The weakness of fault zones is generally explained by invoking an elevated fluid pressure or the presence of extremely weak minerals in a continuous fault gouge horizon. This allows for faults to slip under an unfavourable normal to shear stress ratio, in contrast to E. M. Anderson's theory of faulting. However, these mechanisms do not explain why faults should nucleate in such an orientation as to make them misoriented and non-Andersonian. Here we present a weakening mechanism, involving the mechanical anisotropy of phyllosilicate-bearing mylonite belts, which is likely to influence the nucleation of faults in addition to their subsequent activity. Considering three natural examples from the Alps (the Simplon, Brenner and Sprechenstein-Mules fault zones) and a review of laboratory tests on anisotropic rocks, we apply anisotropic slip tendency analysis and show that misoriented weak faults can nucleate along a sub-planar phyllosilicate-rich mylonitic foliation, constituting a large-scale mechanical anisotropy belt and preventing the development of Andersonian optimally oriented faults.

Bistacchi, A., Massironi, M., Menegon, L., Bolognesi, F., Donghi, V. (2012). On the nucleation of non-Andersonian faults along phyllosilicate-rich mylonite belts. In D. Healy, R. Butler, Z.K. Shipton, R.H. Sibson (a cura di), Faulting, Fracturing and Igneous Intrusion in the Earth's Crust (pp. 185-199). London : Geological Society [10.1144/SP367.13].

On the nucleation of non-Andersonian faults along phyllosilicate-rich mylonite belts

BISTACCHI, ANDREA LUIGI PAOLO
;
BOLOGNESI, FRANCESCA GIOVANNA;
2012

Abstract

The weakness of fault zones is generally explained by invoking an elevated fluid pressure or the presence of extremely weak minerals in a continuous fault gouge horizon. This allows for faults to slip under an unfavourable normal to shear stress ratio, in contrast to E. M. Anderson's theory of faulting. However, these mechanisms do not explain why faults should nucleate in such an orientation as to make them misoriented and non-Andersonian. Here we present a weakening mechanism, involving the mechanical anisotropy of phyllosilicate-bearing mylonite belts, which is likely to influence the nucleation of faults in addition to their subsequent activity. Considering three natural examples from the Alps (the Simplon, Brenner and Sprechenstein-Mules fault zones) and a review of laboratory tests on anisotropic rocks, we apply anisotropic slip tendency analysis and show that misoriented weak faults can nucleate along a sub-planar phyllosilicate-rich mylonitic foliation, constituting a large-scale mechanical anisotropy belt and preventing the development of Andersonian optimally oriented faults.
Capitolo o saggio
weakness of fault zones, anisotropy
English
Faulting, Fracturing and Igneous Intrusion in the Earth's Crust
Healy, D; Butler, RWH; Shipton, ZK; Sibson, RH
2012
367
Geological Society
185
199
Bistacchi, A., Massironi, M., Menegon, L., Bolognesi, F., Donghi, V. (2012). On the nucleation of non-Andersonian faults along phyllosilicate-rich mylonite belts. In D. Healy, R. Butler, Z.K. Shipton, R.H. Sibson (a cura di), Faulting, Fracturing and Igneous Intrusion in the Earth's Crust (pp. 185-199). London : Geological Society [10.1144/SP367.13].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/37655
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