Insights Into the Origin and Deformation Style of the Continental Moho: A Case‐Study From the Western Alps (Italy). Issue 6 (23rd June 2021)

• Record Type: Journal Article
• Authors: Salimbeni, Simone; Agostinetti, Nicola Piana; Pondrelli, Silvia
• Is Part Of: Journal of geophysical research. Volume 126:Issue 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-23
• Subjects: receiver functions -- harmonics decomposition -- Continental Moho -- Ivrea body -- seismic anisotropy; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2020JB021319
• Languages: English
• ISSNs: 2169-9313

Abstract

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 serpentinized 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 (∼0.4–1 km/s) at shallow depths of 5–10 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. Plain Language Summary: We investigate the seismic properties and anisotropy of the crust‐mantle transition in an area of the Western Alps where the continental Moho is unusually shallow. Using the teleseismic P‐to‐S converted waves (Receiver Function) recorded by the stations located above the Ivrea body region, a volume of possibly serpentinized mantle peridotite below exhumed (U)HP crustal rocks well mapped by gravity, magnetic and seismic survey, we investigated the strong seismic velocity contrast at shallow depth and we quantified the seismic anisotropic properties in terms of trend, dip, anisotropy percentage and depth location of the interface of the crust/upper mantle transition. The results obtained in the work evidenced the strong anisotropic behavior and the shallow transition to the Ivrea body (5–10 km), allowing us to point out its origin as due to a unique geologic phenomenon that involved all the structure in three‐dimensional, with similar isotropic and anisotropic parameters from North to South. Key Points: Receiver Functions and harmonics decomposition Continental Moho and Ivrea Body Seismic anisotropy