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

Abstract

Several hypotheses on the origin of the continental Moho are still debated and multiple mechanisms may contribute to its formation. Here, we present quantitative estimation of the seismic properties and anisotropy of the crust-mantle transition in the Western Alps where an example of newly formed (proto)-continental Moho is unusually shallow. We make use of teleseismic P-to-S converted-waves recorded by stations deployed on top of the Ivrea Body (IB), a volume of possibly serpentinised mantle peridotite below exhumed (ultra-)high pressure crustal rocks. The IB has been mapped by gravity, magnetic, active and passive seismic surveys suggesting an extremely shallow Moho. We demonstrate that the P-to-S converted waves propagating through this region display coupled features: (a) they record expected presence of strong seismic velocity contrast at shallow depth as due to the lower crustal and upper mantle transition; (b) they are decomposed due to anisotropic properties of rocks involved. The proto-continental Moho is recognized as an increase in S-wave velocity (~0.4 to 1 km/s) at shallow depths of 5 to 10 km. The presence of anisotropy within the IB and overlying crustal rocks is evidenced by back-azimuthal dependence of the amplitude of P-to-S phases.The strength of anisotropy is ~-14% on average pointing out the presence of metamorphosed/hydrated material (e.g. serpentinite) below the Moho. Anisotropic directions are consistent across Moho in both crust and upper mantle. The similarity of the anisotropy parameters between crust and upper mantle suggests they have been shaped by the same deformation event.

Along-strike variations in the fossil subduction zone of the Western Alps revealed by the CIFALPS seismic experiments and their implications for exhumation of (ultra-) high-pressure rocks

“…However, based on previous studies on crustal anisotropy estimated from azimuthal variations of receiver functions along the CIFALPS profile (Salimbeni et al, 2021), and on radial anisotropy in the European crust from ambient noise tomography (Alder et al, 2021), we believe that the complex 3-D structure of the crust, with layer boundaries dipping in various directions, plays a much stronger part than anisotropy in the variations of waveforms with azimuth. Moreover, crustal anisotropy detected by Salimbeni et al (2021) is mainly located within the Adriatic upper plate, which implies a negligible impact of anisotropy on the analysis of the European Moho and the overlying subduction wedge. With these issues in mind, we selected signals in the back-azimuth range 0-100° to improve the CCP stack and enhance converted phases on east-dipping structures.…”

Tectonic Fabric in the Banda Arc‐Australian Continent Collisional Zone Imaged by Teleseismic Receiver Functions

“…The complicated and azimuthally varying RF waveforms shown in their paper, however, indicate the breakdown of this assumption. Similar RF signals have been used elsewhere to infer lithospheric anisotropy and its tectonic implications (e.g., Audet, 2015;Bar et al, 2019;Birkey et al, 2021;Bourke et al, 2020;Chen et al, 2021;Frothingham et al, 2022;Gosselin et al, 2021;Levin et al, 2021;Nikulin et al, 2019;Olugboji et al, 2016;Salimbeni et al, 2021;Schulte-Pelkum et al, 2021;Sherrington et al, 2004;Vergne et al, 2003). In addition, the small number of RF measurements (<20-60 for more than half of stations) considered in Syuhada et al (2016) may lead to uncertainties in their results.…”

The role of mantle upwelling on the thermal history of theTertiary‐PiedmontBasin at theAlps‐Apenninestectonic boundary

“…Bertotti et al, 2006;Carrapa et al, 2003;Maffione et al, 2008;Maino et al, 2013;Vignaroli et al, 2008). The study area is controlled by the complex dynamics of the Apennine and Alpine slabs, which are driven by processes such as roll back (Liu et al, 2022;Malusà et al, 2021;Salimbeni et al, 2021) and break-off (Carminati et al, 2012;Handy et al, 2010Handy et al, , 2021Kästle et al, 2020;Schlunegger & Kissling, 2015;Vignaroli et al, 2008Vignaroli et al, , 2010.…”