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Mineral chemical and geochronological constraints on the age and provenance of the eastern Circum-Rhodope Belt low-grade metasedimentary rocks, NE Greece |
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| Authors: | Guido Meinhold Thomas Reischmann Dirk Frei |
| Institution: | a Institut für Geowissenschaften, Johannes Gutenberg-Universität, Becherweg 21, D-55099 Mainz, Germany b CASP, University of Cambridge, West Building, 181a Huntingdon Road, Cambridge CB3 0DH, UK c Geologischer Landesdienst, Hessisches Landesamt für Umwelt und Geologie, Rheingaustr. 186, D-65203 Wiesbaden, Germany d Department of Mineralogy and Petrology, National and Kapodistrian University of Athens, Panepistimioupoli Zographou, Athens 15784, Greece e Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark f Centre of Isotopic Research, A. P. Karpinsky All Russian Geological Research Institute (VSEGEI), 74 Sredny Prospect, St. Petersburg, 199106, Russia |
| Abstract: | In north-eastern Greece the mid-greenschist facies Makri Unit and the anchizonal Melia Formation belong to the eastern Circum-Rhodope Belt that forms the uppermost tectonostratigraphic unit of the Rhodope metamorphic nappe pile. The two metasedimentary successions had different source areas, although they now lie in close proximity in the Rhodope Massif. The U-Pb isotopic ages of detrital zircons from a metasandstone of the Makri Unit analysed using LA-SF-ICP-MS and SHRIMP-II gave age clusters at ca. 310-290 Ma and at ca. 240 Ma for magmatic zircons, which may have been derived from Carboniferous-Permian basement rocks of the Thracia Terrane (Lower Tectonic Unit of the Rhodope Massif) that subsequently underwent Triassic rifting. The youngest detrital zircon grains found so far indicate that the metasedimentary succession of the Makri Unit, or at least parts of it, cannot be older than Late Triassic. By contrast, clastic sedimentary rocks of the Melia Formation contain the primary detrital mineral assemblage of epidote, zoisite, garnet, and phengitic mica, which is absent in the Makri Unit, and clearly points to metamorphic rocks being the major source for these sediments. U-Pb analyses of detrital zircons gave a prominent age cluster at ca. 315-285 Ma for magmatic zircons. Inherited cores indicate the involvement of Pan-African and Late Ordovician-Early Silurian crustal sources during Late Carboniferous-Early Permian igneous event(s). Moreover, U-Pb detrital zircon geochronology indicates that the Melia Formation cannot be older than latest Middle Jurassic. We suggest that the Melia Formation was deposited in front of a metamorphic nappe pile with Rhodopean affinities in Tithonian or Cretaceous times. Both the Makri Unit and the Melia Formation have been tectonically juxtaposed from different sources to their present location during Balkan and Alpine orogenic processes. |
| Keywords: | Mineral chemistry Zircon geochronology Hellenides Circum-Rhodope Belt Thrace Greece |
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