Transverse Dinaric zone of increased compression between the Kraški rob and Hrušica Regions, NE Microadria
The Kvarner fault divides the Microadria (Adria microplate, the Adria stable core) into the Po and Adria segments. The Istra block, which is sandwiched between the right-lateral Kvarner Fault and the left-lateral Sistiana Fault lies at the extreme eastern edge of the Po segment. Both faults run transversely to the Dinarides and reach their thrust boundary in the east. The Microadria has been moving towards the Dinarides since the Middle Miocene. The movement of the Istra block is exposed in relation to the neighbouring blocks, so an extensive pushed area (the Istra Pushed Area) was formed in the External Dinarides, which is bent towards the northeast. It is defined by two flexural zones, one lying in the extension of the Sistiana Fault and the other in the extension of the Kvarner Fault. The structure of the Dinaric thrust border on the north-eastern side of the Istra block is complex. Its prominent structural element is the Črni Kal Anomaly, due to which a zone of increased compression developed within the Istra Pushed Area and transversely to the Dinarides (Kraški rob – Hrušica Traverse), which lies between the Sistiana and Kvarner Flexural Zones. In terms of kinematics, it differs greatly from these two, and various geomorphologically responsive deformations have occurred within it. Mt. Vremščica (1027 m), which represents a transpressive anticline within the wider zone of the Raša Fault is the most prominent. In order to understand the genesis of the Classical Karst relief, it is important to know that the Mt. Vremščica ridge rose from the levelled karst surface.