The Role of Peridotite and Pyroxenite Melts in the Origin of the Karapinar Basalts, Cappadocia Volcanic Province, Central Anatolia

Abstract

This study investigates the mantle source characteristics of the Quaternary Karapinar Basalts from the southwestern part of the Cappadocia Volcanic Province (CVP) in Central Anatolia using a combination of whole-rock and olivine major- and trace-element geochemistry as well as olivine oxygen isotope composition. Petrographic features and trace element distributions demonstrate that the Karapinar basalts can be classified into two sub-groups as basalt-1 (KB1/alkaline-calc-alkaline) and basalt-2 (KB2/calc-alkaline). Although these two types of basalts are petrographically, texturally and geochemically different, they exhibit similar orogenic type incompatible trace element patterns in MORB-normalized diagrams. KB1 basalts are relatively primitive (e.g., up to 12 wt. % MgO) and calc-alkaline to mildly alkaline (Ne-normative content up to 5 %) in character, whereas KB2 basalts are enclave-bearing, calc-alkaline (hypersthene-normative plus quartz or olivine) ones with the more evolved composition. The most primitive olivine from the KB1 exhibits normal zoning, from core compositions of Fo(89) to rim compositions of Fo(86), with a concomitant decreasing in Ni and increasing MnO and CaO contents. On the contrary, the KB2 olivines show both inverse and normal zoning in terms of CaO and MnO contents. Moreover, the studied olivine phenocrysts have enriched rims and/or growth zones in Li, Zn, Cr, Ti, Sc, and V contents, which indicates a source containing recycled continental crust and/or magma recharging processes. The olivine from the most primitive samples (KB1; MgO > 10 wt. %) has high Zn/Fe, Fe/Mn, Co, Zn, Ni, Ca, and low Mn/Zn, Co/Fe values indicating melt addition from a pyroxenitic source. Calculations based on the olivine chemistry indicate that the most primitive nepheline normative KB1 rocks originated from the melting of mixed pyroxenitic-peridotitic source that shows the average proportion of similar to 70 % and similar to 30 %, respectively. The mean delta O-18 values of olivine phenocrysts (+ 6.4 %; n = 8) from the Karapinar basaltic rocks are higher than typical mantle olivine (+ 5.1-5.4 %) but overlap known OIB-EMII sources (+ 5.4-6.1 %). Collected data indicate that the Karapinar basalts are the mixing products of partial melts from mantle peridotite and metasomatic pyroxenite generated by the reaction of the subducted oceanic slab-derived melts with the surrounding peridotite, related to the convergence system of the Eurasian and Afro-Arabian plates.