Fırat ŞENGÜN, Erdinç YİĞİTBAŞ, İsmail Onur TUNÇ

Geology and tectonic emplacement of eclogite and blueschists, Biga peninsula, northwest Turkey

Kuzeybatı Anadolu’da bulunan Biga Yarımadası farklı kökende ve yaşta okyanusal topluluklar ve Sakarya Kıtası ile ifade edilen farklı tektonik birliklerden oluşan tektonik bir mozaiktir. Yarımadanın en batı kesiminde bu orojenik mozayiğin bir parçası olan Çamlıca metamorfi k topluluğu alttan üste doğru üç formasyona ayrılmaktadır. Bunlar, Andıktaşı formasyonu, Dedetepe formasyonu ve Salihler formasyonudur. Eklojit fasiyesi metamorfi k kayalar Dedetepe formasyonunun şist-mermer istifi içerisinde tektonik dilimler şeklinde bulunmaktadır. Yaklaşık 2 km uzunluğunda ve 500 m genişliğinde olan bu dilimler iki farklı kaya tipi içermektedir. Bunlar, kuvars-mika şistler ve eklojit/mavişist parajenezi içeren metabazit mercekleridir. Çamlıca metamorfi k topluluğunun Dedetepe formasyonu genellikle Dedetepe ve Çamlıca köyü civarında GB eğimli foliasyona ve KB−GD yönelime sahiptir. Buna karşın eklojit fasiyesi metabazit dilimleri KD−GB yönelim ve KB eğimli foliasyon gösterirler. Eklojit fasiyesi metabazit dilimleri tipik olarak yitim zonunda gelişmiş yığışım kompleksine ait tektonik dilimleri temsil eden düşük sıcaklık eklojitleridir. Mavişistler geç evre makaslama zonları boyunca eklojitlerden dönüşmüşlerdir. Çamlıca metamorfi k kayaları sadece tek evreli yeşilşist fasiyesinde metamorfi zmanın izlerini taşırlar ve sünümlü-yarı gevrek (?) yanal atımlı faylar boyunca eklojit fasiyesi metamorfi zmadan sonra ve Çamlıca metamorfi k kayalarının düşük dereceli metamorfi zması sırasında veya sonrasında eklojit fasiyesi metamorfi k kayalarla bir arada bulunurlar. Yanal atımlı tektonik ile farklı derecedeki metamorfi k kayaların bir araya gelme yaşı birimlerin metamorfi zma yaşı ve bu birimleri örten ortak örtünün yaşı nedeniyle geç Kretase−erken Eosen zaman aralığı olmalıdır.

Biga Yarımadası’nda (KB Anadolu) yeralan eklojit ve mavişistlerin jeolojisi ve tektonik yerleşimi

Th e Biga Peninsula in northwestern Anatolia is a tectonic mosaic, comprising diff erent tectonic units, representing the Sakarya Continent and oceanic assemblages of diff erent origin and ages. Th e Çamlıca metamorphic association, a member of this orogenic mosaic in the westernmost part of the peninsula, is subdivided into three formations, from bottom to top; the Andıktaşı formation, the Dedetepe formation, and the Salihler formation. Eclogitefacies metamorphic rocks occur as tectonic slices within schist-marble intercalations of the Dedetepe formation. Th ese slices, about 2 km long and 500 m wide, include two diff erent rock types; (i) quartz-mica schists, and (ii) metabasite lenses with eclogite/blueschist paragenesis. Foliation in the Dedetepe formation of the Çamlıca metamorphic association generally dips SW and strikes NW−SE around Dedetepe hill and Çamlıca village. In contrast, eclogite-facies metabasite slices strike NE−SW with NW-dipping foliation. Th e eclogite-facies metabasite lenses are typically low-temperature eclogites that may represent tectonic slices of an accretionary complex associated with a subduction zone. Blueschists were produced by retrograde metamorphism from eclogite during late stage shearing. Th e host rocks record only a single-stage greenschist-facies metamorphism and were juxtaposed with the eclogite-facies metamorphic rocks along ductile-semi-brittle (?) strike-slip faults aft er the eclogite-facies metamorphism and during or aft er the low-grade metamorphism of the Çamlıca metamorphic unit. Age constraints on the metamorphic units and the age of the common cover units suggest that this juxtaposition by strikeslip tectonics occurred between the late Cretaceous and early Eocene.

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