Geological and geochemical characteristics of Late Ordovician volcanic levels of the Gözdağ Formation in the İstanbul-Zonguldak Tectonic Unit (NW Turkey): Implications for global events during the Ordovician

The İstanbul-Zonguldak Tectonic Unit is regarded as the easternmost fragment of Avalonia-Carolina and stands for Far East Avalonia. Its stratigraphy also characterized by discontinuous sedimentation from Late Ediacaran to Carboniferous. In western part block, known İstanbul Terrane, Gözdağ Formation represented lagoonal sedimentary rocks consisting shale-sandstone with limestone Middle Ordovician-Lower Silurian age. Here, I report on stratigraphic positions petrographical geochemical data fine- coarse-grained tuffs lavas in Ordovician strata Formation. have pyroclastic porphyritic, vitrophyric aphanitic textures. fine-and are Sandbian Katian ages, Hirnantian according volcanic rocks. Geochemically, the-fine grained High-K calc-alkaline character affinity. They devoid noticeable with-in plate components, deduced presence obvious negative Nb anomalies, they subduction signatures. conjunction literature, fine-grained were deposited a depocenter during Taconic orogeny formed earliest late between Piedmont Terrane Laurentia. shallow marine it last phase consumption Teisseyre-Tornquist Ocean volcanoes occurred arc-related settings. Besides, flowed soft-docking Avalonia Baltica, pre-Caledonian orogeny.