Metamorphic core complex

Metamorphic core complexes are exposed areas of deep crust brought to the surface by crustal extension (stretching). They form, and are exhumed, through relatively fast transport of middle and lower continental crust to the Earth's surface in the form of uplifting welts of hot rock and magma. The resulting doming causes the overlying rock to gravitationally collapse, sliding down and usually away from the uplift along low-angle detachment faults. Brittle, faulted cover rock above the detachment surface lies in direct contact with the ductile middle-lower crust below.

High-grade metamorphic rocks (eclogite-, granulite- to amphibolite- facies) are exposed below the detachment faults (and mylonitic shear zones). Amphibolite- to greenschist-facies, syndeformational metamorphism, and ductile-brittle to brittle deformation are shown on the upper-side (hanging-wall), with tilted geometries.

They range from several miles to over 50 miles across, and usually exhibit several miles of vertical uplift. They are common in areas of localized crustal extension in otherwise thickened fold-thrust belts. The origin of the low angles of the detachment faults were a subject of debate as of 2022.