Relation Between Tectonics and Intrusions in the Western Rhodope Mountains, SW Bulgaria
Abstract
We present an E-W profile through the Western Rhodopes (Bulgaria). It runs through basement rocks, granitic intrusions therein and Tertiary extension-related structures such as the Strouma and the Mesta Graben. Two major alpine units are exposed in the basement, the Pangaion-Pirin complex below and a mixed gneiss unit above. The Pangaion-Pirin unit consists mainly of marbles, variscan orthogneisses, and Tertiary ganitic intrusions and underwent only upper greenschist facies conditions during the alpine cycle. The mixed gneiss unit is made up of different continental and oceanic high-grade metamorphic rocks, including preserved HP and UHP relicts at several localities. U/Pb zircon geochronology was carried out on samples from three granitic intrusions, the Spanchevo, Teshovo and Dolno Dryanovo plutons using LA-ICP-MS at GEUS in Copenhagen. The Teshovo pluton is located in the Pangaion-Pirin complex. Apart from a weak magmatic foliation, it is undeformed and thus intruded posttectonically. Zircons within the assayed samples are single-phased and give well defined crystallization ages of around 32 Ma. The Spanchevo and Dolno Dryanovo plutons are partly deformed bodies within the mixed gneiss unit. Single-phase magmatic zircons and magmatic rims yield ages of around 56 Ma, whereas inherited cores display ages of around 146 Ma. We propose that (1) ductile deformation in the Pangaion-Pirin complex ceased before 32 Ma and (2) penetrative deformation lasted beyond 56 Ma in the mixed gneiss unit above. Due to the lack of inherited variscan cores in zircons from the Spanchevo and Dolno Dryanovo plutons, we infer that the upper complex was not yet placed upon the Pangaion-Pirin complex at 56 Ma. Hence, the southwestward thrusting of the upper complex over the Pangaion-Pirin complex took place between 56 and 32 Ma.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.T11B1876J
- Keywords:
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- 1100 GEOCHRONOLOGY;
- 8000 STRUCTURAL GEOLOGY;
- 8100 TECTONOPHYSICS