The Demirci migmatitic quartzofeldspathic gneisses of the Sünnice Massif, exposed in the İstanbul Zone north of Bolu, have compositions that show them to be paragneisses, associated with subordinate para-amphibolites. They consist principally of metamorphosed, rather calcareous greywackes, with sediment derived from a continental arc source. They occur in the para-autochthon below a nappe pile (Çele meta-ophiolite), deformed and subjected to amphibolite facies metamorphism before the emplacement of late Neoproterozoic metavolcanic rocks later subjected to greenschist-facies metamorphism (Yellice volcanics). As they are overlain in sequence by nappes comprising sections of the Çele meta-ophiolite with ocean floor basalt and island arc tholeiite compositions respectively, the Demirci paragneisses may represent a section of the ancient continental basement on to which the meta-ophiolite was obducted during the Proterozoic.
YİĞİTBAŞ, ERDİNÇ; WINCHESTER, JOHN A.; and OTTLEY, CHRISTOPHER J. (2008) "The Geochemistry and Setting of the Demirci Paragneisses of the Sünnice Massif, NW Turkey," Turkish Journal of Earth Sciences: Vol. 17: No. 3, Article 1. Available at: https://journals.tubitak.gov.tr/earth/vol17/iss3/1