The boundary between the unmetamorphic - very low-grade and low-grade domains in the Southalpine basement s.l. of the Eastern Southern Alps: a review

The Southalpine basement in the Eastern Alps consists of thick metamorphic mainly phyllitic sequences which formed within greenschist facies conditions, and unmetamorphosed to very-low grade Paleozoic sequences in its easternmost part (Palaeocarnic Chain). Many authors tried to localize the boundary between the metamorphic and non-metamorphic domains. Recent studies demonstrated, by means of KI (Kübler Index) data, that the locations of this boundary given in the maps are uncorrect, and that the boundary occurs more eastwards than previously suggested, mainly in correspondence of the Val Bordaglia Line. The present review critically summarizes all data existing in the literature (Kübler Index, Árkai Index, vitrinite reflectance, Colour Alteration Index of Conodonts, fluid inclusions) concerning the location of the eastern boundary of the Hercynian metamorphism, and discusses the occurrence and possible significance of a local Alpine overprint to the east of the Val Bordaglia Line.