Grain Fragmentation and Frictional Melting During Initial Experimental Deformation and Implications for Seismic Slip at Shallow Depths

Pseudotachylytes (solidified friction melts produced during seismic slip) are considered to be rare in the geological record because they should be typical of particular seismogenic environments characterized by water-deficient cohesive rocks. Here we present field and experimental evidence that frictional melting can occur in &#8220;fluid-rich&#8221; faults hosted in the continental crust.Pseudotachylytes were found in the >40 km long Bolfin Fault Zone of the Atacama Fault System (Northern Chile). The pseudotachylytes (1) are associated with a ~1 m thick ultracataclastic fault core which accommodated > 5 km of strike-slip displacement at 6-8 km depth and 280-350&#176;C ambient temperature, (2) cut a ca. 50 m thick damage zone made of sub-greenschists facies hydrothermally altered diorites and gabbros, (3) cut and are cut by epidote+chlorite+calcite bearing veins. The microstructure of the pseudotachylytes include (1) tabular microlites of feldspar hosted in a glassy-like matrix and (2) vesicles filled by post-seismic sub-greenschist facies minerals hosted in a strongly altered matrix of albite, chlorite, and epidote crystals.Experiments reproducing seismic slip in the presence of pressurized water and conducted with the rotary shear apparatus SHIVA on experimental faults made of the sub-greenschists (hydrothermally altered) facies damage zone rocks from the Bolfin Fault Zone, resulted in the production of vesiculated pseudotachylytes. In these experiments, fault weakening mainly occurred by melt lubrication rather than by pore fluid thermal pressurization.The identification of pseudotachylytes and its association with intense pre- and post-seismic hydrothermal alteration challenges the common belief that pseudotachylytes are rare. Consistent with the experimental evidence, pseudotachylytes (1) could be a common coseismic fault product in the continental crust, (2) may easily be produced in fluid-rich hydrothermal environments but, (3) are easily lost from the geological record because they are prone to alteration.

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Frictional melting of peridotite and seismic slip

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jb005990 ◽

2009 ◽

Vol 114 (B6) ◽

Cited By ~ 49

Author(s):

P. Del Gaudio ◽

G. Di Toro ◽

R. Han ◽

T. Hirose ◽

S. Nielsen ◽

...

Keyword(s):

Seismic Slip ◽

Frictional Melting

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Experimental investigation of frictional melting of argillite at high slip rates: Implications for seismic slip in subduction‐accretion complexes

Journal of Geophysical Research Atmospheres ◽

10.1029/2008jb006165 ◽

2009 ◽

Vol 114 (B4) ◽

Cited By ~ 25

Author(s):

Kohtaro Ujiie ◽

Akito Tsutsumi ◽

Yuri Fialko ◽

Haruka Yamaguchi

Keyword(s):

Experimental Investigation ◽

Slip Rates ◽

Seismic Slip ◽

Frictional Melting

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Pseudotachylyte veins in accretionary complexes: melt or mechanical wear?

10.5194/egusphere-egu21-5424 ◽

2021 ◽

Author(s):

Benjamin Moris-Muttoni ◽

Hugues Raimbourg ◽

Romain Augier ◽

Rémi Champallier ◽

Emmanuel Le Trong ◽

...

Keyword(s):

Raman Spectroscopy ◽

Grain Size ◽

Host Rock ◽

Intensity Ratio ◽

Size Reduction ◽

Fault Rocks ◽

Mechanical Wear ◽

Crustal Rocks ◽

Seismic Slip ◽

Frictional Melting

Whether seismic rupture propagates over large distances to generate mega-earthquakes or on the contrary slows down quickly, is heavily dependent on the slip processes operating within the fault core, such as frictional melting or intense grain-size reduction and amorphization. The record, in fossil fault zones, of seismic slip, consists in many instances in Black Faults Rocks (BFR), that consists in a generally thin dark and aphanitic veins similar to volcanic glasses, which cross-cuts sharply a weakly foliated tectonic m&#233;lange, and have been interpreted as resulting from quenching of a melt (i.e. pseudotachylytes). Such interpretation has nevertheless been questioned because identical (micro- and nano-) textures have been observed on intensely comminuted natural fault rocks and on slow creep experiments on crustal rocks.In this study, we report a new dataset of high spatial-resolution Raman Spectroscopy of Carbonaceous Materials (RSCM) profiles across natural BFR from two accretionary complexes. RSCM is sensitive to both temperature and deformation. We have carried out analyses on Okitsu and Nobeoka BFR from the Shimanto Belt and Kodiak BFR from the Kodiak Accretionary Complex to discriminate the slip weakening process. The Raman Intensity Ratio (i.e. R1 in Beyssac et al., 2002) and the Area ratio (RA1 in Lahfid et al., 2010) show a drastic and discontinuous stepped increase along profiles across the BFR, revealing a higher crystallinity. Moreover, in spite of scattering, highest values have been measured on the rim between the BFR and the host-rock. Fluidization structures, interpreted as injection veins, show similar values to the ones in the host rock. Additionally, using an experimentally calibrated kinetics 1D modelling of Intensity ratio evolution with temperature, we compared the natural Raman spectroscopy profiles to different scenarios of temperature increase during seismic slip. In the three examples of BFR from accretionary complexes interpreted as natural pseudotachylytes, RSCM profiles are not consistent with a molten origin and must reflect mechanical wear during deformation.Consequently, these results bear major consequences on the dynamics of faulting in accretionary complexes, as the slip-weakening processes that occur during seismic slip rely on extreme grain-size reduction and fluidization rather than melting.

