The paleokarst origin of the carbonate "Ropočevo breccia" and a closing Neotethys: Regional Geological constraints on the Vardar Zone s.s. (Belgrade area, Central Serbia).

Abstract

An extremely rare carbonate breccia in the Ropočevo area (southern outskirts of Belgrade, near Avala Mt., Central Serbia), provides a clue on the probable mechanism of both its paleokarstification and a tectonic relationship with lithospheric-scale compressional events which have occurred along the latest Jurassic Neotethyan Vardar Ocean margin. Outcropping as a well-lithified block, “Ropočevo breccia” exposes an abundance of large angular, boulder-size clasts composed of recrystallized limestone. It has been used for decorative purposes in the near past. The famous decorative stone “Ropočevo breccia” represents an isolated olistolith-like carbonate block engulfed by the Upper Cretaceous Vardar Zone s.s. turbidites. In the Ropočevo area, two penecontemporaneous turbidite systems are separated by the Alpine west-vergent thrust. However, the “Ropočevo breccia” is related to neither the underlying Lower Cretaceous- nor overlaying Upper Cretaceous turbidites. Such a regional-geological relationship indicates a presence of a pre-Upper Cretaceous tectonic exhumation event, followed by the rather short subaerial paleokarst episode. The suggested paleokarst episode is characterized by the absence of progressive abrasion and of visible roundness of the considerably larger carbonate clasts. The regional geological constraints on the investigated “Ropočevo breccia” show that the isolated “olistolith” is a breccia formed by the end of Berriasian from the clasts formed in a collapsed cave within the primary carbonate sequence of the (latest Tithonian-)Berriasian age. The proposed interpretation is in line with the “Basal unit” of the Lower Cretaceous “Paraflysch” belonging to the well-hidden basal sequence of the East Vardar Zone of Central Serbia. Moreover, the available aeromagnetic data of the Avala Mt./Ripanj-Ropočevo-Kosmaj Mt. sector, corroborate a deep-settled suture underneath the investigated segment of the Vardar Ocean. The results further show that a short tectonic uplift and karstification episode occurred in connection with the compressional interruption, affecting the lithospheric-scale contact between formerly descending and overriding plates. Thus, the short regional-scale lowermost Cretaceous uplift and karstification episode was likely induced by the closure of the Neotethyan Vardar Ocean. This latest Jurassic-earliest Cretaceous collisional event produced a short compressional episode, lifting up the investigated segment of the overriding East Vardar Zone.