Emő Márton

Reconstruction models of the Mediterranean area are typically based on geological and structural observations, and occasionally validated by selected paleomagnetic data. In contrast, the reconstruction of the present study primarily relies on APWPs defined by paleomagnetic data, and is tested against geological and tectonic observations. The study focuses on the Mesozoic displacement history of Adria with respect to the African and European plates. Kinematic reference frames for the large plates are provided by Global APWPs of various definitions, which tightly constrain the expected declinations in both the African and the stable European tectonic frames, but allow some speculations about paleolatitudes between 170 and 130 Ma.The kinematic constraints for Adria are based on a recently published APWP derived from a substantial paleomagnetic dataset, representing stable and imbricated Adria, the Transdanubian Range Unit and the Southern Alps. The dataset was quality-controlled and it was evaluated with different methods (running mean averaging, spline fitting) resulting in closely correlating trends.The GPlates reconstruction is based on the above defined APWPs, visualizing the tectonic displacements within the Africa-Adria-Europe system for selected time periods. Paleo-longitudes, not constrained by the paleomagnetic data, were estimated using structural reconstructions of the region. The outline of Adria microplate is a simplified one, based on the earlier published Greater Adria concept.In the GPlates reconstruction the following important events of this system are highlightedAdria drifted away from Europe after 200 Ma, connected to the initial rifting of the Alpine Tethys Adria rotated clockwise with respect to Africa during 170–150 Ma. This period of time is characterized by hyperextension and initial spreading phases of the Alpine Tethys and also by intra-oceanic subduction in the Neotethys Adria rotated counterclockwise with respect to Africa during 150–120 Ma, when obduction and subsequent shortening took place in the Neotethyan margin, while spreading continued in the Piemont-Ligurian and Valais oceanic branches Adria shifted northward after 150 Ma, in coordination or independently of Africa, moving closer to stable Europe around 115 Ma. This may explain tectonic deformation and/or uplift in several units of African origin. Southward shift of Adria is suggested between 115–100 Ma, when a general deepening of the sedimentary basins is recognized in the Central Mediterranean.

Silicic ignimbrite volcanism played a major role in the Miocene evolution of the Central Paratethys. The most voluminuous ignimbrites identified to date (18.1–14.4 Ma) were emplaced in various paleoenvironments in the North Pannonian Basin, thus they are extremely helpful in regional stratigraphy. Here, we present the discovery of a previously unknown but widespread, youngest member of the “Upper Rhyolite Tuff“, referred to as Dobi Ignimbrite, which shows a distinctive glass geochemistry. High-precision sanidine and plagioclase Ar-Ar dating yielded 13.066±0.019 Ma (earliest Sarmatian stage in Paratethys chronology), significantly shifting the previously claimed termination (i.e. Badenian) of the North Pannonian ignimbrite flare-up. In addition, we demonstrate that, although the Dobi Ignimbrite is underlain by a marine sedimentary succession, it was emplaced on land, as it bears leaves and tree trunk fragments and is rich in charcoal. Despite the highly faulted terrain as well as intense dissection and erosion controlled by the neotectonic evolution of the Pannonian Basin, the observed areal extent (c. 1000 km2) and calculated minimum volume (c. 50 km3) of the ignimbrite may represent a VEI= 6 or 7 eruption, which needs to be further delineated. At the same time, the ignimbrite has a strongly phreatomagmatic character, suggesting an abundant, possibly shallow sea- or residual lake water source that was likely limited to the vent area (e.g. caldera graben). The detected sharp environmental change from submarine to terrestrial, as defined by the timing of ignimbrite emplacement at c. 13 Ma, marks the latest Badenian regressive period, followed by a Sarmatian erosion during the Central Paratethethys evolution.

The systematic paleomagnetic investigations concentrating on the northern part of stable Adria and the External Dinarides provided tectonically applicable results for nearly 200 localities from Italy, Slovenia and Croatia. The ages of the studied localities were tightly controlled by a bed by bed checking of the fossil content. The age of the acquisition of the magnetization was constrained by between-locality fold/tilt test, which often proved the pre-deformation “primary” age of the magnetization. It is important to emphasize that most of the sampled sediments were shallow water carbonates with weak natural remanent magnetizations (about 30% of the sampled localities failed to yield paleomagnetic signal). However, those providing results are extremely valuable, for inclination flattening is practically absent in platform carbonates, therefore the estimation of the paleolatitudes are reliable. The majority of the tectonic models published for the area are in agreement about the existence of two Mesozoic carbonate platforms, an Adriatic and a Dinaric, which came into contact during the Late Eocene-Oligocene thrusting of the latter over the former. They are in the External Dinarides, but the exact boundary between them is a matter of discussion. The tectonostratigraphic complexity of the External Dinarides is the main reason for the large number of models published for the Northern Adriatic area.The paleomagnetic results, which permit to conclude as to the absence or existence of large-scale relative movement between areas, suggest that stable Adria and the whole chain of the Adriatic islands moved in a co-ordinated manner, i.e. the islands represent the imbricated margin of stable Adria, at least from the Aptian onward. During the Late Cretaceous, the area was close (38°N) to the northernmost limit (40°N) of the intensive carbonate production, the carbonate factory. Stable Adria with its imbricated margin exhibits about 30° larger CCW rotation than the High Karst belonging to the Dinaric platform, thus giving further support to considering the chain of the Adriatic island as belonging to Adria. The practically parallel “primary” paleomagnetic declinations characterizing the Northern Adriatic area are at variance with the oroclinal origin of the arcuated shape of the chain of the Adriatic islands and of the thrust front between them and stable Adria. We attribute this shape to the dominance of the Late Cretaceous E-W compression in the northern segment, the Late Eocene-Oligocene NE-SW compression in the central segment, and the N-S oriented Neotectonic compression in the Central Adriatic area. This work was financially supported by the National Development and Innovation Office of Hungary project K 128625.

