Petrogenesis of the Miocene volcanism along the İzmir-Balıkesir Transfer Zone in western Anatolia, Turkey: Implications for origin and evolution of potassic volcanism in post-collisional areas

The Miocene volcanic rocks along the İzmir-Balıkesir Transfer Zone along the western margin of the Menderes Core Complex (MCC) in western Anatolian Volcanic Province (WAVP), where strike–slip deformation is dominant, comprise: (Group 1) early-middle Miocene high-K to shoshonitic rocks with high-Mg# and relatively low SiO2, (Group 2) middle Miocene phonolitic rocks with low-Mg# and intermediate SiO2, (Group 3) early-middle Miocene medium- to high-K series from andesites to rhyolites, (Group 4) middle Miocene rhyolites with distinct trace element compositions; and (Group 5) late Miocene high-MgO basalts, K-trachybasalts and (Group 6) late Miocene high-MgO basaltic andesites. The geochemical features of these rocks are comparable with the other Oligocene to Miocene volcanic rocks, but differ from the Eocene volcanic rocks in WAVP.The geochemical features of the most primitive early-middle Miocene Group 1 rocks indicate that they were derived from an anomalously metasomatized lithospheric mantle. The mineralogical and geochemical properties of garnet–amphibole peridotite from the Ulten Zone (UZP), Eastern Alps, which is thought to represent a fossil metasomatic mantle wedge contaminated by continental subduction, is similar to the model mantle composition previously proposed for the genesis of the mafic rocks. Together with the presence of Eocene to early Miocene continental subduction beneath the Aegean-west Anatolia region, this strongly suggests that continental subduction was an important factor in the genesis of the high-MgO shoshonitic to ultrapotassic volcanism in this post-collisional area. The origin of the Group 3 andesitic to rhyolitic rocks includes; (1) lower crustal melting, (2) mixing between lower crustally-derived and mantle-derived melts, and (3) FC-AFC processes. The late Miocene Group 5 and 6 rocks, however, derived from a more depleted mantle source, indicating that the mantle became depleted over time. The rhyolites of Group 4 are most probably crustally-derived.OIB-type Quaternary Kula volcanics (QKV) were emplaced near the centre of the MCC. Among the late Miocene basalts in the region, only the basalts located close to the QKV show transitional geochemistry between the Miocene volcanic rocks and QKV, indicating that asthenospheric contribution to lavas in the region occurred only near the centre of the MCC.

► Oligocene–Miocene volcanism in western Anatolia differs from those of the Eocene.
► The origin of the Oligocene–Miocene volcanism requires too much crustal components.
► The crustal component might be supplied by continental subduction into the mantle.
► The primitive andesites represent the lower crustal melts mixed by mafic lavas.
► The andesites evolved into the rhyolites via AFC processes.