ACCRETIONAL AND COLLISIONAL OROGENS IN ANATOLIA

The Alpide-Himalayan mountain chain is regarded as a typical example of a continent-continent collision orogeny between Laurasia and Gondwanian blocks. However, this archetype collisional orogeny masks earlier events caused by the collision and accretion of oceanic plateaus and/or oceanic islands to the active Laurasian margin. An example is the latest Triassic Cimmeride orogeny, which can be traced for 1100 km in northern Turkey, and is ascribed to the collision and partial accretion of an oceanic plateau to the active margin of Laurasia. The upper parts of this Nilufer oceanic plateau are preserved as imbricated mafic volcanic slices metamorphosed in eclogite, blueschist and greenschist facies. The rare carbonate interbeds in the mafic volcanic rocks indicate an Early to Mid Triassic formation age, whereas the Ar-Ar phengite ages from the eclogites and blueschists are latest Triassic (201-214 Ma). The tectonic slices of the Nilufer unit are overlain by thick, deformed Upper Triassic clastic sequences, representing a fore-arc fed from the Upper Paleozoic granite thrust sheets of the Laurasian margin. The collision and accretion of the oceanic plateau in the latest Triassic resulted in the growth of the Laurasian margin, similar to the Mesozoic geological history of the western North America.

The Jurassic-Early Cretaceous history in the Anatolian segment is characterized by passive margin sedimentation with no evidence of deformation. The earliest episode of the Alpide orogenic activity in Anatolia was in Campanian, when the northern margin of the Anatolide-Tauride Block was subducted under the oceanic lithosphere leading to HP/LT regional metamorphism (80 Ma Rb/Sr ages). Here, the similarity in timing and mechanism to the HP/LT metamorphism in Oman is remarkable. The HP/LT metamorphism was followed in the Maastrichtian by a classical ophiolite obduction. In the Taurides ophiolites lie over Senonian limestones through intervening sedimentary melange/flysch sequences. In the northern parts of the Anatolide/Tauride Block there is no clear temporal boundary between deformations due obduction and those due to the continent-continent collision. However, the bulk of the Taurides were deformed by thrusting and folding in the Mid-Eocene (Lutetian), which may represent the time of continental collision.