Metamorphic Core Complexes (MCCs) form when a thickened domain with a low-strength lower crust is submitted to extension. These structures are characteristic of post-orogenic extension, and field observations suggest that several MCCs rework a crustal nappe-stack emplaced before extension begins. These MCCs therefore develop within heterogeneous crusts that contain pre-existing dipping heteroge...

Back-arc basins in continental settings can develop into oceanic basins, when extension lasts long enough to break up the lithosphere and allow mantle melting that generates new crust. Often, basement of these is not only composed crust, but also exhumed mantle, fragments intrusive magmatic bodies, a complex mid-ocean ridge system characterised by distinct relocations spreading centre. To bette...