Provenance of sediments during subduction of Palaeotethys: Detrital zircon ages and olistolith analysis in Palaeozoic sediments from Chios Island, Greece

Detrital zircon geochronology and analysis of fossiliferous olistoliths from Chios Island, Greece, are used here to constrain terrane accretion processes and the provenance of crustal sources for sediments during the subduction of (a branch of) the Palaeotethys Ocean. U/Pb ages obtained by ion microprobe (SHRIMP-II) analyses of detrital zircons from a Carboniferous greywacke belonging to the tectonostratigraphic Lower Unit of Chios gave major age groups of 2150–1890 Ma, 640–540 Ma, 505–475 Ma and 365–322 Ma. Detrital zircons from a Permian–Triassic sandstone yielded prominent age clusters of 2200–1840 Ma, 1100–910 Ma, 625–560 Ma and 385–370 Ma. The lack of zircon ages between 1.8 and 1.1 Ga in both samples, coupled with the occurrence of ca. 2 Ga-old zircons, imply a northern Gondwana (NW Africa) source. The conodont fauna recovered from an ‘Orthoceras’-bearing limestone lens from the Carboniferous succession of the Lower Unit indicates a Late Silurian age. The fauna is typical of the Ludfordian Polygnathoides siluricus conodont zone. The material has a conodont colour alteration index (CAI) of about 1–2, indicating very low-grade thermal alteration of less than 100 °C. The closest localities with similar conodont-bearing limestones are to be found in the Balkan region and in the Istanbul Zone of northern Turkey. The occurrence of ‘Orthoceras Limestone’ can be used as an indicator of palaeosource reconstruction. Our new zircon ages in conjunction with provenance analysis of Silurian to Lower Carboniferous olistoliths strongly suggest that the clastic succession of Chios received its detritus from basement rocks of the Sakarya microcontinent in western Turkey and time and facies equivalents of Palaeozoic units from the Istanbul Zone in northern Turkey and the Balkan region due to subduction of a branch of Palaeotethys close to the southern active margin of Eurasia in Late Palaeozoic times. The multidisciplinary approach of this study underlines the importance of terrane accretion during stepwise closure of Palaeotethys.