New Sm-Nd, Rb-Sr, and Pb-Pb isotope data on eclogites and metagabbros from the Austroalpine Koralpe and Saualpe basement nappes of the eastern Alps are presented. These rocks are encased in polymetamorphic gneisses and micaschists that yield t Nd CHUR ages of between 1.04 and 1.81 Ga. ϵ 0 Nd values from seven eclogite whole rocks range between +7.0 and +10.8; 147Sm 144Nd is close to modern DM In a 208pb 206Pb diagram all samples plot very close to the MORB field. Most analyses of the major mineral components, garnet, clinopyroxene, zoisite/epidote, phengite, amphibole and rutile, show disequilibrium in all three isotopic systems. Internal Sm-Nd and Rb-Sr mineral isochron ages range between 53 and 151 Ma. A minimum age of around 100 Ma is estimated for the crystallization of the high-P paragenesis garnet + omphacite + zoisite + kyanite + amphibole + quartz + rutile ± phengite + accessories, on the basis of these results. Later thermal overprint, fluid activity, and retrogression during exhumation of the eclogites involved (re-)crystallization of amphibole and garnet, thus leading in part to geochronologically poorly interpretable isochrons, without strict time significance. The last (eo-Alpine) thermal climax, involving static (re-)crystallization of garnet, staurolite and kyanite within the eclogite host rocks, is defined by concordant Sm-Nd and Rb-Sr isochrons on garnet, white mica, and staurolite at around 90 ± 3 Ma. Biotite Rb-Sr ages from these rocks range between 57 and 92 Ma. Plagioclase, pyroxene, and whole rock, analyzed from a relic gabbro core that shows continuous transition into eclogite from the southern Koralpe, yielded a Sm-Nd isochron of 275 ± 18 Ma, and an initial 143Nd 144Nd ratio of 0.51271 ± 2 ( ϵ t Nd = + 8.4 ± 0.5). This age is interpreted to date primary magmatic crystallization, thus setting also an uppermost time limit for eclogite metamorphism in the study area. The same outcrop yields a Sm-Nd isochron age for garnet and whole rock from the eclogitized gabbro of 93 ± 15 Ma; clinopyroxene from the same assemblage, however, lies clearly off this isochron. Whereas the 93 Ma figure may be regarded as a lower age limit for the eclogite event, an upper age limit of ca. 150 Ma may also be inferred for this metamorphism on the basis of these results. Taking the isotopic data from both Saualpe and Koralpe together, two basically different processes may be responsible for the data scatter and the partly unrealistically young isochrons in the Saualpe eclogites: 1. 1) Incomplete isotopic resetting, even on the grain scale, during the eclogitization of the igneous rocks, leaving cpx partly as a closed system. 2. 2) Ongoing crystallization (primarily of amphibole and/or garnet) after the peak of high-P metamorphism, probably combined with the introduction of a fluid phase with a strongly different isotopic signature from the eclogite host rocks. The results show that the Alpine evolution within the Austroalpine domain began very early (already in Permian times), with continental fragmentation, crustal thinning, and oceanic magmatic activity, close to the northern border of Gondwana. Ongoing extensional processes led to extensive production of basaltic melts close to or within a province of disrupted and strongly reduced continental basement. With the onset of collision at the western end of the Tethys ocean in Upper Mesozoic times, basement and young ocean floor were involved in Alpine subduction and, finally, in nappe tectonics, in forming the “root zone” of the present Austroalpine basement nappes.