Provenance of the Oligocene-Miocene Zivah Formation, NW Iran, assessed using heavy mineral assemblage and detrital clinopyroxene and detrital apatite analyses

摘要

The Oligocene-Miocene Zivah Formation is characterised by alternation of sandstone, conglomerate, and shale that were deposited in a fluvial dominated delta on the shelf of Eastern Paratethys. Petrographically, the sandstones mostly include volcanic rock fragment, plagioclase and minor amounts of K feldspar, quartz, pyroxene, opaque minerals and biotite. Heavy mineral analysis and geochemical analysis of detrital clinopyroxene and apatite have been used to determine the provenance and tectonic setting of the Zivah Formation sandstones, in three outcrop sections from the Moghan region in NW Iran. The heavy mineral assemblage of the Zivah Formation sandstones is dominated by clinopyroxene and apatite with minor amounts of amphibole, zircon, garnet and epidote. The abundance of a mafic heavy-mineral suite such as clinopyroxene relative to metamorphic and felsic heavy mineral suites such as epidote, garnet and zircon indicates that deposition of Zivah Formation is more likely to have occurred at a convergent plate boundary, and sourced by a volcanic arc. The geochemical composition of detrital clinopyroxene grains from the Zivah Formation indicates that these detrital grains probably crystallized from calk-alkaline magmas. They also show an orogenic tectonic setting at the time of deposition of the Zivah Formation. Compositions of detrital apatites of the Zivah Formation are also consistent with the widespread distribution of mafic/intermediate volcanic rocks of both alkaline and calc-alkaline composition. All of these data as well as the composition of volcanic rocks of the southern parts of the Moghan Basin is consistent with the derivation of these sediments from areas with calc-alkaline volcanic rocks like Talysh and Arasbaran (Qharadagh)-Lesser Caucasus.