Deformation record and revised tectonic evolution of the Nízke Tatry Mts. in the Tatric – Veporic junction area: Insights from structural analysis
Abstract: The Nízke Tatry Mts. is a mountain range located in the central part of the Western Carpathians. Throughout history, the studied area has been affected by at least two orogenetic cycles – Variscan and Alpine. Based on structural analyses, it is possible to determine several deformation events. The older deformations (DV), which were accompanied by the Variscan higher-grade metamorphism, are characterised by penetrative tectonic foliations, such as schistosity and gneissic banding, and go hand in hand with folds and lineations. In contrast, the younger deformations (DA) are marked by structural evolution under low-grade (retrograde) metamorphism, phyllitic foliations, crenulation foliation, cataclasis, and minor recrystallisation. The Variscan deformation (DV2) is the earliest pervasive deformation with pronounced evolution of SV2 metamorphic foliation, locally with preserved isoclinal and rootless folds of SV1 planar fabric. Stretching and mineral lineations (LV2) are usually oriented in the ENE–WSW direction. The fabric of DV2 is intensively affected by folds (FV3) and, in many places, marked by development of SV3 axial planes. The Alpine deformation (DA1) was accompanied by low-grade metamorphism and depicted by space to zonal with pervasive foliation (SA1) in some areas. This deformation is characterised by a typical crenulation cleavage, where SV2 planes are folded and produced SA1 foliation. The crenulation and intersection lineations (LA1c) have NE–SW to E–W trends. The DA1 deformation is also accompanied by pronounced evolution of NNW–SSE groove, stretching, and mineral lineation (LA1t). Shortening in the NNW–SSE direction is also evidenced by asymmetric folds with an ENE–WSW orientation of fold axes (FA1) and line intersections (LA1c) with pronounced top-to-the-NNW tectonic transport. The youngest observed Alpine deformation (DA2) is related to an extension of the Tatric crystalline basement with top-to-the-east transport defined by Alpine lineations (LA2) on spaced planar structures (SA2) and correspond to C surfaces.
Chronostratigraphic overview of the Toarcian (Early Jurassic) ammonite fauna from the Mecsek Mountains (Hungary)
Abstract: Many localities worldwide yielded rich Toarcian (Early Jurassic) ammonoid faunas whose diversity history enhanced our understanding of global events and their geographic distribution aided paleogeographic and paleoceanographic reconstructions. However, major differences remain in the intensity of studies as some areas have received significantly less attention, yet their study would improve regional and global correlations and reconstructions. The Toarcian faunas of the Mecsek Mts (SW Hungary) represented one such knowledge gap that is filled herein on the basis of the large Hetényi Collection and other material, totaling more than 5000 specimens. The Toarcian Ammonitina assemblages are outlined, documenting the occurrence of 43 species, of which 14 stratigraphically important species are described systematically. The studied assemblages bear a close affinity to the NW European faunal province, hence the standard ammonite chronostratigraphic scale is conveniently applicable for subdividing the Toarcian sequence of the Mecsek Mts. All of the Toarcian zones and most subzones are documented by their index taxa and the ranges established from NW European localities allow chronostratigraphic assignment of the ammonite-bearing localities in the Mecsek Mts. A comparison with other coeval faunas from the widespread spotted marl facies reveals that taxon richness here is comparable with that recorded from other parts of the Tisza Mega-unit in the Apuşeni Mts and the Eastern Carpathians in Romania. Temporal patterns of diversity changes, with peaks in the Bifrons and Thouarsense zones, may be interpreted in the framework of biotic changes in the aftermath of the Jenkyns Event.
