Pseudotachylyte veins in accretionary complexes: melt or mechanical wear?

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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Influence of host rock composition on permeability reduction in shallow fault zones – implications for fault seal analysis (Vienna Basin, Austria)

Petroleum Geoscience ◽

10.1144/petgeo2020-014 ◽

2020 ◽

pp. petgeo2020-014

Author(s):

Theresa Schröckenfuchs ◽

Volker Schuller ◽

Andras Zamolyi ◽

Elias Mekonnen ◽

Bernhard Grasemann

Keyword(s):

Grain Size ◽

Host Rock ◽

Size Reduction ◽

Core Material ◽

Depth Interval ◽

Burial Depth ◽

Permeability Reduction ◽

Vienna Basin ◽

Rock Composition ◽

Fault Rocks

In order to calibrate equations for fault seal capacities to a specific basin, faults were analysed using core material from several Neogene hydrocarbon fields in the Vienna Basin, Austria. All studied specimens are siliciclastic rocks that were sampled from a depth interval of <2000 m, and share a similar depth at time of faulting, diagenetic conditions and maximum burial depth. Laboratory results showed a permeability reduction in all fault rocks compared to the host rocks. Both the highest and the lowest fault seal capacities were observed in the same fault rock type with a low phyllosilicate and clay content, and classifying as cataclastic deformation bands. Investigating the strong permeability variations within these fault rocks, microscopic analyses revealed that the fault seal potential is strongly linked to the detrital dolomite content in the host rock. Grain-size reduction processes occur preferably in the dolomite grains, accompanied by cementation. Our study suggests that – in addition to using standard fault seal analysis algorithms – accounting for host rock composition and grain-size reduction therein might help to further constrain fault seal behaviour in shallow depths. Fault seal mechanisms need to be understood on field, formation and micro scales before drawing conclusions for a full basin calibration.Thematic collection: This article is part of the Fault and top seals collection available at: https://www.lyellcollection.org/cc/fault-and-top-seals-2019

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Deformation of shale and dolomite in the Lewis thrust fault zone, northwest Montana, U.S.A.

Canadian Journal of Earth Sciences ◽

10.1139/e94-127 ◽

1994 ◽

Vol 31 (9) ◽

pp. 1440-1448 ◽

Cited By ~ 11

Author(s):

S. Gregg Erickson

Keyword(s):

Grain Size ◽

Fault Zone ◽

Rock Type ◽

Hanging Wall ◽

Thrust Fault ◽

Size Reduction ◽

Fault Rocks ◽

Slip Surfaces ◽

Northwest Montana ◽

Planar Fabric

The Lewis thrust fault zone at Marias Pass, northwest Montana, is an example of a fault zone in which hanging-wall dolomite and footwall shale deformed at relatively shallow levels (~7 km). Fabric in the fault zone depends on the rock type. Deformation of dolomite involved coalescence and widening by cataclasis of fractures, formation of anastomosing cataclasite zones that isolate less deformed clasts, and rounding and reduction in size of clasts to produce random-fabric cataclasite. Whereas dolomite deformed by progressive widening of cataclasite zones, shale deformation localized along ultracataclasite zones and slip surfaces that bound shale duplexes. Fault rocks that include both footwall shale and hanging-wall carbonate are characterized by isoclinal, intrafolial folds and a foliation that is defined by alternating shale- and carbonate-rich bands, elongate lenses of carbonate, and preferred orientation of phyllosilicates. Calcitization and subsequent solution of hanging wall rocks incorporated in the shale contributed to the development of this planar fabric. Lenses of hanging-wall carbonate were isolated in footwall shale by the emplacement of shale tongues into the hanging wall along mesoscopic faults. Displacement on the Lewis fault was accommodated by deformation of both dolomite and shale. Grain-size reduction of dolomite, mixing of dolomite and shale, and calcitization of dolomite in the fault zone may have enhanced diffusional processes in the carbonate and thereby weakened the fault zone.

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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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Dynamic strain aging and grain size reduction effects on the fatigue resistance of SA533B3 steels

Journal of Nuclear Materials ◽

10.1016/j.jnucmat.2003.09.009 ◽

2004 ◽

Vol 324 (2-3) ◽

pp. 140-151 ◽

Cited By ~ 15

Author(s):

J.Y Huang ◽

J.R Hwang ◽

J.J Yeh ◽

C.Y Chen ◽

R.C Kuo ◽

...

