Önen, A. Piril; (1994) Ophiolites and related metamorphic rocks of the Kütahya region, NW Turkey. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Izmir-Ankara-Erzincan suture zone is the major Neotethyan suture in northern Anatolia. Two areas of ophiolitic and related metamorphic rocks from this zone have been studied, near to the town of Kütahya. The Besdegirmen area, north of Kütahya, includes dismembered ophiolitic rocks (the Kinik Ophiolite) and consists of serpentinised pyroxenite and peridotites together with gabbros and gabbro dykes. The Kaynarca area, southeast of Kütahya, contains metamorphic sole rocks (mainly amphibolites, amphibole-schists and quartz-schists) at the base of the ophiolite. Microprobe study indicates that the Besdegirmen gabbros contain very calcic plagioclase (An87-100) and magnesio-hornblende as the principal phases. Despite some mineralogical and chemical similarities to rocks reported from arc settings the Besdegirmen gabbros are interpreted as oceanic in origin. Trace element and REE data from gabbro and dyke samples show the patterns which are transitional between midocean ridge and island arc basalts suggesting a backarc setting for the ophiolitic rocks from the Besdegirmen area. Unlike many other Tethyan ophiolites the Kinik Ophiolite appears to represent a fragment of Neotethyan ocean basin, rather than a supra-subduction zone environment. Isotopic dating suggests a Late Cretaceous (Santonian) age for the formation of the Besdegirmen gabbros. For the Kaynarca amphibolites, microscopic and microprobe results prove at least two stages of metamorphism. The first stage is represented by a high grade amphibolite facies metamorphism and late greenschist facies metamorphism resulting in counterclockwise P-T paths. In contrast, the second stage metamorphism is marked by a medium to high pressure overprint of the first stage metamorphic rocks of Kaynarca. The low crossite content of the amphiboles, and the absence of high pressure mineral assemblages such as glaucophane and lawsonite, suggest the transition between blueschist facies and greenschist facies metamorphism for the second stage. Trace element and REE data from the amphibolite samples are comparable to ocean island basalts. The Kaynarca rocks formed as an ocean island, and the Kaynarca sole rocks were formed by intra-oceanic thrusting during the closure of Izmir-Ankara-Erzincan ocean. Isotopic data indicate an earliest Late Cretaceous metamorphic (Turonian-Cenomanian) age for the Kaynarca sole rocks. The sub-ophiolite metamorphic rocks were overprinted by LT-HP metamorphism related to Late Cretaceous subduction. Final emplacement related to the terminal collisional event occurred at the end of the Cretaceous.

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