Open Session - SWISS GEOSCIENCE MEETINGs
Open Session - SWISS GEOSCIENCE MEETINGs
Open Session - SWISS GEOSCIENCE MEETINGs
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60<br />
Symposium 1: Structural Geology, Tectonics and Geodynamics<br />
1.<br />
Metamorphic and igneous evolution of the innermost Dinarides in Serbia<br />
Schefer Senecio*, Egli Daniel*, Frank Wolfgang**, Fügenschuh Bernhard***, Ovtcharova Maria****, Schaltegger Urs****,<br />
Schoene Blair**** & Schmid Stefan*<br />
*Geologisch-Paläontologisches Institut, Bernoullistrasse 32, CH-4056 Basel (senecio.schefer@unibas.ch)<br />
** Geol. Insitute, Slovak Academy of Science, Dubravska Cesta 9, 84005 Bratislava<br />
***Geologisch-Paläontologisches Institut, Innrain 52, A-6020 Innsbruck<br />
****Département de Minéralogie, Rue des Maraîchers 13, CH-1205 Genève<br />
During Early Paleogene collision the innermost Dinarides of Serbia, paleogeographically part of the Adriatic plate, occupy a<br />
lower plate position in respect to the Cretaceous-age Carpatho-Balkan orogen, now constituting the upper plate (Schmid et<br />
al., 2008). This study provides new timing constraints of the igneous and metamorphic events during and after collision that<br />
are crucial for a better understanding of the geodynamic evolution of the Balkan area.<br />
The Kopaonik area in Southern Serbia, a N-S trending mountain range, exposes a part of the Jadar-Kopaonik thrust sheet in<br />
a tectonic window. There, the Kopaonik-Studenica Metamorphic Series, derived from the innermost Adriatic margin and<br />
overlying Western Vardar Ophiolitic Unit, are intruded by the Kopaonik, Drenje and Željin granodiorites, as well as by the<br />
Polumir granite. At the eastern rim of the Jadar-Kopaonik thrust sheet, a Cenozoic suture zone (Sava Zone) separates the<br />
internal Dinarides from the Carpatho-Balkan orogen consisting of Serbomacedonian “Massif” and tectonically overlying<br />
Eastern Vardar Ophiolitic Unit. The Kopaonik-Studenica Metamorphic Series (Paleozoic to Early Jurassic) are overlain by a<br />
Mid- to Late Jurassic ophiolitic mélange below the obducted Western Vardar Ophiolitic Unit. These three units are unconformably<br />
overlain by Late Cretaceous (“Senonian”) flysch that contains large olistoliths, including ophiolitic blocks and reworked<br />
metamorphics. We interpret the weakly metamorphosed N-S-trending “Senonian” flysch as the southern prolongation<br />
of the Sava belt, suturing the internal Dinarides against the Carpatho-Balkan orogen. The intrusion of Oligocene granodiorite<br />
bodies led to contact metamorphism and skarn formation in the Kopaonik-Studenica Metamorphic Series.<br />
We dated the intrusions by U-Pb (ID-TIMS) analyses of single, thermally annealed and chemically abraded zircons. All the<br />
analyses are concordant within analytical error. Two different age groups could be determined: (i) Oligocene intrusions,<br />
ranging from 31.7 to 30.6 Ma, whereby the Kopaonik intrusion yielded the youngest ages (30.94 Ma – 30.70 Ma). The Drenje<br />
and Željin intrusions cluster around 31.5 Ma. Hf isotopes for Drenje and Željin show relatively uniform εHf values ranging<br />
from 3.6 ± 0.5 to 4.3 ± 0.5. The Kopaonik sample, however, shows distinctively lower values ranging from 1.1 ± 0.5 to 1.6 ± 0.5.<br />
This indicates that the Drenje and Željin magmas had a higher juvenile component compared to the Kopaonik intrusion. (ii)<br />
A Miocene age of ca. 18.0 Ma was obtained for the westerly outcropping Polumir granite;, Hf isotopes for this intrusion are<br />
not yet available.<br />
Fission-track analyses for these samples yielded ages of around 28 Ma for zircon and 18 – 23 Ma for apatite. This indicates<br />
rather fast post-emplacement cooling and exhumation, which is most probably tectonically assisted. An extensional tectonic<br />
setting is indicated by numerous normal faults, magmatic foliation in the Drenje locality and syn-intrusive boudinage of<br />
Polumir granitic dykes.<br />
West of the Kopaonik area (Studenica valley) another part of the Kopaonik-Studenica Metamorphic Series crops out in the<br />
form of second tectonic window (so-called Studenica-slice, (Dimitriević, 1997) below the obducted Western Vardar Ophiolitic<br />
Unit, again made up of Paleozoic to Early Jurassic meta-sediments. Most of these series only underwent lower greenschist<br />
facies metamorphism, but in the core of this window, along the Studenica River, amphibolite grade meta-sediments were<br />
found. Ar-Ar dating on sericite fractions (2-6 and 6-12 µ) as well as on amphibole and biotite separates evidence Cretaceous-age<br />
metamorphism, overprinted by a second Paleogene metamorphic overprint of the Studenica Metamorphic Series. While the<br />
Cretaceous event (110 – 85 Ma) reached lowest greenschist facies conditions only, Paleogene metamorphism (40.9 ± 4.9) reached<br />
amphibolite facies conditions and was probably followed by rapid exhumation assisted by normal faulting.<br />
Our data document Cenozoic metamorphism in the innermost Dinarides of Serbia for the first time. This metamorphism is<br />
related to suturing of the Dinarides with the easterly adjacent Carpatho-Balkan orogen (including the Eastern Vardar<br />
Ophiolitic Unit) across the Sava Zone. So far Cenozoic metamorphism was only documented for the Sava Zone in northern<br />
Bosnia (Pamic, 1993; Ustaszewski et al. 2007). Moreover, our high-precision intrusion ages indicate an Oligocene-age intrusive<br />
suite, immediately followed by rapid exhumation according to the fission track data, possibly in a back-arc setting. This<br />
exhumation was then followed by a second magmatic pulse in the Miocene, again followed by rapid exhumation. This second<br />
magmatic and extensional event has to be seen in the context of the formation of the Pannonian basin.