Petrography and geochemistry of Devonian aged metasandstones of Bolkardagi Unit: some constrains on sedimentary procesess, provence and tectonic environment

Abstract

The Devonian metasandstones from allocthonous Bolkardagi Unit outcropping in Central (Bozkir-Konya, Isali formation Gerez member) and Eastern (Kangal-Sivas, Kangal formation Bakirtepe member) Taurides mainly include quartz (monocrystalline and polycrystalline), feldspar (microcline and plagioclase), phyllosilicate (illite, chlorite, C-V, C-S and dickite) and rock fragments (phyllite and quartzite). Polycrystalline quartz, microcline and phyllitic rock fragments found as higher amounts in the Bakirtepe member, but plagioclase in the Gerez member. The metasandstones are represented by a composition of quartz arenite in the Gerez member, whereas of subarkose in the Bakirtepe member. Devonian metasandstones have differences such as lithologic (dominance of sand-size siliciclastic rocks) and mineralogic (more feldspar and quartz, appearance of 1M illites, different phyllosilicate assemblages) with respect to overlying and underlying units with same age. Metasandstones were characterized by high contents of SiO2, Al2O3, Fe2O3 and K2O, and Bakirtepe member is rich in K2O but poor in CaO ana Na2O in comparison with those of the Gerez member depending on feldspar types. Bakirtepe and Gerez members are separated from one another and fed largerly from both sedimentary and magmatic sources according to the ratios of chondrite-normalized trace elements. As a conclusion; The members of Bolkardagi Unit have the same age and similar stratigraphic setting and lithologies, hovewer some important differences with respect to their sources, sedimentations and diagenetic/metamorphic histories. These differences were evaluated as sudden changes in provence through transgression related to Variscan orogeny peculiar to northern units of Taurides rather than continuous sedimentation.