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Impact of Coseismic Frictional Melting on Particle Size, Shape Distribution and Chemistry of Experimentally-Generated Pseudotachylite

Frontiers in Earth Science ◽

10.3389/feart.2020.596116 ◽

2020 ◽

Vol 8 ◽

Author(s):

Leny Montheil ◽

Virginia G. Toy ◽

James M. Scott ◽

Thomas M. Mitchell ◽

David P. Dobson

Keyword(s):

Particle Size ◽

Host Rock ◽

Fractal Dimensions ◽

Rock Composition ◽

Slip Rates ◽

Shape Distribution ◽

Frictional Behavior ◽

Particle Size And Shape ◽

Frictional Melting ◽

Glass Compositions

In natural friction melts, or pseudotachylites, clast textures and glass compositions can influence the frictional behavior of faults hosting pseudotachylites, and are, in turn, sensitive to the processes involved in pseudotachylite formation. Quantification of these parameters in situations where the host rock composition and formation conditions are well-constrained, such as analogue experiments, may yield calibrations that can be employed in analysis of natural pseudotachylites. In this paper, we experimentally-generated pseudotachylites in granitoid rocks (tonalite and Westerly granite) at Pconf = 40 MPa and slip rates of ∼0.1 m s−1, comparable to the conditions under which natural pseudotachylite is known to form in Earth’s upper crust. We find variations in both clast textures and glass compositions that reflect formation processes, and probably influence the frictional behavior of similar natural faults hosting pseudotachylite. Quantification of particle size and shape distribution with a semi-automatic image analysis method, combined with analysis of glass and host-rock composition of these experimentally generated pseudotachylites, reveals that the textures of pseudotachylite material evolved by combinations of 1) comminution, 2) heterogeneous frictional flash melting, and 3) homogeneous (diffusive) clast melting and/or marginal decrepitation. Fractal dimensions of pseudotachylite-hosted clasts (D ∼ 3) that are greater than those of marginal fragmented host rock particles (gouge, D ∼ 2.4), reflect an increase of the intensity of comminution by slip localisation during a pre-melting phase. Chemical analyses demonstrate that these pseudotachylite glasses were generated by frictional flash melting, where host rock phases melt individually. Biotite is the least resistant to melting, feldspar intermediate, and quartz is the most resistant. The peudotachylite glass generated in these experiments has an alkaline composition, is depleted in SiO2 compared to the bulk host-rock, and shows heterogeneous compositions in a single sample related to proximity to host-rock minerals. The percentage contributions of host rock phases to the melt, calculated by a mixing model, shows that glass compositions are dominated by plagioclase and biotite. Within the melt, margins of clasts were dissolved uniformly by diffusion and/or affected by marginal decrepitation, resulting in convex and round shapes with convexities averaging ∼0.8 and circularities averaging ∼0.65.

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Meso- to nano-scale evidence of fluid-assisted co-seismic slip along the normal Mt. Morrone Fault, Italy: Implications for earthquake hydrogeochemical precursors

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2021.117010 ◽

2021 ◽

Vol 568 ◽

pp. 117010

Author(s):

Martina Coppola ◽

Alessandra Correale ◽

Marino Domenico Barberio ◽

Andrea Billi ◽

Andrea Cavallo ◽

...

Keyword(s):

Seismic Slip ◽

Nano Scale ◽

Hydrogeochemical Precursors

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Coseismic and early post-seismic slip associated with the 1999 Izmit earthquake (Turkey), from SAR interferometry and tectonic field observations

Geophysical Journal International ◽

10.1046/j.1365-246x.2003.02001.x ◽

2003 ◽

Vol 155 (1) ◽

pp. 93-110 ◽

Cited By ~ 88

Author(s):

Ziyadin Çakir ◽

Jean-Bernard de Chabalier ◽

Rolando Armijo ◽

Bertrand Meyer ◽

Aykut Barka ◽

...

Keyword(s):

Sar Interferometry ◽

Field Observations ◽

Seismic Slip ◽

Izmit Earthquake

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Polycrystal Simulation of Texture-Induced Grain Coarsening during Severe Plastic Deformation

Materials ◽

10.3390/ma13245834 ◽

2020 ◽

Vol 13 (24) ◽

pp. 5834

Author(s):

Chi Zhang ◽

Laszlo S. Toth

Keyword(s):

Plastic Deformation ◽

Severe Plastic Deformation ◽

Electron Backscatter Diffraction ◽

Texture Evolution ◽

Face Centered Cubic ◽

Shear Texture ◽

Grain Coarsening ◽

Random Texture ◽

Polycrystal Plasticity ◽

Grain Fragmentation

During severe plastic deformation (SPD), there is usually extended grain fragmentation, associated with the formation of a crystallographic texture. The effect of texture evolution is, however, coarsening in grain size, as neighbor grains might coalesce into one grain by approaching the same ideal orientation. This work investigates the texture-induced grain coarsening effect in face-centered cubic polycrystals during simple shear, in 3D topology. The 3D polycrystal aggregate was constructed using a cellular automaton model with periodic boundary conditions. The grains constituting the polycrystal were assigned to orientations, which were updated using the Taylor polycrystal plasticity approach. At the end of plastic straining, a grain detection procedure (similar to the one in electron backscatter diffraction, but in 3D) was applied to detect if the orientation difference between neighboring grains decreased below a small critical value (5°). Three types of initial textures were considered in the simulations: shear texture, random texture, and cube-type texture. The most affected case was the further shearing of an initially already shear texture: nearly 40% of the initial volume was concerned by the coalescence effect at a shear strain of 4. The coarsening was less in the initial random texture (~30%) and the smallest in the cube-type texture (~20%). The number of neighboring grains coalescing into one grain went up to 12. It is concluded that the texture-induced coarsening effect in SPD processing cannot be ignored and should be taken into account in the grain fragmentation process.

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