The metaplutonic Wawa gneiss domain in the southern Superior Province is part of an uplifted block that was exhumed during the Proterozoic, exposing the lower -crustal (~30 km) levels of the late Archean (2720 to 2670 Ma) Abitibi-Wawa orogen. Previous structural and geophysical studies of the midcrustal Wawa gneiss domain reveal subhorizontal shear zones that formed during orogen-parallel extension and correspond to gently dipping seismic reflectors, present at depth elsewhere in the orogen. In order to bracket the age of this extensional deformation, the ages of metre-scale igneous bodies that crystallized before and after extension have been determined in four outcrops using single-grain U-Pb zircon dating techniques. The results constrain the time of extension to the interval between 2660 and 2645 Ma and show that deformation was coeval with pegmatite emplacement, partial melting of tonalite gneisses as old as 2925¿35 Ma, and regional circa 2660 Ma granulite-facies metamorphism of adjacent, more deeply eroded crust. This extension and associated high-grade metamorphism in the Wawa gneiss domain occurred 10 to 25 m.y. after the cessation of regional compression, major transcurrent fault movement, and sediment deposition in the upper structural levels of the orogen. The middle and lower crust was therefore mechanically decoupled from the upper crust during this period of orogen-parallel extension. This intracrustal style of deformation is interpreted to be the consequence of gravitational forces working on a thermally softened middle crust. The detachment of lithosphere from the orogen base is the favored mechanism for generating these forces and for introducing the heat that caused synextension metamorphism. Cyclic construction and delamination of orogen lithosphere could account for even younger metamorphic/strain events evident in nearby exposures of lower crust. ¿ American Geophysical Union 1996