The Geochemistry and Setting of the Demirci Paragneisses of the Sünnice Massif, NW Turkey

The Demirci migmatitic quartzofeldspathic gneisses of the Sünnice Massif, exposed in the Istanbul Zone north of Bolu, have compositions that show them to be paragneisses, associated with subordinate paraamphibolites. 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 basementon to which the meta-ophiolite was obducted during the Proterozoic.