Beyşehir-Hoyran Ofiyoliti İçerisindeki Tektonitlerin Dokusal ve Jeokimyasal Özellikleri: Beyşehir (Konya) Güneyinden Bir Örnek

Year 2018, Volume: 18 Issue: 3, 1067 - 1082, 30.12.2018

Tijen Üner İrem Aksoy

Abstract

Toros Kuşağı içerisinde Kırkkavak ve Ecemiş fayları arasında kalan Beyşehir-Hoyran Ofiyoliti, Jura sonu-Kretase başında kapanmaya başlayan Neotetis Okyanusu’na ait önemli kayıtlara sahiptir. Beyşehir-Hoyran Ofiyoliti inceleme alanında tektonitler (harzburjit, dünit), kümülatlar (gabro, piroksenolit, pegmatoitik gabro) ve ofiyolit tabanı metamorfiklerinden (amfibolit) oluşan bir istif sunmaktadır. Tektonitler ofiyolit istifi içerisinde hacimsel olarak en önemli bölümünü oluşturmaktadır. Genel olarak harzburjitlerden oluşan tektonitler yer yer dünitik ve kromitik seviyeler içermektedir. Foliyasyon-lineasyon gösteren tektonitler, kristal içi kayma, öğütülme ve yeniden kristallenme özellikleri ile üst mantoya ait plastik deformasyonun izlerini taşımaktadır. Harzburjitler genel olarak olivin, ortopiroksen, daha az oranlarda klinopiroksen ve kromit minerallerinden oluşmaktadır. Olivinler özşekilsiz, orta taneli kristaller halinde gözlenirken, ortopiroksenler olivinlere oranla daha iri kristaller şeklinde bulunur. Ortopiroksenler, tane sınırları ufalanmış ikincil olivin mineralleri tarafından çevrelenmiştir. Harzburjitler genel olarak milonitik doku sunmaktadır. Bu birimin en belirleyici özelliği plastik deformasyonun izlerini taşıyor olmasıdır. Makroskobik olarak ortopiroksen ve kromit gibi minerallerdeki yassılaşma ve uzamaya bağlı olarak kayaçta bir foliyasyon düzleminin varlığı ayırt edilebilmektedir. Birimlerde öğütülme ve yeniden kristalleşme izlerine rastlanmaktadır. İnce kesitlerde uzama gösteren olivin ve enstatit minerallerinde sıklıkla deformasyon lamellerine (kink-band) rastlanmaktadır. Yapılan jeokimyasal çalışmalarla Mg# değerlerinin 90,80-92,20, ateşte kayıp (LOI) değerlerinin ise 2,5% ile 8,5% arasında bir değişim göstermektedir. Bu değerler bize harzburjit örneklerinin kısmen serpantinleşme sürecine başladığını işaret etmektedir. Peridotitlerin uyumlu elementlerce zenginleşirken, uyumsuz elementlerce tüketildiği görülmektedir. Bu özellik hem abisal hem de okyanus içi yitim zonu peridotitleri için tipiktir.

Keywords

Beyşehir-Hoyran Ofiyoliti, Tektonit, Plastik deformasyon, Harzburjit

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