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

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.

KEYWORDS:

• Folded
• dykes U-Pb zircon dating
• rift-related late Ediacaran magmatism
• Rheic Ocean
• early Cambrian deformation
• Istanbul-Zonguldak Tectonic Unit

Acknowledgments

This paper is respectfully dedicated to Professor Cazibe (Arıç) Sayar (1925-2021) due to her detailed studies of Ordovician strata in the İZTU. This paper is part of the MSc and Ph.D. theses of the author. The geochemistry analysis expenses funded by İstanbul University Research Fund (Ph.D. thesis Project No: 45751). His Ph.D thesis titled ‘Petrology and Geodynamic Evolution of Dykes Crosscutting the İstanbul-Zonguldak Tectonic Units’ was supported by TÜBİTAK-BİDEB’s 2211-C program. Discussions with T. Ustaömer, E. Yiğitbaş, G. Sunal, E. Bozkurt, A.M.C. Şengör, and M.C. Göncüoğlu are gratefully acknowledged during the Ph.D. thesis. The author thanks R.D. Nance, D. Spahić and A. Okay for constructive reviews of an earlier version of this manuscript. He thanks Z. Üçtaş Özbey for helping to interpret in thin section of dykes. Besides, he thanks Chief-Editor R. J. Stern, Volume-Editor G. Topuz, and E. Yiğitbaş and three anonymous referees for their thoughtful reviews and constructive criticism on his manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the İstanbul Üniversitesi [Ph.D thesis Project No: 45751].