Mesozoic compressional to extensional tectonics in the Central East Iranian Microcontinent: evidence from the Boneh Shurow metamorphic core complex

The Boneh Shurow metamorphic core complex (BSMCC) in the Central East Iranian Microcontinent (CEIM) provides a good example of the Mesozoic succession of nonsynchronous compressional and extensional deformation events attributed to the transitional Cimmerian events. The D1 compression developed subvertical dextral ductile shear zones and corresponds to continental accretion and crustal thickening, producing kyanite- and sillimanite-grade rocks and migmatites in the Early Cimmerian Orogeny in the CEIM. The D2 deformation event is marked by extension during the mid-Cimmerian Orogeny. It is characterized by top-to-the-NE normal sense of shear along a low-angle detachment surface. Field evidence for cross-cutting relationships of D1- by D2-related structures reveals that the occurrence of Barrovian facies metamorphism and associated partial melting in the core of the BSMCC formed during compressional tectonic events. These structures formed before the initiation of extension and the formation of the low-angle detachment shear zone. Finally, during the Late Cimmerian D3 event, the east and west Boneh Shurow reverse faults ruptured on both sides of the MCC. Recognition of the complicated origin and exhumation mechanisms of the BSMCC provides crucial constraints on the prolonged evolution of Palaeo- and Neotethys ocean basins and collisional and post-collisional events in this region.