Early–Middle Jurassic intra-oceanic subduction in the İzmir-Ankara-Erzincan Ocean, Northern Turkey

The Izmir-Ankara-Erzincan suture zone near Çankiri comprises an ophiolite-related rock suite of amphibolite, pyroxene-amphibolite and epidote-amphibolite. The geochemical data reveal that the basaltic protoliths of the Çankiri amphibolite suite are derived from different mantle sources. Amphibolites showing a LREE enrichment in chondrite-normalized REE pattern, relatively high LaN/YbN (8.5-13.1), Sm/Yb (2.8-3.7), Ce/Sm (8.8-9.8), Nb/Yb (14.4-20.5), Th/Nb (1.1-2.6) originate from an OIB-like (Type I amphibolites) mantle source. Those with flat chondrite-normalized REE pattern, low LaN/YbN (~0.6), Sm/Yb (~1.0), Ce/Sm (~2.7) Nb/Yb (~0.6), suggest derivation from a depleted MORB-like (Type II amphibolites) mantle source. A third type of amphibolite is characterized by LaN/YbN (1.54), Sm/Yb (1.1), Ce/Sm (4.5), Nb/Yb (1.1) and Th/Nb (0.3). It is derived from an enriched MORB source and shows characteristics similar to island arc basalts. Amphiboles from these rocks yielded 40Ar/39Ar plateau ages between 177.08±0.96Ma and 166.9±1.1Ma. These dates are interpreted as metamorphic ages of the amphibolitic rocks. They differ significantly from previous ages of amphibolitic rocks (the metamorphic sole rocks) related to Turkish ophiolites. However, similar metamorphic ages have been reported for metamorphic sole rocks of the Hellenic-Dinaric ophiolites further west. The metamorphic sole rocks have been generated in intra-oceanic environments via intra-oceanic subduction/thrusting events. The new age data of the Çankiri amphibolite suite suggest that the Izmir-Ankara-Erzincan ocean was subducted around Early-Middle Jurassic times, i.e. roughly coeval with the oceanic basin(s) generating the Hellenic-Dinaric ophiolites. In the Early-Middle Jurassic time, the tectonic regime in the Izmir-Ankara-Erzincan ocean was compressional and the ocean was closing at that time. The new age data presented here could imply that Jurassic granites which cross-cut basement rocks of the Pontides are related to the northward subduction of the Izmir-Ankara-Erzincan ocean during Jurassic time.