The role of peridotite and pyroxenite melts in the origin of the Karapınar basalts, Cappadocia Volcanic Province, Central Anatolia

[摘要] This study investigates the mantle source characteristics of the Quaternary Karapınar Basalts from the southwesternpart of the Cappadocia Volcanic Province (CVP) in Central Anatolia using a combination of whole-rock and olivinemajor- and trace-element geochemistry as well as olivine oxygen isotope composition. Petrographic features and traceelement distributions demonstrate that the Karapınar 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 inMORB-normalized diagrams. KB1 basalts are relatively primitive (e.g., up to 12 wt. % MgO) and calc-alkaline tomildly 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 olivinefrom the KB1 exhibits normal zoning, from core compositions of Fo89 to rim compositions of Fo86, with a concomitantdecreasing in Ni and increasing MnO and CaO contents. On the contrary, the KB2 olivines show both inverse and normalzoning in terms of CaO and MnO contents. Moreover, the studied olivine phenocrysts have enriched rims and/or growthzones in Li, Zn, Cr, Ti, Sc, and V contents, which indicates a source containing recycled continental crust and/or magmarecharging 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 basedon the olivine chemistry indicate that the most primitive nepheline normative KB1 rocks originated from the meltingof mixed pyroxenitic-peridotitic source that shows the average proportion of ~70 % and ~30 %, respectively. The meanδ18O values of olivine phenocrysts (+6.4 ‰; n = 8) from the Karapınar basaltic rocks are higher than typical mantleolivine (+5.1–5.4 ‰) but overlap known OIB-EMII sources (+5.4–6.1 ‰). Collected data indicate that the Karapınarbasalts are the mixing products of partial melts from mantle peridotite and metasomatic pyroxenite generated by thereaction of the subducted oceanic slab-derived melts with the surrounding peridotite, related to the convergence systemof the Eurasian and Afro–Arabian plates.

[学科分类] 自动化工程

[关键词] Karapınar Basalt;olivine;oxygen;peridotite;pyroxenite;source