T6
The Shkoder-Peja transverse zone (SPTZ) of Northern Albania marks the boundary between the Dinarides and the Albano-Hellenides chains and corresponds to a ~100 km SW-ward shift of the ophiolitic nappe front. Over the last sixty years, it has been variably interpreted as an inherited paleogeographic feature, a dextral strike-slip fault, the hinge of the clockwise (CW) rotating Albano-Hellenides system, and a Miocene-to-recent normal fault. Here we report on the paleomagnetism of 27 Triassic-Cretaceous sites from the Krasta-Cukali and the High Karst domain, both within and north of the SPTZ. Two sites yielded only a pre-tilting magnetization, 15 sites were found to be remagnetized after mid-Eocene-lower Miocene tilt, while 8 sites showed both pre- and post-tilt magnetizations. Both pre- and post-tilt paleomagnetic directions yielded a 60-70° clockwise (CW) rotation with respect to Adria/Africa, except 9 sites from the Koman zone at the ophiolitic nappe boundary showing a smaller 38°±15° CW rotation. Thus, the well-known regional CW rotation of the Albano-Hellenides extends northward in the southern Dinarides, and the SPTZ is not a rotation boundary as previously assumed. The ~70° CW rotation is consistent with available data from the nearby ophiolitic nappe complex, and is assumed to represent the sum of a 30° lower Miocene rotation during thrusting of the Kasta-Cukali over Kruja nappe plus the 40° Miocene-Pleistocene rotation well documented in the external zones of Albania. We suggest that the SPTZ is the heritage of a mid-Triassic transform fault of the Maliac Tethyan ocean, later overprinted by the lower Cretaceous obduction of the Vardar ocean, replacing Maliac since the middle-Jurassic.
How to cite: Feriozzi, F., Siravo, G., and Speranza, F.: The heritage of Tethyan oceanic transform faults within Alpine orogens: The Shkoder-Peja transverse zone (SPTZ) of Northern Albania, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-3, https://doi.org/10.5194/egusphere-alpshop2024-3, 2024.
The Dinarides represent a part of a double-vergent Dinaric – Carpatho – Balkan orogenic chain that formed as a response to the closure of a branch of the Tethys ocean in the latest Jurassic and subsequent convergence between the Adriatic microplate and the European continent, which is still active in the recent times. Different in convergence rates, this driving force of tectonics in the Balkans produced different kinematics of the fault structures in the central part of the Balkan Peninsula. General opinion is that from the Cretaceous times up to the Oligocene the fault kinematics in the area acted in a compressional regime, which, after the extensional episode in the Miocene, continued as a strike-slip regime in the neotectonic time. However, some regional structures seem to show evidence of oblique-slip kinematics much earlier, already in the Late Cretaceous times. Some of these pieces of evidence are related to the existence of intracontinental basalts related to the fault structures, asymmetric pull-apart sedimentary basins, tectonic structures, etc.
In this contribution, we will present the most recent results of the study of one of the most prominent tectonic structures of the Internal Dinarides, the well-known Zvornik fault (suture), and its southward continuation in the area of the Jelica Mts. in western Serbia. We will show evidence of the Late Cretaceous activity of this regional fault and discuss its importance in the context of the formation of Late Cretaceous basaltic magmas and specific sedimentary basins in this area.
Acknowledgement: This research was financed by the Science Fund of the Republic of Serbia through project RECON TETHYS (7744807).
How to cite: Mladenović, A., Gajić, V., Sokol, K., and Prelević, D.: Regional Strike-Slip Structures in the Internal Dinarides: Insights from the Zvornik Fault, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-47, https://doi.org/10.5194/egusphere-alpshop2024-47, 2024.
Volcano-sedimentary successions of Middle Triassic age can be traced along the Dinaridic mountain chain from northern Croatia in the northwest to Montenegro in the southeast. Their deposition is related to a regionally well-marked rifting phase linked to the opening of the Neotethys Ocean. The successions locally vary in thickness and display great facies variability of sedimentary and volcanic/volcaniclastic rocks, reflecting complex geodynamic settings in which they were formed.
