Details

Autor(en) / Beteiligte

• Robustelli Test, Claudio
• Zanella, Elena

Titel

Rock Magnetic Signature of Heterogeneities Across an Intraplate Basal Contact: An Example From the Northern Apennines

Ist Teil von

• Geochemistry, geophysics, geosystems : G3, 2021-12, Vol.22 (12), p.n/a

Ort / Verlag

Washington: John Wiley & Sons, Inc

Erscheinungsjahr

2021

Link zum Volltext

Quelle

Wiley Online Library E-Journals

Beschreibungen/Notizen

• Heterogeneities in the magnetic signature along intraplate shear zones complicate their correlation with the physical processes that are involved in the geodynamic evolution of megathrusts. Isolating the preferred orientation of different magnetic minerals may provide insights into faulting processes, tectonics, and strain partitioning. Studies of exhumed analogs are fundamental to constrain variations in the magnetic properties with respect to a geodynamic context of intraplate shear zones. This study uses a combined statistical and magnetic approach to separate the contribution of coexisting petrofabrics to better interpret the heterogeneities in the magnetic signature. The main results indicate that there is a strong dependency among the variation in the magnetic properties and their anisotropy with the distance from the thrust faults and strain localization within the shear zone. Close to the main thrust, we observed a shear‐related fabric, indicating a high degree of non‐coaxial strain. Away from the thrust faults, the degree of anisotropy and the ellipsoids' oblateness gradually diminishes and subfabrics related to previous tectonic events or less intense deformation become dominant. Our observations also indicate strain decoupling across the basal thrust with dominant vertical uniaxial strain within the footwall. In contrast characterization of the anisotropy of magnetic remanence provides significant information on the variable response of different subpopulations of ferromagnetic minerals to shearing, indicating different degree of reworking or independent deformation processes. Plain Language Summary Giant earthquakes commonly occur at active intraplate zones and to understand their formation and propagation, it is necessary to understand how rocks deform at intraplate shear zones. Variations in physical and rheological properties as well as fluids pressures are significant in controlling the seismicity. The directional variations of the magnetic properties of rocks strongly depends on these properties. This use of magnetic fabrics has been largely applied to convergent margins and mountain chains, but studies on intraplate shear zones that involve heterogeneous materials have been less studied. Our approach is to fully characterize the magnetic properties of rocks from intraplate shear zone and correlate these with geological processes related to the deformation. Key Points Changes in the magnetic properties of fault rocks reveal the degree of tectonic reworking or structural position within the shear zone Anisotropy of remanence experiments unravel distinct deformation stages or the heterogeneous response to the shearing by different grains Systematic studies of exhumed analogs allow to constrain the magnetic properties in terms of localized versus distributed deformation