YO-YO TECTONICS IN A WRENCH ZONE, CENTRAL ANATOLIA

Wrench zones can undergo zone-perpendicular shortening and extension, defining classic transpression and transtension, but also zone-parallel shortening and extension, owing to the interplay between wrench motion and the rheological layering of the crust. Zone-parallel shortening and extension result in yo-yo tectonics: cycles of burial and exhumation with similar structural trends. An example of yo-yo tectonics is the Nigde Massif, central Turkey, which is adjacent to and elongate subparallel to the sinistral Central Anatolian fault zone (CAFZ). The massif is a dome, with a high-grade core metamorphosed and intruded in the Late Cretaceous (78-88 Ma). High-T mineral lineation is consistently oriented NNE throughout the core, similar to the orientation of the CAFZ. Partial exhumation of mid-crustal rocks closely followed metamorphism: biotite and muscovite 40Ar-39Ar ages for the core of the massif are typically 70-76 Ma. In contrast, metamorphic rocks along the eastern margin of the massif, adjacent to the CAFZ, record younger Ar-Ar ages (37-58 Ma) and have more variable mineral lineations. This eastern belt was the source of and is unconformably overlain by early Tertiary sedimentary rocks that have been highly deformed and metamorphosed to greenschist facies. Recumbent/reclined Z-folds with axes plunging SE are associated with top to the SW shearing, subparallel to the CAFZ. The contact between these Tertiary metasediments and basement is a low-angle normal fault, with cataclasite in the basement rocks and top to the SW shear zones in the metasediments. This deformation resulted in the final exhumation of the basement, dated at 9-12 Ma by apatite fission tracks. These data suggest episodic yo-yo tectonics over a period of 70 m.y. Zone-parallel shortening closely followed by extension generated and partially exhumed the high-grade core. Following early Tertiary sedimentation, both the eastern belt and the sedimentary units were deformed in contraction then extension, explaining the metamorphism of the Tertiary sedimentary rocks and the final exhumation of the high-grade core. We propose that the Nigde dome, the eastern belt, and the present-day CAFZ represent progressively exhumed levels of the same sinistral wrench zone that underwent two cycles of yo-yo tectonics.