Petrogenesis of mafic-silicic lavas at Mt. Erciyes, central Anatolia, Turkey

Dogan A. U., Peate D. W., DOĞAN M., Yesilyurt-Yenice F. I., Unsal O.

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, vol.256, pp.16-28, 2013 (SCI-Expanded) identifier identifier


New compositional data are presented for a suite of basaltic andesite to rhyolite flows from the flanks of the Pliocene-Quaternary Mt. Erciyes stratovolcano in Central Anatolia, Turkey. The samples are all part of the most recent (<0.9 Ma) New Erciyes eruptive phase. Temperatures estimated from FeTi-oxides vary from similar to 1000 degrees C in the andesites to similar to 820 degrees C in the rhyolites, while the dacites preserve a very broad temperature range (similar to 620 degrees C-1020 degrees C), consistent with textural and mineral chemistry evidence for their hybrid nature. Oxygen fugacity is about NNO + 1 for most samples. The whole rock compositional data, in conjunction with published data, reveal two distinct trends, one formed by the mafic samples (basalts to basaltic andesites) and one by the silicic samples (andesites-dacites-rhyolites). All Erciyes samples plot above the MORB-OIB array on a Nb/Yb-Th/Yb plot, consistent with involvement of subduction-modified mantle, and their low MREE/HREE ratios imply melting of garnet-free mantle. Ratios of incompatible trace elements demonstrate that the basaltic andesite flows are not related to the basalt flows by closed-system fractional crystallization, but instead are derived from a more enriched mantle source, given their higher La/Sm and lower Zr/Nb. The silicic lavas all have higher Th/Nb than the mafic samples, indicating more extensive crustal assimilation. The silicic lavas show linear compositional trends for major elements and most trace elements for SiO2 contents between 56 wt.% and 72 wt.% that are attributed to mixing processes, consistent with textural observations and mineral data particularly in the intermediate dacite flows (two distinct plagioclase phenocryst populations - clear An(33-53) cores vs. sieve-textured cores of An(59-80); wide compositional range for orthopyroxene phenocrysts - Mg# from 63 to 90). We infer that basaltic melts of a heterogeneous, shallow mantle source ponded in the mid- to lower-crust and underwent variable differentiation accompanied by crustal assimilation to form more evolved melt compositions with SiO2>similar to 55 wt.%. These melts ascended to shallower crustal levels (4-10 km based on amphibole geobarometry) where mixing of diverse melts and entrained crystals gives rise to the linear mixing trends shown by the erupted andesite-dacite-rhyolite lavas. (C) 2013 Elsevier B.V. All rights reserved.