International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

GEOLOGY OF THE VARDAR ZONE OPHIOLITES OF THE MEDVEDNICA MOUNTAIN AREA LOCATED ALONG THE ZAGREB-ZEMPLIN LINE (NW CROATIA)

Pages: 53 - 59

Authors: DAMIR SLOVENEC, JAKOB PAMIC

Abstract: The ophiolite melange of the Medvednica Mountain area, located in the southwestern parts of the Zagorje-Mid-Transdanubian or Sava Zone, is included within the Vardar Zone (VZ) of the Dinarides. The melange represents the northwesternmost parts of the Dinaridic ophiolites, the origin of which was related to the Alpine evolution of the Dinaridic part of the Tethys. The Dinaridic ophiolites represent fragments of Mesozoic oceanic crust generated over 150 Ma starting with a) Late Triassic (?) to Late Jurassic oceanization of the Tethys, Late Jurassic/Early Cretaceous subduction, obduction and formation of the Dinaride Ophiolite Zone (DOZ) to b) Cretaceous–Early Paleogene back-arc basin final subduction and obduction, that is the formation of the VZ. The main Alpine compressional-collisional event, which took place in the Eocene (55–45 Ma) gave rise to the final structuration of the Dinarides and their uplift, and backthrusting of the VZ onto the DOZ. The Medvednica ophiolite melange represents a chaotic complex in which primary sedimentary sequences are rarely preserved due to subsequent tectonism. The melange is characterized by pervasively sheared and fine-grained shaly-silty matrix in which are included smaller (centimetre to hektometre) and larger (kilometre) fragments of various rocks. These are most commonly greywackes, ophiolites, cherts and exotic limestones, the youngest blocks of which are Late Cretaceous and Paleocene in age. For that reason the VZ ophiolite melange is of post-Paleocene age as distinguished from the Jurassic ophiolite melange of the DOZ. The Medvednica ophiolites are represented by tectonic and cumulate serpentinized peridotites, gabbro-diabases and basalts, transformed by postmagmatic processes, into serpentinites, metagabbros, metadiabases and metabasalts. The Medvednica ophiolites can be correlated to the ophiolites from the northwestern part of the Zagorje-Mid-Transdanubian (or Sava) Zone and the Bükk area in northern Hungary. The present position of all these ophiolites can be best explained by the mechanism of extrusion tectonics, for example strike slip faulting as a result of Oligocene and Neogene indenting of Apulia into Eurasia.

Keywords: Late Cretaceous-Paleogene, Medvednica Mt, Zagorje-Mid-Transdanubian (Sava) Zone, Vardar Zone, ophiolite melange, subduction, obduction, extrusion tectonics

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