. They are found in areas close to the forefront of the Tauride thrust and are described as biotite amphibole schist (Bt + Hbl + Act + Plg + Rt ± Zrn), prehnite-pumpellyite-amphibole schist (Prh + Pmp + Act + Plg ± Rt ± Ttn), amphibole schist (Fe2+- Act + Qtz + Plg ± Anl ± Zrn), and amphibolite (Mg-Hbl + Plg ± Zrn ± Rt). They are identified as island arc tholeiites (IATs) based on their major- and trace-element whole-rock chemistry and mineral composition. The mafic dikes intruding into the metamorphic sole rocks and mantle tectonites exhibit tholeiitic affinity (Nb/Y = 0.03--0.13) and are geochemically similar to island-arc basalts. The multiple elements, rare earth element (REE) trends, and related diagrams suggest that the mafic dikes were generated in a supra-subduction zone (SSZ) setting. Geothermobarometric examination based on the chemical compositions of the magnesio-hornblende in the amphibolites indicated that the pressure and temperature during the metamorphism were ~ 2.4 kbar (at depths of roughly 9 km) and ~ 630 °C, respectively. To elucidate the relationship and timing between the formation of the Meydan ophiolite and that of the metamorphic sole rocks, this paper presents new zircon U--Pb geochronological data from two samples of sole rocks, the ages of which are indicated to lie in the range of 81.4 ± 0.69 Ma to 85.4 ± 0.93 Ma (Santonian-Campanian). The precise U--Pb geochronology and the detailed petrographical and geochemical features of the metamorphic sole rocks and the protolith are evaluated to identify the tectonic environments of supra-subduction realms characterizing the South-Eastern Anatolian Orogenic Belt (SAOB). The metamorphic sole rocks were formed as a result of intra-oceanic thrusting during supra-subduction events in the basin throughout the closure of the SAOB in the Late Cretaceous. [ABSTRACT FROM AUTHOR]

40Ar/39Ar radio-isotopic dating of volcanic tuffs intercalated in sediments can provide high accuracy age control on the deposition of sedimentary rocks. State-of-the-art mass spectrometers such as the ARGUS VI+ are able to acquire highly precise ages for relatively small single grains (~90-250 µm for Miocene samples). Single grain measurement can provide insight into the sometimes complex age distributions within volcanic tuffs. The results show that 40Ar/39Ar ages based on multiple grain fusions will not necessarily reflect eruption ages, which can lead to (slight) overestimation of the depositional age. The paper compares multiple and single grain data from different Miocene tuffs in the Central Paratethys, which plays an important role in the establishment of a geological time frame for this area. The examples come from three middle Miocene tuff horizons that span from the Badenian transgression to the Badenian--Sarmatian Extinction Event. The new ages obtained from the Quellgraben section in the Styrian Basin (14.31± 0.27 Ma and 14.03 ± 0.04 Ma) are much younger than the previous dating and together with the new data from the Bernhardsthal-4 well, Vienna Basin (15.12 ± 0.19 Ma) indicate, that the Badenian (Langhian) marine flooding did not reach this area before 15.2 Ma. The new weighted mean age of 12.56 ± 0.10 Ma from the Kamenica nad Hronom section in the Danube Basin dates the transition from marine to terrestrial setting, which is possibly connected with a sea level lowstand at the beginning of the Sarmatian. [ABSTRACT FROM AUTHOR]

The northern extent of the Scandinavian Caledonides includes the Skibotn Nappe Complex of still debated structural position. This paper is focused on part of this complex and presents new U–Th–total Pb monazite dating results for the migmatitic gneiss of the Kåfjord Nappe. The rocks show mineral assemblage of garnet + plagioclase + biotite + white mica + kyanite + rutile ± K-feldspar ± sillimanite. Thermodynamic modelling suggests that garnet was stable at P–T conditions of ca. 680–720 °C and 8–10 kbars in the stability field of kyanite and the rocks underwent partial melting during exhumation following a clockwise P–T path. This episode is dated to 444 ± 12 Ma using chemical Th–U–total Pb dating of the Y-depleted monazite core. Second episode highlighted by growth of secondary white mica resulted from subsequent overprint in amphibolite and greenschist facies. Fluid assisted growth of the Y-enriched monazite rim at 419 ± 8 Ma marks the timing of the nappe emplacement. Age of migmatization and thrusting in the Kåfjord Nappe is similar to the Kalak Nappe Complex, and other units of the Middle Allochthon to the south. Nevertheless, the obtained results do not allow for unambiguous definition of the tectonostratigraphic position of the Skibotn Nappe Complex. [ABSTRACT FROM AUTHOR]

This paper presents geochronological data for the volcanic dykes located in the northern Považský Inovec Mts. The dykes are up to 5 m thick and tens to hundreds of metres long. They comprise variously inclined and oriented lenses, composed of strongly altered grey-green alkali basalts. Their age was variously interpreted and discussed in the past. Dykes were emplaced into the Tatricum metamorphic rocks, mostly consisting of mica schists and gneisses of the Variscan (early Carboniferous) age. Two different methods, zircon SHRIMP and monazite chemical dating, were applied to determine the age of these dykes. U--Pb SHRIMP dating of magmatic zircons yielded the concordia age of 260.2 ± 1.4 Ma. The Th--U--Pb monazite dating of the same dyke gave the CHIME age of 259 ± 3Ma. Both ages confirm the magmatic crystallization at the boundary of the latest Middle Permian to the Late Permian. Dyke emplacement was coeval with development of the Late Paleozoic sedimentary basin known in the northern Považský Inovec Mts. and could be correlated with other pre-Mesozoic Tethyan regions especially in the Southern Alps. [ABSTRACT FROM AUTHOR]