Late palaeozoic magmatism in the basement rocks Southwest of Mt. Olympos, Central Pelagonian zone, Greece: Remnants of a permo-carboniferous magmatic arc.
ABSTRACTWe dated basement rocks from several localities southwest of Mt. Olympos, as well as from a locality near the top of the mountain using the single zircon Pb/Pb evaporation technique. For the samples southwest of the mountain, the ages obtained range from ca. 280 to 290 Ma, with only a few zircon grains being around 300 Ma. By contrast, the sample from near the top of the mountain appears to be slightly younger, with ca. 270 Ma. These ages imply that the granitoids crystallized during Late Carboniferous -Early Permian times, and are therefore younger than the basement gneisses of other regions of the Pelagonian zone, which yielded zircon ages of around 300 Ma (e.g. Yarwood & Aftalion 1976, Mountrakis 1983, De Bono 1998, Engel & Reischmann 2001. However, the ages obtained in the present study are identical, within error, to the muscovite Ar-Ar cooling ages from Mt. Ossa (Lips 1998). Our geochronological data show that the magmatic evolution for this part of the basement of the Pelagonian Zone lasted at least 30 Ma. 985http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/07/2020 07:36:31 | -988http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/07/2020 07:36:31 | -990http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/07/2020 07:36:31 | -992http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 11/07/2020 07:36:31 |
The northern part of the Pelagonian Zone experienced a polyphase deformation and metamorphism. Four groups of K/Ar biotite and white mica ages document (I) Hercynian emplacement of plutonic rocks, (II) Eohellenic nappe stacking associated with penetrative deformation / recrystallisation, (III) a Paleocene event in the Mesocoic cover rocks in Greece and (IV) a westward movement of West Pelagonian nappes during Eocene to Oligocene time. First zircon/apatite fission track ages clustering around 70 Ma and 45 to 30 Ma.
The geometry of kinematics and the deformation history of the Pelagonian nappe pile during the Alpine orogeny have been studied in Northern Greece and FYROM. Deformation was started in Middle-Late Jurassic time and was initially associated with ocean-floor subduction followed by ophiolites obduction, nappe stacking and duplication of the Pelagonian continent. The footwall Pelagonian segment from top to bottom was metamorphosed under greenschist to amphibolit facies conditions and a relative high pressure (T = 450o to 620o C and P = 12,5 to 8 kb). Blueschist facies metamorphic assemblages of Late Jurassic age are immediately developed between both hangingwall and footwall Pelagonian segments. Transgressive Late Jurassic-Early Cretaceous neritic limestones and clastic sediments on the top of the obducted ophiolites are maybe related to extension and basins formation simultaneously with the nappe stacking and metamorphism at the lower structural levels of the Pelagonian nappes. Contractional tectonics and nappe stacking continued during the Albian-Aptian time. Simultaneously retrogression and pressure decreasing taken place at the tectonic lower Pelagonian footwall segment. Low grade mylonitic shear zones, possible related to extension, are developed during Late Cretaceous time simultaneously with basins formation and sedimentation of neritic Late Cretaceous to Paleocene limestones and flysch. Intense shortening and imbrication under semi-ductile to brittle conditions occurred during Paleocene to Eocene time resulting the onset of the dome like formation of the footwall Pelagonian segment. The next stages of deformation from Oligocene to Quaternary are related to brittle extension and the final uplift and configuration of the Pelagonian nappe pile.
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