MANTLE SOURCE CHARACTERISTICS OF THE NE-BASANITES FROM NORTH EASTERN EDGE OF THE ARABIAN PLATE

Abstract

The Quaternary nepheline basanites are firstly observed volcanic products of Arabia-Eurasia collision on Bitlis Suture Zone which is an accumulation of Precambrian to Cretaceous metamorphic rocks, Late Cretaceous – Eocene and Middle Eocene volcano-sedimentary units thrust over the Arabian platform between late Eocene and Middle Miocene after the convergence between Anatolian and Arabian plates. Nepheline basanites are composed of clinopyroxene, olivine, Ti-magnetite, Cr spinel, and nepheline. They are characterized by low SiO2 (40.16-41.96 wt %), high MgO contents (8.54-9.73 wt %) and similar Sr-Nd isotopic compositions with Arabian Plate volcanics. Independent barometers indicate that crystallization takes place over a wide range of pressure 8–20 kbar and melt cooled from about 1301°C-1035°C. Trace elements together with Sr isotopic compositions inferred negligible assimilation of the local upper crustal material. The calculated average pressure and temperature of mantle melting for ne-basanites is 2,85 kbar and 1353oC respectively. FC3MS (wt. % FeO/CaO-3*MgO/SiO2) parameter and melting models using REE data reveal that Çatak basanites are products of amphibole and phlogopite bearing metasomatised lithospheric mantle in garnet stability field. Results of thermobarometric calculations together with the recent geophysical data point out melting originated from the base of Arabian lithospheric mantle.