Trace Element Content and U-Pb Geochronology of Detrital Rutile in the Cretaceous-to-Eocene Julian and Brkini Flysch Basins (SE Alps and NW Dinarides, Italy and Slovenia)

The Cretaceous-to-Eocene Julian (JB) and Brkini (BK) flysch basins have recently been studied for their heavy mineral assemblages; however, the rutile component has so far been neglected. To fill this gap, this study explores their detrital rutile trace element contents and U-Pb ages to define their possible provenance(s). In JB, there are very few rutile grains, mainly related to amphibolite–eclogite facies metamorphic units, with about 80% metapelitic grains. Among the few rutile grains from JB, only eight gave robust U-Pb ages. These ages are all Palaeozoic, resembling those of the closure/opening of the Rheic Ocean and the Variscan orogeny. In BK, the number of rutile grains is much higher than in JB, testifying to differences in the supply areas. The rutile grains are mainly in the amphibolite–eclogite facies, but they decrease, moving upward, accompanied by an increase in UHT. The metapelitic rutile component is higher than 74%. When considering the BK rutile grains, there are no Palaeozoic ages at the bottom of the sequence, while they are newly visible upward. In BK, the most abundant rutile grains show Mesozoic ages that can be considered as representatives of the opening/closure of the Vardar Ocean and the ophiolite emplacement in the Dinarides area.