The Belluno Thrust between Monte Coppolo and Monte Agaro (Eastern Southern Alps, Northern Italy)

The Eastern Southern Alps are a southverging postcollisional thin skinned chain, which develop between Periadriatic Lineament and Venetian Plain in Northern Italy. Four are the main thrusts building the chain: Marmolada, Valsugana, Belluno and Bassano Thrusts. Marmolada is a pellicular structure involving Upper Permian-Middle Triassic succession; Belluno represents the propagation of Valsugana indentation involving the crystalline basement intruded by Lower Permian Cima d’Asta body; Bassano and Montello are the more recent foothills structures. All these thrusts are N90 to N70 oriented, propagating southwards from Early Miocene to Recent (Castellarin et al., 2006). At M. Coppolo the stratigraphic sequence includes the peritidal dolostones of Upper Triassic Dolomia Principale and the peritidal limestones of Calcari Grigi Group. It includes M. Zugna Fm. with abundant chert nodules, defining a strong subtidal environment, Loppio Oolite, Rotzo Fm. and Toarcian Grigno Oolite (Trevisani, 1991), very similar to Massone Oolite of Sarca Valley. These oolitic bars mark the western and eastern border of Trento Platform during Lias. Aalenian encrinites of San Vigilio Oolite, Middle-Upper Jurassic Rosso Ammonitico, Lower Cretaceous Maiolica and Upper Cretaceous Scaglia Rossa Fms follow, marking the final drowing of Trento Platform causing pelagic conditions. The Belluno Thrust (BT), W-E oriented, extends from Pieve Tesino to Caporetto bordering the northern margin of Belluno syncline (D’Alberto et al., 1995). BT is highlighted by anticline of M. Coppolo–M. Agaro, involving the entire stratigraphic succession with the northern limb gently dipping northwards (Brocon Pass) and the southern one vertical to overturned. The Belluno Thrust split into three southverging structures from North to South: M. Piad Line, a steep deepening reverse fault cutting the M. Coppolo Anticline hinge; Sasso Falares Line dipping 50° northwards along which the Coppolo Anticline thrusts over the Calcari Grigi-Maiolica succession arranged in an another anticline representing the Sasso Falares-Val Nuvola Duplex (SFVND); Belluno Line s.s. dipping 30° northwards, along which M. Zugna Fm. thrusts over Maiolica, bordering southwards the SFVND. The shortening is about 5-6 km. A new outcrop of BT at Pugnai shows the architecture of thrust. Castellarin A., Nicolich R., Fantoni R., Cantelli L., Sella M. & Selli L. 2006. Structure of the lithosphere beneath the Eastern Alps (Southern Sector of the TRANSALP Transect).Tectonophysics 414, 259-282. D’Alberto L., Boz A. & Doglioni C., 1995. Structure of the Vette Feltrine (Eastern Southern Alps). Mem. Sci. Geol., 47, 189-199. Trevisani, E., 1991: Il Toarciano-Aaleniano nei settori centro-orientali della Piattaforma di Trento (Prealpi Venete). Rivista Italiana di Paleontologia e Stratigrafia, 971, 99-124.