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A layer of relict, high-temperature, prograde eclogite has been discovered within felsic granulite of the Gfö hl Nappe, which is the uppermost tectonic unit in the Moldanubian Zone of the Bohemian Massif, the easternmost of the European Variscan massifs. Pressure-temperature conditions for eclogite (≥890°C, 18.0 kbar) and felsic granulite (c. 1000°C, 16 kbar) place early metamorphism of the polymetamorphic Gfö hl crustal rocks within the eclogite facies, and preservation of prograde compositional zoning in small garnet grains in high-temperature eclogite requires very rapid heating, as well as cooling. Mantle-derived garnet and spinel-garnet peridotites are associated with the high temperature-high pressure crustal rocks in the Gfö hl Nappe, and this distinctive lithological suite appears to be unique among European Phanerozoic orogenic belts, implying that tectonic processes during the late stages in evolution of the Variscan belt were different from those in the Caledonian and Alpine belts. The unusually high temperatures and pressures in Gfö hl crustal rocks, mineralogical evidence for rapid heating and cooling, juxtaposition of lithospheric and asthenospheric mantle with crustal rocks, and widespread production of latestage granites indicate that culmination of the Variscan Orogeny may have been driven by lithospheric delamination and asthenospheric upwelling.

Garnet peridotites and pyroxenites have been reported from 11 of the 15 or so high-pressure/ ultrahigh-pressure (HP/UHP) terranes in Eurasia. Most of these ultramafic rocks are Mg-Cr types, derived from depleted upper mantle, but some are more Fe-rich and originated by crystallization in ultramafic-mafic igneous complexes. The peridotites are polymetamorphic, with HP/UHP gar net-bearing assemblages being followed by a succession of retrograde assemblages related to exhu mation and cooling; some also contain evidence for a pre-HP/UHP stage, such as spinel inclusions in garnet or the presence of Ti-clinohumite. Equilibration conditions have been calculated from all available analyses of garnetiferous assemblages, by application of the olivine-garnet Fe-Mg exchange thermometer and the Al-in-orthopyroxene barometer, resulting in two distinct P-T regimes for garnet peridotites-one at high P/T in the coesite and diamond fields, and another at low P/T in the vicinity of the spinel-to-garnet transition.Garnet peridotites are thought to have evolved in at least four different tectonothermal settings, including: (1) emplacement of peridotites into oceanic or continental crust, followed by transport of peridotites and associated crust to UHP conditions by a subducting plate; (2) transfer of peridotites from a mantle wedge to the crust of an underlying, subducting plate; (3) origination from upwelling asthenosphere that passed through a high-temperature spinel peridotite stage, followed by cooling into the garnet peridotite field; and (4) extraction of garnet peridotites from ancient subcontinental lithosphere, perhaps by deep-seated faulting within a continental plate.