The Influence of Metasomatic Alteration on the Frictional Properties of Serpentinite-Bearing Gouge in the Bartlett Springs Fault, Northern California

Swiatlowski, Jerlyn L.; Moore, Diane E.; Lockner, D. A.

doi:10.1130/abs/2017am-303925

Cited by 2 publications

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“…All experiments using simulated chlorite fault gouge showed (near‐)steady state sliding characterized by a coefficient of friction ( μ ) ranging from 0.19 to 0.39 (Table ). These values are consistent with steady state μ values of 0.2 to 0.4 reported from experiments using water‐saturated chlorite‐rich fault rocks (Behnsen & Faulkner, ; Brown et al, ; Ikari et al, ; Moore & Lockner, , ; Morrow et al, ; Smith et al, ; Swiatlowski et al, ). At a first glance, this suggests that the effect of temperature on frictional strength is limited.…”

Section: Discussionsupporting

confidence: 86%

Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts

et al. 2019

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Chlorite is abundant at hypocentral depths in subduction zones and is likely to play a key role in controlling megathrust slow slip and catastrophic rupture. However, no data exist on the frictional properties of chlorite(-rich) fault rocks under the hydrothermal conditions relevant for the subduction seismogenic zone. We report results from experiments conducted under such conditions, using chlorite powders prepared from single crystal clinochlore (Mg-chlorite), as well as limited experiments using a stack of single crystal sheets. Shear experiments were carried out at effective normal stresses (σ n ) of 100 to 400 MPa, pore fluid pressures (P f ) of 50 to 220 MPa, and at temperatures (T) of 22 to 600°C, using stepped displacement rates (v) from 0.3 to 100 μm/s. The gouges are characterized by a coefficient of friction (μ) of 0.2-0.3 at T ≤ 400°C and 0.3-0.4 at 500-600°C, while (a-b) values showed positive values for nearly all conditions tested, except at 300°C. Microstructures of gouges sheared at T ≤ 300°C show evidence for widespread comminution, compared with a lower porosity at 600°C. Experiments using a stack of single crystal sheets showed μ ≤ 0.008 at low displacements (<3 mm) followed by hardening, while microstructures are suggestive of slip along (001), folding and tear of cleavage planes, and gouge production. Our results have important implications for the mechanisms controlling megathrust fault slip under greenschist facies conditions in a subduction zone and shed new light on the strain accommodation mechanisms within sheared gouges versus single crystals composed of phyllosilicates.

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Section: Discussionsupporting

confidence: 86%

Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts

et al. 2019

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“…Both the saponite-free and saponitebearing gouge samples remain velocity strengthening at P-T conditions corresponding to~9 km depth of burial (290°C and 140 MPa effective normal stress). The BSF serpentinite gouge (#5) shows the same weakening and velocity-strengthening behavior when sheared between granite driving blocks (Swiatlowski et al, 2017a(Swiatlowski et al, , 2017b as was found for antigorite serpentinite by Moore and Lockner (2013). The different Mg-phyllosilicate-rich mineral assemblages that comprise the SAFOD and BSF gouges can therefore promote stable slip (creep) in both the shallower and deeper portions of the seismogenic zone.…”

Section: 1029/2018tc005307mentioning

confidence: 74%

“…The metasomatically altered rocks at the top of the serpentinite thrust sheet are delimited in Figure b. From this position, the serpentinite rising within the BSF could incorporate them into the fault gouge, facilitated by the low strengths of the talc (e.g., Escartin et al, ; Moore & Lockner, ; Swiatlowski et al, , ) and chlorite subzones (Moore & Lockner, ; Swiatlowski et al, , ). Although not included in Figure b, a reaction zone presumably could be present at the base of the serpentinite thrust sheet, as well.…”

Section: Discussionmentioning

confidence: 99%

“…In this paper, we describe the mineralogy, porphyroclast textures, and mineral and bulk chemistry of the fault zone materials, which we conclude represent the higher pressure-temperature (P-T) equivalents of those recovered from the SAFOD drill hole. Swiatlowski et al (2017aSwiatlowski et al ( , 2017bSwiatlowski et al ( , 2018 are investigating the frictional properties of the gouge, which they find correspond to those of the SAFOD foliated gouges. We propose a possible tectonic model for incorporation of the serpentinite-rich material into the BSF from a source near the base of the seismogenic zone and discuss the implications of the model for seismic hazard along the fault.…”

Section: 1029/2018tc005307mentioning

confidence: 99%

“…The frictional properties of the BSF fault gouge (Swiatlowski et al, 2017a(Swiatlowski et al, , 2017b(Swiatlowski et al, , 2018 will be reported in detail elsewhere; a brief summary is presented here. Swiatlowski et al (2018) found that the coefficient of friction, μ (defined as the ratio of shear stress to effective normal stress) of gouge samples #2-4 (Table 2 and Figure 10) is~0.15-0.20 at 110°C, within the same range as found for the SAFOD foliated gouges at similar temperatures (Coble et al, 2014;French et al, 2015;Moore et al, 2016).…”

Section: 1029/2018tc005307mentioning

confidence: 99%

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Serpentinite‐Rich Gouge in a Creeping Segment of the Bartlett Springs Fault, Northern California: Comparison With SAFOD and Implications for Seismic Hazard

2018

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An exposure of a creeping segment of the Bartlett Springs Fault (BSF), part of the San Andreas Fault system in northern California, is a ~1.5‐m‐wide zone of serpentinite‐bearing fault gouge cutting through Late Pleistocene fluvial deposits. The fault gouge consists of porphyroclasts of antigorite serpentinite, talc, chlorite, and tremolite‐actinolite, along with some Franciscan metamorphic rocks, in a matrix of the same materials. The Mg‐mineral assemblage is stable at temperatures above 250–300 °C. The BSF gouge is interpreted to have been tectonically incorporated into the fault from depths near the base of the seismogenic zone and to have risen buoyantly to the surface where it is now undergoing right‐lateral displacement. The ultramafic‐rich composition, frictional properties, and inferred mode of emplacement of the BSF serpentinitic gouge correspond to those of the creeping traces of the San Andreas Fault identified in the SAFOD (San Andreas Fault Observatory at Depth) drill hole. This suggests a common origin for creep at both locations. A tectonic model for the source of the ultramafic‐rich materials in the BSF is proposed that potentially could explain the distribution of creep throughout the northernmost San Andreas Fault system.

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The Influence of Metasomatic Alteration on the Frictional Properties of Serpentinite-Bearing Gouge in the Bartlett Springs Fault, Northern California

Cited by 2 publications

References 0 publications

Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts

Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts

Serpentinite‐Rich Gouge in a Creeping Segment of the Bartlett Springs Fault, Northern California: Comparison With SAFOD and Implications for Seismic Hazard

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