2D Kinematic Modelling of the Gorski Kotar Region (NW Croatia): Influence of Lower Jurassic Extension on Cenozoic Deformation in the Northern External Dinarides

The Dinarides fold-and-thrust belt formed during the Cenozoic collision between the Adriatic microplate and Eurasia. In the External Dinarides, thick carbonate platform deposits dominate, and structures generally strike NW–SE with SW-directed thrust vergence due to Eo-Oligocene shortening. In the Gorski Kotar region (NW Croatia), structures shift to a N–S trend with localized east-directed thrusting. Field data and geological profiles suggest that before Cenozoic contraction, the area experienced E–W-directed extension during the Lower Jurassic, leading to a ~2.7 km thick syn-rift sequence, about ten times thicker than coeval strata in adjacent regions.

To investigate thickness variations and structural architecture, we developed three geological cross-sections based on field measurements and geological maps. These were used in 2D kinematic forward models to simulate deformation over time. Raman Spectroscopy of Carbonaceous Material (RSCM) was applied to the highest structural unit to assess thermal maturity.

RSCM results show that Permian strata overlying Jurassic and Triassic units were heated to 227 ± 15 °C, implying ~7 km exhumation, assuming a geothermal gradient of 30 °C/km. The cross-sections reveal a NE- to E-directed passive roof thrust developed above a complex triangular structure. This present-day architecture is largely inherited from Lower Jurassic extension, accommodated by WSW-dipping normal faults. Lower Jurassic extension across the Adriatic shelf contributed to basin development in the Eastern Alps, Southern Alps, Apennines, and Dinarides, representing an early phase of intracontinental rifting prior to the opening of the Piemont-Liguria Ocean. These results emphasize the long-lasting influence of inherited structures on Cenozoic deformation.