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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. [ABSTRACT FROM AUTHOR]

One of the major issues for understanding the tectonic evolution of continental regions is how pre-existing discontinuities influence the style and distribution of deformation, which is often not obviously and uniquely connected to the plate-boundary kinematics. Iran represents one of the most instructive regions to study continental deformation, as here the present-day Arabia–Eurasia convergence is accommodated in a very wide area over a range of structures. The tectonic boundary between the Lut and the Tabas blocks of Central Iran currently accommodates part of the Arabia–Eurasia convergence by right-lateral strike-slip faults, associated with NNW–SSE oriented fold-related thrust. During Middle-Late Jurassic, this boundary was the location of a large-scale shelf-lagoon carbonate platform-slope-to-basin depositional system, mainly controlled by the activity of a N–S oriented normal fault system. In this study, the geometry and the kinematics of the deformation at the tectonic boundary between the Lut and the Tabas blocks, are reconstructed from an integrated anisotropy of magnetic susceptibility (AMS) and structural analysis in the Upper Jurassic Garedu Red Beds Fm., outcropping at the core of a NNE–SSW oriented syncline in the northern Shotori Range. AMS and structural results indicate that the Upper Jurassic Garedu Red Beds Fm. syncline can be defined as a transected fold, where the mismatch between fold hinge and magnetic fabric/cleavage is about 15° counter-clockwise, suggesting that this fold system formed as a consequence of right-lateral transpressional tectonics. Results from this study thus document the evolution of Jurassic normal faults to a transpressional tectonic boundary between the Tabas and Lut crustal blocks sometime between the Lower Cretaceous and Palaeocene. [ABSTRACT FROM AUTHOR]

Paleomagnetic results from Oligocene- Miocene sedimentary units in central Iran are used to reconstruct the history of Neogene tectonic deformation of this region. Paleo magnetic data show that in central Iran, crustal blocks bounded by sets of strikeslip faults are rotated to accommodate NNE-SSW shortening related to Arabia-Eurasia convergence. Counterclockwise rotations of 20°--35° have been measured in the Tabas and Anarak areas, south of the Great Kavir fault, characterized by the presence of N-S to NNW-SSE right-lateral strike-slip faults. Conversely, in the Great Kavir and Torud areas, where ENE-WSW left-lateral strikeslip faults have been recognized, paleomagnetic results are less conclusive because the small amount of measured clockwise rotation shows a statistical uncertainty, which also includes the possibility of no rotation. Some of these faults have been active during the Quaternary up to present day, suggesting the possibility that block rotation is still occurring in central Iran. [ABSTRACT FROM AUTHOR]

• Block rotations in Central Iran. • Clockwise and counterclockwise controlled by tectonics. • Role of N–S right-lateral and E–W left-lateral strike-slip in accommodating Arabia-Eurasia convergence. In Central Iran, most of the Late Cenozoic to Present shortening has been accomplished in the Zagros, in the Alborz, and Kopeh-Dagh mountain ranges. Between these active mountain belts, a minor amount of shortening is observed and the deformation style is characterized by active strike-slip faults that bound relatively aseismic blocks. Two main strike-slip fault systems are presently active in different regions of Central Iran: South of latitude 34 °N, active deformation is accommodated on ∼N–S oriented right-lateral strike-slip faults, and north of latitude 34 °N, E–W left-lateral strike slip faults prevail. In this work, we investigated two different structures, representative of the two different strike-slip systems occurring in Central Iran: the Yazd fold system located in an area dominated by the occurrence of NNW-SSE oriented right-lateral strike slip faults, and the Ferdows fold system that developed at the western termination of the E–W left-lateral strike-slip Dasht-e-Bayaz fault. Paleomagnetic results show opposite vertical-axis rotations related to the different orientation and sense of movement of strike-slip fault systems, suggesting that in Central Iran the N–S oriented right-lateral and E–W oriented left-lateral strike-slip faults play significant roles in accommodating the Arabia-Eurasia convergence, by rotating counterclockwise and clockwise in the horizontal plane, respectively. [ABSTRACT FROM AUTHOR]

