Reconstructing the evolution of the Miocene Sinj Basin through U-Pb zircon geochronology (Dinarides Lake System, Croatia)

In the Dinarides, a series of intramontane basins hosted long – lived lakes that developed during the Miocene, known as the Dinarides Lake System. Sinj Basin is one of the best studied among them, providing insights into the paleogeographic evolution of the region. A chronostratigraphic framework was initially established in the NW part of the basin using paleomagnetic data and calibrated by Ar-Ar dating of intercalated volcaniclastic deposits. However, the tectonic setting and timing of deposition are still a matter of debate, as subsequent U-Pb dating of Miocene bauxites in the SE part of the basin demonstrated that lacustrine flooding was diachronous. This study aims to provide new constraints on the evolution of the Sinj Basin based on U-Pb zircon geochronology of volcaniclastic deposits from the NW, central, and SE parts of the basin. After the separation of the heavy-mineral fraction from the samples, individual zircon grains were handpicked using a binocular microscope. These were imaged for typology with a scanning electron microscope, before being mounted in epoxy resin. Subsequently, cathodoluminiscence images were produced from polished mounts to gain information about internal structures. U-Pb isotope analyses were obtained using laser ablation‑inductively coupled plasma mass spectrometry (LA–ICP–MS). The obtained ages range between ~18 and ~15 Ma and provide new constraints on the timing of initial lacustrine flooding, and will aid in refining the timing of the Miocene extensional episode. Additionally, a wide spectrum of detrital zircon ages was obtained, reflecting the pre-Miocene geodynamic history of the Dinarides.