THE UTILITY OF DETRITAL RUTILE U-PB AND TRACE ELEMENTS IN ACCRETIONARY OROGENIC SETTINGS

Sedimentary provenance is a powerful tool to reconstruct convergent margin evolution. However, single mineral approaches struggle to track sediment flux from mafic and metamorphic sources, which are especially important in accretionary orogenic settings. Here, we present new detrital rutile U-Pb geochronology and trace element geochemistry from the Anatolian segment of the Alpine-Himalayan orogen that demonstrate the challenges and opportunities of using detrital rutile in provenance studies. Rutile trace element geochemistry preserves the original growth conditions, whereas U-Pb dates are a medium-temperature chronometer corresponding to the most recent metamorphic event. Trace elements are applied in several ways: (1) Cr, V, and Zr isotopes classify TiO2 polymorphs; (2) Zr-in-rutile thermometry reconstructs the peak metamorphic temperature of source regions; (3) Cr and Nb contents discriminate between metamafic and metapelitic sources. Detrital rutile U-Pb presents several analytical challenges: around two-thirds of the analyses were discarded due to abnormal U-Pb signal intensities, likely due low U concentration and inclusion lamellae. As is common with rutile, a significant proportion of U-Pb analyses are discordant. Thus, we explore various common Pb corrections. Despite these challenges, the detrital rutile results provide key provenance constraints in Anatolia. Detrital rutile grains are predominantly sourced from Late Triassic-Early Jurassic greenschist and blueschist facies rocks with both mafic and pelitic lithologies. This corresponds to sediment derived from the Karakaya Complex, a Paleozoic subduction-accretion complex or oceanic plateau that was accreted and metamorphosed in the Mesozoic then exhumed to the surface during the Alpine-Himalayan Orogeny. As a case study for reconstructing accretionary orogens, the results from Anatolia are relevant to convergent margins globally. Late Triassic-Early Jurassic ages are nearly absent from the detrital zircon record, emphasizing that a multi-mineral approach provides a more holistic provenance reconstruction. Grains with lower temperatures and mafic affinities are dominated by low-U contents, highlighting that low-U rutile comprise an important detrital population despite the analytical challenges.