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Protoliths of highly metamorphosed gneisses from the Erzgebirge are deduced from the morphology, age and chemistry of zircons as well as from whole rock geochemistry and are compared with lower-grade rocks of Lusatia. Gneisses with similar structural appearance and/or geochemical pattern may have quite different protoliths. The oldest rocks in the Erzgebirge are paragneisses representing meta-greywackes and meta-conglomerates. The youngest group of zircon of meta-greywackes that did not undergo Pb loss represents the youngest igneous component for source rocks (about 575 Ma). Similar ages and zircon morphology reflect the subordinate formation of new zircon grains or only zircon rims in the augengneiss from Bärenstein and Wolkenstein, which probably represent metamorphic equivalents to Lower Cambrian twomica granodiorites from Lusatia. Bulk rock chemistry, intense fracturing and high U and Th concentrations of zircons suggest deformation-induced and fluid-enhanced recrystallisation of zircon grains. Temperatures during tectonic overprinting-too low to reset zircon ages-indicate mid-or upper crustal levels for shearing recorded in these augengneisses. Lower Cambrian (*540 Ma) granodiorites are widespread in Lusatia but are exclusively represented by the Freiberg gneiss dome in the Eastern Erzgebirge. Ordovician protolith ages were recorded by zircons from the augengneisses of the Reitzenhain-Catherine dome and the Schwarzenberg dome (Western Erzgebirge) documenting significant regional differences between the eastern and the western Erzgebirge (*540 vs. *490 Ma). In the Western Erzgebirge, most meta-volcanic rocks (muscovite gneisses) and meta-granites (mainly red augengneisses) yield Ordovician zircon ages, whereas in the Eastern part, similar rocks mainly recorded Lower Cambrian protolith ages. Zircon overprinting was highest within discrete tectonic zones where the combination of fluid infiltration and deformation induced variable degrees of recrystallisation and formation of a new augengneiss structure. Variable degrees of Pb loss caused age shifts that do not correspond to changes in zircon morphology but may be associated with U and Th enrichments. Major changes in bulk rock composition appear to be restricted to discrete zones and to (U)HP nappes, whereas gneisses with a MP-MT metamorphic overprint basically show no geochemical modifications.

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 l 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.

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