The Cimmerian accretionary wedge of Anarak: a Variscan subduction complex in Central Iran

The Iran microplate is part of the Cimmerian blocks which rifted off Gondwana in the Early Permian and collided with the Southern Eurasian margin in the Late Triassic due to the closure of the Palaeotethys ocean. The presence of several ophiolite belts in Iran dating between Late Palaeozoic to Triassic poses several questions on the possible existence of various sutures marking the closure of the Palaeotethys ocean between Eurasia and Iran. Late Palaeozoic complexes with a Carboniferous “Variscan” age have been also described in N Iran, along the Alborz range, and in NE Iran, along the Late Triassic Palaeotethys suture, and they are generally related to the Late Palaeozoic evolution of the southern Eurasian margin, consisting of a mosaic of small continental blocks. In this general frame, the Anarak Metamorphic Complex (AMC), located in Central Iran, presently far from the pre-Late Triassic suture zones, is still an open problem. Detailed structural, petrographic and geochemical analyses have been carried out in these last years through the DARIUS PROGRAMME and an Italian PRIN. The AMC, which consists of several metamorphic units including dismembered “ophiolites”, displays different tectono-metamorphic evolutions. The Morghab and Chah Gorbeh complexes, mainly consisting of metapelites associated with metabasites and thick marble layers display a M1 metamorphism characterized by blueschist relicts along the S1 foliation in the former, and greenschist assemblages in the latter. They share a similar D2 deformational and M2 metamorphic history showing a prograde metamorphism with syn- to post-kinematic growth of blueschist facies phase assemblages. Prograde metamorphism characterized by the syn- to post-D2 growth of sodic amphibole has been recognized also in marbles at the contact between this unit and serpentinites. Evidence of HP/LT metamorphism also occur in Mg-riebeckite-bearing metapillow lavas and serpentinites, which are characterized by the coexistence of lizardite with antigorite. Structural analyses showed that the Chah Gorbeh and Morghab units and the “ophiolites” have been tectonically coupled within an accretionary wedge before the D2 folding stage. The other units of the AMC lack evidence of HP metamorphism around Anarak, especially the Lakh Marble, a large thrust sheet that occupies the uppermost structural position in the AMC. Available radiometric ages of undeformed trondhjemites intrudeding the wedge, as well as our new data constrain the subduction event at the end of the Carboniferous, before 290 Ma. These data suggest that the AMC may be part of an allochthonous crustal fragment being part of the Variscan belt developed along the southern Eurasian margin before the Cimmerian collision of Iran. Subsequent deformational events occurring during the Mesozoic and the Cenozoic, up to the Miocene, dismembered the original structure of the wedge accompanying its displacement to the present day position.