Petrological and structural features of the pre-alpine metamorphic rocks in the Biga peninsula (NW Anatolia)

The Biga Peninsula in northwestern Anatolia is a tectonic mosaic representing the continent and oceanic assemblages of different origin and ages. Kazdağ Group, Çamlıca Group, Ezine Group, Kemer metamorphics are different from each other in terms of their metamorphic basements. The Çamlıca Group occurring on the western end of the Biga Peninsula has a Variscan basement. The presence of Variscan basement was revealed for the first time by this study. The Variscan basement consists of the metavolcanic rocks occurring on the lowest part of the Çamlıca Group. Zircon ages from the metavolcanic rocks obtained by LA-ICPMS yielded 328,6 ± 3,5 Ma and 343,3 ± 2,5 Ma. This Early Carboniferous age is interpreted as the protolith age of the metavolcanic rocks.Eclogite-facies metamorphic rocks occur as tectonic slices within the Çamlıca Group. The eclogite-facies metabasite lenses are typically low - temperature eclogites that may represent tectonic slices of an accretionary complex associated with a subduction zone. Blueschists were produced by retrograde metamorphism from eclogite during late stage shearing. Field observations and petrographic analysis of this study document the presence of blueschist facies for the first time, in addition to eclogite-facies metamorphism on the Biga Peninsula. The host Çamlıca rocks record only a single-stage greenschist-facies metamorphism and were juxtaposed with the eclogite-facies metamorphic rocks along ductile?semi-brittle (?) strike-slip faults after eclogite-facies metamorphism and during or after the low-grade metamorphism of the Çamlıca Group. Zircons from the eclogite/blueschists have been estimated as average 338,1 ± 1,8 Ma (Early Carboniferous). This age gives the crystallization age of the HP metabasic rocks.The Örenli metamorphics occurring on the northwestern part of the Kazdağ Group mainly made up of low grade schist, marble and metabasite intercalations. These rocks directly occur on the high grade metamorphic rocks of the Kazdağ Group with tectonic contact. Petrographical and geochemical data show that metaophiolites of the Tozlu formation derived from old oceanic crust and underwent amphibolite-facies metamorphism.Isotopic data from this PhD thesis are highly similar to other Variscan basements of Armorica terrane within the Europe. Therefore, the Variscan basements within the Sakarya Zone represent eastern continuation of the Armorican terrane.