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Sub-ophiolite metamorphic rocks from NW Anatolia, Turkey

2000-09-01
Onen, AP
Hall, R
The metamorphic rocks from near Kutahya in north-west Anatolia record different stages in the history of closure of the Neo-Tethyan Izmir-Ankara-Erzincan ocean. Sub-ophiolite metamorphic rocks within the Tavsanli zone are a tectonically composite sequence of quartz-mica schists, amphibole schists, amphibolites and garnet amphibolites. They show increasing metamorphic grade towards the base of the ophiolite. A first metamorphic event, typical of sub-ophiolite metamorphic sole rocks, was characterized by high-grade assemblages, and followed by retrograde metamorphism. A second event was marked by a medium-to high-pressure overprint of the first-stage metamorphic assemblages with assemblages indicating a transition between the blueschist and greenschist facies. The chemistry of the sub-ophiolite metamorphic rocks indicates an ocean island basalt origin, and Ar-Ar dating indicates a high temperature metamorphic event at 93 +/- 2 Ma. Counter-clockwise P-T-t paths recorded by the sub-ophiolite metamorphic rocks are interpreted to result from intra-oceanic thrusting during the closure of the Izmir-Ankara-Erzincan ocean, initiating subduction, which formed the high-temperature assemblages. Further subduction then produced the widespread blueschists of the Tavsanli zone during the Late Cretaceous. Later cold thrusting obducted the ophiolite (with the metamorphic sole welded to its base), ophiolitic melanges and blueschists onto the Anatolide passive margin in the latest Cretaceous. All these events pre-date the final Anatolide-Pontide continent-continent collision.