A new interpretation for the nature and significance of mirror-like surfaces in experimental carbonate-hosted seismic faults

Pozzi, Giacomo; Paola, N. De; Nielsen, S. B.; Holdsworth, R. E.; Bowen, Leon

doi:10.1130/g40197.1

Cited by 47 publications

(117 citation statements)

References 19 publications

(34 reference statements)

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“…Exhumed faults provide a record of thermal, chemical, and rheological changes to fault materials by earthquake processes (Niemeijer et al, 2012;Rowe and Griffith, 2015). Fault mirrors (FM), common in fault damage zones, track these phenomena at micro-to nanoscales (e.g., Siman-Tov et al, 2013;Ault et al, 2015;Kuo et al, 2016;Pozzi et al, 2018). FMs are thin (<1 mm) high-gloss, light-reflective slip surfaces comprising layered nanoparticles, and they have been observed in carbonate, quartzite, granite, chert, and hematite (e.g., Power and Tullis, 1989;Fondriest et al, 2013;Kirkpatrick et al, 2013;Siman-Tov et al, 2013;Evans et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…FMs are thin (<1 mm) high-gloss, light-reflective slip surfaces comprising layered nanoparticles, and they have been observed in carbonate, quartzite, granite, chert, and hematite (e.g., Power and Tullis, 1989;Fondriest et al, 2013;Kirkpatrick et al, 2013;Siman-Tov et al, 2013;Evans et al, 2014). Field studies and low-to high-speed deformation experiments on rock and gouge indicate FMs form by different processes and at variable slip rates (Verberne et al, 2013;Siman-Tov et al, 2015;McDermott et al, 2017;Pozzi et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Nanoscale evidence for temperature-induced transient rheology and postseismic fault healing

Ault

Jensen

McDermott

et al. 2019

Geology

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Friction-generated heat and the subsequent thermal evolution control fault material properties and thus strength during the earthquake cycle. We document evidence for transient, nanoscale fault rheology on a high-gloss, light-reflective hematite fault mirror (FM). The FM cuts specularite with minor quartz from the Pleistocene El Laco Fe-ore deposit, northern Chile. Scanning and transmission electron microscopy data reveal that the FM volume comprises a <50-μm-thick zone of polygonal hematite nanocrystals with spherical silica inclusions, rhombohedral twins, no shape or crystallographic preferred orientation, decreasing grain size away from the FM surface, and FM surface magnetite nanoparticles and Fe2+ suboxides. Sub–5-nm-thick silica films encase hematite grains and connect to amorphous interstitial silica. Observations imply that coseismic shear heating (temperature >1000 °C) generated transiently amorphous, intermixed but immiscible, and rheologically weak Fe-oxide and silica. Hematite regrowth in a fault-perpendicular thermal gradient, sintering, twinning, and a topographic network of nanometer-scale ridges from crystals interlocking across the FM surface collectively restrengthened fault material. Results reveal how temperature-induced weakening preconditions fault healing. Nanoscale transformations may promote subsequent strain delocalization and development of off-fault damage.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nanoscale evidence for temperature-induced transient rheology and postseismic fault healing

Ault

Jensen

McDermott

et al. 2019

Geology

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“…These observations strongly suggest that MSSs are not related to any dynamic weakening mechanisms, and that their seismic origin remains debatable at best. Rather, as pointed out by Pozzi et al [139], MSSs seem to demarcate a rheological discontinuity between an ultrafine-grained zone, which internally deforms via thermally-activated and grain-size dependent deformation mechanisms, i.e., the PSZ, and the adjacent, coarser-grained wall rock, which deforms by brittle processes (grain fracturing). The fact that patchy MSSs formed in LVF tests are found at different topographic levels throughout the PSZ (Figure 6a) indicate that they probably formed as isolated patches rather than as a single, through-going film.…”

Section: Mss-bearing Pszs As Indicators For Past Seismic Slip?mentioning

confidence: 89%

“…The role of effective normal stress, and of cumulative displacement, on the formation of (patchy) MSSs with progressive shear strain in LVF tests remains to be investigated. Pozzi et al [139] recently reported on the microstructural development of MSS-bearing PSZs with progressive shear strain in HVF experiments on simulated calcite faults (σn = 25 MPa, v up to 1.4 m/s). Using polished sections prepared normal to the slip vector they observed that, after an initial stage of slip (Σx ≈ 7 cm), sharp discontinuities develop which are In general, MSSs are characterized by extremely low surface roughness, especially in a direction parallel to the shear direction [136,137].…”

