⁴⁰Ar/³⁹Ar and U-Pb geochronology of the Iran Tepe volcanic complex, Eastern Rhodopes

The Iran Tepe volcanic complex occurs in the south-eastern part of the Eastern Rhodope massif. The rocks are represented by calc-alkaline and high-K calc-alkaline basaltic andesite to dacite epiclastics, lava flows and dikes, which are crosscut by andesitic and latitic dikes and rhyolitic dykes from the Planinets dyke swarm. Stratigraphic data and existing K/Ar ages suggest that the Iran Tepe volcanic complex is Upper Eocene (35-39 Ma), and is one of the oldest volcanic structures in the Eastern Rhodopes. However, new ⁴⁰Ar/³⁹Ar laser fusion and incremental step-heating experiments on biotites and isotope dilution – thermal ionization mass spectrometry (ID-TIMS) U-Pb age data on single zircons from the bottom and top lava flows and dykes more precisely constrain the ages and time span of volcanic activity, and show that the volcanism is younger. Volcanic activity started with calc-alkaline andesites and dacites at the beginning of the Oligocene (~33.9 Ma) and culminated with the intrusion of latitic dykes at ~33.0 Ma. Rhyolites from the Planinets dyke swarm yield a similar age (32.8 Ma), but their genetic relationship with the more mafic Iran Tepe lavas remains unclear.