57.Türkiye Jeoloji Kurultayı, Ankara, Turkey, 8 - 12 March 2004, pp.131-132
Precambrian metamorphic basement of Istanbul — Zonguldak Unit, in 'western Pontide, is represented by an oro genie collage that composed mainly of distinctly different metamorphic units. Components of this orogenic collage are represented, by Çele metaophiolite. Yellice Metavolcanics, Demirci Metamorphics, and Dirgine metagranite. Field, relations and structural characteristics of these units were studied, and, geochemical analyses on representative samples, obtained from the Sünnice, Almacık, and Armutlu areas. Th.e studies reveal that the Çele metaophiolite displays disrupted components of a complete suprasubduction ophioUtic suite. The Yellice metavolcanic sequence contains fragments of both an ensimatic island arc and a back-arc basin association built on the ophiolite. The Demirci Metamorphics represent reworked continental fragments fanning the base of the metamorphic massifs. These different metamorphic units were intruded by the Dirgine granitic pluton of 570-590Ma (Chen et al,2000; Ustaömer et al, 2003),,, after their amalgamation., The metamorphic tectonic units and the granite are overlain collectively by a thick Paleozoic sedimentary cover known as the Istanbul-Zonguldak Unit. The sequence ranges in age from Lower Ordovician to Carboniferous. The orogenic event that led to the amalgamation of the different tectonic entities is partly penecontemporaneous with the Pan-African orogeny, supporting the view that the basement of the Istanbul-Zonguldak Unit formed a link between the Pan-African and- Trans-European Suture Zones. Metamorphic grade of the Precambrian basement decreases steadily upwards from amphibolite fades to greenschist fades., This is mainly due • to the last major phase of metamorphism. In the Sünnice, Älmacik, and Armutlu massifs., the overlying Paleozoic sequence also shows low-grade metamorphism that does not go beyond the lower limit of the greenschist fades. The contact between the basement and Paleozoic cover sequence was detached. This tectonic contact is a, major north dipping normal fault The data indicates that the Paleozoic sequence, which was initially deposited above the Sünnice Group' rocks, was later detached from its root along a low-angle listric normal fault . ' • The first common cover sedimentary succession, which covers both the Sünnice Group and the Paleozoic sequence is the Lower Cretaceous Ulus Group., This unit is interpreted to be deposited within a newly developed extensional basin. The extension affected, the regionally deformed, uplifted and eroded terrain.