Abstract
The composite Poshteh Pluton, at the northeastern margin of the Central Iranian Microplate near Taybad in eastern Iran, is positioned at a critical tectonic junction, south of the inferred main Paleotethys suture and along the major regional Doruneh Fault system. It consists of two distinct intrusions. Quartz monzonite is dated in this study by zircon U–Pb ID-TIMS to 215.8 ± 0.5 Ma, an age that coincides with the time of closure of the Paleotethys during the late collisional stages of the Eo-Cimmerian Orogeny. It is geochemically very similar to coeval plutons present along and north of the Paleotethys suture, where they intruded Carboniferous-Permian arc sequences, ophiolites and flysch. The Poshteh quartz monzonite is located south of the suture in a position similar to the Anarak and related complexes further west, which previously have been interpreted as reflecting Mesozoic and Cenozoic disruption of the Eo-Cimmerian Orogen by extensional and transtensional processes. The Triassic quartz monzonite was subsequently invaded by granite at 41.23 ± 0.31 Ma. The emplacement was in part structurally controlled by the Doruneh Fault system and associated to hydrothermal alteration and Fe mineralization. The granite is thus a coeval member of a widespread late Eocene to Oligocene plutonic suite in the region, and likely the result of delamination and melting of the subcontinental lithosphere.