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

Bruno Tomljenović1, Igor Vlahović1, Ivo Velić1, Bojan Matoš1, Josipa Velić1, Lilit Cota2, Goran Bejdić2, Tamara Troskot-Čorbić3 & Vladimir Veseli3

1University of Zagreb, Faculty of Mining, Geology and Petroleum Engineering, Pierottijeva 6, HR-10000 Zagreb, Croatia (e-mail: [email protected]); 2INA Exploration & Production, V. Holjevca 10, HR-10002 Zagreb, Croatia; 3INA Exploration & Production, Lovinčićeva bb, HR-10000 Zagreb, Croatia

H TECTONIC PRESUMED SLO Zagreb KINEMATICS DEPOSITION HYDROCARBON SYSTEM Black Sea ~ ~ EVENT AGE ~ ~ ~ ~ ~ ~ Study ~ ~ Adriatic Seaarea BiH Mediterranean Sea ~ ~ ~ Middle Triassic and Upper Jurassic ~ ~ ~ ~ 0 100 km ~ ~ MNE ~ ~ ~ ~ source rocks only partly involved in top- Onset of the Velebit Breccia formation NE thrusting could be still preserved in Predominantly top-NE and penecontemporaneous beginning of the original structural position either in thrusting and formation of marine gravity flow deposition (‘flysch’) Middle–Late Eocene a footwall or in areas not affected by the 1 the Velebit thrust-sheet of a in a complex foreland and piggyback 1 thrusting event; M.-U. Eocene clastic de- passive-roof duplex geometry depositional system of the External Di- posits could represent a good seal (espe- narides cially where predominantly composed of marls) Continuation of marine gravity flow dep- Formation of major km-scale anticlines Top-SW imbrication and osition (flysch) in a more distal SW-part in the frontal SW part of the External fault-propagation folding as- of the complex foreland and formation of Dinarides locally still preserving Middle Late Eocene–Oligocene sociated with onset of dextral piggyback depositional system gradually Triassic and Upper Jurassic source rocks 22 slip along the Split–Karlovac infilled by coarse-grain alluvial plain and in their cores and Upper Eocene–Oli- line alluvial fan deposits in the proximal parts ogocene clastics on their crests (as po- The External Dinarides form a thin-skinned fold- (Promina Beds) tential seal) thrust belt extending in NW–SE direction along the The final stage of the dextral Final stages of infilling of the former fore- Late stage in salt migration could con- 3 Oligocene–Miocene(?) slip along the Split–Karlovac land and piggyback basins and formation tribute in both formation of local traps northeastern Adriatic coast. They comprise the re- 3 line and rising of salt diapirs of Dinaric Lake System and seals gional-scale tectonic units derived from the Adriatic microplate, being composed of more than 7 km-thick

succession of predominantly carbonate and subordi- supposed front of the Velebit Thrust nate clastic and igneous rocks of Carboniferous to 1 2–3 2–3 Miocene age. 1 The majority of the carbonates accumulated from the Late Triassic to Late Cretaceous, when the Adriatic Carbonate Platform became gradually af- restored offset of fected by generally NE–SW directed compression c. 20 km along the Srb- due to the collision between the Adriatic and Euro- fault pean plates.

During the Eocene–Oligocene the deposition 2–3 3 2–3 1 1 was restricted into several NW–SE trending basins 2 of both the foredeep and the piggy-back type, con- trolled 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 right slip of for more than a century, the present-day structural c. 10 km along the Srb-Knin architecture of the External Dinarides is presumed fault 2–3 2–3 3 as being almost exclusively the result of two tecton- ic phases: the phase of Late Eocene–Oligocene SW- 5565000 5575000 5585000 5595000 5605000 verging and SW-propagating thrusting, overprinted 4935000 5615000 A 5625000 3 by the younger, presumably Miocene, phase of dex- 4925000 1' B -1 5635000 Srb

4915000 4 2' tral wrenching. 5645000 Gračac E

5655000 4905000 A B

However, according to our recent multidiscipli- 3' N 4895000 10 km nary investigation focused on Kimmeridgian source- 4885000 4' Glamoč 5' 1 Glamoč-1 3 Knin D 4875000 A 1 LEGEND: 2 3 G 2 rocks of the central part of the External Dinarides Stratigraphic units in the cores HR BIH of the anticlines and synclines: 1 F Palaeogene Triassic 4865000 Vrlika 6' Permotriassic Cretaceous (evaporites) in Croatia, the first order NW–SE striking thrust D Jurassic Palaeozoic Drniš C 4855000

Structures and structural elements structures characterised by the opposite vergence, the Velebit Thrust thrust contact

4845000 anticline axis syncline axis 5 B i.e. the NE tectonic transport direction are clearly reverse fault right strike-slip fault Sinj C HR BIH Faults from the Split–Karlovac fault zone: E fault 6 A Srb–Knin fault B –Muć fault F Cetina fault 5615000 5625000 5635000 5645000 5655000 distinguished. As the NE-verging map-scale struc- C Kijevo–Sinj fault D Livanjsko polje fault G Dinara fault tures were also reported from the neighboring areas, it may be concluded that the NE-vergent thrusting 3 was the oldest and prevailing tectonic phase in for- 3 3 2 1 1 mation 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 associat- ed with the NE-vergent structures.

2–3 3