Geochemical constraints on the provenance of Oligocene- Miocene siliciclastic deposits (Zivah Formation) of NW Iran: implications for the tectonic evolution of the Caucasus

摘要

In this study, the whole-rock geochemistry of 35 Oligocene-Miocene sandstone and shale samples from the Zivah Formation, Moghan area (NW Iran) were collected and analyzed for evaluation of their provenance, tectonic setting and the intensity of paleo-weathering. Low to moderate values of the chemical index of alteration (mean CIA=53/68 for sandstones/shales) and relatively high values of index of compositional variability (mean ICV=1.23/1.08 for sandstones/shales) suggest weak chemical weathering and an immature source. These results support for the semi-arid and semi-humid paleoclimate conditions in the source area. The geochemistry results reveal that the sediments were deposited in a basin related to the island arc and active continental margin tectonic settings, probably indicating the time of initial collision between Arabia and Eurasia. The enrichment of Cr, Ni and Vin the sandstone and shales are consistent with mafic input from the source area. However, La/Th vs. Hf and La/Sc vs. Co/Th plots revealmixed source of felsic and intermediate volcanic rocks. The data indicate that the sediments most likely originated from a mixture of mafic, intermediate and felsic igneous source areas, possibly as the erosional products of localized topography of the Talysh and the Lesser Caucasus mountains (south to southwest), created by compression in the Moghan region during the syncollisional development of the Caucasus.