Unravelling the Tectonic Evolution of the Dinarides – Alps – Pannonian Basin Transition Zone: Insights from Structural Analysis and Low-Temperature Thermochronology from Ivanščica Mt., NW Croatia
Authors: Vukovski Matija , Špelić Marko , Kukoč Duje , Troskot-Čorbić Tamara , Grgasović Tonći , Slovenec Damir , Tomljenović Bruno 
Published: February 2024

A comprehensive study, including geological mapping, structural and thermochronological analysis, has been carried out on Ivanščica Mountain (NW Croatia), with the aim to contribute in reconstruction of the tectonic history of the Dinarides, Southern/Eastern Alps and Pannonian Basin transitional zone. Implementation of structural and thermochronological methods enabled a subdivision of Ivanščica Mt. into three structural domains (from bottom to top): Ivanščica Parautochton, Ivanščica Imbricates and Oligo-Neogene sedimentary cover. In addition, a sequence of deformational events in tectonic history of this transitional zone is proposed, comprising three extensional and four contractional events starting from Middle Triassic until present times. Oldest deformational events indicating Middle Triassic (D1) and Early Jurassic (D2) extensional phases were recognised only in volcano-sedimentary record. The oldest contractional event (D3) is related to obduction of the Neotethyan ophiolitic mélange over Upper Triassic to Lower Cretaceous succession of the eastern margin of the Adriatic microplate, which resulted in thermal alteration of the Ivanščica Imbricates structural domain in Berriasian - Valanginian times (~ 140 Ma). This event was soon followed by another contractional event (D4), which resulted in thrusting and imbrication of the Adriatic passive margin successions together with tectonically emplaced ophiolitic mélange, thermal alteration of the footwall successions, fast exhumation and erosion. Apatite fission track data together with syn-tectonic deposits indicate Hauterivian to Albian age of this event (~ 133–100 Ma). These Mesozoic structures were rotated in post-Oligocene times and brought from initially typically Dinaridic SE striking and SW verging structures to recent SW striking and NW verging structures. Following extensional event (D5) manifested in the formation of SE striking and mostly NE dipping normal listric faults, and ENE striking dextral faults accommodating top-NE extension in the Pannonian Basin. Deformations were coupled with hanging wall sedimentation of Ottnangian to middle Badenian (~ 18–14 Ma) syn-rift deposit as observed from the reflection seismic and well data. Short lasting contraction (D6) was registered in the late Sarmatian (~ 12 Ma). The youngest documented deformational event (D7) resulted in reactivation of ENE striking dextral faults, formation of SE striking dextral faults as well as the formation of E to NE trending folds and reverse faults. This event corresponds to Late Pannonian (~ 6 Ma) to recent NNW-SSE contraction driven by the indentation and counterclockwise rotation of Adriatic microplate. Recognized tectonic events and their timings indicate that Ivanščica was mainly affected by deformational phases related to the Mesozoic evolution of the Neotethys Ocean as well as Cenozoic opening and inversion of the Pannonian Basin. Mesozoic tectono-sedimentary evolution of Ivanščica Mountain exhibits clear Dinaridic affiliation, more precisely, that of the Pre-Karst zone of the Dinarides.