Timing of the Quaternary ElazIg Volcanism,Eastern Turkey, and its Significance for Constraining Landscape Evolution and Surface Uplift

The eastern part of the Anatolian plateau in eastern Turkey has experienced dramatic landscapeevolution in the Late Cenozoic, surface uplift having been associated with the disruption of former lake basins and the development of the modern high-relief landscape, incised by the upper reaches of the River Euphrates and its major tributary, the Murat. Overall, the altitude of the plateau decreases gradually westward, and it has been assumed that uplift on any given timescale has varied regionally in a similar manner. However, using the Ar-Ar method, we have dated an episode of basaltic volcanism around the city of Elazig¤ to ~1.8–1.9 Ma (two alternative calculation procedures give ages of 1885±16 ka and 1839±16 ka; both ±2σ). The disposition of this basalt indicates no more than ~100 m of incision by the River Murat on this timescale in this area, in marked contrast to neighbouring localities where much more incision on similar timescales is indicated by the geomorphology. We interpret these variations as consequences of flow in the lower continental crust induced by surface processes, theflow being vigorous because the lower crust in this region is highly mobile due to the high Moho temperature. We thus suggest that the ~1.8–1.9 Ma Elazig volcanism was triggered by outflow of lower crust following the emptying at ~2 Ma of the adjacent Malatya lake basin; the resulting local removal of part of this lower-crustal layer can also account for the limited amount of subsequent net crustal thickening and surface uplift that has occurred locally. Local patterns such as this are superimposed onto the regional westward tilting of the surface of the Anatolian Plateau, which has facilitated the disruption of former lake basins such as this.