Detrital zircon and rutile U–Pb dating of garnet-mica schist in the Istranca (Strandja) Massif (NW Türkiye): Mineral chemistry and metamorphic conditions

The Strandja Massif is one of the important metamorphic Massifs of Türkiye. The Strandja Massif consists of metasedimentary, and metamagmatic rocks such as migmatite, ortho- and paragneiss, metagranite, garnet-mica-schist, calcschist and marbles. For the first time, mineral chemistry analyzes of garnet-mica schists were performed to better understand the degree of metamorphism, and possible P-T conditions were defined in the north-northwest of the Strandja Massif. Based on almandine garnet and Fe-biotite mineral chemistry, garnet bearing mica-schist are affected by lower amphibolite facies metamorphism under 6.1 kbar pressure and approximately 547 °C. Moreover, detrital zircon UPb dating was performed on 107 points to describe the maximum depositional age of this garnet-mica schist. The youngest zircon Pb/U age obtained as 198 ± 17 Ma (98 % concordant, Th/U = 0.74) and the oldest Pb/U age yielded as 1896.8 ± 33.4 Ma (100.12 % compatible, Th/U = 0.63). Additionally, a zircon UPb concordia protolith age of 302.33 ± 1.79 Ma was obtained from orthogneisses. In-situ rutile-in garnet UPb dating shows that garnet-mica schists underwent metamorphism at 119 ± 49 Ma. P-T conditions and age of metamorphism show that these rocks effected by the lower amphibolite facies metamorphism during late Jurassic – early Cretaceous period.