Tectonic implications of paleomagnetic results from the Northern Adriatic area: an overview

Abstract

<p>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. <br />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.<br />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. <br />This work was financially supported by the National Development and Innovation Office of Hungary project K 128625.</p>