Cataclastic and crystal-plastic deformation in shallow mantle-wedge serpentinite controlled by cyclic changes in pore fluid pressures

Rheology of Naturally Deformed Antigorite Serpentinite: Strain and Strain‐Rate Dependence at Mantle‐Wedge Conditions

“…At conditions where dissolution‐precipitation creep is less efficient than other grain‐scale mechanisms, such as, but not limited to, at higher strain rate (and higher differential stress), cooler temperatures or larger grain size, we expect increased activity of other deformation mechanisms. For example, at strain rates employed in laboratory creep experiments (∼10 −5 s −1 ), that are greater than inferred for the NMR (∼10 −12 s −1 ; Tulley et al., 2020), deformation commonly results in localized shear zones showing cataclastic textures (Chernak & Hirth, 2010; French et al., 2019; Gasc et al., 2017; Hirauchi et al., 2020; Proctor & Hirth, 2016), that are uncommon in naturally deformed antigorite (Figure 3a; Hirauchi et al., 2021; Padrón‐Navarta et al., 2012; Wassmann et al., 2011). This is consistent with an increase in the activity of frictional mechanisms toward higher strain rates.…”

“…This is consistent with an increase in the activity of frictional mechanisms toward higher strain rates. Frictional mechanisms (including face‐on‐face sliding) should also be more active where effective stresses are low (Bos & Spiers, 2002; Hirauchi et al., 2021), for example, in regions of high fluid pressure along subduction plate boundaries. Variations in the relative contributions of frictional and viscous mechanisms are also consistent with the suggestion that antigorite may host earthquake slip at higher strain rates (Wang et al., 2020).…”

“…Structures within natural antigorite shear zones such as those exposed in the Voltri massif, Italy (300°C–640°C, 0.6–2.2 GPa; Auzende et al., 2015; Hermann et al., 2000), Zermatt‐Saas zone, Western Alps (550°C ± 50°C, 2 ± 0.5 GPa; Wassmann et al., 2011), Sanbagawa belt, Japan (465°C ± 15°C, 1.01 ± 0.06 GPa; Hirauchi et al., 2021), Cerro del Almirez massif, Spain (615°C ± 15°C, 1.75 ± 0.15 GPa; Padrón‐Navarta et al., 2012) and Val Malenco, central Alps (Liu et al., 2020) provide a chance to constrain deformation mechanisms at natural strain rates. Observations of crystal distortion (Auzende et al., 2015; Hirauchi et al., 2021; Padrón‐Navarta et al., 2012) suggest dislocation‐related deformation, which some interpret as the dominant deformation mechanism (Hirauchi et al., 2021; Padrón‐Navarta et al., 2012). Antigorite formed in strain shadows (Hirauchi et al., 2021; Wassmann et al., 2011), and microfractures (Auzende et al., 2006, 2015) indicates local precipitation, and truncated chemical zoning patterns suggest local dissolution (Liu et al., 2020).…”

“…Observations of crystal distortion (Auzende et al., 2015; Hirauchi et al., 2021; Padrón‐Navarta et al., 2012) suggest dislocation‐related deformation, which some interpret as the dominant deformation mechanism (Hirauchi et al., 2021; Padrón‐Navarta et al., 2012). Antigorite formed in strain shadows (Hirauchi et al., 2021; Wassmann et al., 2011), and microfractures (Auzende et al., 2006, 2015) indicates local precipitation, and truncated chemical zoning patterns suggest local dissolution (Liu et al., 2020). Such observations are consistent with dissolution‐precipitation creep, which is interpreted by Wassmann et al.…”

Stress Balance in Synthetic Serpentinized Peridotites Deformed at Subduction Zone Pressures

“…The results here, nonetheless, provide clues on the stress distribution in, and strength contrasts between, rocks when subject to relatively high stresses and high strain rates which may arise in subduction zones. They could be relevant to ductile deformation of serpentinized zones (or shear zones reactivation) upon stress transfer from loaded parts of the subduction zones (e.g., models by Montési & Hirth, 2003, Regenauer‐Lieb & Yuen, 2008, Montési, 2013, Goswami & Barbot, 2018, observations by Hirauchi et al., 2021), where high stresses/fast strain rates may transiently be achieved, and to events that occur on timescales of hours to days, such as slow slip events. Since they are carried out under high pressures (>GPa) and at a temperature close to 350°C, our results could be particularly relevant for the rheology of the so‐called stable sliding zone of the interface between the slab and mantle, for the transition between stable sliding and seismic zones, and for understanding the stress state(s) within cold subducting slabs.…”