Abstract An important, 2.4 km-thick Triassic succession is exposed at Nakhlak (central Iran). This succession was deformed during the Cimmerian orogeny and truncated by an angular unconformity with undeformed Upper Cretaceous sediments. This integrated stratigraphic study of the Triassic included bed-by-bed sampling for ammonoids, conodonts and bivalves, as well as limestone and sandstone petrographic analyses. The Nakhlak Group succession consists of three formations: Alam (Olenekian–Anisian), Bāqoroq (?Upper Anisian–Ladinian) and Ashin (Upper Ladinian). The Alam Formation records several shifts from carbonate to siliciclastic deposition, the Bāqoroq Formation consists of continental conglomerates and the Ashin Formation documents the transition to deep-sea turbiditic sedimentation. Petrographic composition has been studied for sandstones and conglomerates. Provenance analysis for Alam and most of the Ashin samples suggests a volcanic arc setting, whereas the samples from the Bāqoroq Formation are related to exhumation of a metamorphic basement. The provenance data, together with the great thickness, the sudden change of facies, the abundance of volcaniclastic supply, the relatively common occurrence of tuffitic layers and the orogenic calc-alkaline affinity of the volcanism, point to sedimentation along an active margin in a forearc setting. A comparison between the Triassic of Nakhlak and the Triassic succession exposed in the erosional window of Aghdarband (Koppeh Dag, NE Iran) indicates that both were deposited along active margins. However, they do not show the same type of evolution. Nakhlak and Aghdarband have quite different ammonoid faunal affinities during the Early Triassic, but similar faunal composition from the Bithynian to Late Ladinian. These results argue against the location of Nakhlak close to Aghdarband.

Abstract New structural, sedimentological, petrological and palaeomagnetic data collected in the region of Nakhlak–Anarak provide important constraints on the Cimmerian evolution of Central Iran. The Olenekian–Upper Ladinian succession of Nakhlak was deposited in a forearc setting, and records the exhumation and erosion of an orogenic wedge, possibly located in the present-day Anarak region. The Triassic succession was deformed after Ladinian times and shows south-vergent folds and thrusts unconformably covered by Upper Cretaceous limestones following the Late Jurassic Neo-Cimmerian deformation. Palaeomagnetic data obtained in the Olenekian succession suggest a palaeoposition of the region close to Eurasia at a latitude around 20°N. In addition, the palaeopoles do not support large anticlockwise rotations around vertical axes for central Iran with respect to Eurasia since the Middle Triassic, as previously suggested. The Anarak Metamorphic Complex (AMC) includes blueschist-facies metabasites associated with discontinuous slivers of serpentinized ultramafic rocks and Carboniferous greenschist-facies ‘Variscan’ metamorphic rocks, including widespread metacarbonates. The AMC was formed, at least partially, in the Triassic. Its erosion is recorded by the Middle Triassic Bāqoroq Formation at Nakhlak, which consists of conglomerates and sandstones rich in metamorphic detritus. The AMC was repeatedly deformed during post-Triassic times, giving origin to a complex structural setting characterized by strong tectonic fragmentation of previously formed tectonic units. Based on these data, we suggest that the Nakhlak–Anarak units represent an arc–trench system developed during the Eo-Cimmerian orogenic cycle. Different tectonic scenarios that can account for the evolution of the region and for the occurrence of this orogenic wedge in its present position within Central Iran are critically discussed, as well as its relationships with a presumed ‘Variscan’ metamorphic event.

Abstract New Late Ordovician and Triassic palaeomagnetic data from Iran are presented. These data, in conjunction with data from the literature, provide insights on the drift history of Iran as part of Cimmeria during the Ordovician–Triassic. A robust agreement of palaeomagnetic poles of Iran and West Gondwana is observed for the Late Ordovician–earliest Carboniferous, indicating that Iran was part of Gondwana during that time. Data for the Late Permian–early Early Triassic indicate that Iran resided on subequatorial palaeolatitudes, clearly disengaged from the parental Gondwanan margin in the southern hemisphere. Since the late Early Triassic, Iran has been located in the northern hemisphere close to the Eurasian margin. This northward drift brought Iran to cover much of the Palaeotethys in approximately 35 Ma, at an average plate speed of c . 7–8 cm year −1 , and was in part coeval to the transformation of Pangaea from an Irvingian B to a Wegenerian A-type configuration.

ABSTRACT A significant part of the convergence between the Iranian and Arabian plates since the late Cenozoic has been accommodated by several strike-slip faults, especially in the eastern and central areas of Iran. The Great Kavir fault is one of the cases in which there is little consensus regarding its kinematics, mechanism of development, and tectonic history, mainly due to a lack of detailed studies. Field and satellite image studies of the Pees Kuh Complex, a well-preserved Cenozoic structure that developed upon the Great Kavir fault near Jandaq, in central Iran, suggest a virtually perfect, positive-flower structure. It is argued that the Pees Kuh Complex is the result of a combination of both left strike-slip and reverse dip-slip displacements on the Great Kavir fault. The main structural elements comprising this flower structure are as follows: a Paleogene sedimentary assemblage, composed of an array of thrust faults with NW to EW trends, thrusted upon the Great Kavir block; a few reverse faults with N to NW dips at the southern side of the Great Kavir fault; several synthetic en echelon faults; and a number of antithetic NW-trending en echelon faults. In addition, left-stepping en echelon folds with NW-trending axial planes are recognizable. The Pees Kuh Complex shows a thrust sequence of an upward-verging antiform structure including overturned folds formed of middle to late Eocene marl and sandstone beds. These sheets have a nearly vertical position at their roots, mainly confined to the Great Kavir fault, which changes to a horizontal position further along the fault. Because the thrusts transported middle-late Eocene rocks atop Oligocene-Miocene red beds and are, in turn, covered by Pliocene-age continental beds, the age of the Pees Kuh Complex is inferred to be younger than the Miocene. Considerable left-lateral displacement of the Great Kavir fault in the Jandaq area is confirmed by geometrically measured counterclockwise rotation of ~20° of the faulted blocks around approximately vertical axes relative to the Great Kavir fault in the Godar-e-Siah area. This study, in addition to other previous lithological evidence gathered from the Jandaq area, demonstrates deformation of the Pees Kuh Complex as a reactivation of an older regional fracture, such as a suture zone, as the Paleogene sedimentary rocks were subjected to a different stress field in late Cenozoic times.