Mineral chemistry and P-T conditions of the Karakaya volcanites at Kırka-Afyon-Isparta volcanic province, Afyon, Turkey

Abstract

The Kırka-Afyon-Isparta Volcanic Province (KAIVP) is one of the best known regions in Turkey for the origin and petrological evolution of the high potassium volcanic activity. The temporal and spatial variability of volcanic rocks in the region exerts significant control over their geochemical diversity. Alkaline and ultrapotassic volcanic rocks of the Afyon volcanism are the first products of asthenospheric origin after the orogenesis in western Anatolia. We have determined the mineralogical and petrographic properties of the Karakaya volcanites surrounding Afyon with the help of microprobe analyses. Estimated thermobarometers are calculated. The Karakaya volcanites have been grouped into four different units according to their their mineralogical, petrographic and geochemical characteristics: Seydiler ignimbirite, basaltic trachyandesite, trachyandesite, trachyte and lamproite. Most samples display hypocrystalline porphyritic texture, whereas samples of lamproite unit have a holocrystalline texture. Generally, volcanic units also exhibit some textural evidence of disequilibrium crystallisation, such as sieve texture and corrosion in plagioclase phenocrysts, zoning and inclusions in clinopyroxene phenocrysts. Mineral thermobarometric estimations in all suites were tested on clinopyroxene and feldspar compositions, considering different authors’ approaches. Values of temperatures and pressure range from 1105 to 1273ºC and 5.6 to 12.2kbar, respectively. The temperature and pressure values calculated from the mineral-melt associations in the volcanics suggest that the Afyon Volcanites were affected by magma mixing processes and crystallised at different depths during the transport of magma.