Considerable evidence exists for large-scale migration of CO2-rich fluids through the lower continental crust in the Late Archean and Early Proterozoic, with transfer of heat producing elements and H2O to higher levels. The evidence manifest in the large charnockitic terrains of this age includes deformation-related charnockitic alteration of gneisses, nearly ubiquitous CO2-rich fluid inclusions in minerals, depletion of large-ion-lithophile elements (LILE), partucilarly Rb, relative to typical upper curstal rocks, similar depletion of 18O in paragneisses and petrographic and geochemical evidence of open-system replacement of amphibole gneiss by charnockite. A conveyor-belt upper mantle source appears to have been necessary for prolonged CO2 supply in high-grade crustal metamorphism, most plausibly by deep subduction of marine carbonate under continental interiors. This plate tectonic mode seems consonant with crustal thicknening and orogenic patterns inferred for most charnockitic terrains and with CO2 transport mechanisms constrained by experimental petrology. ¿ American Geophysical Union 1987