Keyword(s):

Grain Size ◽

Dynamic Strain Aging ◽

Fatigue Resistance ◽

Strain Aging ◽

Size Reduction ◽

Dynamic Strain

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Grain size reduction by utilizing a very thin CrW seedlayer and dry-etching process in CoCrTaNiPt longitudinal media

Journal of Applied Physics ◽

10.1063/1.372866 ◽

2000 ◽

Vol 87 (9) ◽

pp. 6860-6862 ◽

Cited By ~ 14

Author(s):

Satoru Yoshimura ◽

D. D. Djayaprawira ◽

Tham Kim Kong ◽

Yusuke Masuda ◽

Hiroki Shoji ◽

...

Keyword(s):

Grain Size ◽

Dry Etching ◽

Size Reduction ◽

Etching Process

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Grain size reduction effect of barium titanate embedded in silica xerogel

Materials Letters ◽

10.1016/j.matlet.2008.01.081 ◽

2008 ◽

Vol 62 (17-18) ◽

pp. 2947-2949 ◽

Cited By ~ 1

Author(s):

J.R. Martínez ◽

J.A. de la Cruz-Mendoza ◽

S.A. Palomares-Sánchez ◽

G. Vázquez-García ◽

G. Ortega-Zarzosa ◽

...

Keyword(s):

Grain Size ◽

Barium Titanate ◽

Size Reduction ◽

Silica Xerogel ◽

Reduction Effect

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Grain size reduction strategies on Eurofer

Nuclear Materials and Energy ◽

10.1016/j.nme.2018.06.023 ◽

2018 ◽

Vol 17 ◽

pp. 129-136 ◽

Cited By ~ 4

Author(s):

L. Pilloni ◽

C. Cristalli ◽

O. Tassa ◽

I. Salvatori ◽

S. Storai

Keyword(s):

Grain Size ◽

Size Reduction ◽

Reduction Strategies

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Influence of Severe Plastic Deformation on the PLC Effect and Mechanical Properties in Al 5XXX Alloy

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.114.171 ◽

2006 ◽

Vol 114 ◽

pp. 171-176 ◽

Cited By ~ 3

Author(s):

Joanna Zdunek ◽

Pawel Widlicki ◽

Halina Garbacz ◽

Jaroslaw Mizera ◽

Krzysztof Jan Kurzydlowski

Keyword(s):

Mechanical Properties ◽

Plastic Deformation ◽

Grain Size ◽

Severe Plastic Deformation ◽

True Strain ◽

Tensile Tests ◽

Size Reduction ◽

Hydrostatic Extrusion ◽

Stress Strain ◽

Chatelier Effect

In this work, Al-Mg-Mn-Si alloy (5483) in the as-received and severe plastically deformed states was used. Plastic deformation was carried out by hydrostatic extrusion, and three different true strain values were applied 1.4, 2.8 and 3.8. All specimens were subjected to tensile tests and microhardness measurements. The investigated material revealed an instability during plastic deformation in the form of serration on the stress-strain curves, the so called Portevin-Le Chatelier effect It was shown that grain size reduction effected the character of the instability.

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Properties of Nanoscaled Multiphase Structures and Non-Equilibrium Solid Solutions Obtained by Severe Plastic Deformation [Abstract + Supplemental Data]

MRS Proceedings ◽

10.1557/proc-977-0977-ff01-04 ◽

2006 ◽

Vol 977 ◽

Author(s):

Xavier Sauvage ◽

Xavier Quelennec ◽

Peter Jessner ◽

Florian Wetscher ◽

Reinhard Pippan

Keyword(s):

Mechanical Properties ◽

Plastic Deformation ◽

Grain Size ◽

Severe Plastic Deformation ◽

Solid Solutions ◽

Atom Probe ◽

Size Reduction ◽

Pure Metals ◽

Pure Cu ◽

Non Equilibrium

AbstractGrain size reduction induced by severe plastic deformation (SPD) and the resulting mechanical properties have been widely investigated for pure metals but less is known and reported about multi-phase materials. To study the grain size reduction mechanisms in multiphase structure subjected to SPD, two copper based composites (Cu-10%Fe and Cu-43%Cr) were severely deformed by torsion under high pressure. The grain size achieved with these composite materials is much smaller than in pure metals. It is for example in a range of 10 to 20 nm for the Cu-43%Cr composite, e.g. one order of magnitude lower than in pure Cu processed by SPD. Three dimensional atom probe data show also the formation of non equilibrium supersaturated solid solutions. The mechanisms of the deformation induced intermixing are discussed together with its influence on the mechanical properties.

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