The temporal evolution of the Zagros Simply Folded Belt is constrained by a magnetostratigraphic sequence containing a progressive unconformity on the southern limb of the Kuh-e Ghol Ghol anticline, in the Central Fars. The investigated~1400 m thick sequence exposes a regressive megacycle containing, from bottom to top, open and shallow marine marls and sandy limestones, fine-to coarse-grained fluvial deposits and alluvial conglomerates. Correlating the magnetostratigraphic section with the geomagnetic polarity time scale constrains the transition from marine to fluvial sediment deposition at~6 Ma. This transition was accompanied by a change in the accumulation rate from~15 cm/ka to~40 cm/ka, as measured on lithified sediments. Alluvial river deposits first occurred at~3.2 Ma. The Kuh-e Ghol Ghol anticline began to grow at~3.8 Ma, witnessing fastest limb rotation rates of 40°/Ma at~3.3 Ma. Reporting magnetostratigraphic sections and ages of growth strata on a map of NE Fars reveal an~1 cm/a, southwestward migration rate of the deformation front during the middle and late Miocene.

Previous interpretations of a Jurassic subduction in Iran were based on trace element classification diagrams for granitoids, but their reliability is questionable, underscored by modern examples of continental break-up zones such as the Baja California. We present new field observations, bulk rock geochemistry, Sr and Nd isotope analyses and U-Pb zircon geochronology to assess the age and tectonic setting of previously undated intermediate to felsic magmatic rocks cropping out in the Precambrian basement of NW Iranian Azerbaijan. The geochronology revealed an uneven distribution in space and time: Late Jurassic (159-154 Ma) intrusions and dikes are alkaline to calc-alkaline. Their melt source is mantle dominated with a distinct continental contribution disclosed by radiogenic isotopes and abundant inherited zircon cores. Mid-Cretaceous (112-96 Ma) plutonic bodies and associated volcanic rocks occur only to the east of the major Siah Cheshmeh-Khoy Fault. They have geochemical signatures typical of a metasomatized mantle. In consistence with the sedimentation history of the area, our new interpretation attributes the Late Jurassic magmatism to thinning of a continental lithosphere in a rift-related setting. Mid-Cretaceous magmatism was produced by oceanic subduction beneath the Central Iran continent. We interpret the 40-Ma age gap between the two magmatic episodes as the time of opening of the oceanic basin witnessed by the Khoy ophiolite in the study area.

The north-south-trending Sistan suture zone in east Iran results from the Paleogene collision of the Central Iran block to the west with the Afghan block to the east. We aim to document the tectonic context of the Sistan sedimentary basin and provide critical constraints on the closure time of this part of the Tethys Ocean. We determine the provenance of Eocene-Oligocene deep-marine turbiditic sandstones, describe the sandstone framework, and report on a geochemical and provenance study including laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon ages and 415 Hf isotopic analyses of 3015 in situ detrital zircons. Sandstone framework compositions reveal a magmatic arc provenance as the main source of detritus. Heavy mineral assemblages and Cr-spinel indicate ultramafic rocks, likely ophiolites, as a subsidiary source. The two main detrital zircon U-Pb age groups are dominated by (1) Late Cretaceous grains with Hf isotopic compositions typical of oceanic crust and depleted mantle, suggesting an intraoceanic island arc provenance, and (2) Eocene grains with Hf isotopic compositions typical of continental crust and nondepleted mantle, suggesting a transitional continental magmatic arc provenance. This change in provenance is attributed to the Paleocene (65-55 Ma) collision between the Afghan plate and an intraoceanic island arc not considered in previous tectonic reconstructions of the Sistan segment of the Alpine-Himalayan orogenic system.

Urmia Lake is a large-scale hypersaline lake that experienced a drastic water-level fall due to natural and anthropogenic forces during the last two decades. Construction of a causeway in the central part of the lake after 1989 has divided the lake into northern and southern parts and caused an extreme change of the lake hydrochemical system. Precipitation of evaporite minerals as crust on the lake floor was caused by the combination of lake level fall and increasing water salinity. However, some parameters controlling rates of salt deposition and dissolution and temporal and spatial variation in salt thickness in Lake Urmia are poorly understood. This study reviews 90 sediment cores from various parts of the lake to put forward a better understanding of the salt depositional system and salt thickness variations in the basin for the last 40 years (1977–2017). Our results indicate that the sedimentary system of Urmia Lake changed rapidly during the last two decades from a permanent hypersaline lake with predominantly fast terrigenous–biochemical sedimentation to a seasonally changing playa sedimentary environment with predominance of evaporite minerals. These changes are responsible for rapid salt deposition that generated a salt-crust with a maximum thickness of 2.95 m overlying Holocene terrigenous sediments. The salt-crust thickness and the water depth have a positive correlation for water depth greater than 1 meter, which means that salt-crust thickness increases where water depth increases. While the thickness of shallow deposits are affected by fresh-water dissolution. In addition, the average salt precipitation rate in the northern and the southern parts of the lake is 466 and 266 times higher, respectively, than the average (0.3 mm/y) sedimentation rate before the lake shrinkage. Similar to other large hypersaline lakes such as the Great Salt Lake (USA) and the Aral Sea (Central Asia), the manmade intervention at Urmia Lake (damming of the catchment, extension of agricultural fields, and causeway construction in the middle part of the lake) threatens its further hydrologic existence.

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