Workshop DWO 17

DWO 17
Date: to be defined, 8 hours - Place: Florence
Convener: I. Zagorchev (Bulgaria)
The workshop will focus on problems of general geologic interest relative to Cenozoic stratigraphy, igneous activity, tectonics, paleogeography and geodynamics. It is closely linked to two field trips (B26 and P36) and TRANSMED Transect III. The topics to be discussed are closely related to the extensional collapse of orogens, especially to rifting and detachment tectonics. Problems of seismic and geotechnical hazard will be also raised.
Enrollment (min/max): 10-50 - Fee: free of charge

Sketch map for the Alpine orogenic structure of the Balkan Peninsula

Extensional collapse of the Late lpine orogens on the Balkan Peninsula (abstract, submitted to the 32 nd IGC)      Ivan Zagorchev

Marginal, island-arc and back-arc basins marked in Late Cretaceous times he final stages of Tethyan closure on the Balkans. Compression events ccurred in latest Cretaceous, Mid Eocene, and latest Oligocene - earliest Miocene times. Two principal types of orogens are outlined: (i) orogens (Dinarides-Albanides-Hellenides; Vardarides) issued from ormer Tethyan oceanic and marginal basins (subduction-related imbrication of oceanic crust with elements of the continental slope and marginal arcs),and (ii) orogens (Srednogorie, Balkanides) issued from peri-Tethyan basins and epicontinental  island arcs, rifts, and flysch and molasse troughs.Extensional collapse in former oceanic domains inherited former trends and vergencies. Throughout Late Cretaceous to Palaeogene and Neogene times,a gradual replacement of marginal flysch basins with island arcs, and further on, with marine and continental molasse basins occurred. Neotectonics was controlled by deep-seated processes (formerly subducted lithospheric slabs).Extensional collapse in orogens issued from peri-Tethyan basins had mostly a local significance. Foreland flysch basins were replaced by molasses. Intra-orogenic grabens formed at the neotectonic stage. Most interesting processes occurred in the area of the "plateau" (Morava-Rhodope) situated between the major orogens, and characterized by a thickened continental crust. Shallow marine basins ingressed locally in Late Cretaceous and Palaeogene times. Collapse of the thickened crust triggered in Late Eocene - Early Oligocene times melting at different depths, with magma mixing and extensive volcanism.

Sketch map for the Neogene and Quaternary structure of the Balkan Peninsula

The pattern of the fluviolacustrine systems changed dramatically during the major tectonic episodes
(boundaries Maastrichtian/Danian, Middle/Late Eocene, Early/Late Oligocene,
in earliest Miocene, and from the Badenian and Sarmatian onwards).

Neogene and Pleistocene fluviolacustrine systems
Cartoon illustrating the extensional orogenic collapse
(Palaeo-Strouma and Palaeo-Mesta)in the northern peri-Aegean region

(after I. Zagorchev, in press)

Various extensional processes and mechanisms are recorded: continuing role of subducted lithospheric slabs; isostatic phenomena related to areas of irregularly thickened and/or thinned continental crust; deep irregular melting processes; crustal extension and necking; strike-slip along major fault belts with related pull-apart; updoming of vast regions with rifting in the crest areas or along former wrench faults of regional importance. Listric and low-angle normal faults played a secondary role in the course of 3D block rotations and tilting.

Geological Institute of the Bulgarian Academy of Sciences
Author: Ivan Zagorchev
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