Petrographic and geochemical evidence for magma mixing and crustal contamination in the post-collisional calc-alkaline Yozgat volcanics, Central Anatolia, Turkey

Petrographic, major-oxide, and trace-element data are presented for the Yoz gat volcanics. These rocks range in composition from basalts through basalt ic andesites and andesites to dacites. Major-oxide variations are largely e xplicable in terms of fractional crystallization, involving removal of obse rved phenocrysts and microphenocrysts. However, complex zoning patterns ant i resolution phenomena shown by phenocrysts in these lavas, and observed ep itaxitic pyroxene growth around quartz xenocrysts imply that they are hybri ds formed by a mixing process. In addition, observed enrichments in crustal elements such as K, Rb, Ba, Sr, and P provide clear evidence for the crust al assimilation of granitoid and metasedimentary xenoliths. The following m odel is suggested for the evolution of the Yozgat volcanics. The primitive magma underwent fractionation in an intracrustal magma chamber to yield mor e evolved liquids. influx of hot, primitive magma into the magma chamber pr omoted vigorous convection-crustal assimilation and eruption of the volcani c rocks in the study area.