A NEW APPROACHING TO PETROGENESIS AND AGE DATA OF ALKALINE VOLCANICS CUTTING THROUGH DAĞKÜPLÜ OPHIOLITE, NORTHWESTERN SİVRİHİSAR (ESKİŞEHİR)

Abstract

In northwestern Anatolia, the ophiolite nappes related with Neotethyan Ocean, the continent fragments,granitoids and volcanic rocks were found along İzmir - Ankara - Erzincan Suture Zone (İAEKZ) as a results of thecollision of Sakarya Continent and Anatolid - Taurid Platform. In northwestern Sivrihisar (Eskiþehir), phonolitesand trachytes with alkaline characteristic cut the ophiolite nappe. Late Cretaceous aged ophiolite nappe containing ultramafic - mafic rocks thrusted over Anatolid - Taurid Platform. Alkaline volcanics were ranged as domesclose and parallel to the ophiolite thrust line. According to 39Ar/40Ar geochronological data on phonolites the ageof these rocks are determined as 23-25 Ma (Late Oligocene - Early Miocene). Alkaline volcanics show enrichmentin LILE (Ba, Sr, Rb, Th) and HFSE (Nb,Ta, Hf, Zr) relative to MORB. Also, light rare earth elements (LREE) havehigher values than those of HREE values. However, Pb contents of alkaline rocks are considerably high.According to the geochemical results, phonolites and trachytes were generated from asthenospheric magma,enriched with fluid-melting processes linked to the previous subducted slab. These alkaline lavas have used thedeep strike-slip faults created by extensional regime during the ascending and have undergone to a crustal contamination