We report paleomagnetic results from Alborz, Ala-Dagh, Binalud and Kopeh-Dagh mountainchains (northern Iran), with the aim of reconstructing the rotation history and the origin ofcurvature of these orogenic chains. The analyzed deposits are the sedimentary successions ofthe Shurijeh (Cretaceous) and Upper Red Formation (Miocene). Paleomagnetic resultsindicate that this mountain chain system originated as a linear mountain belt thatprogressively acquired its present day curvature through opposite vertical axis rotations alongits strike. The curvature of the arc was entirely acquired after the middle-late Miocene, whichis the age of the youngest investigated sediments (Upper Red Formation). Overall, ourpaleomagnetic data indicate that the mountain chains in North Iran can be considered anorocline. Our results define, for the first time, the rotational history of the entire Northern Irancurved mountain belt, and enable us to reconstruct the paleogeographic and tectonic evolutionof northern Iran in the framework of Arabia-Eurasia continental deformation. Thekinematics inferred by the pattern of paleomagnetic rotations is at odds with thepresent day kinematics of northern Iran, characterized by the westward extrusionof the South Caspian block, and by a left lateral shear between Central Iran andthe central and western sectors of the Alborz Mts. By integrating paleomagneticdata with stratigraphic, thermochronological, structural and GPS information, wepropose that the initiation of South Caspian subduction and the activation of westwardextrusion of South Caspian block occurred diachronously and that the initiation of thepresent-day kinematics of northern Iran was quite recent (Lower Pleistocene, ∼2Ma). [ABSTRACT FROM AUTHOR]

An integrated AMS and structural study was carried out in order to reconstruct the geometry of the Tabas fold system and the tectonic evolution of this sector of Central Iran.The Tabas area is situated in the northern part of the Tabas block, where the Tabas Basin hosts a NNW–SSE trending fold system developed along the western foothills of the Shotori range. The Neogene sedimentary cycle of the Tabas Basin includes red marls with gypsum layers of the Upper Red Formation, which crop out along the cores of major anticlines and are overlain by a thick succession of fluvial and alluvial-plain conglomerates. In the southern and northern sector of the Tabas Basin these Neogene sediments are extremely thin, allowing in some places the fluvial conglomerates to lie directly on the pre-Neogene substratum, whereas toward the central and western part of the basin, they reach a thickness of several hundred meters. In the Tabas fold system, 15 sites in the Neogene Upper Red Formation were sampled for AMS investigation. A mesoscopic structural analyses in the Tabas Neogene fold system was carried out with the aim to describe the geometry of the folds and of the associated brittle deformation to define the mechanism that drove the kinematic evolution of the thrust related fold system. In particular, two structural cross sections were carried out along the Sardar and Esphak river valleys because they develop almost orthogonal to the main anticlines, offering an excellent exposure of the Neogene and Quaternary units. In the Tabas area, AMS analysis shows, in most of the sites, a magnetic foliation parallel to the bedding plane, reflecting the diagenetic to post-diagenetic compaction processes. In some other cases the magnetic foliation is sub-vertical and not related to bedding, suggesting a tectonic overprint. At the same time, the maximum susceptibility (Kmax) direction and the intermediate susceptibility (Kint) direction axes are well clustered, with a mean NNW-SSE trend for Kmax direction (magnetic lineation), suggesting a tectonic origin of the magnetic lineation. In particular, the magnetic lineation is well defined in most of the analysed sites and it shows a preferred orientation, which finds a correlation with the main tectonic elements recognized in the study area. The magnetic lineation shows a N-S to NW-SE preferred orientation in all the analysed sites, which corresponds, at the site scale, the main fold-axis orientation, which ranges from a N-S trend to a NW-SE trend. The magnetic lineation is also orthogonal to the main slip direction (N70°E) deduced by slickenside orientation on the thrust fault planes soon after the 1978 Tabas earthquake. [ABSTRACT FROM AUTHOR]

In this work we present new AMS and structural results from the Ferdows active fold–thrust system (Lut block, Central Iran). AMS analyses show that the Miocene units of the Upper Red Formation have a well defined magnetic fabric of tectonic origin, with both magnetic lineation and magnetic foliation oriented parallel to the regional fold axes. In most of the cases the magnetic fabric, acquired when the bedding was still horizontal, is related to different degrees of LPS shortening. In some other cases, the magnetic foliation is vertical and oblique to the bedding, suggesting that in the Ferdows thrust–fold structure a cleavage system, not visible at the outcrop scale, has been developed as a consequence of later shortening related to the activity of the thrust system, responsible of the recent earthquakes in the area. Results from this study establish a relationships between the recent tectonics of the area and the evolution of the magnetic fabric and demonstrate that a well defined magnetic fabric of pure tectonic origin can also develop in poorly deformed rocks lacking field evidence of pervasive internal deformation. [ABSTRACT FROM AUTHOR]

