engleski

Structure and tectonic evolution of the Velebit Mt. in the central part of the External Dinarides

Detailed outcrop-scale analysis of fault-slip data, in combination with data presented on published geological maps, were used for a reconstruction of the structural architecture and tectonic evolution of the Velebit Mt., the most prominent geomorphological structure in the central part of the External Dinarides in Croatia. The analysis of kinematic indicators recorded by major fault planes indicates the prevalence of dip-slip and top-to-NE motions, verifying that these faults are NE-verging thrusts rather than NE-dipping normal faults as previously thought. Consequently, we challenge earlier tectonic models that interpret the Velebit Mt. structure as a SW-vergent antiformal stack or thrust duplex formed above the major NE-dipping thrust system (TARI KOVAČIĆ & MRINJEK, 1994) or as a complex transpressional structure formed during the late-orogenic escape tectonic phase along an inherited crustal fault zone (GRANDIĆ et al., 2004 ; KORBAR, 2009). Instead, we use the concept of a passive roof duplex within a triangle structure. Thereby, the Velebit structure represents a stack of NE-verging backthrusts formed above a SW-vergent compressional duplex. Our interpretation was recently tested by BALLING et al. (2017) by construction of forward modelled balanced cross sections. Additionally, we analysed a large set of fault-slip data comprising more than 1000 measurements collected in the carbonate breccia exposed along the SW mountain slope at about 60 measurement sites. Curiously, the majority of recorded fault-slip data comprise structures with a normal sense of shear indicating orogen-perpendicular (NE-SW) to orogen-parallel (NW-SE) extension. According to the very good preservation and high frequency of occurrence, these extensional structures may have played an important role in formation of the extremely voluminous carbonate breccia exposed along the SW mountain slope. Accordingly, we propose that these structures resulted from a state of stress characterised by radial extension induced by gravitational collapse and spreading as a result of the uptilting of the SW-dipping Velebit monocline. Therefore, our interpretation is only partly in accordance with KORBAR (2009) who suggested that divergent extension and gravity gliding was a major mechanism in formation of the carbonate Jelar breccia in general.

Velebit Mt. ; External Dinarides ; passive roof duplex

nije evidentirano