Sedimentary rocks in these successions range from the outer margin and upper slope deposits, characterized by coarse- and fine-grained resedimented shallow-marine carbonate material, to open-marine deposits including pelagic limestone and radiolarian chert. Locally, specific low-diversity fossil assemblages and the high proportion of organic matter in sediments indicate deposition in a restricted environment where primary production was limited to the upper part of the water column (Goričan et al. 2015).
Stratigraphically stacked, volcanic and volcaniclastic lithologies range in composition from basaltic to rhyolitic and are present as doleritic subvolcanic intrusions, basaltic effusions and several volcaniclastic facies. Autoclastic basaltic facies and resedimented autoclastic facies are formed by the fragmentation caused by the rapid cooling of lava in contact with cold seawater and subsequent redeposition of the newly formed clasts. Rhyolitic pietra verde tuffs are interpreted as products of explosive volcanic eruptions distributed in pelagic environments by gravitational mechanisms, including air-fall and pyroclastic density currents. Locally, medium- to fine-grained volcanogenic turbidites represent unconsolidated pyroclastic detritus redeposited during or shortly after eruptions. Geochemical data show that parental magmas responsible for generating these volcanics/volcaniclastics had a calc-alkaline to shoshonitic composition and are interpreted to have formed during continental rifting in ensialic and mature arc settings.
Biostratigraphic data indicate pelagic conditions generally lasted from the Middle Anisian to the Late Ladinian, with local variations. Late Anisian age (Reitziites reitzi Ammonoid Zone) is inferred for the oldest pietra verde tuffs with radiolarians from intercalated chert. Basaltic volcanic/volcaniclastic rocks yielded K-Ar and Ar-Ar ages of 241.1±5.2 and 244.5±2.8 Ma. These ages indicate the coeval existence of bimodal volcanism comparable to the modern East African Rift System.
Middle Triassic volcano-sedimentary successions of the Dinarides testify about an active rift in the Dinarides between the Middle Anisian and the Late Ladinian. Extensional movements of the lithospheric blocks created horst-and-graben topography with pelagic sediments and volcaniclastic detritus accumulating on the subsided blocks. Laterally still active carbonate platform areas supplied carbonate detritus to these pelagic environments. Deep-rooted normal faults served as conduits for the ascent of basaltic magma and the formation of associated volcaniclastic facies. However, with the main Neotethyan rift located further to the east, extension in this area of the Dinarides ceased in the Ladinian, resulting in the filling of pelagic areas and the reestablishment of shallow-marine carbonate sedimentation.
References:
Goričan Š, Kolar-Jurkovšek T, Jurkovšek B (2015) Paleoecology of Middle Triassic Low Diversity Radiolarian Fauna from Mt. Svilaja (External Dinarides, Croatia). In: Tekin UK, Tuncer A (eds) Proceedings of 14th INTERRAD: an International Conference on Fossils and Recent Radiolarians, 22-26 March 2015, Antalya, Turkey. Radiolaria 35, 142–143.
How to cite: Kukoč, D., Smirčić, D., Slovenec, D., Belak, M., Grgasović, T., Horvat, M., Šegvić, B., and Vukovski, M.: Tracing the aborted Middle Triassic Neotethyan rift along the Dinarides, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-48, https://doi.org/10.5194/egusphere-alpshop2024-48, 2024.
Many questions regarding the geodynamics of the Vardar Tethys have mostly been settled, including the timing of the ophiolite obduction in the Balkans and the configuration of oceanic domains during the Jurassic period. However, the terminal stages of the evolution of Vardar branch of the last Tethyan ocean in the Balkans, specifically the time of its final closure, remains controversial. Current consensus favors a late ocean closure during the Late Cretaceous [1]. Although the timing of the obduction of the Balkan ophiolites indicate a closure in the latest Jurassic/earliest Cretaceous, the discovery of Upper Cretaceous magmatic rocks in the Sava-Vardar suture, interpreted as ophiolites, lead some authors to extend the life of the last Tethyan ocean to the latest Cretaceous. However, more recent findings call into question the oceanic character of these rocks [2], and propose a possible intra-continental environment for their origin. Another strong argument for the existence of an active subduction during the Cretaceous is the presence of the Timok Magmatic Complex (TMC) as part of the larger Apuseni-Banat-Timok-Srednogorje metallogenic belt. In this communication, we present our preliminary results of numerical modelling of Cretaceous geodynamics in the Balkans. We adopt the perspective that the magmatic rocks in the Sava-Vardar Zone do not represent ophiolites, and argue for ocean closure by the earliest Cretaceous, consistent with our previous models of Jurassic ophiolite obduction in the Balkans [3]. We try to account for the Cretaceous magmatism in the Sava-Vardar Zone and TMC in the context of an already closed ocean at the surface. To this end, we model the dynamics of the already subducted slab that is still attached, whereas the ocean lithosphere is completely consumed. The slab consists of the subducted oceanic lithosphere and a smaller portion of the basement of Adria. This slab undergoes detachment which is followed by the rise of its shallower parts and delivery of subducted rock material into favorable conditions for partial melting. The models are based on both an idealized configuration as well as the spontaneous continuation of our previous models of the Tethys closure.
