Ar-40-Ar-39 ages and petrogenesis of middle Eocene post-collisional volcanic rocks along the Izmir-Ankara-Erzincan suture zone, NE Turkey

The central and northeastern of Turkey were shaped by the transition from collisional to post-collisional tectonics and coeval magmatism during Early Cenozoic. However, the temporal and spatial evolution of the magmatism during the middle Eocene remains elusive. In this paper, we provide petrological, isotopic and radiometric data from two middle Eocene volcano-sedimentary successions, from the northern (Almus) and southern (Yildtzeli) parts of the Izmir-Ankara-Erzincan Suture Zone, and discuss their generation in the post-collisional setting. Our results indicate that the volcanic units from these regions display similar stratigraphic and petrological evolution during the narrow window of activity (44.4-44.8 Ma), which is constrained by Ar-Ar dating. The lower parts of the volcano-stratigraphic sections contain hawaiite, and trachybasalts that have a mildly alkaline, nepheline-normative character (Vla subseries), together with clinopyroxene-hornblendite xenoliths. The middle portions of the sections contain basaltic andesitic to dacitic lavas that become tholeiitic/calcalkaline in character (Vlb subseries). In the middle to upper parts of the successions, tholeiitic/calc-alkaline basaltic andesite (V2a subseries) and nepheline-normative mildly alkaline basalts (V2b subseries) become dominant, marking the end of the volcanic episode.