The P-T paths for metamorphic complexes from the Precambrian shields and
fold belts of different ages may result from advection, i.e. one-cycle
convective processes in the lithosphere. This conclusion has been
exemplified by the metamorphic evolution of several well-known
complexes, for which an advective model can be successfully applied.
Numerical simulations of the above processes in terms of Newtonian
rheology by using a two-dimensional finite element program have been
conducted.
Two representative models for intracontinental gravitational ordering
initiated presumably by mantle activity are considered: (i) a thermally
activated multi-layered rhythmic sequence and (ii) huge rising diapiars
causing circulation, in which crustal lithologies underwent high-P
metamorphism (above 10-15 kbar) and subsequent ascent toward the Earth's
surface.