Abstract: In the Neka Valley (Eastern Alborz, Iran), glaucony-bearing marine sediments of early-middle Santonian age directly overlie Palaeozoic to Triassic units deformed during the Eo-cimmerian orogenic event (Late Triassic). The Upper Cretaceous open marine sediments were deposited on a flat surface lacking any evidence of pedogenesis. The geochemical and morphological features of glaucony grains, which characterize the base (1 to 1.5 m) of the Upper Cretaceous succession, indicate an autochthonous origin of the highly-evolved glaucony, denoting a long-lasting period of low sedimentation rate. The development of glaucony in the observed stratigraphic position is indicative of a rapid drowning of the former Cimmerian relief that cannot be explained by a eustatic rise alone: the palaeo-depth needed for the development of glaucony and for the presence of the observed bathyal foraminifera assemblages is greater than the maximum eustatic excursion documented in the Cretaceous. The occurrence of glaucony in this stratigraphic position reflects thus an important episode of increased subsidence rates, related to a geodynamic event framed in a time-interval of major plate reorganization in the complex puzzle of the Iranian plates: the subsidence event that caused the development of the glauconitic horizon in the Neka Valley could likely represent the effect of a Santonian stage of the complex and long-lasting story of the opening of the Caspian Sea. [Copyright &y& Elsevier]

Abstract: Structural analyses carried out in the southern-central Alborz (Iran) have shown that the evolution of this belt has been strongly conditioned by the inversion of pre-existent extensional faults. Inversion tectonics has been identified especially in the southern part of the belt, and it is related to the reactivation of grabens formed in the foreland of the Late Triassic Eo-Cimmerian orogen, resulting from the accretion of the Iranian block to Eurasia. Three main associations of structures—active during the late Cenozoic—have been distinguished: (1) E–W thrust faults and folds followed by the activation of (2) E–W right-lateral strike-slip faults associated to large ENE–WSW trending en échelon folds, and finally (3) ESE–WNW to SE–NW thrust faults and left-lateral strike-slip faults inverting in some cases previous E–W right-lateral faults. Central Alborz is strongly controlled by the geometry of pre-existing tectonic discontinuities, which are responsible for strain partitioning between strike-slip and reverse faults during convergence. These results provide new insights on the style and evolution of this complex intracontinental belt, which can be considered a significant example of transpressive tectonics. [Copyright &y& Elsevier]

Highlights: [•] AMS used to solve the ambiguity on the tectonic or sedimentary origin of magnetic lineation. [•] Comparison of magnetic fabric with available tectonic and sedimentary data. [•] The magnetic lineation in the Shemshak Group sandstones is tectonically originated. [•] AMS is a valuable tool to study deformation processes in sedimentary rocks. [Copyright &y& Elsevier]

[Display omitted] • Magnetic fabric in the central Tarom Basin records NE-SW layer parallel shortening. • Magnetic fabric in the SW margin of the basin is a primary sedimentary fabric. • NE-SW orogen-perpendicular syndepositional extension occurs in the SW margin. • Normal faults in the SW margin were induced by gravity instabilities. • Middle-late Miocene extension is not regionally pervasive. The upper plate of the Arabia-Eurasia collision zone experienced orogen-perpendicular to orogen-parallel extension from 25–22 to 10–9 Ma. Although such an extension occurred during widespread collisional deformation, it is not clear if it is a local feature or if represents a major phase of upper plate extension. In this study we combine anisotropy of magnetic susceptibility (AMS) with fault kinematic analysis and sedimentologic data from 16.2- to 7.6-My-old deposits of the Upper Red Formation of the intermontane Tarom Basin (NW Iran). These strata present syndepositional, normal faults and offer the possibility to gain new insights into the spatial extent of such a Miocene extension. AMS data from the central and northern sectors of the basin document a tectonic fabric with a magnetic lineation parallel to the strike of the orogen, suggesting a compressional tectonic overprint. Conversely, the southern margin of the basin presents a purely sedimentary magnetic fabric despite a ~NE–SW orogen-perpendicular extension. This suggests that basin formation was not driven by extensional tectonics. Rather, the normal faults are gravity instabilities induced as also documented by coeval landslide deposits. This allows concluding that the orogen-perpendicular extension observed in few sectors of the collision zone is not regionally pervasive and hence it is not controlled by large-scale processes. Combined, our results indicate that if orogen-parallel extension associated with tectonic denudation and metamorphic core complex development occurred in certain sectors of the collision zone (Takab complex), it must have ended before 19–16 Ma, when widespread upper plate contractional deformation started. [ABSTRACT FROM AUTHOR]