Tectonic evolution of the northwestern Internal Dinarides as constrained by structures and rotation of Medvednica Mountains, North Croatia

Abstract

This paper attempts to explain the tectonic history and possible reasons for the change of trend of the northwestern part of the Internal Dinarides in a transitional area between the Southeastern Alps, central Dinarides and Tisia, north of Zagreb. Structural and palaeomagnetic data collected in pre-Neogene rocks at Medvednica Mountains, combined with palaeomagnetic data available from Neogene rocks in the surrounding area, point to the following conclusions:(1) The reason for dramatic deflection in structural trend of the Internal Dinarides in the area north of Zagreb is a 1308 clockwise rotation and eastward escape of a tectonic block comprising Medvednica Mountains and the surrounding inselbergs, bounded to the north by the easternmost tip of the Periadratic Lineament. In Medvednica Mountains, the main period of tectonic escape and associated clockwise rotation occurred in the Late Palaeogene, possibly in the Oligocene-earliest Miocene.(2) When rotated into the original position, the trend of observed pre-Neogene structures of Medvednica Mountains becomes parallel to the major structural trend of the central Dinarides. In view of their original orientation, these structures are interpreted in the following way:(a) The first D1 deformational event is attributed to the Aptian-Albian nappe stacking in the central-northern Dinarides that was accommodated by a top-to-the-north directed shearing and northward propagation of already obducted ophiolites of the Central Dinaridic ophiolite zone. This nappe stacking, which resulted in a weak regional metamorphism in tectonic units underlying the ophiolites, was orogen-parallel or at a very acute angle to known structural (and possibly palaeogeographic) trends. This implies a major left-lateral shear component along the former Adriatic margin and obducted Dinaridic ophiolite zone.(b) This was followed by Early Albian orogen-perpendicular shortening (D2) that was accommodated by folding and top-to-the-west thrusting. This deformation resulted in gradual cooling of the metamorphic stack and also in uplift and erosion of the higher structural units.(c) The D3 deformational event was driven by renewed E -W shortening that took place after the Paleocene, most probably during the Middle Eocene-Oligocene, i.e. synchronous with the main Dinaridic tectonic phase of the External Dinarides. This shortening was probably triggered by collision and thrusting of Tisia over the northern segment of the Internal Dinarides.(d) This was finally followed by D4 pervasive, right-lateral N-S shearing that is tentatively interpreted as being related to the right-lateral shearing of the Sava zone during the Eocene-Oligocene.(e) Following the main period of tectonic escape and induced clockwise rotation along the Periadriatic fault, possibly in the Oligocene-earliest Miocene, the Medvednica Mountains and the surrounding area were affected by repeated extensions and inversions since the Early Miocene to recent times. Palaeomagnetic data suggest that in the Early Miocene (but probably before the Karpa...

Identification of tectonically active areas using DEM: a quantitative morphometric analysis of Mt. Medvednica, NW Croatia

“…Geo log i cally, this nar row bound ary zone cor re sponds to the NW-strik ing Kašina Fault zone (Fig. 4B), which is in ter preted as a right-lat eral strike-slip fault by pre vi ous stud ies (e.g., Prelogoviae et al, 1998;Tomljenoviae and Csontos, 2001;Tomljenoviae et al, 2008). How ever, the sig nif i cant lo cal re lief dif fer ences within the two fault sides sug gest that, in ad di tion to the pro posed right-lat eral strike-slip com po nent, this fault zone ac com mo dated a prom i nent nor mal dis place ment.…”

“…Its pres ent-day po si tion and trend are ex plained by an east ward dis place ment (tec tonic es cape) and approx. 130° clock wise ro ta tion of the tec tonic block com pris ing Medvednica and its sur round ing inselbergs dur ing the Lat est Paleogene-Ear li est Neo gene (Márton et al, 2002;Tomljenoviae et al, 2008). These move ments were prob a bly re lated to the ini tial stage of Mio cene east ward ex tru sion of wedge-shaped crustal blocks of the East ern Alps-Pannonian Ba sin tran si tion.…”

“…2) has been strongly af fected by Late Mio ce ne-Qua ternary de for ma tions de scribed above. The cen tral part of the moun tain is an asym met ric antiform com posed of mid-Cre taceous (122-110 Ma) greenschists and over ly ing lower-grade metasedimentary rocks (e.g., Belak et al, 1995;Judik et al, 2004Judik et al, , 2008Lugoviae et al, 2006;Tomljenoviae et al, 2008). This unit has been overthrusted by a Ju ras sic ophiolitic mélange (Halamiae et al, 1998(Halamiae et al, , 1999Babiae et al, 2002;Lugoviae et al, 2006;Slovenec and Lugoviae, 2008) that is pre served in an ad jacent synform to the north.…”

“…Medvednica drain age bas ins that we then com pared to sepa rate those rep re sent ing tec toni cally ac tive vs. in ac tive sub-areas. These new data were then com pared with the re sults from pre vi ous geomorphologic, neotectonic and seismotectonic stud ies of this area (Heaeimoviae, 1984(Heaeimoviae, , 2000Prelogoviae et al, 1998;Tomljenoviae and Csontos, 2001;Tomljenoviae et al, 2008;Herak et al, 2009). …”

A map-view restoration of the Alpine-Carpathian-Dinaridic system for the Early Miocene

“…It also leads to a good alignment of the internal Dinarides and their two fragments, which are preserved in the bükk and Medvednica Mountains (tomljenović et al 2000;tomljenović 2000Dimitrijević et al 2003;schmid et al 2008;tomljenović et al 2008). the opposed subduction polarity between Alps-Western carpathians and Dinarides demands, however, substantial post-collisional geometrical modifications of this suture (Laubscher 1971).…”