First evidence for the subduction initiation and boninitic magmatism from the Armutlu Peninsula (NW Turkey): geodynamic significance for the Cadomian magmatic arc system of the Gondwanan margin

ABSTRACT

The Cadomian Orogeny was active along the northern margin of Gondwanaland during the Late Neoproterozoic–Early Cambrian period. Remains of this orogenic activity are traced from Western Europe to the Himalayas, including some metamorphic basement rocks of Turkey. In this study, we provide new whole-rock and mineral chemistry, and zircon U–Pb age data for the metagabbro and metagranites in the Armutlu Peninsula, north of the Intra Pontide suture zone (IPSZ), which are the equivalent of the Cadomian basement of the İstanbul Zone (İZ). Geochemically, the metagabbros show an extreme depletion in Nb, Zr, Th, and Hf; low TiO₂ contents; and high Mg# values exhibiting boninitic affinity, which are commonly associated with fore-arc settings. The metagranites are calc-alkaline and high-K calc-alkaline in character. They are slightly enriched in LREE and have similar features to shear-type plagiogranites. The yielded zircon U-Pb crystallization ages are 564 ± 4.4 Ma for metagabbros and 561 ± 9.5 Ma (Late Ediacaran) for metagranites. In this study, we provide additional information for the Cadomian basement of the İZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products.

KEYWORDS:

• Cadomian Orogeny
• Boninitic gabbro
• Gondwana
• Armutlu Peninsula
• Proto-Tethyan ocean
• intra-oceanic subduction zone
• plagiogranite

Research Highlights

We provide new geochronology, geochemistry, and mineral chemistry data of metagabbros representing the first Cadomian boninitic magmatism and of metagranites in the northern part of Armutlu Peninsula (NW Turkey).

The zircon age data and geochemical characteristics of the studied plutons show that the plutons were formed in the magmatic arc system associated with the Gondwanan margin during the Ediacaran period.

Geochemical data revealed that the metagabbros have boninitic affinity representing an initiation of an intra-oceanic subduction zone. The age of subduction initiation is 564±4.4 Ma, the emplacement time of metagabbros.

Shortly after the emplacement of the gabbros, metagranites with tonalitic composition were intruded the metagabbros as shear-type plagiogranites that could develop in the intra-oceanic subduction zones.

Acknowledgments

We are grateful to Osman Kendir of Ayzemin Engineering Co. (Yalova) for logistical support during our field work. We would also like to thank Assoc. Prof. Dr Vural Oyan (Van Yüzüncü Yıl University) for his help during the modelling of nature of mantle.

Disclosure statement

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

Supplementary Material

Supplemental data for this article can be accessed here.