A MISSING PROVENANCE: SANDSTONE PETROGRAPHY AND DETRITAL ZIRCON-RUTILE GEOCHRONOLOGY OF THE CARBONIFEROUS FLYSCH OF THE ISTANBUL ZONE

The Istanbul Zone is widely regarded as being part of the Avalonian terranes of central and western Europe. The Lower Carboniferous flysch of the Istanbul Zone of the Pontides is an over 1500-m-thick turbiditic sandstone-shale sequence marking the onset of the Variscan deformation. The petrography of the sandstones and the geochronology of the detrital zircons and rutiles from the Carboniferous flysch were studied to establish its provenance. The sandstones are feldispathic to lithic greywackes and subgreywackes with roughly equal amounts of quartz, feldspar and lithic clasts. The amount of feldspar in the sandstones decreases upwards in the sequence at the expense of quartz and lithic fragments. In the discrimination diagrams 21 sandstone samples lie mainly in the field of dissected arc. 205 detrital zircons and 30 detrital rutiles from four sandstone samples were analyzed with laser ablation ICP-Ms. The detrital zircons show a bimodal age distribution with Neoproterozoic (620 to 550 Ma) and latest Devonian to earliest Carboniferous ages (362 to 355 Ma) ages. There are a few Paleoproterozoic and Neoarchean zircons; absent are Mesoproterozoic and Grenvillan (650-1800 Ma) zircons. The REE patterns and Th/U ratios of the zircons indicate a magmatic origin. The rutile ages are exclusively latest Devonian to earliest Carboniferous. Sandstone petrography and detrital zircon-rutile ages indicate two main sources for the Trakya Formation: a) Neoproterozoic granitoidic basement, b) latest Devonian to earliest Carboniferous magmatic and metamorphic rocks. A granitoidic Neoproterozoic basement is described under the Palaeozoic series of the Istanbul Zone, however, latest Devonian to earliest Carboniferous magmatic rocks are unknown from the Eastern Mediterranean region.