Tectono‐sedimentary evolution of the northern Iranian Plateau: insights from middle–late Miocene foreland‐basin deposits

Abstract

Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia-Eurasia collision zone offer the unique possibility to study middle-late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long-term evolution of the Iranian Plateau, including the regional spatio-temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle-late Miocene crustal shortening and thickening processes led to the growth of a basement-cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland-basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement-cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle-flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.

Cenozoic Exhumation and Foreland Basin Evolution of the Zagros Orogen During the Arabia‐Eurasia Collision, Western Iran

“…Similar discrepancies in timing and deformation style have been documented for the Arabia-Eurasia Zagros collisional zone, which involves an orogenic plateau complex often considered an active analogue for the more mature Indo-Asian system (e.g., Ballato et al, 2016;Hatzfeld & Molnar, 2010 collision to latest Middle Eocene-Late Eocene time (e.g., Hempton, 1985;Perinçek, 1979;Yiğitbaş & Yılmaz, 1996). However, it is evident from structural, stratigraphic, and thermochronometric data that accelerated orogenic exhumation, Zagros fold-thrust belt development, and coarse-clastic foreland sedimentation likely did not manifest until the Miocene Gavillot et al, 2010;Koshnaw et al, 2017;Pirouz et al, 2017).…”

“…This is supported by geophysical studies that show less pronouncement of underthrusting along strike of this study area near the Turkish‐Iranian border, despite having similar elevations (Paul et al, ). The bulk of orogenic plateau growth was more likely governed by crustal shortening and thickening processes (e.g., Ballato et al, ). Diminished crustal shortening during Arabian underthrusting (Late Eocene‐Middle Miocene) led to low‐rate exhumation/uplift restricted to the SSZ and other isolated areas, which migrated into the internal Iranian Plateau (UDMZ) during accelerated subduction around 18–17 Ma.…”

“…This was later overprinted by a broad Oligo‐Miocene retroforeland flexural or sag basin with local transtensional strain (Ballato et al, ; Morley et al, ). Deformation associated with Zagros shortening migrated to the Urumieh‐Dokhtar Magmatic Arc by ~15–20 and intensified at ~11–5 Ma, causing broad regional uplift and fold‐thrust deformation associated largely with dextral transpression (Ballato et al, ; François, Agard, et al, ; Morley et al, ). The southern boundary of the UDMZ is cryptic in the NW Zagros, but along strike to the SE its suture zone with the SSZ is marked by the Nain‐Baft ophiolite belt, which represents a short‐lived Mesozoic ocean basin that closed in the Late Cretaceous to Paleocene (Moghadam et al, ; Stampfli & Borel, ).…”

“…Numerical and geophysical studies generally have attributed orogenic plateau evolution in the Arabia‐Eurasia collision zone to mantle drivers such as delamination of lithospheric mantle beneath Eurasia (François, Burov, et al, ; Hatzfeld & Molnar, ). It remains unclear whether regional uplift of the Zagros and Iranian Plateau was achieved rapidly since 10–5 Ma or incrementally since the Eocene or Late Oligocene (Agard et al, ; M. B. Allen & Armstrong, ; M. B. Allen et al, ; Ballato et al, , ; François, Agard, et al, ). The Iranian Plateau may also have had a precollisional hypsometric heritage related to subduction of Neotethys beneath Eurasia.…”

Open-source modular solutions for flexural isostasy: gFlex v1.0

“…This allows it, for example, to be a part of a flexural backstripping toolchain or a model of glacial-isostatic adjustment. Backstripping calculations may be performed by simply removing the sedimentary load (Roberts, 1998), or, in the case of a foreland basin, by inverting for the mountain belt loading history and lithospheric elastic thickness that would be required to produce the basin (Ballato et al, 2016). A programmatic approach is also useful for scenarios in which material infills a depression, but not over the whole domain and/or not with uniform density.…”