1.57-Ga Magmatism in the South Carpathians: Implications for the Pre-Alpine Basement and Evolution of the Mantle under the European Continent: A Discussion

Drăguşanu and Tanaka (1999) provide intriguing new chemical and isotopic analyses of amphibolites and gneisses from the Cumpăna Group, the oldest lithostratigraphic unit in the Getic-Supragetic unit of the South Carpathians (Balintoni 1975; Pana 1994). Ten amphibolite whole-rock data points form a linear trend in a plot of measured Nd/Nd against Sm/Nd (Drăguşanu and Tanaka 1999, fig. 3). Drăguşanu and Tanaka interpreted this as a 1.57-Ga isochron. This age corresponds to the oldest determined magmatism in the south Carpathians and, if true, would be instrumental in elucidating the tectonomagmatic evolution of the Carpathian basement, which is obscured by younger orogenic cycles such as the Hercynian (Variscan) and the Alpine. The Variscan and Alpine events are consistent with a variety of geologic and thermochronologic data from the Getic-Supragetic unit of the South Carpathians (Dallmeyer et al. 1996). In contrast, no geochronologic evidence is available to support the existence of relics of prior orogenic cycles in this unit. It appears that Precambrian metasedimentary rocks are present in the Getic-Supragetic unit, based on Nd model ages performed on a variety of metasedimentary basement rocks (D. Pana and P. Erdmer, unpub. data). However, no pre-Hercynian magmatic events have been determined so far in the Getic-Supragetic unit. The Drăguşanu and Tanaka (1999) data are the first to suggest the existence of relics of an older orogen (e.g., an older accreted terrane?) in the Getic-Supragetic realm. The purpose of this discussion is to explore alternatives to two main conclusions of the Drăgu-