Antigorite, the high-temperature, high pressure polymorph of serpentine, is the most abundant hydrous phase within the upper mantle. It is responsible for the seismic shear-wave anisotropy measured in many subduction systems which is attributed to strain-induced lattice preferred orientation. This orientation phenomenon occurs in accordance to two mechanisms, depending on many factors among which we mention strain rate and fluid concentration. Both mechanisms drive the orientation of the antigorite (001) plane parallel to the shear plane (fault plane). However, one mechanism brings about a concentration of the a-axis subparallel to the shear direction, whereas the other mechanism brings about a concentration of the a-axis orthogonal to the shear direction (Katayama et al. 2009). By an experimental analysis based on scanning force microscopy performed on (001) oriented antigorite single crystals (Campione & Capitani, 2013), we show that the basal surface of this mineral is characterized by a strong frictional anisotropy, reaching levels as high as 100%. Friction is observed to be higher along the a-axis and lower orthogonal to it, displaying an overall orthotropic symmetry in the sliding plane. By virtue of the aforementioned crystal preferred orientation, the shear interface of thrust faults, depending on the orientation mechanism, might be subjected to a hardening process or to a weakening process. The final result is that the fault might evolve as seismic or aseismic, respectively. This seismic bivalence is not the only peculiarity stemming from the frictional anisotropy of antigorite. We show also that, in the framework of the said hardening process, slip trajectories might be substantially declined from the plate convergence direction. Campione, M. & Capitani, G.C. (2013): Subduction-zone earthquake complexity related to frictional anisotropy in antigorite. Nature Geoscience, 6, 847-851. Katayama, I., Hirauchi, K., Michibayashi, K., Ando, J. (2009): Trench-parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge. Nature 461, 1114-1117.

Campione, M. (2016). The bivalence and anomalies of antigorite in thrust fault mechanics. Intervento presentato a: 2nd European Mineralogical Conference: "Minerals, fluids, and rocks: Alphabet and words of Planet Earth", Rimini.

The bivalence and anomalies of antigorite in thrust fault mechanics

CAMPIONE, MARCELLO
2016

Abstract

Antigorite, the high-temperature, high pressure polymorph of serpentine, is the most abundant hydrous phase within the upper mantle. It is responsible for the seismic shear-wave anisotropy measured in many subduction systems which is attributed to strain-induced lattice preferred orientation. This orientation phenomenon occurs in accordance to two mechanisms, depending on many factors among which we mention strain rate and fluid concentration. Both mechanisms drive the orientation of the antigorite (001) plane parallel to the shear plane (fault plane). However, one mechanism brings about a concentration of the a-axis subparallel to the shear direction, whereas the other mechanism brings about a concentration of the a-axis orthogonal to the shear direction (Katayama et al. 2009). By an experimental analysis based on scanning force microscopy performed on (001) oriented antigorite single crystals (Campione & Capitani, 2013), we show that the basal surface of this mineral is characterized by a strong frictional anisotropy, reaching levels as high as 100%. Friction is observed to be higher along the a-axis and lower orthogonal to it, displaying an overall orthotropic symmetry in the sliding plane. By virtue of the aforementioned crystal preferred orientation, the shear interface of thrust faults, depending on the orientation mechanism, might be subjected to a hardening process or to a weakening process. The final result is that the fault might evolve as seismic or aseismic, respectively. This seismic bivalence is not the only peculiarity stemming from the frictional anisotropy of antigorite. We show also that, in the framework of the said hardening process, slip trajectories might be substantially declined from the plate convergence direction. Campione, M. & Capitani, G.C. (2013): Subduction-zone earthquake complexity related to frictional anisotropy in antigorite. Nature Geoscience, 6, 847-851. Katayama, I., Hirauchi, K., Michibayashi, K., Ando, J. (2009): Trench-parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge. Nature 461, 1114-1117.
No
abstract + slide
Scientifica
Seismic anisotropy, frictional anisotropy, slip trajectories, atomic force microscopy,
English
2nd European Mineralogical Conference: "Minerals, fluids, and rocks: Alphabet and words of Planet Earth"
http://emc2016.socminpet.it/abstracts/abstracts-lists.html
Campione, M. (2016). The bivalence and anomalies of antigorite in thrust fault mechanics. Intervento presentato a: 2nd European Mineralogical Conference: "Minerals, fluids, and rocks: Alphabet and words of Planet Earth", Rimini.
Campione, M
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/137714
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