The metatasiliciclastic-carbonate sequence of the Acquadolce Unit (Eastern Elba Island): new petrographic data and paleogeographic interpretation

The Acquadolce Unit (upper part of Trevisan's Complex II) consists of a phyllitic-quartzitic succession with calcschist and metagraywacke intercalations and a serpentinite wedge at the top. This unit was generally correlated to the Dogger-Eocene metasediments of the Tuscan Paleozoic-Jurassic succession of the Apuan Alps but, more recently, has been attributed to the Ligurian or Piedmontese Domain (e.g. the "Schistes Lustrés" of the Gorgona Island). In this paper we present a detailed petrographic study of both the Acquadolce Unit and the Metasedimentary Unit of the Gorgona Island. In particular, we found significant mineralogical analogies between the lithotypes and tectono-metamorphic imprint of the two successions. The hypothesis that the Acquadolce Unit can be ascribed to a "Schistes Lustrés"-type succession is also supported by the relatively high-pressure (probably >8kbar) estimated for the D1 deformation phase of the Acquadolce Unit from the K-white mica composition. The Acquadolce Unit is attributed to the metamorphic Ligurian-Piedmontese successions, allowing a redefinition of the main geological boundaries in the Tuscan Archipelago.