engleski

Contrasting deformation styles across the Split-Karlovac Fault (External Dinarides) induced by reactivation of pre-existing structures

It is widely known that the main deformation in orogens is located along pre-existing fault zones, which occur either at facies transitions or at inherited and reactivated structures. This is also the case in the External Dinarides, where long-lasting convergence between Eurasia and Adria deformed and inverted the Mesozoic Adriatic Carbonate Platform in Cenozoic times. The growth of the Adriatic carbonate platform was controlled by the interplay of eustatic sea level changes and tectonic subsidence, but also by underlying pre-existing faults, leading to a structurally complex and laterally heterogeneous carbonate platform. Here, we address the role of such pre-existing faults on pronounced along-strike variations in shortening across the Split-Karlovac Fault during Cenozoic contraction in the External Dinarides. From geological maps, it is known that exposed Late Permian gypsum are exclusively related to the eastern side of the Split-Karlovac Fault (SKF). This suggests that the Late Permian evaporites formed the main detachment for the eastern segment. The geologically most viable kinematic forward model across the western part and an unpublished cross section across the eastern part reveal that the SKF separates two structural blocks with contrasting deformation styles. Nappe stacking (doubling) of the Carbonate Platform characterize the eastern segment, whereas the western part is related to a SW-vergent antiformal stack with a stratigraphically much deeper detachment, which formed the Bruvno anticline. A missing Permian to Lower Triassic succession suggests that the Bruvno anticlinal dome formed a (possibly fault-bounded) structural high during that time. We suspect that during Mid-Eocene contraction, the SW-bounding normal fault of such a high was reactivated as a large-scale top-to-the-NE backthrust, which inhibited further propagation of the deformation front towards the SW. Our kinematic forward model also suggests that the SKF was initiated as a thrust fault along a Late Jurassic facies boundary, which in turn was inherited from Late Permian times. Shortly after its initiation, the SKF developed into a dextrally transpressive tear fault. This led to nappe stacking in the eastern part and synchronous deformation of the Bruvno anticline in the western part. Passive W-ward tilting of the backthrust in the hangingwall of the Bruvno Anticline resulted in the uplift of the Velebit monocline, which hence became subject to accelerated erosion. Interestingly, in the foreland of this unique structural setting, a Mid-Eocene to Late Oligocene flexural basin was established – the Promina basin. This basin was solely filled by reworked calcareous material from the External Dinarides. Based on field observations we conclude that the establishment of the Split-Karlovac Fault, the uplift of the Bruvno and Velebit anticlines as well as the subsidence of the Promina flexural foreland basin happened simultaneously and started in Mid-Eocene times.

Reactivation of pre-existing structures, Split-Karlovac Fault, External Dinarides

nije evidentirano