Petrogenesis of Early Cenozoic Sarıcakaya–Nallıhan Volcanism in NW Turkey: Implications for the Geodynamic Setting and Source Characterization of the Balkanatolia Magmatic Realm

Sarıcakaya–Nallıhan Volcanism was generated within the Balkanatolia Magmatic Realm between 48 and 44 Ma (by ⁴⁰Ar–³⁹Ar age determination) and is represented by three different volcanic units all displaying subduction-related geochemical signatures, such as depletion in HFSE and enrichment in LREE and LILE. The first unit (V1) consists of nepheline-normative, olivine basalts with OIB-like affinity. The second (V2) and third (V3) units are represented by more evolved compositions such as basaltic-andesitic, andesitic, and dacitic-rhyolitic lavas. Even the most basic lavas have elevated Mg# values (62–69), and they are far from representing the true mantle melts. Source characterization of Sarıcakaya–Nallıhan Volcanism reveals that there might be two possible mantle sources for the primary melts of the lavas: (i) metasomatized peridotitic mantle fluxed by sedimentary melts, or (ii) accreted mélange. The direct melting of the mélange-like lithologies is a more favorable mechanism for the Middle Eocene (44–40 Ma) magmatism in Balkanatolia since the Hf–Nd trace element, Nd isotopic systematics and petrological modelling efforts supported the latter. Overall, Early Cenozoic magmatism within this realm was characterized, first (58–44 Ma) by contractional and later (44–40 Ma) by extensional tectonics and the late-stage magmatic phase in the area was possibly controlled by melting of accreted mélange-like lithologies. The presented data indicate that mélange melting might be much more common than envisaged for the magmatism in the Alpine–Himalayan orogenic belt.