Gneiss domes and orogeny

Many gneiss domes record positive feedback between decompression and partial melting of orogenic middle crust. Exhumed orogens are riddled with gneiss domes cored by migmatites that underwent dehydration melting during decompression. The decreasing buoyancy associated with increasing melt fraction drives further decompression at near-isothermal conditions as the partially molten crust rises diapirically. This combination of processes may explain the generation and retention of large volumes of crustally derived melt recorded in many deep-seated migmatite terranes and inferred for active orogens. In exhumed orogens, the signature of the rapid ascent of partially molten crust is a gneiss dome cored by migmatite +/- granite. The large volume of material involved in the vertical transfer of partially molten crust indicates that the formation of gneiss domes is an efficient mechanism for heat advection during orogenesis.