Acknowledgement: This research was financed by SRI based on Contract no. 451-03-66/2024-03/200126 as well as the Science Fund of the Republic of Serbia through project RECON TETHYS (7744807). VC acknowledges the support of the Serbian Academy of Sciences and Arts (F9 and F17).
References:
[1] Van Hinsbergen, D. J., Torsvik, T. H., Schmid, S. M., Maţenco, L. C., Maffione, M., Vissers, R. L., ... & Spakman, W. (2020). Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic. Gondwana Research, 81, 79-229.
[2] Sokol, K., Prelević, D., Romer, R. L., Božović, M., van den Bogaard, P., Stefanova, E., ... & Čokulov, N. (2020). Cretaceous ultrapotassic magmatism from the Sava-Vardar Zone of the Balkans. Lithos, 354, 105268.
[3] Stanković, N., Gerya, T., Cvetkov, V., & Cvetković, V. (2023). Did the Western and the Eastern Vardar ophiolites originate through a single intra-oceanic subduction? Insight from numerical modelling. Gondwana Research, 124, 124-140.
How to cite: Stanković, N., Mladenović, A., Prelević, D., Cvetkov, V., and Cvetković, V.: Can the dynamics of a subducted slab account for the Upper Cretaceous magmatism in the Sava-Vardar Zone and Timok Magmatic Complex? A Numerical Modelling Approach., 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-66, https://doi.org/10.5194/egusphere-alpshop2024-66, 2024.
The NNW–SSE-trending Vardar suture zone was formed as a result of the Late Triassic to Early Jurassic opening of the Vardar Ocean as a branch of Neotethys, followed by subduction and collision of the Adria- and Europe-derived continental microplates during Early Cretaceous. The paleogeography and kinematics of the closure of the Vardar Ocean are still a matter of debate, and two main models exist based on the differences between Eastern and Western Vardar ophiolites. A simpler, one-ocean model invokes one oceanic domain subducted beneath the European plate, with a slab-rollback generating Eastern Vardar ophiolite in a back-arc basin. In contrast, a two-ocean model assumes the existence of two separate oceanic basins (relict Paleotethys and Vardar) consumed by doubly-vergent subduction. To test these two contrasting models, we present new tectonic, kinematic, and anisotropy of magnetic susceptibility (AMS) data from the Vardar zone in southern Serbia, where a complete section from one continental margin to another is superbly exposed. From east to west, the main lithotectonic elements across the suture are: (1) the Serbo-Macedonian Massif, composed of medium- to high-grade orthogneisses and paragneisses with lenses of marble, quartzite, and amphibolite, representing the European margin; (2) the Cretaceous flysch, younging westward; (3) the Goč–Kopaonik and Radočelo metamorphic complexes, composed of Early Paleozoic volcano-sedimentary successions (phyllites, marbles, and metabasites), that crop out within the suture; (4) obducted ophiolites dominated by serpentinized peridotite (Ibar being the largest) and their metamorphic soles; (5) deep-marine, pelagic successions (shales, cherts, limestones); and (6) Drina–Ivanjica belt, dominated by low-grade albite–sericite slates, representing the Adria-derived microplate. The flysch successions have been strongly shortened and folded into upright, tight to isoclinal folds and thrust over the ophiolites in some places with top-to-the-WSW kinematics. The ophiolites are frequently cross-cut by a dense network of brittle-ductile shear zones anastomosing around rigid (less serpentinized) peridotite blocks. The sense of shear locally varies, but generally is top-to-the-WSW(SW). The AMS data in the Ibar ophiolite indicate simple-shear-dominated strain along the eastern ophiolite–flysch contact with magnetic foliations moderately dipping to the NE to SW and bearing down-dip magnetic lineations, whereas magnetic fabric of the inner part of the ophiolite indicates pure-shear-dominated strain with more variable orientation of the principal susceptibilities. The easterly sub-ophiolitic Goč–Kopaonik and Radočelo complexes preserve an older fabric predating ophiolite emplacement, except near-contact zones that are strongly sheared. In contrast, the westerly metamorphic sole and pelagic successions dip uniformly beneath the ophiolite. Finally, the Drina–Ivanjica belt is dominated by a pre-collisional flat fabric. Taken together, the obtained data suggest regionally consistent top-to-the-WSW(SW) kinematics of thrusting and ophiolite emplacement across the Vardar suture zone and along with westward-younging of deformation and flysch deposition support the one-ocean model.
