Investigation of geochemical andisotopic characteristics of old alluvium of Ankara Stream (Ankara)

The purpose of this study is investigate geochemical and isotopic characteristics of the old alluvial deposits of Ankara Stream Major, trace and rare earth elements (NTE) contents of the old alluvial deposits of Ankara Stream are determinedand, geochemicallyare classified as lithic arenites. Average chemical index of alteration (KAİ), plagioclase index of alteration (PAİ) and index of compositional variability (BDİ) values of the old alluvial deposits are determined as 58.6, 58.7 and 1.58, respectively, and KAİ exhibits a positive correlation with δ18O isotope values.Ancient alluvial deposits are exposed to the simple sedimentary cycling history, which indicates that geochemical compositions of sediments were controlled by the composition of source materials. 87Sr/86Sr isotope valuesof analyzed samplesare depleted to upper continental crust, whereas δ18O, 143Nd/144Nd isotope and negative ƐNd(0) valuesare similar to upper continental crust. The studied sediments were significantly polluted by Ni, As and a lesser by Pb, Cu, Zn, Co, Hg, Sb, Bi and these heavy metals are industrial origin. As a result;likely low-to-moderate degrees of chemical weathering of these deposits show an increase tectonic activity and erosion and semiarid to arid conditions in the studied area. Old alluvial deposits are derived from particle to intermediate – to felsic sources and the deposits are chemically immature. Additionally, these sediments were contaminated by materials from industrial sources.