Türkiye Jeoloji Bülteni

Petrographic and Geochemical Features of Calc-alkaline and Alkaline Plutonic/Subvolcanic Rocks in the Cappadocia Region (Nevşehir, Central Anatolia)

Abstract: In the Cappadocia region, the Bayramhacı, İdişdağı, Göynük, Karadağ, Yeşilöz, Akçataş plutonic and/orsubvolcanic rocks exposing in the northern part of the Nevşehir province and Acıgöl plutonic rocks cropping out atthe south are included to the Central Anatolian Granitoids. The Akçataş pluton, exposing at the south of Nevşehir,has monzogranite composition and rarely contain mafic microgranular enclave (MME) and K.feldspar megacrysts.Magmatic rocks in the northern section have quite different compositions varying from monzogranite to quartz monzonit / monzodiorite - monzonite - phonolitic tephrite / tephritic phonolite. Quartz monzonitic / monzodioriticrocks dominantly contain MME and large K.feldspar megacrysts. Monzonitic rocks are in contact with the porphyriticsubvolcanic rocks which contain K-feldspar or leucite megacrysts.The monzogranitic rocks in the region are of subalkaline, high-K series calc-alkaline character and I-type leucogranite. Quartz monzonite, monzonite / monzodioritic rocks show compositions of subalkaline, high-K calc-alkalineto shoshonitic with I-type melt character. Monzonitic and phonolitic tephrite / tephritic phonolite rocks exhibit yieldA-type melt characteristics with alkaline and shoshonitic composition. Magmatic rocks with different compositionspresent different trace element abundance. Light rare element (LREE) enrichment ratios tend to increase frommonzogranite ((La/Yb)n = 4.58 – 12.11) to quartz monzonite / monzodiorite ((La/Yb)n = 12.06 – 33.78) and monzoniteand phonolitic tephrite / tephritic phonolite rocks ((La/Yb)n = 23.29 – 82.17). In Ocean ridge granite normalizedelement diagrams, all magmatic rocks show large ion lithophile elements (LILE: K, Rb, Ba) enrichment with respectto high field strength elements (HFSE: Ta, Nb, Hf, Zr, Y) indicating that they were formed in a subduction zone and/or collisional tectonic setting. However, alkaline magmatic rocks are represented by significant LIL (K, Rb, Ba, Th)and HFS (Ta, Nb, Ce and Zr) enrichment compared to calc-alkaline magmatic rocks. The petrographic and wholerock chemistry data from the Cappadocia Region indicate that studied magmatic rocks were formed by subductionzone magmatism and the contribution from subcontinental lithospheric mantle is much noticeable for the A-typeplutons.