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

Topuz G., Altherr R., Schwarz W., Siebel W., Satir M., Dokuz A.

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, vol.150, no.4, pp.441-455, 2005 (SCI-Expanded) identifier identifier


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 Izmir-Ankara-Erzincan suture. A relatively shallow pluton intrusion depth (similar to 5 to 8 km) was estimated from Al-in-hornblende geobarometry and contact metamorphic assemblages. The emplacement age is tightly constrained to similar 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 epsilon(Nd) values range from -0.3 to -1.2 and initial Sr-87/Sr-86 ratios from 0.70491 to 0.70529. It is suggested that the magmas formed by partial melting of mafic lower crust at elevated pressures (similar to 1 to 2 GPa).