Post-collisional plutonism with adakite-like signatures: The Eocene Saraycik granodiorite (Eastern Pontides, Turkey)

The post-collisional Saraycik granodiorite intruded into a late Paleocene to early Eocene nappe pile that formed during collision of the Pontides in the North and the Anatolide-Tauride platform in the South, leading to the formation of the İzmir-Ankara-Erzincan suture. A relatively shallow pluton intrusion depth (∼5 to 8 km) was estimated from Al-in-hornblende geobarometry and contact metamorphic assemblages. The emplacement age is tightly constrained to ∼52 Ma by two Ar-Ar plateau and total fusion ages on biotite. The main mass of the pluton consists of metaluminous to peraluminous biotite granodiorite and hornblende-biotite granodiorite. In addition, up to 10-m thick dacitic and <25-cm thick aplitic dikes occur. Granodiorites and dacites show many close compositional similarities to high-silica adakites from supra-subduction zone settings, but tend to be slightly more felsic and to have a higher aluminium saturation index. Chondrite-normalized (cn) rare earth element patterns are characterized by high ratios of (La/Yb) _cn , concave-upward shapes of the HREE and a lack of significant Eu anomalies. In conjunction with relatively high abundances of Ba and Sr as well as low abundances of Y, HREE and Sc, these patterns suggest a feldspar-poor, garnet ± amphibole-rich fractionating mineral assemblage (residue). All samples have very similar Nd-Sr isotopic characteristics, regardless of rock type. Initial ε _Nd values range from -0.3 to -1.2 and initial ⁸⁷ Sr/ ⁸⁶ Sr ratios from 0.70491 to 0.70529. It is suggested that the magmas formed by partial melting of mafic lower crust at elevated pressures (∼1 to GPa).