Authors: BORIS NATALIN, GÜRSEL SUNAL, MUHARREM SATIR, ERKAN TORAMAN
Abstract: The Strandja Massif, Thrace Peninsula, NW Turkey, forms an important link between the Balkan Zone of Bulgaria, which is usually correlated with Variscan orogen in Central Europe, and the Pontides, where Cimmerian structures are the most prominent. The massif is composed of a Palaeozoic basement and a Triassic metasedimentary cover. The basement is made of various granite gneisses, paragneisses, and schists that are intruded by large plutons of monzonitic metagranites. Detrital zircon studies have revealed Ordovician (433 and 446 Ma) and Carboniferous (305 Ma) ages of the metasedimentary rocks. The isotopic age of the granite gneisses is 308-315 Ma (Carboniferous, Bashkirian-Moscovian) as single zircon evaporation method and conventional U-Pb technique show. The Palaeozoic basement was deformed and metamorphosed before the emplacement of the large monzonitic metagranite plutons yielding zircon ages from 309±24 to 257 Ma (Moscovian-Permian). Geochemical features of the Carboniferous and Permian magmatic rocks indicate a subduction-related tectonic setting similar to coeval rocks exposed in the Balkan zone of Bulgaria. The Triassic metasedimentary cover unconformably overlies the basement with basal conglomerate and arkosic sandstone that pass upward into a thick pile of lithic metasandstones and a metasandstone/pelitic schist alternation. Calcareous metasandstones and black slates appear at the highest structural levels. The Triassic succession reveals obvious orogenic features judged from its great thickness, sedimentary features indicating high-energy currents and the presence of intermediate pillow lavas. Both the basement and the cover units were affected by strong deformation and epidote-amphibolite to greenschist facies metamorphism during the Late Jurassic-Early Cretaceous. This event was terminated by the emplacement of a nappe of unmetamorphosed Jurassic limestones and dolomites occurring at the top of the structural column. Kinematic indicators in mylonites at the base of the nappe suggest its original location in the south. The Strandja Massif shows remarkable similarity to the late Palaeozoic-early Mesozoic Silk Road arc that evolved at the southern margin of Eurasia due to the northward subduction of Palaeo-Tethys (Natal'in & Şengör 2005). The fragments of this arc are exposed in Caucasus, Iran, South Tien Shan, Pamir, and Kunlun. The Precambrian history of the Strandja Massif, as recorded by detrital and inherited zircon ages, reveals many common features with the Baltica-Timanide collage including its fragments distributed in Central Asia. Various sets of data and correlations with surrounding tectonic units show that the Strandja Massif is a fragment of the long-lived, Ordovician to Triassic Silk Road magmatic arc, which evolved on the northern side of Palaeo-Tethys.
Keywords: tectonics, stratigraphy, geochronology, Palaeo-Tethys, tectonic evolution, Strandja Massif, Balkan, NW Turkey
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