Petrographic and geochemical analyses of Early Miocene volcanic units in the Bigadiç borate basin, western Anatolia-Turkey: evidences of magma mixing/mingling processes

Year 2010, Volume: 31 Issue: 2, 141 - 168, 01.03.2010

Fuat Erkül Sibel TATAR Erkül Cahit Helvacı

Abstract

Keywords

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Erken Miyosen Bigadiç bor havzasındaki volkanik birimlerin petrografik ve jeokimyasal özellikleri: magma karışımının kanıtları, Batı Anadolu-Türkiye

Abstract

Batı Anadolu’daki Senozoyik yaşlı alkali ve kalkalkali karakterli volkanizmanın en iyi gözlendiği bölgelerden birisi kuzeydoğu doğrultulu Bigadiç bor havzasıdır. Bazalttan riyolite bileşim gösteren volkanik kayaçların oluşum yaşları 23-17.8 milyon yıl arasındadır. Bigadiç çevresinde, temel kayaçlar üzerindeki Erken Miyosen yaşlı istifler gölsel, flüvyal ve evaporitik tortullar ile bunları kesen kuzeydoğu doğrultulu volkanik çıkış merkezlerinden üretilen lav ve volkaniklastik kayaçlar ile temsil edilmektedir. İki farklı evrede gelişen bu volkanik birimler litolojik, petrografik ve bileşimsel özelliklerine göre, Kocaiskan volkanik birimi, Gölcük bazaltı, Sındırgı, Kayırlar ve Şahinkaya volkanik birimleri olmak üzere beş birim altında incelenmiştir. Gölcük bazaltı hariç, diğer tüm volkanik birimlerde yaygın olarak görülen yuvarlağımsı elipsoidal anklavların boyutları birkaç milimetreden birkaç santimetreye kadar değişmektedir. Kalkalkali bileşim sergileyen Kocaiskan, Sındırgı, Şahinkaya ve Kayırlar volkanik birimleri orta-yüksek, hafif alkali bileşimli Gölcük bazaltı ise yüksek K’ludur. Kalkalkali birimlerin nadir toprak element dağılım desenleri birbirlerine benzerlik göstermektedir. Bu birimler hafif nadir toprak elementlerince zenginleşme gösterirken, hafif alkali bileşimli Gölcük bazaltında ise daha az zenginleşme görülmektedir. Eu anomalisi Kocaiskan ve Sındırgı volkanik birimlerinde, Şahinkaya, Kayırlar ve Gölcük birimlerine göre daha belirgindir. Bigadiç ve çevresinde eş yaşlı alkali-kalkalkali birlikteliği ile karakterize bimodal volkanik kayaçların oluşumunda, magma karışım süreçleri etkili olup, kabuksal kökenli ve manto kökenli iki farklı magma kaynağı etkindir

Keywords

Bigadiç, hafif alkali-kalkalkali, kabuksal kökenli ve manto kökenli magma kaynağı, karışım dokuları, mafik mikrogranüler anklav, Miyosen

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