Provenance, palaeoweathering and tectonic setting of the Ediacaran Bayandor Formation in NW Iran: Implications for the northern Gondwana continental margin during the late Neoproterozoic

Abstract

The tectonic evolution of Iran during the late Neoproterozoic and early Paleozoic is usually expressed in two models including passive (conventional) and active (alternative) margin tectonic models. The passive margin model proposes rifting of peri-Gondwanan terranes and strike-slip tectonics in a non-magmatic setting while the active margin model suggests the existence of a subduction zone and the formation of a continental arc (known as “Cadomian” arc) along the northern Gondwana margin. The Ediacaran siliciclastic Bayandor Formation from the Soltanieh Mountains in western Alborz records the geological history of Iran during the late Neoproterozoic through its provenance, as aims of our studies, which allows palaeoweathering and tectonic setting reconstructions. Thin-section petrographic analysis of the Bayandor Formation sandstones reveal that the feldspar-rich sandstones including minor values of chert rock fragments have characteristics of both active continental margin settings and recycled orogen provenances. The chemical index of alteration (CIA) indicates a moderate degree of chemical weathering in the source area. Most of the Bayandor Formation sandstones were derived from a dissected arc and a minor number of the samples seem to be derived from a basement uplift and recycled orogen provenance. Geochemical discrimination diagrams using major and trace elements indicate both active continental margin and island arc tectonic settings for the Bayandor Formation sandstones. The results indicate that it is more likely that deposition of this formation took place along an active continental margin and the Cadomian basement of NW Iran comprises a series of metagranites and metamorphic rocks and may have contributed some sediment to the localized Neoproterozoic–Cambrian basins. Other sources were likely located in the basement provinces particularly the Arabian–Nubian Shield that is consistent with the results of this study.