The topographic analysis as a tool to reconstruct the recent evolution of Elba Island: a preliminary study

Elba, the main island of the Arcipelago Toscano (Tuscany, Italy), is a fragment of the Apennines. It is structurally characterized by the overthrusting of several tectonic units, made of sedimentary rocks (Carboniferous to Eocene) and oceanic crust (Cretaceus), partially affected by metamorphism. Since Miocene, the island, together with the Tuscany area, has been affected by the magmatic activity accompanying the Tyrrhenian basin extension. In particular normal faults controlled the emplacements of igneous intrusions (the Elba plutons of Mt. Capanne and Porto Azzurro) in late Miocene. In this framework, we carried out the topographic analysis of the island, focusing on two main topics: stream long profiles and topographic features. Although stream long profiles generally show a concave-up shape, most of them are relatively straight and some are convex. Moreover, they also show several knickpoints and knickzones, that appear not related to bedrock lithology changes, suggesting that they are still adjusting their course in response to recent uplift. By analysing the topography of Elba, we found out several low sloping (>15°) surfaces, mostly placed on interfluves, at elevations ranging between 15 m and 700 m a.s.l. Marine deposits lay on the low slope surfaces up to an elevation of 120 m. According to correlation to the nearby coastal belt of Tuscany, where similar deposits have been referred to the Middle-Upper Pleistocene, it seems possible to assign the same ages to the Elba deposits. The sequence of the upper surfaces suggests the occurrence of a previous uplifting. On the basis of the collected data, we could conclude that the Elba island has been uplifted at least since the Middle Pleistocene, testifying its involvement in the general Quaternary arching of the Apennines (maximum rate ~1 mm), even if at a much less rate (~0.2-0.1 mm/yr).