Ophiolites and related metamorphic rocks from the Kütahya region, north‐west Turkey

Abstract

AbstractThe Izmir‐Ankara‐Erzincan suture zone is the major Neotethyan suture in northern Anatolia. Two areas of ophiolitic rocks from this zone have been studied. The Beşdeǧirmen area, north of Kütahya, includes dismembered ophiolitic rocks (the Kinik Ophiolite) and consists of serpentinized pyroxenites and periodotites together with gabbros and gabbro dykes. The Kaynarca area, south‐east of Kütahya, contains medium to low grade metamorphic rocks (mainly amphibolites, amphibole schists and quartz schists) at the base of the Kinik Ophiolite. These two areas are probably joined under the Neogene cover.The Beşdeǧirmen pyroxenites contain spinel with a Cr number [Cr/(Cr + Al)] < 0·60 and are similar to peridotites from mid‐ocean ridge (MOR) settings. Gabbro samples contain very calcic plagioclase (An87–100) and magnesio‐hornblende as the principal phases; prehnite and zeolite are the most common late stage fracture infillings. The chemistry and mineralogy of the gabbros have features similar to rocks from both MOR and arc settings.For the Kaynarca amphibolites there are at least two stages of amphibole growth. The first stage amphiboles are brownish green calcic varieties. In contrast, the second stage amphiboles record a medium to high pressure overprint with the growth of fibrous, bluish green varieties. The low crossite content of the amphiboles, and the absence of lawsonite, suggest the transition between blueschist and greenschist facies metamorphism. Trace element and rare earth element data from the amphibolite samples are comparable with oceanic island basalts.Isotopic dating suggests a Coniacian‐Ypresian age for the formation of the Beşdeǧirmen gabbros, significantly younger than the Jurassic ages previously suggested for the formation of the main Izmir‐Ankara ocean. Unlike many other Tethyan ophiolites the Kinik Ophiolite appears to represent a fragment of a Neotethyan ocean, rather than a supra‐subduction zone environment. We suggest a back‐arc basin setting for the formation of the Beşdeǧirmen ophiolitic rocks.The Kaynarca rocks formed as an oceanic island or seamount and the Kaynarca amphibolites were formed by intra‐oceanic thrusting during the closure of the Izmir‐Ankara‐Erzincan ocean. Preliminary isotopic data suggest an Albian‐Campanian age for this sub‐ophiolite metamorphism. The sub‐ophiolite metamorphic rocks were overprinted by low temperature‐high pressure metamorphism related to Late Cretaceous subduction. Final emplacement is related to the terminal collisional event which occurred at the end of the Cretaceous.