Almac?k Complex-an exhumed lower to middle crust in northwest Anatolia

The Almacik Complex is a tectonic unit of high-grade metamorphic rocks in the Intra-Pontide Suture Zone in northwest Turkey. It consists mainly of amphibolite, metaultramafic rock, and gneiss, which are intruded by numerous pre-, syn-, and posttectonic felsic veins. The Almacik Complex is variously interpreted as a Cretaceous or Neoproterozoic ophiolite, or a Permian mafic-ultramafic complex representing the middle to lower crust of the Sakarya Zone. Herein, new petrological and geochronological data were presented from the Almacik Complex. Two-pyroxene geothermometry in the metawebsterites indicated that the Almacik Complex has undergone upper amphibolite-facies metamorphism at 750 +/- 30 degrees C and 8 +/- 4 kbar. U-Pb zircon and Ar-Ar ages from 11 samples indicate the presence of late Neoproterozoic, Permian, and Jurassic thermal events. Most of the Almacik Complex consists of late Neoproterozoic amphibolites and gneisses, representing the basement of the Istanbul Zone. This basement was intruded by voluminous mafic magma during the Late Permian. The basement and the Permian ultramafic-mafic rocks subsequently underwent upper amphibolite-facies metamorphism during the Jurassic, possibly at the base of a magmatic arc.