DID THE CENTRAL ANATOLIAN CANKIRI BASIN FORM AS A RESULT OF AN OLIGO-MIOCENE RAYLEIGH-TAYLOR INSTABILITY? IMPLICATIONS FOR EARLY MIOCENE PLATEAU DEVELOPMENT IN CENTRAL ANATOLIA

The ~125 km north-south by ~75 km east-west Central Anatolian Cankiri Basin presently resides at an elevation of ~1 km. The Cankiri Basin is host to early Oligocene brick-red gypsum deposits, nodular anhydrites, laminated claystones, mudstones, and lesser amounts of bedded sandstones. Late Oligocene deposits consist of red and brown bedded sandstones, conglomerates, and mudstones. Collectively, these deposits are highly transposed and thicken to >600 m towards the basins southern margin. Early – middle Miocene deposits overlie Oligocene sedimentary rocks along an angular unconformity and consist of alternating graded, conglomerates and sandstones, mudstones, laminated claystones, lignite layers, and cross bedded sandstones. Due west of the Cankiri Basin, a >1500 m thick accumulation of potassium-rich magmas erupted from 18-20 Ma.

In early Oligocene times, the Cankiri Basin was characterized by fluvial and alluvial systems along its northern and eastern margins. Further south, a large lake system developed. In late Oligocene times, the basin contracted. Miocene times are characterized by smaller isolated lake and river systems separated by uplifted fault blocks. Potassium-rich magmas located due west of the Cankiri Basin, erupted from 18-20 Ma and are interpreted to signify the point at which upwelling sub-lithospheric mantle replaced a gravitationally unstable eclogitic root.

Basins hypothesized to form as a result of Rayleigh-Taylor instabilities exhibit ~100 km wide elliptical geometries and reflect initial subsidence in >40 km thick crust driven by the growth of a basal eclogitic root. Subsequent gravitational foundering of this root after ~10 Myr may result in isostatic rebound and basin inversion culminating with a flux of mantle affinity magmatism. Indeed, Rayleigh-Taylor instabilities are hypothesized to be forming today, deep within the 2-5 km high, Eastern Anatolian, Central Andean, and Tibetan Plateaus. Geologic observations from the Central Anatolian Cankiri Basin and surrounding region are most consistent with the early Oligocene growth and late Oligocene gravitational foundering of a dense eclogitic root. If correct, modern-day analogs indicate that north-central Turkey was likely characterized by an internally drained orogenic plateau at elevations of >2 km by the early Miocene.