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

Abstract

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 ²⁰⁶Pb/²³⁸U age obtained as 198 ± 17 Ma (98 % concordant, Th/U = 0.74) and the oldest ²⁰⁶Pb/²³⁸U 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.