Oligocene–late Miocene basin evolution in the Yengejeh syncline in the Central Iranian Basin in response to the Arabia–Eurasia orogeny

Abstract

The Central Iranian Basin has developed during a multi-episodic collision between the Arabian and Eurasian continents since the late Eocene–early Oligocene, following the subduction of the Neo-Tethys Ocean. Herein, we present detailed sedimentological and provenance data of the Oligocene–upper Miocene synorogenic strata, including the unconformity-bounded Lower Red, Qom, and Upper Red formations, in the Yengejeh syncline in the NW termination of Central Iran, to analyze stratigraphy, depositional environments, and provenance. Our results indicate that the sedimentary system has evolved in five stages coeval with regional deformational and volcanic events: a) deposition of the Lower Red Formation in an alluvial fan containing the first appearance of Sanandaj–Sirjan metamorphic clasts sourced from the proximal southwestern Takab Complex, exhumed by the onset of Arabian–Eurasian soft collision in late Eocene–early Oligocene; b) Burdigalian transgression of the Qom Sea and shallow-water carbonate sedimentation influenced by continuous pyroclastic inputs and lava flows from an active volcanic center; c) deposition of the M1 unit of the Upper Red Formation in a continental sabkha in arid climate conditions during Burdigalian–Langhian and the first appearance of internal clasts derived from the folded Qom Formation layers due to the Arabian–Eurasian hard collision; d) fluvial deposition of the M2 unit during the Langhian–Tortonian with sediments derived from the Qom Formation and Takab Complex; and e) deposition of the uppermost siliciclastics of the M2 unit at the edge of an alluvial fan during the late Miocene, after a period of pyroclastic fallout in the Tortonian. In general, the source-to-sink relationship is controlled by the development of tectono-topographic relief in the crystalline core of the Zagros Mountains that configured the source areas in the Sanandaj–Sirjan metamorphic belt supplying the NW termination of Central Iran through a well-developed drainage system towards the Caspian Sea. Coeval with the deformational events, magmatic phases supplied a large volume of volcaniclastic inputs both before the Neo-Tethys slab break-off and after the hard continental collision. The depositional environments and provenance of the studied sedimentary record provide an analog for the development of synorogenic hinterland basins worldwide along with the well-known Altiplano Basin of the Andes and Hoh Xil Basin of Tibet.