The Central and Southern Adriatic islands, situated offshore of the Split-Dubrovnik segment of the mainland, belong to the External Dinarides. Their dominant tectonic trend is W-E, significantly different from the general Dinaric NW-SE orientation. For this reason, they are often regarded as belonging to a distinct tectonic unit, and sometimes a vertical axis counterclockwise (CCW) rotation is invoked to explain the deviation from the general tectonic trend.In this paper, new paleomagnetic results are presented from Late Jurassic through Paleocene shallow water limestones from the Central and Southern Adriatic islands. For the localities sampled for paleomagnetic investigation, the sedimentological properties and the stratigraphic ages, based on the foraminifera population, were checked by microscopy investigation. The paleomagnetic analysis was carried out on field oriented drill cores, according to standard laboratory processing. The results were evaluated statistically on locality level. Overall-mean paleomagnetic directions were computed for several age groups and the age of the acquisition of the remanence was estimated from between-locality fold tests for a number of age groups. Comparison with earlier published results from the Northern Adriatic islands and from Stable Adria lead to the conclusion that the Central and Southern Adriatic islands had not rotate with respect to the Northern ones and even more importantly, stable Adria and the offshore External Dinarides must have moved as an integrated unit, at least from the Albian on.This work was financially supported by the National Development and Innovation Office of Hungary project K 128625.

In the Southern part of Montenegro three main tectonic units are distinguished. The Dalmatian (South-Adriatic) zone is in the lowermost tectonic position and comprises shallow water Cretaceous carbonates, bauxites, Middle Eocene nummulitic limestones, transitional marls, and Upper Eocene flysch. It is thrusted over by the Budva zone characterized by deep water sediments of Triassic through Paleogene ages with tuffitic layers in the Ladinian. The uppermost unit is the High Karst zone developed in a carbonate platform environment from the Middle Triassic till the end of the Cretaceous. In this unit flysch sedimentation started after the K/T boundary.From the above units we drilled and oriented in situ a total of 248 samples representing nine localities from the Dalmatian, six from the Budva and five from the High Karst zone, respectively. The harder rocks were drilled with portable gasoline powered, the softer ones with an electric drill. The laboratory measurements, demagnetizations, statistical evaluations of the measurements were carried out using standard methods in the Paleomagnetic Laboratory of the Mining and Geological Survey of Hungary. From the Dalmatian zone, the Upper Cretacous limestones have diamagnetic susceptibilities, very weak NRM, which either failed to provide statistically acceptable results (two localities) or obtained their remanence quite recently. The five flysch and transitional marl localities have well-defined AMS fabrics as well as paleomagnetic directions. The AMS fabrics must have been imprinted in a NE-SW oriented compressional strain field, which resulted in moderately strong fabrics with NW-SE oriented AMS lineations, perfectly following the Dinaridic trend recognized in Croatia. One locality, the only one with moderate tilt and rather poor statistical characteristics suggest post–Eocene CCW, while those with steep dips have well-defined paleomagnetic directions, which are aligned with the intermediate AMS direction. The positive tilt test, however, provides an overall mean direction with absurdly shallow inclinations, which suggest that we are not dealing with “real” paleomagnetic directions, but maybe with magnetic anisotropy governed NRMs.The rocks in the Budva zone show a large variation in lithological sense as well as in their magnetic properties. Except a Pietra Verde localitiy, the magnetic susceptibilities are weak, we can not define AMS fabrics, yet most of the localities yielded fairly good paleomagnetic results, which suggest pre-folding age of the acquisition followed by a large CW rotation of unit.From the High Karst, only a single Lower Jurassic pelagic limestone provided paleomagnetic results which exhibit CW rotation. The others had weak magnetizations, diamagnetic susceptibilities and no or scattered magnetic signals.This work was financially supported by the National Development and Innovation Office of Hungary project K 128625, by the Geological Survey of Montenegro and Ministry of Science and Education of Serbia project No. 176016.