Neo-Alpine evolution of the Southern Eastern Alps

Abstract

The Eastern Southern Alps, located to the east of the N Giudicarie Line, have been originated by polyphase compressional evolution of Tertiary age. The oldest structural system corresponds to the Mesoalpine (Eocene) and early Neoalpine (Oligomiocene) compressional events, which originated the Dinaric system (NW–SE trending) present in the NE side of the Southern Alps. The subsequent tectonic belt is the Valsugana structural system, ENE–WSW trending, Serravallian– Tortonian in age. The intense activity of this compressional event is documented both by stratigraphic and structural data and by fission track studies which indicate uplifting of some 4 km in the hangingwall of the Valsugana overthrust between 12 and 8 Ma B.P. The more external structures NE–SW trending are located in the Montello–Friuli zone which were generated by the Messinian–Pliocene compressions (whose principal stress axis is SE–NW oriented). Structural and kinematic links between the Montello–Friuli belt and the Giudicarie zone have been recognized by new analytical data documenting that the Schio–Vicenza fault system transferred compressive deformations to the Giudicarie belt, where, the previous structures (belonging to the Valsugana system) were strongly enhanced by the subsequent compressions. Since the Montello–Friuli belt and the Schio–Vicenza system developed during the Messinian–Pliocene Adriatic compressional event, the out-of-sequence tectonic reactivations in the Giudicarie belt have to be considered mostly Messinian–Pliocene in age rather than Tortonian, as previously proposed. This compressional Adriatic event produced wide deformations in the Alps, both internally, like in the Montello–Friuli and Giudicarie, and, very likely, also externally, as in the Jura and the frontal external French Western Alps. The three structural systems here described are clearly represented in a N–S trending balanced profile crossing the Central Dolomites, close to the Italian trace of the Central European Profile (CEP) where a seismic reflexion acquisition campaign is presently in progress according to the German, Austrian and Italian joint program of the TRANSALP Project. The crustal and lithospheric interpretation using available data (revision of previous refraction profiles) assumes strong indentation of the Adriatic lithosphere to the N coupled by southward delamination of the Adriatic crust, coherent with the setting of the upper crust shown in the balanced cross section. Similar indentation processes were recognized up to date only in the Western and Central Alps (CROP–ECORS and NFP20 Profiles).