Petrography and Geochemistry of the North of Ilgin (Konya) Metavolcanic Rocks

In this study, investigated the geology, mineralogy, petrography and geochemistry of metavolcanic rocks in northern Ilgın (Konya). There are two Paleozoic and Mesozoic metamorphic rock groups in the study area. Alluvium and Neogene sediments are unconformably layered over these rocks. Paleozoic metamorphic group include metasediments and metacarbonates. This metamorphic group consist of metaconglomerate at their base and continue upward as metasandstone, metaquartzite, phyllite, schist, metachert, and metacarbonate at the top. Mesozoic metamorphic group consists of metasediments, metacarbonates, and metavolcanic rocks. There is metaconglomerate at the base and continue upward shale, metasandstone, and metacarbonate at the top. The main difference between the two groups is that the Mesozoic metamorphic group contains metavolcanic rocks. These metavolcanic rocks, which are the main subject of this study, occur at five different locations within the study area. These are Dereköy – Kurtlukaya Hill, Küçüktokmak Hill, Kocatokmak Hill, Göleç Hill, and Avdan Village. Metavolcanic rocks are commonly observed as massive metalavas, but in some areas they exhibit a significant degree of foliation. These rocks include quartz, feldspar, and muscovite. In some areas, quartz veins cut the rocks, and in others, iron oxides are observed. The metavolcanic rocks that are the main target of this study are metariolitic - alkaline metariolitic rocks. The rocks have undergone slight metamorphism, and foliation is clearly visible in some samples. The rocks consist of an average of 40-50% matrix and 50-60% quartz, alkali feldspar, muscovite and plagioclase minerals and exhibit a hemicrystalline porphyritic texture. The matrix of the rocks consists of fine-grained quartz, alkali feldspar and sericite minerals. These rocks’ SiO₂ contents vary between 63.60-71.97%; K₂O contents vary between 3.4-10.52%; Al₂O₃ contents vary between 15.78-18.56%; Fe₂O₃ contents vary between 0.94-4.26% and TiO₂ contents vary between 0.02-0.57%. The rocks are calc-alkaline and shoshonitic in character. In addition, the rocks are peraluminous and silica-saturated. Trace element analysis shows that Ba is present in high concentrations (88–391 ppm) in  the rocks. Samples from Avdan and Dereköy have high Zr values (424–597 ppm) and Rb values (190–360 ppm). Eu values ​​(0.06–0.55) are low in all samples. Low Eu and high Ba are state that crustal contamination. The spider diagrams shows a decrease in Sr, Hf, and Ti elements, especially Eu, and an increase in other elements in the rocks. The negative anomalies observed in Sr and Eu elements indicate that fractional crystallization of feldspars. Enrichment of elements such as Th, Nb, and Zr indicate that crustal contamination. These rocks exhibit a relatively LREE-rich, HREE-poor composition, and show fractionation from LREEs to HREEs in normalized distribution pattern according to chondrite. The formation of the rocks includes fractional crystallization, assimilation-fractional crystallization, magma mixing and crustal contamination events. Ilgın metavolcanic rocks were formed as a result of magmatic activity that developed simultaneously with the collision after orogeny in the within plate environment.

Keywords: Geochemistry, Ilgın/Konya, metavolcanic rocks, petrography, Turkey.