Scholarly record

MAJOR, REE, TRT, LILE AND HFS ELEMENT BEHAVIOR IN THE ALTERATION OF THE KONYA VOLCANITES

N. Karakaya, M. C. Karakaya

Abstract

Mainly high-K, calc-alkaline, Late Miocene to Pliocene volcanic rocks cropped out of Konya area in Central Anatolia, Turkey. The volcanic rocks are predominantly andesitic to dacitic in composition and rarely basalt, basaltic andesite, basaltic trachyandesite and pyroclastics. Mineralogic compositions, major, trace and REE element composition of the investigated rock samples was analyzed. Kaolinite, illite, Ca-montmorillonite, alunite, jarosite, minamiite and silica polymorphs were formed by widespread and intense hydrothermal alteration in or around of the volcanic products. Nearly all major and trace elements are more or less mobile in the samples. The most prominent geochemical characteristics of altered parent rocks include substantial variations in the concentrations of Na, Ca, Mg, Fe, and partly K. Fe2O3+MgO and Na2O+CaO content are between 5.97 and 8.48 in parent rocks which is typically dacite. Increasing alteration intensity is coupled with a gradual decrease in these elements, in weakly altered rocks 5.31 and 7.0, while in moderately altered rocks 1.21 and 0.63, respectively. The element contents culminating in intensely altered kaolinitic (1.29 and 0.55) and alunitic rocks (0.22 and 0.55). This decreasing trend is indicative of plagioclase destruction and formation of argillization and sericitization. Loss of alkalis and Fe and Mg causes to enrichment of Al and Si in altered rocks and seems to be an important alteration effect for the area as well. Al is mainly enriched all rocks group, Fe+Mg were leached, except weakly altered ones. These elements show important decrements relative to parent and weakly altered rocks. The parent rock has a CIA of 49.85. CIA of weakly altered rocks is 51.41 and has a REE pattern almost identical to the parent rock. Moderately weathered rock has a CIA of 85.35 and is depleted in total REEs relative to the parent. REE patterns and total REE contents of the kaolinitic with CIA value of 97.87 and alunitic samples having CIA value of 79.43 are different from each other and the parent and the other rock groups. The total REE, TRTE and LIL element content are higher in alunitic rocks than the other alteration products. The HFS elements are shown visible changes in studied sample suites, meanwhile its concentrations is lower in kaolinitic rocks than the other sample groups. Slightly negative Eu anomalies were observed in parent and weakly altered rocks while the other sample groups show no Eu anomaly. The HFS and TRT elements are slightly mobilized in weakly altered rocks, whereas enriched in other alteration types. Elements commonly assumed to be immobile (e.g., Y, Zr, Nb, Hf, TiO2, Al2O3, REE) show variation in mass calculation. LIL elements showed enrichment over REE and MREE, and similar behavior, while opposite to HFSE. A clear increment of trans-transition elements (TRTE) were found in mainly in alunitic and partly in kaolinitic samples.

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