The Montello Thrust and the Active Mountain Front of the Eastern Southern Alps (Northeast Italy)

Abstract

New field and subsurface data are combined to define the geometry and evolution of the mountain front of the eastern Southern Alps. The Montello thrust (MT), the southernmost frontal structure, is reconstructed by recently published well-located microseismicity and is connected at depth with the larger Bassano-Valdobbiadene (BV) thrust. The latter started at 10–9 Ma, whereas the MT evolved at 8–6 Ma, as documented by growing unconformities in the foreland deposits and the nature of the natural gas in the anticline culmination. The latter, named Montello anticline, is growing from the upper Miocene to the Quaternary, as shown by surfaces of abrasion and deposition, including the Biadene windgap. The folded bottom of the windgap is a fan unit recently dated to the MIS 3. The MT is presently creeping and its deformation rates are much lower than previous estimates. Most of the late Miocene to Pleistocene deformation at the front of the eastern Southern Alps is accounted for the BV thrust. The reconstructed average shortening rates are in agreement with the geodetic velocity field from literature. The BV and MT are a unique active thrust system with variable slipping and locked patches, whose interactions should be further studied.