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Double-Vergent Thrusting in the External Dinarides of Croatia: Consequences on Deposition, Tectonics and Hydrocarbon System Evolution

Bruno Tomljenović, Igor Vlahović, Ivo Velić, Bojan Matoš, Josipa Velić, Lilit Cota, Goran Bejdić, Tamara Troskot-Čorbić, and Vladimir Veseli

The External Dinarides form a thin-skinned fold-thrust belt extending in NW–SE direction along the northeastern Adriatic coast. They comprise the regional-scale tectonic units derived from the Adriatic microplate, being composed of more than 7 km-thick succession of predominantly carbonate and subordinate clastic and igneous rocks of Carboniferous to Miocene age.

The majority of the carbonates accumulated from the Late Triassic to Late Cretaceous, when the Adriatic Carbonate Platform became gradually affected by generally NE–SW directed compression due to the collision between the Adriatic and European plates.

During the Eocene–Oligocene the deposition was restricted into several NW–SE trending basins of both the foredeep and the piggy-back type, controlled by the propagating thrust sheets. They were characterized by mostly carbonate deposition on ramps and deep-marine deposition in distal parts.

As a result of continuous geological explorations for more than a century, the present-day structural architecture of the External Dinarides is presumed as being almost exclusively the result of two tectonic phases: the phase of Late Eocene–Oligocene SW-verging and SW-propagating thrusting, overprinted by the younger, presumably Miocene, phase of dextral wrenching.

However, according to our recent multidisciplinary investigation focused on Kimmeridgian source-rocks of the central part of the External Dinarides in Croatia, the first order NW–SE striking thrust structures characterised by the opposite vergence, i.e. the NE tectonic transport direction are clearly distinguished. As the NE-verging map-scale structures were also reported from the neighboring areas, it may be concluded that the NE-vergent thrusting was the oldest and prevailing tectonic phase in formation of this part of the Dinarides. Hence, it is of the major importance for reconstruction of tectonic and hydrocarbon system evolution and the origin of massive and voluminous carbonate breccia associated with the NE-vergent structures.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013