GEOCHEMICAL AND PETROLOGIC EVOLUTION OF OTLAKBAŞI BASALTIC VOLCANISM TO THE EAST OF LAKE VAN

Abstract

Collision-related Otlakbaşı volcanism to the east of Lake Van occurred by eruptions from extensional fissures. In this study, it is investigated new Ar-Ar age data and major, trace and rare earth elements characteristics of the Otlakbaşı basaltic volcanism. The Ar-Ar age data indicate that this basaltic volcanism erupted in Early Pliocene time in contrast to its previously known as Quaternary age. The volcanic products are basaltic composition and close to alkaline-subalkaline division line. Results of fractional crystallization accompanied by assimilation (AFC) modeling imply that fractional crystallization can be negligible compared to crustal contamination in the evolution processes of the magma chamber and ratio of the crustal contamination to the fractional crystallization (r values) varies from 0.1 to 0.35. Enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high strength field elements (HFSE) and behavior of mobile elements (Ba and Th) reveal that the mantle source region of the Otlakbaşı basaltic volcanism might have been enriched by melts that were derived from subducted sediments. Depletion in Rb and K elements of the fractionated-corrected samples indicate that amphibole and/or phlogopite could be the presence in the mantle source. Results of partial melting model studies show that this basaltic volcanism can be predominantly produced by the melting of the spinel peridotite source. Metasomatized spinel bearing lithospheric mantle may be responsible for the eruption of the Otlakbaşı basaltic volcanism.