The Deep Structure of the Alps Based on the CIFALPS Seismic Experiment: A Synthesis

Abstract

The European Alps are the site where classic geologic concepts such as nappe theory, continental subduction, and slab breakoff have been first proposed. However, the deep tectonic structure of the Alps has long been poorly constrained by independent geophysical evidence. This review paper summarizes the main results of the CIFALPS passive seismic experiment, which allows us to propose an updated image of the deep structure of the Alps at the scale of the lithosphere and the upper mantle. The concepts and ideas summarized in this article provide a baseline for further advances in the fields of Alpine tectonics and in the analysis of active continental margins more generally. MALUSÀ ET AL.

Insights Into the Origin and Deformation Style of the Continental Moho: A Case‐Study From the Western Alps (Italy)

“…Considering the trade-off between type of anisotropy as explained in Appendix A1, the plunge axis directions are remarkably in agreement with the directions which characterise the main tectonic structures of the study region, i.e. all dipping toward the inner part of the Western Alps arc, with a tendency to flatten toward the east (Malusà et al, 2021).…”

“…Comparable values are found for station CT50 (to the south) and lower values to the north (CT54 and CT55). Considering the trade‐off between type of anisotropy as explained in Appendix A , the plunge axis directions are remarkably in agreement with the directions which characterize the main tectonic structures of the study region, that is, all dipping toward the inner part of the Western Alps arc, with a tendency to flatten toward the east (Malusà et al., 2021 ). We suggest that such distribution could be related to different stages of deformation along the collisional front, reaching the maximum deformation in correspondence of CT31 located at the top of the Dora Maira dome, where the IB intruded at shallower depth, and near the highest values of Bouguer anomaly, that is close to CT34 station.…”

“…All rights reserved. extension as summarized in Figure 5b of Malusà et al (2021). Conversely, in the region where the IB is supposed to extend (from X=180 to X=270 km, Figure 3), two continuous and positive pulses indicate shallower (~10 km) and deeper (up to 70 km) dipping interfaces.…”

“…The presence of the IB offers a unique opportunity to take a picture in great detail of a process that is usually buried at un‐reachable depth (i.e., where resolution of standard seismic techniques is poor). We exploit the information contained in the data recorded by the CIFALPS temporary seismic experiment (Zhao et al., 2016 and Malusà et al., 2021 for an extensive review). We apply standard RF analysis to the relevant stations of the CIFALPS network to invert for both the isotropic and anisotropic structures of the crust and upper mantle.…”

Receiver function mapping of the mantle transition zone beneath the Western Alps: New constraints on slab subduction and mantle upwelling

“…According to a preliminary interpretation of the recent teleseismic tomography data obtained by Paffrath et al (2020), Agard and Handy (2021) proposed that the steeply dipping subducted slab is mostly of European origin and that a gap exists in-between the subducted lithosphere with strong dip and the slab remnants in the MTZ on the 660-km discontinuity. A low-velocity anomaly was imaged from 100 km to 250 km on the lower plate side of the Western Alps slab, extending with lower amplitudes down to the transition zone (e.g., Koulakov et al, 2009;Zhao et al, 2016a), which was attributed to thermal origin and may be linked to a counterflow induced by rollback of the Apenninic slab (Zhao et al, 2016a;Malusà et al, 2021). Hua et al (2017) proposed that the high-velocity anomalies in the mantle under the Alps coexist with negative radial anisotropy, which could be triggered by a subducting slab and the mantle flow it induced.…”