Anatomy and kinematic evolution of an ancient passive margin involved into an orogenic wedge (Western Southern Alps, Varese area, Italy and Switzerland)

Abstract

We make use of own geological mapping, interpretations of seismic reflection profiles and deep geophysical data to build a lithospheric-scale cross-section across the European Western Southern Alps (Varese area) and to model a progressive restoration from the end of Mesozoic rifting to present-day. Early phases of Alpine orogeny were characterized by Europe-directed thrusting, whereas post-Oligocene shortening led to basement-involving crustal accretion accompanied by backfolding, and consistent with the kinematics of the adjoining Ivrea Zone. Wedging was favored by a significant component of reactivation of the inherited Adriatic rifted margin. Our results also suggest that, during the collisional and post-collisional tectonics, lithosphere dynamics drove diachronically the onset of tectonic phases (i.e., wedging and slab retreat), from east to west, across the Western Southern Alps.

A new UHP unit in the Western Alps: First occurrence of coesite from the Monviso Massif (Italy)

“…Figure 1: a) Tectonic map of the Western Alps (modified after Balestro et al, 2017, Ghignone et al, 2020, Scaramuzzo et al, 2022and Manzotti et al, 2022 7°03'47"E). We hope for a respectful behaviour for this outcrop and for the whole area.…”

Holocene Deformations at the Po Plain–Southern Alps Transition (Lake Maggiore, Italy): Inferences on Glacially vs. Tectonic-Induced Origin

“…In the study area, the main tectonic structures are represented by a northwest verging backthrust, the Gonfolite backthrust, and related splays [50,59,60,84]. This structure remains buried under the Plio-Pleistocene deposits of the Po Plain related to the Miocene tectonic events that led to the emplacement of the outermost South Alpine forethrusts [48,50,85]. In correspondence to the southern termination of Lake Maggiore (Figure 1), a set of minor thrusts and backthrusts has been identified by Fantoni and Bello [86].…”

“…Sedimentation rates accelerated with the onset of major Late Pleistocene-Holocene glaciations [43]. Notably, the Po Plain facing the Alpine chain was widely shaped by the Last Glacial Maximum (LGM) fluvioglacial deposits that have been eroded and terraced by post-glacial rivers [44][45][46][47][48]. In these Holocene deposits, signs of near-surface deformation, such as faults, folds, and fluid escape structures, have been identified via subsurface and seismic profiles, remote sensing, drilling [49,50], seismic activity [51], and GPS and InSAR data [52,53].…”