Geological setting, petrology and geochemistry of metasedimentaries and high-K metavolcanics in the north of Ilgın (Konya), SW Turkey

Ilgın (Konya) kuzeyindeki metasedimanter ve metavolkanik kayaçların jeolojisi ve jeokimyası

Abstract

The Afyon-Bolkardağ Zone is one of the metamorphic belts, along with the Tavşanlı Zone, Menderes Massif and Lycian Nappes in western Anatolia, eastern Mediterranea. The study area included by thiz zone is located in the north of Ilgın (Konya-Turkey). Two main metamorphic groups and cover series unconformably overlaid each other from Ilgın of Konya province are reported in this study. From bottom to top, these are: Paleozoic metasedimentary group, Mesozoic metasedimantary and metavolcanic group, Neogene covers and Quaternary alluvium. The Paleozoic group is 1000m in thickness observed particularly in the west and middle part of the study area. This group is derived from the metamorphics of conglomerate, sandstone, siltstone, claystone, limestone and quartzite. Metaconglomerates consist of chert, shale, quartz and green schist fragments in clayey-sandy matrix. Metasandstones are grayish color, grain-supported, well-consolidated and carbonate cemented and bedding is from fine to medium. Phyllites are made up of mainly thin mica flakes and rarely fine-grained quartz and feldspar. Metacherts are thin-bedded, gray in color. Metacarbonates include elongated, flatted calcites, muscovite, chlorite, tourmaline and quartz. Metaconglomerates, at the base of Mesozoic group, purple-pinkish in color pass gradually laterally and vertically into metasandstones. Metasandstones are grayish-reddish-greenish color, mostly 5-30 cm and rarely 10 m in thickness. Metacarbonates are generally dolomitic limestone and dolomite and gray, white and yellow in color. They are in upper levels of Mesozoic group. In this study, we stated that rhyolitic metavolcanics are different from others formerly cited in Ilgın (Konya). These rocks are light-dark gray and green colors. These are mostly metalavas and metatuffs unmapped in scale and thin bedded within schists. The black white alteration surfaces are widespread in the rocks considered lava origin. The foliation is marked in the passing into the schists and muscovites are wieved along foliation plains. The Paleozoic metasandstone and schist samples have high content of SİO2 Na20 values of Paleozoic samples vary from zero to 2.15% and a higher value ofK20 (5.8 %) is found in some samples. The values of high Rb and low Sr in some samples are significant. Schists have 64.2-81.33% Si02. These values suggest that the Paleozoic group is felsic lithologies and acidic in character. Ba values are in the range of 6-485 ppm. On the other hand, some samples have high Zr values (486 ppm). The high contents of Rb may have resulted from the presence of muscovite in these rocks. Na20 and K20 values are very low whereas Sr values are high in dolomitic metacarbonates. Magma composition changes due to mineral fractionations. K20, CaO, MgO, Fe203 and Ti02 show negative correlations with increasing Si02 whereas Na20 shows positive correlation. As the Si02 content increases, the Sr, Ba, Co, Th, Sc and Hf contents decrease and the Rb content increases. However, Cs shows variation. Linear correlations can be explained by fractional crystallizations whereas such unlinear trends as negative and/or positive correlations can be explained by partial alterations and magma mixing in major and trace element diagram. Metavolcanics have 75-80% groundmass and 20-25% phenocrysts. Phenocrysts are quartz, K-feldspar, remnant sanidine and albite. Feldspars occur mostly as K-feldspar (Or 85.97 Ab 3_e An 0-2)- Matrix is composed of microcrystalline quartz, K-feldspar, sericite and rarely muscovite. The metavolcanics have 66-77% Si02, 5.8-10.6% K20, 0.08-1.77% Na20, 12-18% Al203, 0.1-0.4% MgO,

Özet

lgın bölgesinde (Konya); Paleozoyik metasedimanterler, bunlar üzerinde uyumsuz Mesozoyik metasedimanterler ve metavolkanikler ve tüm bunları açısal uyumsuzlukla örten Neojen çökeller ve alüvyon yer alır. Çalışma alanının genellikle batı ve orta kesiminde yaygın olarak izlenen Paleozoyik topluluğun kalınlığı 1000 m'ye kadar ulaşır ve çakıltaşı, kumtaşı, silttaşı, kiltaşı, kireçtaşı ve kuvarsitlerin metamorfık türevlerinden oluşur. Mesozoyik topluluk tabanda metakonglomera ile başlayıp üste doğru daha ince taneli ve nihayet karbonatlardan oluşan metasedimanterler ile bunlar arasındaki metalavlar ve metatüflerden oluşmaktadırlar. Mesozoik topluluk içindeki metavolkanik kayalar, yüksek-K'lu riyolitlerin düşük derecede metamorfızmaya uğramış lav ve tüf-leridir. Bunların mineral bileşimi; %75-80 matriks (ince taneli kuvars, K-feldspat ve serizit) ile %20-25 oranındaki fenokristallerden (kuvars, K-feldspat, Or94.97, Ab2-cAno-o.74, kalıntı sanidin ve albit) oluşur. Matrikste serizitleşme, feldspatlaşma ve silisleşme belirgindir, birincil doku ayırt edilebilmektedir. Yüksek-K' lu metavolkanikler (K2O: % 7-11) kalkalkali karakterlidirler. Nadir toprak element dağılımı; (La/Lu)^: 0.87-215.54 ve (Eu/Eu*)n'- 0.0024-0.23 aralığını (negatif Eu anomalisi) verir. Paleozoik metamorfık grupta kloritoid ve stilpnomelanın varlığı ve Mesozoik metamorfık grupta bu minerallerin olmayışı metamorfızma derecesinin alttan üste doğru azaldığını gösterir. Muskovit K-Ar değerlerine göre (Paleozoyik metamorfık grup örneği: 96.9±1.4My, Mesozoyik metamorfık grup örnekleri; 70.2±1.0My, 65.6±1.0My ve 64.4±1.0My) bölge çok evreli metamorfızmanın etkisinde kalmış ve metamorfızmanın son evresi Üst Kretase-Alt Paleosen 'de gelişmiştir. Metavolkanik tüm kaya K-Ar değerleri 60.4±0.9My, 62.6±0.9My ve 64.1 ±2.0My olarak elde edilmiştir.