Devonian magmatism in the western Sakarya Zone, Karacabey region, NW Turkey

摘要

The Karacabey Pluton is a large magmatic body in the northwestern Turkey overthrust by the probable Triassic metamorphic rocks of the Lower Karakaya Complex. Both the metamorphic rocks and the Karacabey Pluton are unconformably overlain by a Lower Jurassic and younger sedimentary sequence. The Karacabey Pluton was regarded as a Carboniferous intrusion based on the previous K-Ar biotite geochronological data. Here, we provide new geological, geochemical and geochronological data from the Karacabey Pluton. Zircon U-Pb results from two samples yielded ages of 393.8 +/?2.7 to 395.9 +/?4.09?Ma, suggesting that the granitoids intruded in the crust throughout the Early to Middle Devonian. The Karacabey Pluton consists mainly of biotite and locally hornblende bearing granitoid with lesser amounts of S-type leucocratic granodiorite, all of which are cut by pegmatitic bodies. It belongs to the high-K calc-alkaline series with distinct Nb and Ta anomalies in multi-element spider diagram. Sr and Nd isotopes’ initial values are 0.709–0.712 and 0.511–0.512, respectively. εNd(i) values range between ?7.8 and ?9.4. The isotopic characteristics of the rocks indicate lower crustal sources of both metapelitic and metaigneous origin. Geochemical features of the rocks suggest that they developed in an arc-related environment, along with the other Devonian granitoids described from the Biga Peninsula in northwest Turkey. The granitoid shows a low-temperature alteration/metamorphism marked by recrystallization of quartz, sericitization of the feldspar and formation of late chlorite, epidote and muscovite. Possibly because of these, the Ar–Ar biotite ages are scattered with a possible concentration at around Permo–Carboniferous boundary. Zircon (U-Th)/He geochronology suggests that after the granitoid was reburied during Early Jurassic to Early Cretaceous sedimentation, there was renewed uplift and erosion during the Late Cretaceous (Turonian), which is possibly related to the closure of the Intra-Pontide Ocean in the north.