How to cite: Tkáčiková, T. and Žák, J.: Single or double subduction? New constraints from structural analysis and magnetic fabric from the Vardar suture zone, Serbia, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-23, https://doi.org/10.5194/egusphere-alpshop2024-23, 2024.
The complex geodynamic evolution of the northernmost Neotethys is the subject of ongoing controversy. Key issues revolve around the waning stages of the Tethyan ocean(s) in the Balkans and the timing of the Europe-Adria collision. Some researchers propose that this collision occurred in the Late Jurassic, while others argue it happened at the end of the Cretaceous along the Sava Zone. The latter hypothesis suggests that the Cretaceous Sava Ocean is a remnant of the youngest Tethyan oceanic realm, left behind after a major convergence in the Jurassic.
In this study, we present recent findings from magmatic, sedimentary, and basement formations within the Sava Zone. Our goal is to constrain the timing, origin, geodynamic environment, and lifespan of the purported Cretaceous Sava Ocean. The central scientific question we address is whether the Sava Zone represents: (i) a relic of the Neo-Tethyan Ocean that closed in the late Cretaceous, or (ii) a diffuse tectonic boundary between earlier collided Gondwana-related blocks and Europe, characterized by a system of pull-apart basins and transtensional tectonics.
Cretaceous igneous formations are found on both sides of the Sava-Vardar suture Zone, in the Dinarides (Gondwana) and Serbian-Macedonian Mass (Europe). These formations predominantly consist of basalts, with subordinate occurrences of lamprophyres, trachybasalts, and andesites, none of which exhibit ophiolitic geochemical characteristics. They show heterogeneous geochemical affinities, primarily derived from (metasomatized) continental lithospheric mantle. Notably, there are clear geochemical differences between the lavas in the Dinarides (depleted) and those in Europe (enriched due to metasomatism).
Our recent zircon provenance data from Cretaceous sediments in the Sava Zone offer new insights into the closure of the Tethys in the Balkans. We first analysed numerous zircon grains from various basement units. Our results indicate that zircons from both the Dinarides and Europe contain ubiquitous Neoproterozoic (Cadomian) and well-defined Silurian-Ordovician (±Devonian) populations. Carboniferous (Hercynian) zircons (>300 Ma) are predominant on the European side, whereas they are somewhat younger (~300 Ma) in the Dinarides. Permotriassic zircons constitute the strongest geochronological signal in all examined Dinarides samples (Africa) likely representing a ubiquitous signal in all Gondwana-affinity units in the Balkans, but are absent on the European side.
Our zircon provenance data from Cretaceous formations in the Sava-Vardar suture Zone show the ubiquitous presence of Permotriassic zircons, constituting the strongest geochronological signal in all samples. If our findings are correct, the basin on the European margin was partially filled from the Adriatic side during the Lower Cretaceous, which suggests the non-existence of a vast (>350 km) Sava (Tethys) Ocean.
Acknowledgement: This research was financed by the Science Fund of the Republic of Serbia through project RECON TETHYS (7744807).
How to cite: Prelević, D., Sokol, K., Mladenović, A., Gajić, V., and Cvetković, V.: Reconstruction of the Tethys’ Waning in the Balkans, 16th Emile Argand Conference on Alpine Geological Studies, Siena, Italy, 16–18 Sep 2024, alpshop2024-38, https://doi.org/10.5194/egusphere-alpshop2024-38, 2024.
