The Kemer Metamorphic Complex (NW Turkey): A subducted continental margin of the Sakarya Zone

High-pressure and ultrahigh-pressure metamorphic rocks crop out widely in the northern Aegean. In many instances their ages and tectonic setting are poorly constrained. Here we report newly discovered high-pressure rocks of continental crustal origin and of Late Cretaceous age southwest of the Marmara Sea. They occur at the contact between the Rhodope-Strandja Zone in the north and the Sakarya Zone in the south. The Kemer Metamorphic Complex is composed mainly of mica schist, calcschist and marble with minor metabasite and serpentinite. The mica schists contain garnet, phengite (3.30-3.44 c.p.f.u), (±) paragonite, albite, epidote, calcite, chlorite and titanite. The high-pressure metamorphic origin of the mica schists is shown by the high silica contents of the white micas and by glaucophane inclusions in garnet. In the metabasites the mineral assemblage is garnet, barroisite, epidote, albite, titanite, quartz, phengite and chlorite; no evidence is left for the former presence of high-pressure minerals. Metamorphic conditions are constrained by mineral equilibria: a 560-640°C temperature at a minimum pressure of 10 kbar. The metamorphism is dated at 64-84 Ma by the Rb-Sr phengite-whole rock method. The Kemer Metamorphic Complex is in tectonic contact with an accretionary ophiolitic mélange consisting of limestone, basalt, serpentinite, greywacke, radiolarian chert and metabasite. Some of the metabasites in the mélange contain Na-amphibole and lawsonite, indicating a subduction origin. The ages of the limestone blocks in the mélange range from Late Triassic to Late Cretaceous and that of the radiolarite blocks from Middle Jurassic to Early Cretaceous, indicating an oceanic domain dating back to Late Triassic at least. The Kemer Metamorphic Complex and the Çetmi Mélange are intruded by a granodiorite of Early Eocene (52 Ma) age and are unconformably covered by a Late Eocene volcano-sedimentary succession. The lithology of the Kemer Metamorphic Complex resembles a continental margin rather than an oceanic accretionary complex. This and the presence of a Late Cretaceous magmatic arc in the north (Sredna-Gora-Pontide) suggest that the Kemer metamorphic rocks were initially deposited on the northern passive margin of the Sakarya Zone, which was subducted under the Rhodope-Strandja continental domain.