Mafic and ultramafic rocks within the Söğüt metamorphics of the Sakarya Composite Terrain, NW Eskişehir, Turkey: Preliminary field and petrological findings

Yaşar, İsmail Doğancan
Sayıt, Kaan
The Söğüt Metamorphics are interpreted as the pre-Variscan basement of the Sakarya Composite Terrane. In the Central Sakarya area, the unit outcrops as slivers of an E-W trending belt disconformably overlain by the Jurassic Bakırköy Formation and Bilecik Limestones on the north. The Sakarya Metamorphics are thrust via the Tuzaklı-Gümele fault onto the Tertiary rocks in the south, which in turn disconformably overlie the ophiolitic mélanges of the İzmir-Ankara Suture Belt. The Söğüt Metamorphics are intruded by the early Carboniferous Sarıcakaya Granitoid, which is elongated E-W and consists of blasto-mylonitic granodiorite, quartz-diorite, and granite, cut by pink aplitic and pegmatitic dykes. The Sarıcakaya Granitoid displays calc-alkaline, I-type geochemical features and is interpreted to have formed in a magmatic arc setting. The age of the Söğüt Metamorphics are interpreted as pre-Carboniferous based on the U-Pb zircon ages obtained from the intruding granites (319-327 Ma). The mafic and ultramafic rocks are observed as bands, lenses, boudins or tectonic slices with highly sheared contacts within the host ortho- and para-gneisses having E-W trending foliation. The dominating rocks are amphibolites that were affected by the amphibolite facies metamorphism together with their host gneisses. The peak metamorphic conditions are defined by the cordierite-sillimanite-biotite paragenesis of the para-gneisses. The presence of migmatite fabrics in amphibolites and their host rocks, both in outcrop and thin-section scale is indicative for partial melting conditions. Overprinting retrograde metamorphism is defined by epidote-chlorite-muscovite paragenesis. Considering their field relations and petrographic features, amphibolites were divided into two protolithic groups as “fine-grained concordant amphibolites” and “coarse-grained metagabbros”. The next group of mafic and ultramafic rocks, on the other hand, are boudins of melano-and leuco-gabbro and serpentinite with well-developed cumulate texture. They were previously named the “Tozman Metaophiolite” and occur as discontinuous lenses, tectonically incorporated into the Söğüt Metamorphics. In this study, both unit’s preliminary metamorphic and petrologic features, petrogenetic correlation, and possible emplacement mechanism are discussed on the basis of field and petrographical observations, which will be later combined with the geochemical studies.
Citation Formats
İ. D. Yaşar and K. Sayıt, “Mafic and ultramafic rocks within the Söğüt metamorphics of the Sakarya Composite Terrain, NW Eskişehir, Turkey: Preliminary field and petrological findings,” presented at the IESCA 2019, İzmir, Türkiye, 2019, Accessed: 00, 2021. [Online]. Available: