Major, trace and rare earth element (REE) characteristics of tuffs in the Yenice-Saraycık area (Demirci, Manisa), Western Anatolia, Turkey

Abstract

Geochemical investigation was carried out on tuffs intercalated with Neogene volcano-sedimentary rocks in the Yenice-Saraycık area (Demirci, Manisa), Turkey. The tuffs are classified as peraluminous and they show calc-alkaline character. They represent mainly rhyolitic to rhyodacitic composition.These silicic vitric tuffs are mostly either altered to zeolites (clinoptilolite–heulandite type) or clays. Their chondrite-normalized REE distribution patterns are remarkably similar. These patterns display light REE (LREE) enrichment with nearly flat heavy REE (HREE) and the strong negative Eu anomalies (Eu/Eu*=0.12–0.51). The existence of negative Eu anomaly is an indicator of feldspar fractionation. In primitive mantle-normalized diagram, all tuffs show nearly parallel patterns characterized by sharp negative anomalies of Nb, P and Ti along with positive anomalies of K and Pb. These findings demonstrate that they originated from a strongly evolved magma which was probably contaminated by crustal material. The negative Ti, Nb and P anomalies also show a subduction-related origin.On the other hand, the alteration of tuffs to zeolites has a prominent effect on their major, trace and REE abundances. Zeolitic tuffs are clearly enriched in Ca, Mg, P and LOI and depleted in Na, K and Mn when compared to unaltered tuff. They have also relatively lower U content but higher Ba, Sr, Cs, Pb, Zn, Ni, As and Sb. Furthermore, a little mobility of HREEs relative to LREEs is seen in most of the zeolitic samples. The loss of alkaline (Na+ and K+) and gain of alkaline-earth elements (Ca2+ and Mg2+) show that zeolitic alteration may have occurred under alkaline conditions. The source for the Ca2+ and Mg2+ gains is presumably groundwater circulating through the carbonate rocks of study area. The remarkable loss of U is probably related to the mobility of U during the alteration of vitric tuffs under the prevailing alkaline conditions. The significant increase of Ba, Sr, Cs, Pb, Zn, Ni, As and Sb in the zeolitic tuffs is most likely due to the ability of both zeolites and clays adsorb these elements.