Naslov
Structural and Palaeomagnetic data from the border zone between Alps, Dinarides and Pannonian Basin (Medvednica and Samoborsko Gorje Mts., Croatia): Implications for geodynamic evolution of the area

Autori
Tomljenović, Bruno ; Csontos, Laszlo ; Marton, Emoe ; Marton, Peter ;

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Annales Universitatis Scientiarum Budapestinensis, Sectio Geologica, Tomus XXXV. / Csontos, Laszlo - Budimpešta : Eötvös Loránd University, 2003, 121-122

Skup
VIth Alpshop Workshop

Mjesto i datum
Sopron, Mađarska, 14.09.2003. - 16.09.2003

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Structural geology; Tectonics; Palaeomagnetism; Medvednica Mt.; Samoborsko Gorje Mt.; Croatia; Geogynamic evolution

Sažetak
In north-western Croatia there are several highly deformed pre-Neogene units of both Alpine and Dinaridic origin. During Neogene-Quaternary times, repeated transtension and transpression resulted in complex displacements of the pre-Neogene units. We carried out structural analysis and paleomagnetic measurements in order to 1) correlate recently differently oriented pre-Neogene structures ; 2) reconstruct their original orientation 3) understand their meaning for the geodynamic evolution of the area. As a result of structural analysis, we distinguish at least four deformational events (D1-D4) in pre-Ottnangian times. D1: Late Jurrasic-Early Cretaceous greenschist-facies metamorphism in the Medvednica Mt. It includes synmetamorphic, localy mylonitic foliation and lineation characterized by monoclinic fabric elements that indicate top-NE shearing.. By accounting for subsequent rotations documented by paleomagnetic data, the original shearing direction would be top-NNW, probably related to obdution of ophiolite nappe(s) over the eastern edge of Adria. D2: Cretaceous (post-Albian - pre-Senonian) shortening. This event produced tight to isoclinal folds in the metamorphic complex of Medvednica, accompanied by SE-dipping S2 axial plane cleavage and NE-trending L2 intersection (foliation/cleavage) lineation. When reconstructed to the original orientation, D2 structures trend NNW, thus indicating deformational event characterized by WSW-ENE-directed shortening. We suppose that during D2 folding the metamorphic complex was structurally in the lower position with respect to the ophiolitic complex. D3: Paleocene- Eocene top-WSW thrusting and folding, which produced recently SE-dipping thrusts and NW-verging folds accompanied by SE-dipping cleavage observed both in the low-grade metamorphic complex and in the Late Cretaceous-Paleocene Gosau. At outcrop scale, the mesoscale folds are isolated and cut by reverse faults, frequently developed in sets showing kinematic and structural pattern correlative to brittle-ductile shear zones, unambiguously indicating top-NW tectonic transport direction in the Medvednica and top-WSW shearing direction in Samoborsko gorje Mt. D4: Paleogene-pre-Ottnangian pervasive reactivation of earlier (D3) SE-dipping penetrative surfaces in the Gosau sequences of Medvednica Mt. These surfaces act as oblique right lateral slip planes. Palaeomagnetic declinations in all Neogene rocks showed ca. 30&ordm ; CCW rotation. In Ottnangian somewhat greater, in Middle Miocene – Pliocene sediments somewhat smaller rotation was recorded. A similar CCW rotation is recorded in other areas of the Dinarides, as well as in Slavonian Mountains. In Senonian deposits ca. 100&ordm ; CW rotation was measured. All these declinations are interpreted as magnetizations during rock deposition. Palaeomagnetic results from Miocene – Pliocene sediments in and around the Medvednica suggest a general bulk 30&ordm ; CCW rotation, which may be related to the rotation of the Adriatic microplate. This also means that prior to Miocene the Dinarides were striking N-S and not NW-SE as now. Declinations measured in Gosau sediments from the Medvednica may be interpreted in terms of large CW rotation or pre-Ottnangian age. This rotation possibly affected the other inselbergs of Northern Croatia, too. Their different structural strike is therefore explained by this major rotation. When reconstructed, the structural transport directions and tectonic order is conformable to those experienced in the main body of the Dinarides. The large rotation is explained by the transpressive right lateral activity of the Periadriatic Line during Late Paleogene – earliest Miocene. We speculate that during pervasive right lateral shear a smaller crustal flake was torn off the Dinarides and was rotated and incorporated into the Zagorje – Transdanubian shear zone.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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