Provenance of Upper Devonian Ilanqareh Formation (NW Iran), assessed using petrography and major element geochemistry

Abstract

In this study, a combination of petrographic and major element geochemical methods was employed on sandstones and shales of Upper Devonian Ilanqareh Formation, northwest of Iran, aimed at investigating the tectonic setting and the weathering degree of rocks in the source area. The index of compositional variability (ICV below 1) indicated that the studied quartzarenite and subarkose sandstones were not in the first cycle. Petrographic studies showed the existence of a craton interior provenance for these sandstones and geochemical studies identified recycling of older formations as an important source of these deposits. The chemical index of alteration (CIA values of 78.18 to 90.42 for sandstones and 91.55 to 91.93 for shale samples) indicated that the samples were affected by the high degree of weathering due to the humid climate in the source areas. Geochemical discrimination diagrams revealed that the samples were deposited in a passive margin. According to the paleogeography, this passive margin was the margin of a rift basin in the northwest of Gondwana, and the Ilanqareh deposits were derived from the Arabian-Nubian shield and the recycling of the Lower Palaeozoic sandstones in the region.