The Saxonian Granulites represent a major exposure of high-pressure rocks within the mid-European Variscan belt. The granulites emerge in an extensional dome structure beneath a low-grade Paleozoic cover. The boundary between the granulites and their cover is a crustal-scale shear zone with transport top to the SE, juxtaposing high-pressure (HP) granulites against greenschist-grade rocks. Seismic reflection and refraction profiling reveal that the granulite dome and its western continuation up to the SW margin of the Bohemian Massif are underlain by a reflective layer up to 1 s two-way time (TWT) thickness (~3.5 km), with P wave velocities Vp generally above 6.0 and up to 7.0 km/s (probably a sheet of metabasic rocks). This layer exhibits a NE trending antiformal structure, in line with the granulite antiform, with an apex at ~1.2 s TWT. The outcrop of felsic granulite forms a local cap on the NE part of this high-velocity layer. A magnetotelluric survey has revealed high resistivity in the upper crust and a zone of high conductivity under the high-velocity layer, in the middle and lower crust, terminating ~10 km to the south of the granulite outcrop. Similar high-grade rocks occur in the Erzgebirge antiform SE of the Saxonian Granulites, but their exhumation was later followed by grossly westdirected stacking with medium-pressure and low-pressure rocks, followed by backthrusting toward the SE and late open folds. Isotopic data both from the Saxonian Granulites and the Erzgebirge indicate HP metamorphism ~360--370 Ma, followed by a granulite stage at 350--340 Ma. This is entirely incompatible with the record of low-grade sediments overlying the crystalline rocks, which document subsidence and marine sedimentation lasting until ~330 Ma. This paradox is explained by tectonic underplating, differential thinning of the hanging wall lithosphere, and extensional unroofing of the high-grade rocks derived from one of the subduction zones adjacent towards the NW and SE. Tectonic underplating and exhumation of the granulites must have occurred under the floor of a marine basin. ¿ 1999 American Geophysical Union