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

Emanuele Scaramuzzo,Andrea Di Capua,Raffaele Bitonte,Pablo Granado,Franz A Livio

doi:10.1186/s00015-021-00404-7

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.

Highlights

The European Southern Alps represent a noteworthy example of an ancient passive margin that was later involved into an orogenic wedge, from initial subduction to continental collision and indentation (e.g., Butler, 1986; Handy et al, 1999; Manzotti et al, 2014; Schmid et al, 2017)
Anatomy and kinematic evolution of an ancient passive margin involved into an orogenic wedge (Western Southern Alps, Page 3 of 21 4 Varese area, Italy and Switzerland) the Western Alps at upper crustal depths (e.g., Handy et al, 1999; Schaltegger & Brack, 2007; Schmid et al, 2017)
The folds belonging to Set 1 (Fig. 6a) are N60E striking, with the axis gently plunging to the SW, and they indicate a tectonic transport to the NW

Summary

Introduction

The European Southern Alps represent a noteworthy example of an ancient passive margin that was later involved into an orogenic wedge, from initial subduction to continental collision and indentation (e.g., Butler, 1986; Handy et al, 1999; Manzotti et al, 2014; Schmid et al, 2017). The extent to which the backfolding of the Adriatic crust can be traced towards the Central Southern Alps (Fig. 1), is unknown, apart from the evidence that upturned Mesozoic crustal faults (i.e., the Lugano-Valgrande Fault; Fig. 1) continue east of Lake Como (e.g., Bertotti et al, 1999) These two apparently opposite views could probably reflect an important along-strike transition between different structural levels, namely a transition from the involvement of mantle, lower crust and Paleozoic basement in the Western Southern Alps to a shallower stack including Mesozoic rocks and thin upper crustal slices, to the east. This along-strike change offers an opportunity to integrate all these observations into a geometrically and kinematically consistent evolutionary model

Methods

Results

Discussion

Conclusion