Geochronology and Sr-Nd-Pb isotope geochemistry of eocene mafic volcanism in nw anatolia: Constraints on petrogenesis and mantle source characteristics

Early to Late Eocene magmatic activity produced mafic to intemediate lavas, dikes, pyroclastic rocks and coeval granitic intrusions, forming ~ E-W trending magmatic belt in north of Izmir-Ankara suture zone (NW Anatolia). This study reports new 40Ar/39Ar geochronology, major-trace element geochemistry and Sr-Nd-Pb isotope data from Eocene mafic lavas and dikes of this magmatic belt in order to constrain mantle source charateristics and evolution of mafic volcanism beneath NW Anatolia. Ranging from basalt, basaltic andesite to basaltic trachyandesite, mafic dikes and lavas include both calc-alkaline and transitional (calc-alkaline to tholeiitic) affinity. They are slightlymoderately enriched in large ion lithophile elements and light rare earth elements with respect to high field strength elements and show negative Nb, Ta, and Ti anomalies typical of subduction related magmatic suites. Basaltic lavas and dikes are characterized by 87Sr/86Sr(i) compositions ranging from 0.70530 to 0.70415, positive εNd (2.7-6.6) and restricted Pb-isotope compositions (²⁰⁶Pb/²⁰⁴Pb:18.6-18.7, 207Pb/204Pb:15.6-15.66 and ²⁰⁸Pb/²⁰⁴Pb: 38.60-38.87). The ⁴⁰Ar/³⁹Ar cooling ages (37.8-41.1 Ma) obtained from this study combined with radiometric ages from literature indicate that mafic volcanism was dominant between early and late Eocene. ⁴⁰Ar/³⁹Ar ages, geochemistry and Sr-Nd-Pb isotope data indicate the involment of a depleted (MORB-like) mantle modified by earlier subduction event(s) in the genesis of Eocene basaltic lavas and dikes. The break-off of Neotethyan slab may have caused the rise of asthenospheric mantle below NW Anatolia, resulting in a linear zone of asthenospheric upwelling in the study area.