Geochemistry of the Zeolite-rich Miocene Pyroclastic Rocks from the Gördes, Demirci and Şaphane Regions, West Anatolia, Turkey

Abstract: The western Anatolian Miocene volcano-sedimentary basins in the Gördes, Demirci and Şaphane regions host abundant heulandite/clinoptilolite (hul/cpt) bearing widespread zeolitized pyroclastic rocks. Lithostratigraphy of these zeolitic pyroclastic levels show comparable association. Petrography and geochemistry of all the samples show mainly rhyolithic and rhyodacitic character and ash size vitric tuffs. Polarized microscopy and X-ray diffraction determinations of the samples show composition of 55–95 wt % hul/cpt and accessory of smectite, illite/mica, opal–CT, quartz, K–feldspar, plagioclase and opaque minerals. Geochemical results obtained from the studied samples represent hul/cpt–rich facieses formed under the moderate alkaline conditions in these pyroclastic units. Correlation of geochemical results and concentration of hul/cpt in these pyroclastic rocks gives some chemical data on zeolitization process and on adsorption and ion-exchange character of hul/cpt type of zeolites. Depleted and enriched elements by zeolitization have similar ionic radii in general. Ca and H₂O clearly increased, Si, Na and Si/Al ratio decreased in hul/cpt bearing Lower-Middle Miocene pyroclastic rocks of western Anatolia. Additionally, Sr, Nb, Th, Ni, Hf, Cs, Pb and Ta increased, and Zr, Co, W and most of the rare earth elements (REE) decreased in highly hul/cpt–rich pyroclastics.