Provenance of detrital rutiles from the Jurassic sandstones in the Central Sakarya Zone, NW Turkey: U-Pb ages and trace element geochemistry

Abstract

This provenance study focuses on detrital rutile grains from Jurassic sandstones of the Bayırköy Formation in the central Sakarya Zone. Cr and Nb concentrations of detrital rutile grains in the Jurassic sandstones vary from 18 to 6855 μg/g and 70–13440 μg/g, respectively. Source area discrimination based on the Cr-Nb concentrations shows that 79 % of the detrital rutile grains originated from metapelitic and 21 % from metamafic rocks. The calculated rutile formation temperatures vary from 471 to 798 ℃ with an average temperature of 635 ℃ at P=10 kbar. Zr-in-rutile thermometer gives overlapping temperatures for all detrital rutile grains from both the metapelitic and metamafic sources. This demonstrates that most of the detrital rutiles sourced from metapelitic and metamafic rocks underwent similar metamorphic conditions and have similar metamorphic history. The U-Pb rutile dating yielded ages for the detrital rutiles in the time range of 346 to 319 Ma, which gives the age of metamorphism for the potential source rocks. Trace element compositions, Zr-in-rutile thermometer and U-Pb rutile geochronology show that detrital rutile grains were predominantly derived from early Carboniferous rocks that underwent metamorphism in amphibolite-facies conditions. Amphibolite-facies rocks of the Sarıcakaya Massif in the central Sakarya Zone seem to be the primary source lithologies for the detrital rutiles in the Jurassic Bayırköy Formation as it comprises previously-mentioned source lithologies and has a close geographic position to the area studied. Carboniferous Variscan metamorphism was followed by emplacement of numerous post-collisional granitoids in the central Sakarya Zone.