Paleotectonic position of the Strandja Massif and surrounding continental blocks based on zircon Pb-Pb age studies

Detrital zircon ages from metasedimentary rocks of the Strandja massif have been used to reveal its tectonic history, initial position, and some aspects of the Paleozoic motion of this continental block within the Tethyan domain. The age of the metamorphic basement of northwestern Turkey has thus far been uncertain. Estimates of the depositional age of metasedimentary rocks range from Precambrian to late Paleozoic, hindering correlation of the massif with other tectonic units. In this study, new evaporation Pb-Pb ages of detrital zircons show that biotite schists constituting the central part of the metamorphic basement were deposited later than 430 Ma and prior to 315 Ma. Biotite schists exposed along the southern boundary of the basement were deposited between 300 and 271 Ma. Episodes of pre-Carboniferous magmatic activity that are inferred from detrital ages cluster around 460-433, 575-525, 700-600, 875-800, 1050-950, 2200-2100, and 2450 Ma. Some of these age ranges correlate with the ages of Late Carboniferous inherited zircons in orthogneisses (315-300 Ma) of the Strandja massif. Pan-African or/and Cadomian ages at 575-525 and 700-650 Ma, respectively, are characteristic of magmatic events in other continental blocks of Turkey (e.g., the Istanbul Zone), as well as in crystalline complexes of surrounding regions - e.g., Crete, the Cyclades massif, the Vardar Zone, and the Sredna Cora Zone. The magmatic history of the source areas of the Strandja detrital zircons prior to the Ordovician is correlative with both the Avalonian and the Armorican tectonic units of Western Europe. Zircon core ages obtained from Late Carboniferous orthogneisses in the Strandja massif are correlated with units derived from the North African sector of Gondwana because of the absence of Mesoproterozoic ages. The basement metasediments of the Strandja massif reveal heterogeneous source areas, which were fed by the North African (Annorica) and the South American (Avalonia) basements. The presence of Mesoproterozoic zircon ages in metasediments of the Strandja massif indicates the proximity of the Strandja massif to Avalonian (or Baltica) derived units during the Late Silurian-Carboniferous interval.