Magnetic fabric evidences of deformation in mélanges - Claudio Test - 2021 MagIC Workshop (1/21/21)
Channel: Magnetics Information Consortium (MagIC)
Date: 2021-01-27

"Magnetic fabric evidences of multiple deformation in tectonic mélanges: an example from the Northern Apennine (NW Italy)" by Claudio Test, Claudio Robustelli Test

Lightning poster talk presented at the virtual 2021 MagIC Workshop (https://earthref.org/events/MAGIC/2021/) - Rock and Paleomagnetism through Time and Space. Jan 19th-21st, 2021.

Abstract:
Claudio Robustelli Test(a,b), Elena Zanella(a,b), Andrea Festa(a)

(a) Dipartimento di Scienze della Terra, Università degli Studi di Torino, via Valperga Caluso 35, 10125 Torino, Italy
(b) CIMaN-ALP, Centro Interuniversitario di Magnetismo Naturale - Alpine Laboratory of Paleomagnetism, via Luigi Massa 4, 12016 Peveragno, Italy

Chaotic rock bodies and mélanges commonly occur in subduction-accretion complexes and convergent margin settings throughout the world where their origin can be associated to multiple episodes of deformation.

Similarities between block-in-matrix fabric makes challenging the recognition of their origin and thus their temporal and spatial tectonic evolution. In fact, commonly the final mélange fabric records only the latest and more pervasive process of their formation.

We present the results obtained by the comparison between magnetic (anisotropy of magnetic susceptibility - AMS - and anisotropy of magnetic remanence - ARM - experiments) and mesoscale structural fabrics of non-metamorphic tectonic mélanges in the exhumed Late Cretaceous to early Eocene Ligurian accretionary complex in the Northern Apennines (NW Italy).

Our findings reveal distinct subfabrics depending on the intensity of the reworking related to tecto
nic shearing and the structural position of the mélanges within the accretionary complex (i.e., the proximity to the main thrust fault).

Close to the main thrust the magnetic fabric is dominantly oblate with magnetic foliation consistent to the S-C fabric and/or mélange foliation and a straightforward correlation between the magnetic lineation and the shear sense.

Away from the thrust faults the degree of anisotropy as well as the ellipsoids oblateness gradually diminishes. Thus, the presence of subfabrics related to previous tectonic events became dominant. In conclusion, our results show the potential of rock magnetic methods in distinguishing the superposition of deformation events, revealing strain partitioning/concentration and thus to better understand the tectonic stages of the geodynamic evolution of subduction-accretion complexes.