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Friction of Mineralogically Controlled Serpentinites and Implications for Fault Weakness

Tesei, T.; Harbord, C.W.A.; De Paola, N.; Collettini, C.; Viti, C.

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Authors

T. Tesei

C.W.A. Harbord

C. Collettini

C. Viti



Abstract

Serpentines are common minerals in several major tectonic faults in a variety of geodynamic settings and have variable frictional strength and complex deformation processes. Here we present friction experiments carried out on a suite of serpentine samples that include veins of antigorite, lizardite and fibrous serpentine (chrysotile and polygonal serpentine) together with massive samples of retrograde (lizardite and chrysotile rich) and prograde (antigorite‐rich) serpentinites. These samples were characterized from the hand specimen down to the nanoscale to precisely constrain their mineralogical composition and are interpreted to represent typical fault rocks and host rocks in serpentine‐bearing shear zones, respectively. Experiments were performed at effective normal stress from 5 to 120 MPa, at temperatures of 25 °C and 170 °C and water‐saturated, i.e. under the faulting conditions of the brittle upper lithosphere. Friction of antigorite samples, either massive or vein, is relatively high μ = 0.53. Retrograde, massive serpentinites, constituted primarily of lizardite and fibrous serpentines are frictionally weak, μ = 0.30. End‐members lizardite and fibrous serpentines are even weaker, 0.15 < μ < 0.19, and this weakness is unchanged at high temperature. We document deformation of lizardite and fibrous serpentines occurring predominantly via mode II cracking, crystal/fiber folding, and frictional sliding, which account for the observed mechanical weakness. When combined with frictional reactivation analysis, our data provide mechanical evidence for fault weakness inferred from earthquake dip distributions at oceanic outer rises and low‐angle normal faults beneath rifted continental margins and at slow/ultraslow spreading mid‐ocean ridges.

Citation

Tesei, T., Harbord, C., De Paola, N., Collettini, C., & Viti, C. (2018). Friction of Mineralogically Controlled Serpentinites and Implications for Fault Weakness. Journal of Geophysical Research. Solid Earth, 123(8), 6976-6991. https://doi.org/10.1029/2018jb016058

Journal Article Type Article
Acceptance Date Jul 12, 2018
Online Publication Date Aug 15, 2018
Publication Date Aug 15, 2018
Deposit Date Jul 23, 2018
Publicly Available Date Feb 10, 2019
Journal Journal of Geophysical Research. Solid Earth
Print ISSN 2169-9313
Electronic ISSN 2169-9356
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 123
Issue 8
Pages 6976-6991
DOI https://doi.org/10.1029/2018jb016058

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Published Journal Article (Advance online version) (3.2 Mb)
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Copyright Statement
Advance online version Tesei, T., Harbord, C. W. A., De Paola, N., Collettini, C. & Viti, C. (2018). Friction of Mineralogically Controlled Serpentinites and Implications for Fault Weakness. Journal of Geophysical Research: Solid Earth, 123(8): 6976-6991, 10.1029/2018JB016058 (DOI). To view the published open abstract, go to https://doi.org/ and enter the DOI.





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