TEPEKENT (KONYA-ORTA ANADOLU) YÖRESİNDEKİ VOLKANİK KAYALARIN PETROGRAFİSİ, JEOKİMYASI VE PETROLOJİSİ

Öz

Bu çalışmada, Tepekent yöresi (Konya-Orta Anadolu) yüzeyleyen Miyosen yaşlı riyolitik, dasitik ve bazaltik lav akıntıları ve bunların piroklastiklerinin petrografisi, mineralojisi, jeokimyası ve petrolojisi incelenmiştir. İncelenen kayalar Toplam alkali-silika (TAS) diyagramına göre yüksek potasyum içerikli bazaltik traki-andezit, dasit ve riyolit bileşiminde kayalardır. Bununla birlikte incelenen bazaltik traki-andezitler Na2O-K2O içeriklerine göre şoşonit olarak da adlandırılmaktadır. Dasitik kayalar yer yer mm’den dm’ye değişen boyutta anklav içermektedir. Anklavlar TAS diyagramında traki-bazalt alanına düşmekte olup ana kayalarından daha mafik bir bileşim sergilemektedir. Bazaltik traki-andezitler holokristalin porfirik doku gösterirken, dasitler değişen volkanik cam içerikleri ile hipokristalin porfirik doku sergilemektedir. Bazaltik traki-andezitler olivin, klinopiroksen, plajiyoklaz ve Fe-Ti oksit içermekte, nadiren zeolitleşme ve olivinlerde iddingsitleşmeler göstermektedir. Dasitler amfibol, biyotit, plajiyoklaz, Fe-Ti oksit ve nadiren de kuvars mikro fenokristallerinin içerisine dağıldığı, aynı minerallerin mikrokristallerine ilaveten volkanik camdan oluşan hamur içeriğine sahiptir. Dasitik ana kayalarda yer alan anklavlar ana mafik mineral olarak amfibol içermekte olup, magma mixing anklavlarında sık sık rastlanan ince taneli dokuya sahiptir, bununla birlikte, bıçaksı biyotit, söndürülmüş amfibol ve elek dokulu plajiyoklaz gibi dokusal özellikler sergilemektedir. Riyolitler ise kuvars, plajiyoklaz ve Fe-Ti oksit mikrofenokristalinin yanı sıra önemli derecede sanidin ve biyotit içermektedir. Bununla birlikte dasitlere göre daha fazla volkanik cam içeriğine sahip olup, hipohiyalin porfirik doku sergilemektedir. İncelenen kayaların Okyanus Ortası Sırtı Bazaltları’na (OOSB) göre normalize iz element diyagramında, büyük iyon yarıçaplı litofil element bileşiminde (BİYE, Sr, K, Rb, U ve Th) bir zenginleşme izlenirken, yüksek alan enerjili elemente (YAEE, Nb, Ta, Ti) bileşiminde ise bir fakirleşme görülmektedir. Kondrite göre normalize nadir toprak element dağılımları, (La/Lu)N genel olarak 14-15 arasında değişim göstermektedir ve amfibol fraksiyolaşmasını anlatan kaşık desenli bir dağılım sunmaktadır. Riyolitlerde ise plajiyoklaz fraksiyonlaşmasını ifade eden belirgin biçimde negatif Eu anomalisi ve sanidin fraksiyonlaşmasına işaret eden önemli derecede negatif Ba anomalisi gözlemlenmektedir. Elde edilen veriler ışığında, incelenen volkanik kayaların yitim izi taşıyan çarpışma sonrası bimodal volkanizmanın ürünleri olduğu ve zenginleşmiş litosferik mantodan türemiş oldukları önerilmektedir.

Anahtar Kelimeler

• Anklav
• Dasit
• Bazalt
• Bimodal
• Kalkalkalen
• Litosferik
• Şoşonit

Petrography, Geochemistry and Petrology of Volcanic Rocks in Tepekent Region (Konya-Central Anatolia)

Abstract

In this study, the petrography, mineralogy, geochemistry and petrology of Miocene aged rhyolitic, dacitic and basaltic lava flows and their pyroclastics cropping out in the Tepekent region (Konya-Central Anatolia) were investigated. The investigated rocks are basaltic trachy-andesite, andesite, dacite and rhyolite rocks with high potassium content according to the Total Alkali-Silica (TAS) diagram. However, the basaltic trachy-andesites examined are also called shoshonite according to their Na2O-K2O content. Dacitic rocks contain enclaves varying in size from mm to dm. The enclaves fall into the trachy-basalt area in the TAS diagram and exhibit a more mafic composition than the host-rocks. Basaltic trachy-andesites show holocrystalline porphyric texture, while dacites display hypocrystalline porphyric texture with varying volcanic glass contents. Basaltic trachy-andesites contain olivine, clinopyroxene, plagioclase and Fe-Ti oxide, show zeolitisation in places and iddingsitization in olivines. Dacites have a paste content consisting of volcanic glass in addition to microcrystals of the same minerals, in which amphibole, biotite, plagioclase, Fe-Ti oxide and occasionally quartz micro-phenocrysts are dispersed into it. Enclaves located in dacitic host-rocks have the fine-grained texture often found in magma mixing enclaves, however, they are composed of bladed biotite, quenched amphibole and sieve-textured plagioclase. Rhyolites contain significant amounts of sanidine and biotite as well as quartz, plagioclase and Fe-Ti oxide microphenocryst. However, they have more volcanic glass content than dacites and exhibit hypohialine porphric texture. In the Mid-Ocean Ridge Basalts (MORB) normalized trace element diagram an enrichment is observed within large ion radius lithophile elements (LILE, Sr, K, Rb, U and Th) composition, while a depletion is observed. within the high field strength elements (HFSE, Nb, Ta, Ti) contents. Rare earth element distributions normalized to chondrite, (La/Lu)N generally vary between 14-15 and present a spoon-patterned distribution describing amphibole fractionation. In the rhyolites, on the other hand, a clearly negative Eu anomaly, which expresses the plagioclase fractionation, is observed. In the light of the obtained data, it is suggested that the investigated volcanic rocks are post-collisional bimodal volcanism products bearing subduction marks and are derived from the enriched lithospheric mantle.

Keywords

• Basalt
• Bimodal
• Calc-Alkaline
• Dacite
• Enclave
• Lithospheric
• Shohonite
• Anklav
• Dasit
• Bazalt
• Bimodal
• Kalkalkalen
• Litosferik
• Şoşonit

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