Stress analysis from the southern part of Moravian Karst (Czech Republic)
Abstract: Data from three quarries in the southern Moravian Karst (SE Czech Republic), namely fault-slip data and calcite twinning data, enabled a side-to-side comparison of two paleostress analysis techniques. TwinCalc (www.eltekto.cz) was used to analyse 8 samples of calcite veins, yielding 20 stress states and MARK was used to analyse the fault-slip data yielding 10 stress states. 26 out of these 30 stress tensors were sorted into four stress phases (P1–P4) using a stress tensor similarity cluster analysis based on angles between stress tensor 9D vectors. The oldest phase is P4 – N–S trending compression. P1 is younger, and responsible for the reactivation of NW–SE striking dextral strike-slip faults. Both are post-Cretaceous pre-Langhian phases. The second-to-last phase is P3 associated with WNW–ESE striking mostly normal faults. This stress state had been active during the Miocene before the Tortonian P2 phase. The last phase is the Tortonian P2 phase, which is characterised by NNE–SSW striking dextral strike-slip faulting.
Geochronology and petrogenesis of the lower Miocene felsic rocks: New evidence for initiation of post-collisional magmatism in the SW Malatya – Eastern Anatolia (Turkey)
Abstract: The Southeast Anatolian Orogenic Belt (SAOB) consists of various tectono-magmatic and tectono-stratigraphic units such as metamorphic massifs, granitoids, ophiolites and volcanic rocks. In this study, we report new zircon U–Pb LA-ICP-MS ages, Sr–Nd isotope analysis and whole-rock geochemistry from Miocene felsic (dacitic and rhyolitic) rocks cross-cutting the Permo–Triassic Malatya metamorphic complex to determine the source of magmatism and magmatic processes in the region. The zircon U–Pb crystallisation ages are between 16.66 ± 0.23 Ma and 16.83 ± 0.094 Ma, implying the start of the post-collisional volcanism in the Early Miocene (Burdigalian) period. Volcanic rocks have calc-alkaline and high-K calc-alkaline characters. The 87Sr/86Sr values for the felsic volcanics range between 0.707098 and 0.711703. The initial 143Nd/144Nd ratios are between 0.512446 and 0.512469, and the εNd values vary from −3.12 to −3.66. The Nd (TDM) model ages are between 1.05 and 1.13 Ga. Negative εNd values and Nd (TDM) model ages show great similarities with the Precambrian basement in Turkey, Iran and the Arabian peninsula. Energy-constrained assimilation–fractional crystallisation (EC-AFC) models testing different crustal sources using Sr–Nd isotope data show that primary magmas contain significant crustal melt contributions. Geochemical data indicate that the felsic rocks may have originated from crust-derived melts mixed with lithospheric mantle-derived mafic melts during its residence in the upper crust in a post-collisional tectonic setting.
Tectonic inversion of Late Miocene extensional deformations in northeastern Tunisia (Cap Bon Peninsula–Sahel area)
Abstract: The tectonic inversion of the Miocene extensional basins (Cap Bon Peninsula–Sahel area, northeastern Tunisia) is an important process that accommodates the crustal shortening in the northeastern Tunisian edge with the ongoing collision between the African and European plates. Field observations and microtectonic measurements have revealed two main Late Miocene tectonic events: (1) A NE–SW trending extensional tectonic event that would create titled blocks, horsts, and grabens, as well as slump features. These structures were controlled by numerous conjugate systems of syndepositional normal faults. On a regional scale, the NW-trending faults controlled the Miocene sedimentation and subsidence rate in the Takelsa, Dakhla, Saouaf, and Zeramdine syn-rift grabens and (2) the NW-directed post-Tortonian compression, the so-called “Alpine/Atlasic event” that was identified by NE–SW-oriented reverse slip movements and associated folds. The latter compressional event began in the latest Miocene and continued through the Plio–Quaternary, which thus led to the complete inversion of the Miocene basins by the ongoing African and European plates’ convergence. A significant neotectonic uplift of the Abderrahmane, Korbus, and Skanes areas recorded the switch from Late Miocene crustal extension to post-Tortonian to Quaternary compressional tectonics. In fact, the present-day petroleum trap configuration of the northeastern offshore Tunisia is highly controlled to the Miocene–Quaternary tectonic inversion. The sandy levels along the thick Tortonian section provided the most preferred target for petroleum exploration. They exhibit considerable variations in thickness controlled by Late Miocene to Quaternary tectonic trends.