Dursunbey (Balıkesir)- Foça (İzmir) Erken-Orta Miyosen Volkaniklerinin İzotop Jeokimyası

Batı Anadolu Erken-Orta Miyosen volkanizması geniş yüzlekler sunar. Bu geniş volkanizmanın farklı fasiyesleri, özellikle, İzmir-Ankara Zonu'nun kuzeyinde ve güneyinde yoğunlaşır. Bu çalışmada, Dursunbey (Balıkesir) ve Foça (İzmir) bölgelerinde yüzlek veren Erken-Orta Miyosen yaşlı volkanik birliklerin ana, iz-element ve Sr-Nd izotop jeokimyaları değerlendirilmektedir. İki ayrı bölgeden, alttan üste doğru, elde edilen bu jeokimya verileri ışığında, Batı Anadolu Erken-Orta Miyosen volkanizmasının kökenine ait evrimsel süreçlere yaklaşımlarda bulunulmaktadır. Birinci bölge, Dursunbey'in doğu ve batısında yer alan, alttan-üste doğru- dasitik-trakidasitik ve riyolitik bileşimli kayaları kapsar. İkinci bölge, Foça'nın doğusunda yer alan, alttan üste doğru, Dumanlıdağ Kalderası'nın andezitik-trakiandezitik bileşimli volkanikleri ile Foça-merkezine yakın kesimlerdeki, genç riyolitik volkaniklerden yapılıdır. Dursunbey volkaniklerinin ilksel 87Sr/86Sr oranları (0.70838- 0.71362) arasında olup, Foça bölgesi ortaç-felsik bileşimli volkaniklerine göre ilksel 87Sr/86Sr oranları (0.70723-0.70805) daha yüksektir. Aynı bölgelerdeki volkaniklerden elde edilen ilksel 143Nd/144Nd ve eNd oranlarında da, Dursunbey'den Foça'ya doğru hafif artış gözlenir. AFC modellemelerine göre, Dursunbey ve Foça bölgelerinin alt seviyelerini oluşturan volkaniklerin, üst seviyelerde yer alan volkaniklere göre kabuksal kirlenme oranları daha yüksektir. İncelenen bölgelerdeki volkaniklerin izotop jeokimyaları birlikte değerlendirildiğinde, Dursunbey-Foça volkaniklerinin kıtasal kabuk baskın olmak üzere, olası mantodan etkilenmiş hibrit bir magmadan türemiş olduğu söylenebilir.

Isotope Geochemistry of the Early-Middle Miocene Dursunbey (Balıkesir)-Foça (Izmir) Volcanics

Widespread outcrops of the Early-Middle Miocene volcanism can be found in the western Anatolia. Different facies of this volcanism are particularly common along the northern and the southern parts of the Izmir-Ankara Zone. In this paper, major, trace and isotope compositions (Sr-Nd) of the Early-Middle Miocene Dursunbey (Balikesir), and Foça (Izmir) volcanics are evaluated. In the light of this geochemical data (from bottom to top) from these two regions, new approaches for the magmatic evolution of the Early Miocene magma-source are suggested. The first study area comprises, from bottom to top, dacitictrachydasitic and rhyolitic volcanic rocks of the Dursunbey. The second area embodies the andesites and trachyandesitic rocks of the Dumanlıdağ Caldera in the eastern part of the Foça, whereas younger rhyolitic volcanics (domes) are located in the central part of the Foça. The initial Sr/86Sr ratios of the Dursunbey volcanics are between 0.70838-0.71362, which are higher than intermediate to felsic rocks ratios of the Foça volcanics (0.707230.70805). The initial volcanics are also relatively higher than the initial Nd-isotope ratios of the Foça volcanics. According to the AFC estimated models, lower parts of the Dursunbey and Foça volcanics are more likely to be affected from the crustal contamination than upper parts of these volcanics. When the isotopic geochemistry of the studied areas are taken into consideration together, the Dursunbey and Foça volcanics are dominantly contaminated by continental crust and likely with a contribution of mantle derived hybrid magma.

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