Viscous collision in channel explains double domes in metamorphic core complexes

In hot orogens, gneiss domes are a response to upper crustal stretching and lower crustal flow. Two-dimensional thermal-mechanical modeling shows that localization of extension in the upper crust triggers, in the deep crust, oppositely verging horizontal flows that converge beneath the extended region. Upon viscous collision, both flowing regions rotate upward to form two upright domes of foliation (double domes) separated by a steep median high-strain zone. In such systems, horizontal shortening in the infrastructure develops in an overall extensional setting. Dome material follows a complex depth-dependent strain history, from shearing in the deep crustal channel, to contraction upon viscous collision in the median high-strain zone, to extension upon advection into the shallow crust. This depth-dependent strain history is likely a general feature of dome evolution, and is arguably well preserved in double domes such as the Montagne Noire (France) and Naxos (Greece) gneiss domes.