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 Istanbul Zone (IZ). 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 IZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products.