Misoriented faults in exhumed metamorphic complexes: Rule or exception?

Low angle normal faults and other weak faults are common in the metamorphic core of collisional orogens. They frequently show a phyllosilicate-rich mylonitic foliation that was reactivated under brittle conditions. Experimental and theoretical works indicate that mechanical anisotropies exert a subs...

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Bibliographic Details
Published in:Earth and planetary science letters 2011-07, Vol.307 (1), p.233-239
Main Authors: Massironi, Matteo, Bistacchi, Andrea, Menegon, Luca
Format: Article
Language:English
Subjects:
anisotropic slip-tendency
Anisotropy
Brittleness
European Alps
Failure
Faults
Friction
Metamorphic
metamorphic complexes
misoriented faults
Shear
Slip
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Summary:Low angle normal faults and other weak faults are common in the metamorphic core of collisional orogens. They frequently show a phyllosilicate-rich mylonitic foliation that was reactivated under brittle conditions. Experimental and theoretical works indicate that mechanical anisotropies exert a substantial influence on shear failure and frictional sliding, eventually inhibiting the nucleation and propagation of new Andersonian shear fractures and favoring the localization of brittle failure along the pre-existing foliations. Metamorphic phyllosilicate-rich rocks may show a friction coefficient varying from 0.6, at high angles to the foliation, to 0.2–0.4, for shear along the inherited foliation. To test the influence of mechanical anisotropies on the development of non-Andersonian faults, we have applied a modified slip tendency analysis to three misoriented phyllosilicate-rich faults of the European Alps. The analysis accounts for anisotropy in friction coefficients, and has been named “Anisotropic Slip Tendency analysis”. Here we show that brittle deformation along misoriented phyllosilicate-rich foliations is more probable than the development of new Andersonian faults. The presence of a well developed network of weak, phyllosilicate-rich faults may influence the overall structural style and mechanical properties of the brittle lithosphere in collisional orogens. ► Phyllosilicates rich horizons control brittle faulting in metamorphic terrains. ► Anisotropic Slip Tendency analysis accounts for anisotropy in friction coefficients. ► Misoriented faults are more probable than Andersonian ones in metamorphic complexes.
ISSN:0012-821X
1385-013X
DOI:10.1016/j.epsl.2011.04.041