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Insights into the origin and deformation style of the continental Moho: a case-study from the Western Alps (Italy)
  • Simone Salimbeni,
  • Nicola Piana Agostinetti,
  • Silvia Pondrelli
Simone Salimbeni
Istituto Nazionale di Geofisica e Vulcanologia

Corresponding Author:[email protected]

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Nicola Piana Agostinetti
University of Vienna
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Silvia Pondrelli
Istituto Nazionale di Geofisica e Vulcanologia
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Several hypotheses about origin of the continental Moho are still debated, suggesting its multi-genetic origin. Here, we present quantitative estimation of the seismic properties and anisotropy of the crust-mantle transition in the Western Alps where newly formed (proto)-continental Moho is unusually shallow. We make use of teleseismic P-to-S converted-waves recorded by 12 stations deployed on top of the Ivrea body (IB), a volume of possibly serpentinised mantle peridotite below exhumed (U)HP 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 due to the proto-continental Moho; (b) they are decomposed out of the radial plane due to anisotropic properties of rocks involved. The proto-continental Moho is recognized as a sharp increase in S-wave velocity (~0.6 to 1.1 km/s) at shallow depth of 5 to 15 km. The presence of anisotropy within the IB and overlying crustal rocks is testified by back-azimuthal dependence of the amplitude of P-to-S phases. The strength of anisotropy is large (12 ± 2 %) 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, with a dip of 30° increasing eastward the main profile. The similarity of the anisotropy parameters between crust and upper mantle suggests they have been shaped by same deformation event.
Jun 2021Published in Journal of Geophysical Research: Solid Earth volume 126 issue 6. 10.1029/2020JB021319