Integrated provenance analysis of Zakeen (Devonian) and Faraghan (early Permian) sandstones in the Zagros belt, SW Iran

摘要

Successions of a controversial period of time in the Zagros and Arabian Plate stratigraphic column, including Zakeen (Devonian) and Faraghan (early Permian) formations are investigated for their provenance characteristics. Nearly similar depositional environments of the formations, regardless of 70-80 My hiatus between them, is the main motivation for this study. Evidence from various methods are put together to reconstruct a comprehensive image of their provenance. Results from petrographic and detrital mode analysis indicate a continental block provenance for of the sandstones of both formations. In addition, evidence of recycling is evident from some rock fragments in the conglomeratic facies. Heavy mineral diversities are limited to the ultra-stable species which represent consistent morphological characteristics in both formations. However, the values of rutile: zircon index (RZi) showed intermittent changes from low RZi to high RZi intervals in both formations. Detrital zircon age data in previous studies represented the same source for these two formations, which also remained unchanged from Neo-Proterozoic to late Paleozoic successions. Zircon grains' morphology, however, showed remarkable difference between the Zakeen and Faraghan formations on the one hand and successions deposited in the basin prior to the tectonic movements of mid-Paleozoic time on the other. Outcomes of this study show that, although each single technique may shed light on a particular aspect of the greater provenance problem, by integration of all the data, important evidence of recycled nature of these successions could be confirmed. Changes in the thickness of the Paleozoic units, the nature of their stratal surfaces, along with the information from magmatic events in the area provide a tectono-stratigraphic framework for northern margin of Gondwana in which the recycled nature of these successions is justifiable. The recycled nature of the studied formations on the one hand, and their identical provenance on the other, raise a challenge for the timing proposed for two tectonic activities of middle Paleozoic and mid-Carboniferous.