First U–Pb SHRIMP zircon and 40Ar/39Ar ages of metarhyolites from the Afyon–Bolkardag Zone, SW Turkey: Implications for the rifting and closure of the Neo-Tethys

The Afyon–Bolkardag Zone (ABZ) is one of the most important metamorphic zones in Turkey. This zone consists of metasedimentary and metavolcanic rocks, which have undergone regional greenschist facies metamorphism. The metavolcanic rocks are dominated by rhyolite, dacite, and trachyandesite. In the Ilgin (Konya) area, the low grade metavolcanics were originally rhyolitic lavas and tuffs. We present new precise Sensitive High-Resolution Ion MicroProbe (SHRIMP) 206Pb–238U age analyses of zircons and 40Ar/39Ar age data of phengite from metarhyolites that enable a more precise reconstruction of the ABZ. SHRIMP analyses of euhedral or sub-euhedral magmatic zircons from two metarhyolite samples yield weighted means 230 ± 2 Ma and 229 ± 2 Ma. These ages are interpreted as formation age of rhyolitic volcanics, implying they were formed in the Late Triassic time (Carnian). We suggest that these Upper Triassic magmatic rocks were formed in an extensional tectonic setting on the northern active margin of Gondwana, which led to the development of the northern branch of the Neo-Tethys. 40Ar/39Ar dating of two phengite samples from metarhyolites gave plateau ages of between 63.7 ± 0.1 Ma and 62.6 ± 0.1 Ma. These dates are interpreted as the metamorphic age of these volcanic rocks, and as the age of metamorphism that affected the ABZ. Consequently, these earliest Tertiary ages also constrain the timing of the closure of the Neo-Tethys.

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► The metarhyolite rocks of the ABZ erupted during Late Triassic time.
► Metamorphism occurred during the Paleocene.
► Upper Triassic volcanism in an extentional tectonic setting.