Age and implication of Late Ediacaran dykes in the İstanbul-Zonguldak Tectonic Unit (NW Turkey): Implications for the rifting of the Rheic Ocean

Abstract

ABSTRACT The İstanbul-Zonguldak Tectonic Unit is a part of Avalonia-Carolina and represents Far East Avalonia. It includes Ordovician to Carboniferous deposits which unconformably overlie Late Neoproterozoic metamorphic rocks. Timing of its detachment from West Gondwana-land, thus rifting of the Rheic Ocean, is poorly known. Here, I report on dacite, diabase and andesite dykes of Late Ediacaran igneous crystallization ages from the basement rocks and rift-deposits in the İstanbul-Zonguldak Tectonic Unit (NW Turkey). They are folded about a consistent axis and have porphyritic to intersertal textures. U-Pb dating on igneous zircons from folded dykes yielded Late Ediacaran ages of ca. 556.2 ± 2.2 Ma (2σ) and 552.1 ± 2.8 to 549.2 ± 2.3 Ma (2σ). Late Ediacaran dykes show calc-alkaline and alkaline affinities, and contain with-in plate components. Rift-related Late Ediacaran magmatism shows that the Yellice arc changed from an arc to a back-arc basin and the rift-deposits formed during the late Ediacaran due to the arc rifting. In conjunction with the data from literature, I suggest that the rift-related magmatism is related to the rifting event during the late Ediacaran, leading to the detachment of this continental block from the West Gondwana-land, thus to the opening of the Rheic Ocean, and Early Cambrian deformation event correspond to the adding of the Kraishte terrane with Far East Avalonia. The docking of the Kraishte terrane led to the deformation of Late Ediacaran dykes. Overall, these data indicate that the depositional time of sedimentary rocks in the continental fragment should have started during the late Ediacaran instead of Ordovician.