Textural and Compositional Evidence for Magma Mixing in the Evolution of the Çamlıdere Volcanic Rocks (Galatean Volcanic Province), Central Anatolia, Turkey

Authors: ELİF VAROL, ABİDİN TEMEL, ALAIN GOURGAUD

Abstract: The Çamlıdere area, in the Galatean Volcanic Province (Ankara), Turkey, is composed of rhyolitic, andesitic, trachytic, dacitic and locally basaltic rocks. The older volcanic rocks in the studied area are rhyolitic and the younger ones basaltic. The phenocrysts from all the volcanic rocks exhibit some petrographic disequilibrium features such as: (a) coexistence of reversely, normally and oscillatory zoned sieved or unsieved plagioclase in the same rock; (b) wide compositional variation of An% in feldspar phenocrysts; (c) sieved, unsieved, normally and reversely zoned pyroxenes occur together in a single rock; (d) some orthopyroxene phenocrysts are surrounded by clinopyroxene; (e) reaction textures, and normal and reverse zoning of amphibole; (f) euhedral phenocrysts such as plagioclase, pyroxene coexist with resorbed phenocrysts of the same type. Such features indicate that a wide change of melt composition and/or temperature occurred in the magma reservoir or conduit during the production of the Çamlıdere volcanic rocks and may reflect an open-system process such as magma mixing. Injection of mafic magma into a felsic magma could generate a chemically zoned magma chamber and subsequent magma mixing process. This process is also supported by major elements modelling. However, a simple mixing process is not consistent with the formation of all Galatean volcanic rocks, and fractionation of basaltic parental liquids led to evolved magmas.

Keywords: Çamlıdere, Turkey, zoning, sieved texture, reaction texture, magma mixing

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