Internal deformation of the Dolomites Indenter, eastern Southern Alps: An integrated field, thermochronology and physical analogue modelling approach

The Dolomites Indenter (DI) represents the front of the Neogene to ongoing N(W)-directed continental indentation of Adria into Europe. Deformation of the DI is well studied along its rim, documented by important fault zones as, e.g., the Periadriatic fault system (PFS), the Giudicarie belt, and the Valsugana and Montello fault systems. With this study, we aim to investigate the internal deformation of the DI and its eastern continuation towards the Dinarides including the interference of Dinaric SW-directed and Alpine SE-directed folds and thrusts. What also remains unsolved at present is the relationship between deep-seated mantle dynamics and their control on the geometry and internal deformation of the DI. Our approach to unravel this tectonic history is a combination of (i) compilation and acquisition of detailed structural field data within the DI, (ii) collection of a new and comprehensive low-temperature thermochronological dataset covering the entire DI, and (iii) crustal- to lithospheric scale physical analogue experiments.

The existing but limited thermochronological dataset already indicates the presence of relative vertical motions within the DI after the onset of indentation, including mostly Miocene Apatite fission track (AFT) ages along the PFS and the Valsugana fault and two age clusters of Triassic to Jurassic AFT data. One cluster represents the Monti Lessini east of Riva del Garda, the second is located SE of Bozen, in the footwall of the Truden line. Are these Mesozoic AFT age clusters resulting from tectonic vertical movements and/or are they linked to inhomogeneities within the DI, like the Mesozoic platform-basin geometries or the Permian Athesian Volcanic Complex? Ongoing thermochronological investigations aim to clarify these issues.

By using crustal-scale (as a first step) physical analogue models, we aim to study (i) the impact of Jurassic E-W extension and (ii) the effect of crustal strengthening on the NW-SE directed deformation of the DI since Neogene times. Jurassic NNE-SSW trending normal faults led to a platform-basin-topography resulting, from west to east, in the Lombardian basin, Trento platform, Belluno basin, and Friuli platform (Winterer & Bosellini, 1981) but were inverted during Alpine orogeny. Moreover, the Trento platform approximately coincides with the extent of the up to ~2 km thick (Avanzini et al., 2013) Permian Athesian Volcanic Group. We simulate rigid Permian magmatic rocks, which could have led to a critical strengthening of the crust, in our analogue experiments by incorporating an additional strong domain to the lower upper crust. This, together with studying the influence of structural inheritance on the geometry and kinematics of Dinaric and Alpine deformation in the Southern Alps, allows us to model various deformational styles and -wavelengths of the DI during Neogene indentation.

This study will contribute substantially to the understanding of internal deformation and thus enable conclusions to be drawn about the processes at lithospheric scale also addressed by AlpArray.

References:

Avanzini, M. et al. (2013): Note illustrative della carta geologica d'Italia, foglio 026 Appiano. Roma, Servizio Geologico d'Italia, 324 pp.
Winterer, E. L., & Bosellini, A. (1981): Subsidence and Sedimentation on Jurassic Passive Continental Margin, Southern Alps, Italy. AAPG Bulletin, 65(3), 394-421.