Lithospheric density model along the CEL09 profile and its geological implications
Abstract: We present a new 2D lithospheric density model along the seismic profile CEL09 crossing the Bohemian Massif, the Western Carpathians, and the Pannonian Basin. The resulting model consists of five principal layers: sediments, upper crust, lower crust, lower lithosphere, and asthenosphere. The thicknesses of the Neogene sedimentary basins vary from 0 to ~5.5 km while the Paleogene flysch sediments dip to a depth of ~6.5 km. The most complex upper part of the upper crust in the Bohemian Massif is represented mainly by low-density granitoid plutons (~2.60–2.68 g cm−3), metamorphic rocks (~2.69–2.74 g cm−3) and high-density basic and ultrabasic bodies (~2.78–2.79 g cm−3). In the Western Carpathians, this layer is formed by the crystalline Malé Karpaty Mts. (2.66–2.67 g cm−3), Trans-Danubian range (2.73–2.74 g cm−3), and the pre-Cainozoic basement of the sedimentary basins (2.67–2.74 g cm−3). The densities of the lower part of the upper crust range from 2.78 g cm−3 (in the Western Carpathian–Pannonian region) to 2.77–2.80 g cm−3 (in the Bohemian Massif). In the lower crust, four different sectors were modelled. In the Saxothuringian, they are divided into two layers, the upper layer (2.84–2.85 g cm−3) and the lower layer (3.12 g cm−3). The Moldanubian has the thickest lower crust (~20 km) with a density of 2.98 g cm−3; the lower crust in the Moravo–Silesian has a density of 2.97 g cm−3. The Western Carpathian–Pannonian region is represented by slightly lower densities of 2.94–2.96 g cm−3. The gravity modelling indicates that the Western Carpathians were overthrusted by ~30 km onto the Bohemian Massif resulting in a neo-transformation of the crust/mantle and related lithosphere after subduction.
Upper Neoproterozoic garnet-bearing granites in the Zeber-Kuh region from east central Iran micro plate: Implications for the magmatic evolution in the northern margin of Gondwanaland
Abstract: This paper reports, for the first time, on a garnet-bearing granite body at Zeber-Kuh and interprets its petrogenesis, age and tectonic setting within the context of the evolution of the Cadomian subduction system. The primary minerals imply an origin at pressures greater than 8–6 kbars (~ 25 km depth) and at temperatures above 700 °C with >10 % water. The Zeber-Kuh granite is in tectonic contact with neighboring rocks. This igneous body has average SiO2 of 71 wt. %, average Al2O3 of 14 wt. %, 3.1–3.6 wt. % Na2O, 3.0–6.2 wt. % K2O and 3.3–0.1 wt. % MgO. The granite is characterized by light rare earth element (LREE)-enrichment, relatively flat heavy rare earth element (HREE) patterns with a small negative Eu anomaly and moderately fractioned REE patterns [average (La/Yb)N = 11.32]. Decreasing Fe2O3T, MgO, CaO, TiO2, Ba, Eu and Sr with increasing SiO2 contents are consistent with fractional crystallization and can be related to fractionation of plagioclase, clinopyroxene, hornblende, and apatite. Two granite samples yielded U–Pb zircon ages of 533±3 and 534±6 Ma, which regionally correspond to the younger Cadomian magmatism. Cathodoluminescence images of zircon grains from the studied samples show well-developed oscillatory bands, typical of felsic magmas zircons, and Th/U ratios range from 0.79 to 0.45 with an average of 0.60. The REE patterns of the zircons show progressive enrichment from LREE to HREE with a positive Ce anomaly and a negative Eu anomaly.The garnet-bearing granite of Zeber-Kuh represents the final stage of Cadomian magmatism along an extensional continental arc adjacent to the northern active margin of Gondwanaland.