Section: Nanocrystalline Principal Slip Zones Formed In Fault-slip Exmentioning

confidence: 99%

Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

2019

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Principal slip zones (PSZs) are narrow (<10 cm) bands of localized shear deformation that occur in the cores of upper-crustal fault zones where they accommodate the bulk of fault displacement. Natural and experimentally-formed PSZs consistently show the presence of nanocrystallites in the <100 nm size range. Despite the presumed importance of such nanocrystalline (NC) fault rock in controlling fault mechanical behavior, their prevalence and potential role in controlling natural earthquake cycles remains insufficiently investigated. In this contribution, we summarize the physical properties of NC materials that may have a profound effect on fault rheology, and we review the structural characteristics of NC PSZs observed in natural faults and in experiments. Numerous literature reports show that such zones form in a wide range of faulted rock types, under a wide range of conditions pertaining to seismic and a-seismic upper-crustal fault slip, and frequently show an internal crystallographic preferred orientation (CPO) and partial amorphization, as well as forming glossy or "mirror-like" slip surfaces. Given the widespread occurrence of NC PSZs in upper-crustal faults, we suggest that they are of general significance. Specifically, the generally high rates of (diffusion) creep in NC fault rock may play a key role in controlling the depth limits to the seismogenic zone.In this paper, we aim to elucidate the significance of nanocrystalline PSZs in Earth's upper crust. We start with background on fault mechanics and upper-crustal seismogenesis, and summarize some key physical properties of nanophase materials which, when applied to fault rock, are expected to be of major importance in controlling fault strength and stability. We go on to review the micro-and nanostructural characteristics of natural and experimentally-formed nanocrystalline PSZs, and list reports from the literature of PSZs characterized by grains <100 nm in size. Our work demonstrates that nanocrystalline PSZs form under a wide range of conditions pertaining slow (a-seismic) and fast (co-seismic) upper-crustal fault slip. Also, we observe that they are frequently characterized by an internal crystallographic preferred orientation, and by the presence of amorphous materials and/or glossy fault plane interfaces known as "mirror-slip" surfaces. Given the abundant observations of nanocrystalline PSZs in field exposures of faults, as well as in experiments, we suggest that they are of general importance to upper-crustal fault deformation. The physical properties of nanocrystalline fault rock may play a key role in natural earthquake cycles, especially in controlling the depth distribution of upper-crustal seismicity. Fault Zones, Earthquakes, and the Seismogenic ZoneThe presence of long-lived, localized zones of shear deformation in the crust, or fault zones, implies that the fault rocks within are weaker than the surrounding country rocks and that their weakness is persistent [14,15]. The strength of the upper-crust is classically approximated using a Cou...

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“…It is found that a large number of nanoparticles are developed in fault zones (Cai et al, ; Carpenter et al, ; Chester et al, ; Fondriest et al, ; Huang et al, ; Siman‐Tov et al, ; Wang & Sun, ), and these nanoparticles are considered to be associated with fault weakening (De Paola, ; Han et al, ; Siman‐Tov et al, ). To verify the aforementioned notion, many friction experiments have been conducted in recent years, for example, by adding spherical nanoparticles (metallic oxides and carbonatites; Han et al, ) or fault gouges to experimental faults (De Paola et al, ; Fondriest et al, ; Han et al, ; Pozzi et al, ; Siman‐Tov et al, , ; Zhang & He, ). The high‐velocity rotary shear experiments results show that spherical nanoparticles can lubricate the faults and reduce the friction dramatically at the onset of fault sliding, thus weakening the faults (De Paola et al, ; Han et al, , ; Siman‐Tov et al, ).…”

Section: Introductionmentioning

confidence: 99%

Formation Conditions for Nanoparticles in a Fault Zone and Their Role in Fault Sliding

Zhang

Huang

et al. 2019

Tectonics

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Recent high-velocity rotary shear experiments results show that spherical nanoparticles can reduce fault friction dramatically during seismic slip. But questions like what are the roles of the nanoparticles in the whole slip are largely open problems.In this study, two types of nanoparticles were found in the Red River fault zone, including agglomerated nanoparticles in the ductile shear zone and spherical nanoparticles adjacent to the brittle faults. To ascertain the formation of these nanoparticles and explore the role of nanoparticles, the experiments under high temperature and pressure were conducted. The results of the experiments and of the previous studies suggest that the spherical nanoparticles can produce at the low temperature, which may lubricate the fault and significantly reduce the dynamic coefficient of friction. With the rise in temperature, the spherical nanoparticles are elongated or deformed to the agglomerated nanoparticles, which may no longer lubricate the fault, and lead the fault slip to slow down until it stops. Accordingly, this paper summarizes the role of these nanoparticles throughout the whole process of fault sliding.Plain Language Summary Nanoparticles are widely found in the nature ductile shear zone and experimental faults, but there is controversy on their formation; it is still not clear how the nanoparticles affect the fault for the entire process of sliding. In this paper, two types of nanoparticles were found in the Red River fault zone, including agglomerated viscoplastic nanoparticles and spherical nanoparticles. Based on these findings, we carry out simulation experiments under high temperature and pressure, to ascertain the formation conditions of these nanoparticles and explore the role of nanoparticles during the entire fault sliding. The results of the simulation experiments and of the previous friction experiments, reveal that two types of nanoparticles are formed in different temperature and pressure, which maybe play different roles (weaken or strengthen the fault) in the whole sliding. Specifically, at the onset of sliding, spherical nanoparticles are formed and acted as dynamic weakening to lubricate the fault. With the temperature rising, spherical nanoparticles are transformed into agglomerated viscoplastic nanoparticles, and dynamic friction increases. The agglomerated viscoplastic nanoparticles may be the primary reason for an increase in the dynamic friction, and even a halt to the fault during a later stage.

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A new interpretation for the nature and significance of mirror-like surfaces in experimental carbonate-hosted seismic faults

Cited by 47 publications

References 19 publications

Nanoscale evidence for temperature-induced transient rheology and postseismic fault healing

Nanoscale evidence for temperature-induced transient rheology and postseismic fault healing

Nanocrystalline Principal Slip Zones and Their Role in Controlling Crustal Fault Rheology

Formation Conditions for Nanoparticles in a Fault Zone and Their Role in Fault Sliding

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