Timing Aegean extension: Evidence from in situ U–Pb geochronology and cathodoluminescence imaging of granitoids from NW Turkey

•Three Biga Peninsula (NW Turkey) plutons record the timing of Aegean extension.•Color CL imaging and zircon dating show the rocks experienced a multi-stage history.•Late Eocene–Early Oligocene ages record final subduction and initial crystallization.•Late Oligocene–Late Miocene ages record extension and pluton exhumation.•Based on the ages, a model is presented for the plutons' extension and exhumation.

The Biga Peninsula of NW Turkey hosts granitoid plutons that record the timing of extension in the Aegean region. Here we focus on three plutons, the Kozak, Eybek, and Kestanbol and apply new methods to obtain a detailed tectonic history of their generation and exhumation. In situ (in thin section) ion microprobe zircon geochronology and color cathodoluminescence (CL) imaging of zircon grains and whole thin sections show these granites experienced magma mixing, brittle deformation, and significant fluid-rock interactions. Zircon ages range from the Late Eocene to Late Miocene with two ages from a single grain that are Permian. The Late Eocene–Early Oligocene ages record the end stages of subduction during the closure of a branch of the Neo-Tethyan Ocean, whereas Late Oligocene–Late Miocene ages record the plutons' extension and exhumation. We present a model in which Kozak, Eybek, and Kestanbol magmas were initially generated by fluid-flux melting from dehydration of the subducting Anatolide–Tauride block, as evidenced by the Late Eocene to Early Oligocene ages. Late Oligocene ages document the initiation of extension in the Biga Peninsula region and correlate to ages timing exhumation of the Kazdağ Massif. Early Miocene ages indicate continued Aegean extension in the southern Biga Peninsula region at this time.

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