A metamorphic core complex is a large, dome-shaped structure composed of high-grade metamorphic rocks that have been exposed at the Earth’s surface through extension and thinning of the crust. These complexes provide insights into the processes of crustal extension, exhumation of deep-seated rocks, and the evolution of mountain belts.
Reference: Crittenden, M. D., Coney, P. J., & Davis, G. H. (1980). “Cordilleran Metamorphic Core Complexes.” Geological Society of America Memoir 153.