  The stability of the lithospheric mantle beneath the ancient cratonic cores
of continents is primarily a function of chemical modification during the
process of melt extraction. Processes by which stable continental lithosphere
may be destabilized are not well-understood, although destabilization by
thickening and removal of negatively-buoyant lithospheric mantle in
"delamination" events has been proposed in a number of tectonic settings. In
this paper we explore an alternative process for destabilizing continents,
namely, thermal and chemical modification during infiltration of metasomatic
fluids and melts into the lithospheric column. We consider observations
pertinent to the structure and evolution of the Colorado Plateau within the
western United States to argue that the physical and chemical state of the
margins of the plateau have been variably modified and destabilized by
interaction with melts. In the melt-infiltration process explored here, the
primary mechanism for weakening and rejuvenating the plate is through thermal
effects and the feedback between deformation and melt-infiltration. We
speculate on the nature and geometry of a melt-modulated interaction zone
between lithosphere and asthenosphere and the seismically-observable
consequences of variable melt-infiltration into the margins of regions of
thick, stable lithosphere such as the Colorado Plateau and the Archean Wyoming
Province within North America.
