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.

Inversion of extensional basins parallel and oblique to their boundaries: Inferences from analogue models and field observations from the Dolomites Indenter, eastern Southern Alps

“…The Late Triassic to Jurassic platform-basin configuration was shortened and inverted; the Dinaric foldand-thrust belt got overprinted by overall SSE-directed deformation (Mellere et al, 2000;Placer et al, 2010). From north to south, the major Neogene faults within the eastern Southern Alps are (i) the Valsugana fault system, including Valsugana and Belluno thrusts and its N-directed back-thrusts, the Villnöss/Funes and Würzjoch/Passo delle Erbe faults (ii) the blind Bassano-Valdobbiadene thrust with the Bassano anticline in its hanging wall and its N-directed back-thrust, the Val di Sella back-thrust (Selli, 1998), and (iii) the blind Montello thrust with the Montello anticline in its hanging wall, representing the most external structural feature of the eastern Southern Alps (Picotti et al, 2022).…”

“…Pliocene sediments are folded above the frontal triangle zone of the Montello thrust (Doglioni, 1992;Ortner et al, 2016). According to recent studies of Anderlini et al (2020), Jozi Picotti et al (2022), the Bassano-Valdobbiadene and the frontal Montello thrusts are seismically active at present. Mesozoic structures are frequently reactivated during the Neogene, as, e.g., the Permian normal Calisio and Schio-Vicenza faults as strike-slip faults or cross-cut in shallower angles as, e.g., the dextral Paleo-Valsugana fault (Selli, 1998).…”

“…According to Doglioni (1992), E-dipping Mesozoic normal faults have predominantly been cut and involved in the alpine fold-and-thrust belt without major reactivations, whereas W-dipping Mesozoic normal faults seem to often be strongly deformed and reused as thrust planes or by sinistral transpression, as it is the case for, e.g., the Giudicarie belt. In the eastward prolongation of the Bassano-Valdobbiadene thrust, at the transition of Belluno basin and Friuli platform, the Caneva line (i.e., Cansiglio line) represents a lateral ramp (Doglioni, 1991;Schönborn, 1999;Picotti et al, 2022). Neogene The amount of shortening along the Valsugana fault system is approximately 15 km (Selli, 1998).…”

“…1b,14b). Especially striking are the (i) tighter spacing of thrusts in basinal areas (e.g., Belluno basin), and (ii) curved thrust fronts at platform-basin transitions, e.g., of the Belluno thrust both at the transition from Trento platform to Belluno basin (Zampieri and Grandesso, 2003) as from Belluno basin to Friuli platform or Bassano-Valdobbiadene thrust at the transition from Belluno basin to Friuli platform (Picotti et al, 2022). Observation from (i) match with field descriptions from the eastern Southern Alps, where the spacing of thrusts is tighter within the Belluno basin than on the Trento platform (Doglioni, 1991;Doglioni and Carminati, 2008).…”

Tectonic Evolution of the Eastern Southern Alps (Italy): A Reappraisal From New Structural Data and Geochronological Constraints

“…The Eastern Southern Alps (ESA) of the European Alps represent an excellent natural laboratory where to study the tectonic evolution of a complex and active FTB. Despite the efforts invested so far by the scientific community to assess the seismogenesis of the ESA (e.g., D'Agostino et al., 2005; Galadini et al., 2005; Anselmi et al., 2011; Bignami et al., 2012; Cheloni et al., 2014; Danesi et al., 2015; Viganò et al., 2015; Serpelloni et al., 2016; Anderlini et al., 2020; Picotti et al., 2022), their long‐lived tectonic evolution remains mostly constrained by structural and stratigraphic data. Such data have been used since the '90s to document that the ESA stem from a series of distinct tectonic phases ensued from the Cretaceous to the Neogene in response to different paleostress field orientations (e.g., Caputo et al., 2010; Castellarin & Cantelli, 2000; Castellarin et al., 2006; Selli, 1998; Venzo, 1939).…”