Rapid Eocene extension in the Chapedony metamorphic core complex, Central Iran: Constraints from 40Ar/39Ar dating
Abstract The Neybaz Chatak detachment system accommodated NNE directed extension along the southwest Central Iranian Plateau during Eocene time. The detachment is mainly exposed as southeast and north west dipping low angle normal fault for more than 100 km along strike of a NE trending structural dome. Structural data and abundant migmatite, granite and diorite show features typical for a (mantled) gneiss dome. Coupled with peak P T conditions of ca. 3 kbar and 650 750 degC, new hornblende, muscovite, biotite, and K feldspar 40Ar/39Ar ages together with published U Pb zircon and U Th/He apatite and zircon ages imply rapid cooling from ca. 750 degC to 60 degC of the Chapedony complex between 49 and 30 Ma. The Neybaz Chatak detachment comprises low grade hydrous mylonites with 40Ar/39Ar white mica ages of ca. 43 Ma interpreted to date activity along the shear zone. Ca. 20 100 m thick cataclasites and hydrothermal chlorite breccias separate the footwall from the overlying hangingwall unit. The documentation of Eocene coeval compression in the Neotethyan suture and extension in Central Iranian Plateau has important implications for the understanding of the dynamics of collisional orogenesis.