Variscan Sm-Nd and Ar-Ar ages of eclogite facies rocks from the Erzgebirge, Bohemian Massif

摘要: The Erzgebirge Crystalline Complex (ECC) is a rare example where both 'crustal' eclogites and mantle-derived garnet-bearing ultramafic rocks (GBUs) occur in the same tectonic unit. Thus, ECC represents key complex for studying processes such as crustal thickening or incorporation of material into continental crust. This study provides first evidence that high- pressure metamorphism Variscan age. Sm-Nd isochrons define ages 333+6 (Grt-WR), 337 f 5 360 7 (Grt-Cpx-WR) (eclogites) 353 Ma (Grt-WR) (garnet- pyroxenite). @Arf9Ar spectra phengite from two eclogite samples give plateau 348 2 355 Ma. overlap isotopic systems with blocking temperatures differ by about 300" C indicates extremely fast uplift rates. Minimum cooling rates were 50" Myr-'. As consequence, closure temperature specific system minor importance, correspond to time high-pressure metamorphism. Despite textural equilibrium metamorphic excess W"C, clinopyroxene, garnet whole rock do not three-point isochron three four samples. clinopyroxenes seem have inherited their signature magmatic precursors. Rapid burial within only few million years might be reason observed disequilibrium. cNd values (+4.4 +6.9) suggest protoliths derived long-term depleted mantle, probably MORB source, whereas isotopically enriched garnet-pyroxenite (E~,, - 2.9) represent subcontinental mantle material, emplaced crust prior during collision. similarity different types suggests shared history.