Akademik Veri Yönetim Sistemi
INTERNATIONAL JOURNAL OF EARTH SCIENCES, cilt.98, sa.3, ss.601-625, 2009 (SCI-Expanded)
We document the staircase of terraces of the River Tigris in the Diyarbak & r area of SE Turkey, in the northern Arabian Platform, and improve control on the ages of these terrace deposits by dating of overlying basalt flows using the unspiked K-Ar technique. These fluvial terraces are formed of polymict gravel, including clasts derived from the Anatolian metamorphic terrane farther north as well as of local basalt. At least 9 Tigris terraces have been recognised so far, the highest of which, similar to 200 m above present river level, marks the local transition from stacked deposition to fluvial incision, the timing of which is bounded between the mid Late Miocene and the Middle Pliocene. Our K-Ar dating indicates a hiatus in fluvial incision in the late Early Pleistocene, as basalts dated to 1.22 +/- A 0.02 and 1.07 +/- A 0.03 Ma overlie Tigris gravels at very similar levels, similar to 60-70 m above the present river. The lower terraces record the subsequent entrenchment of the modern Tigris valley following an increase in incision rates in the early Middle Pleistocene, evident from the disposition of younger basalt, dated to 0.43 +/- A 0.02 Ma, capping fluvial gravel only similar to 21-22 m above the present river level. Numerical modelling can account for the observed uplift history, as the response to coupling between surface processes and induced flow in the lower crust, with the mobile lower-crust thin (similar to 5-7 km thick), consistent with the known presence of a thick layer of mafic underplating at the base of the crust beneath the Arabian Platform.