Petrology and zircon U–Pb dating of granitoid rocks in the Highiş massif (SW Apuseni Mts., Romania): Insights into Permian plutonic–volcanic connections
Abstract: Permian granitoids in the Highiş massif (SW Apuseni Mts., Romania) are anorogenic (A-type), having a peraluminous, subalkaline, alkali-calcic or calc-alkalic, and ferroan character with granodioritic to granitic compositions. Trace elements suggest the crustal origin of the studied samples that derive from a common or similar source associated with post-collisional rifting. Based on trace elements and zircon U–Pb ages (~268–263 Ma), a plutonic–volcanic connection was revealed between the Highiş granitoids and the Mid-Permian (~267–260 Ma) felsic volcanic rocks that are widespread in the Tisza Mega-unit. Felsic plutonic and volcanic rocks (along with mafic–intermediate plutons and lavas in the Apuseni Mts.) represent a Mid-Permian, cogenetic magmatic system. Our results suggest that the study area belongs to the Tisza Mega-unit, in contrast to recent studies considering it as part of the Dacia Mega-unit. Despite the Europe-derived nature of the Tisza Mega-unit, its Permian igneous formations are significantly younger than those of the stable Europe (~300–290 Ma). However, the studied rocks show correlations with some analogous formations in the ALCAPA Mega-unit, including Permian A-type granitoids and felsic volcanic rocks in the Western Carpathians (Gemeric, Veporic, and Silicic Units). On the other hand, many other rocks of similar age in the Western Carpathians and Eastern Alps bear completely different geochemical compositions (S-type character). The latter suggest at least two main types of magma source coevally within the Permo-Triassic post-orogenic setting in the Central European Variscides.
Heavy mineral analysis of the Turonian to Maastrichtian exotics-bearing deposits in the Western Carpathians: What has changed after the Albian and Cenomanian?
Abstract: Turonian to Maastrichtian exotics-bearing deposits from the Pieniny Klippen Belt (Klape and Kysuca units) and from the Považský Inovec Mts. (Western Carpathians) were analyzed for heavy minerals and compared with similar, yet older Albian–Cenomanian deposits. The Turonian to Maastrichtian deposits are petrographically more variable in composition in the entire range, from quartz arenites to litharenites. Percentages of the main heavy minerals are similar on both stratigraphic levels, i.e., they are dominated by chrome-spinels, zircon, tourmaline, apatite, and rutile. Garnet is more common in the Turonian to Maastrichtian samples, while titanite, kyanite, monazite, hornblende, blue amphibole, pyroxenes, epidote, staurolite, and sillimanite are quite rare. Statistical factor analysis indicates dominance of ophiolites and older sediments in the source areas. One important factor is an influx of garnet, with the weakest factor being related to the influx of tourmaline and apatite, which may indicate low-grade metamorphics. Spinels were derived from harzburgites (supra-subduction peridotites). The majority of tourmalines were derived from metasediments, Fe3+-rich quartz–tourmaline rocks, calc-silicate rocks, and metapelites and granitoids. Some had complex zonation with two phases of tourmaline (schorl–dravite and bosiite), or tourmaline intergrown with quartz. These were likely derived from ophiolitic sources. Garnets are predominantly almandinic and derived from rocks that had been metamorphosed up to the amphibolite facies, or magmatic rocks. Common pyrope–almandinic garnets indicate their source from granulites and eclogites. The main change after the Albian–Cenomanian period is the more expressed presence of the continental crust segments in the source area in comparison with ophiolites.
Shallow to marginal marine ichnoassemblages from the Upper Pliocene Slama Formation (Lower Chelif Basin, NW Algeria)
Abstract: The Slama Formation (Upper Pliocene, Lower Chelif Basin, Algeria) displays siliciclastic deposits distributed in five determined stratigraphic members: Lower Sandstone Member, Lower Marls Member, Middle Sandstone Member, Upper Marls Member, and Upper Sandstone Member. It is characterised by low to moderate ichnofossil diversity consisting of 16 ichnotaxa: Arenicolites isp., Conichnus conicus, Gyrolithes polonicus, G. variabilis, Gyrolithes isp., Macanopsis isp., Macaronichnus segregatis, Ophiomorpha cf. annulata, O. irregulaire, O. nodosa, Palaeophycus isp., Skolithos linearis, Skolithos isp., Thalassinoides horizontalis, T. paradoxicus, and T. suevicus. Trace fossils are grouped into four ichnoassemblages. The Thalassinoides ichnoassemblage (Lower Sandstone Member and Lower Marls Member) represents a mixed Cruziana/Skolithos ichnofacies. The Skolithos ichnoassemblage (Middle Sandstone Member) represents the archetypical Skolithos ichnofacies and corresponds to middle shoreface settings. The Macaronichnus–Gyrolithes ichnoassemblage (Upper Marls Member) indicates shoreface/foreshore contact. The Ophiomorpha ichnoassemblage (Lower Sandstone Member) can be interpreted as the proximal Skolithos ichnofacies, which possibly corresponds to foreshore settings. The suggested dominant, regressive phase corresponds to the second half of the Upper Pliocene eustatic cycle in the northern Tell Atlas foreland domain.