Deformation in cemented mudrock (Callovo–Oxfordian Clay) by microcracking, granular flow and phyllosilicate plasticity: insights from triaxial deformation, broad ion beam polishing and scanning electron microscopy

Desbois, Guillaume; Höhne, Nadine; Urai, János L.; Bésuelle, Pierre; Viggiani, Gioacchino

doi:10.5194/se-8-291-2017

Cited by 51 publications

(52 citation statements)

References 87 publications

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“…Therein, gouge injection occurs into less pressurized host rock fractures where the gouge-bounding micrometer-thin shear zone failed. Contrary to rather brittle, i.e., spontaneous, localized failure of the OPA in common laboratory experiments, the in situ gouge fabric suggests a long-term creep behavior and distributed shear along micrometer-thin shear zones (see "dry" experiments in Giger et al, 2008;Desbois et al, 2017), where fluid flow is drastically inhibited perpendicular to shear, but temporarily enhanced parallel to shear inside the gouge. In direct shear experiments, Bakker et al (2017) showed for synthetic OPA gouges that a clay-enriched gouge has a lower friction coefficient than gouge with an unaltered OPA composition.…”

Section: Physical Rock Properties Of Gougementioning

confidence: 79%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich

Urai

Vollmer³

et al. 2018

Solid Earth

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Abstract. We studied gouge from an upper-crustal, lowoffset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (Switzerland). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste.The gouge occurs in thin bands and lenses in the fault zone; it is darker in color and less fissile than the surrounding rock. It shows a matrix-based, P-foliated microfabric bordered and truncated by micrometer-thin shear zones consisting of aligned clay grains, as shown with broad-ion-beam scanning electron microscopy (BIB-SEM) and optical microscopy. Selected area electron diffraction based on transmission electron microscopy (TEM) shows evidence for randomly oriented nanometer-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P foliation. For the first time for the OPA, we report the occurrence of amorphous SiO 2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains compared to the undeformed OPA.We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation" consisting of fluid-mediated removal of calcite from the deforming OPA during shearing and (ii) "clay smear" consisting of mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this.Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge that is weaker than the OPA because of the lower fraction of hard grains. For gouge, we infer a more ratedependent frictional rheology than suggested from laboratory experiments on the undeformed OPA.

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Section: Physical Rock Properties Of Gougementioning

confidence: 79%

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Laurich

Urai

Vollmer³

et al. 2018

Solid Earth

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“…Imaging grain-scale deformation microstructures (at sub-micrometre scale) in clay-rich geomaterials is challenging because such materials are difficult to prepare with conventional methods without intensive damage to microfabrics. Microstructural studies are nevertheless required to fully understand the bulk rheology of these materials (Morgenstern and Tchalenko, 1967;Logan et al, 1979, Lupini et al, 1981Rutter et al, 1986;Logan et al, 1992;Saffer and Marone, 2003;Dehandschutter et al, 2004, Dehandschutter et al, 2005aDehandschutter et al, 2005b;Colletini et al, 2009;Haines et al, 2009;Haines et al, 2013;Kaufhold et al, 2016;Desbois et al, 2017a). Ion beam methods (FIB: Focussed Ion Beam; BIB: Broad Ion Beam) enable the preparation of high-quality cross sections and, in combination with scanning-electron microscopy (SEM), currently pave the way to new fields of qualitative and quantitative investigations of phyllosilicate-rich geomaterials (Desbois et al, 2009;Milliken & Reed, 2010;Heath, 2011;Klaver et al, 2012;Hemes et al, 2013;Houben et al, 2013;Desbois et al, 2014;Houben et al, 2014;Laurich et al, 2014;Warr et al, 2014;Hemes et al, 2015;Klaver et al 2015;Hemes et al, 2016;Laurich et al, 2017;Laurich et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Ion beam methods (FIB: Focussed Ion Beam; BIB: Broad Ion Beam) enable the preparation of high-quality cross sections and, in combination with scanning-electron microscopy (SEM), currently pave the way to new fields of qualitative and quantitative investigations of phyllosilicate-rich geomaterials (Desbois et al, 2009;Milliken & Reed, 2010;Heath, 2011;Klaver et al, 2012;Hemes et al, 2013;Houben et al, 2013;Desbois et al, 2014;Houben et al, 2014;Laurich et al, 2014;Warr et al, 2014;Hemes et al, 2015;Klaver et al 2015;Hemes et al, 2016;Laurich et al, 2017;Laurich et al, 2018). This approach allows investigating deformed phyllosilicate-rich geomaterials at nanometre-resolution with unprecedented clarity (Laurich et al, 2014;Desbois et al, 2017a;Laurich et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Schuck¹,

Desbois²,

Urai³

2019

Preprint

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Boom Clay is a soft, slightly overconsolidated, uncemented claystone considered as potential host material for a radioactive waste repository in Belgium. We studied the evolution of microfabrics in samples which were shortened to 20% bulk strain in consolidated-undrained (CU) triaxial experiments at effective confining pressures of 0.375, 0.750 and 1.5 MPa, respectively.Results show a geomechanical behavior in agreement with previous studies, with total strain partly localized in shear zones and partly diffuse outside the shear zones. The diffuse strain is accommodated by pore compaction without any discernible microstructural changes compared to the starting material. In the shear zones, pore collapse reduces SEM-visible porosity and further deformation mechanisms within the shear zones are particulate flow (grain boundary sliding), particle rotation and the formation of microcracks. There is no evidence for comminution of quartz and feldspar grains. Strain localization on macro- and mesoscale is governed by viscosity contrasts between harder clasts (e.g. quartz and feldspar) embedded in a soft, porous, phyllosilicate-rich matrix.Our microstructures are comparable to those observed in Boom Clay deformed naturally and in the Excavation Damaged Zone of the Underground Research Facility. This suggests that our results are representative of Boom Clay’s geomechanical behavior at the microscale.

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“…even concluded that amorphous silica was not found in the OPA and that neoformed quartz cement formed during diagenesis is well preserved with un-corroded crystal planes. The mineral assemblage of amorphous material and clays is typical in several gouge localities, although in more mature fault gouges (Power and Tullis, 1989;Di Toro et al, 2004;Hadizadeh et al, 2012;Janssen et al, 2013;Kirkpatrick et al, 2013;Kameda et al, 2017). Figure 15.…”

Section: Diffusive Mass Transport (Pressure Solution Precipitation Anmentioning

confidence: 99%

Comment to the reviewers

Laurich¹

2017

Preprint

View full text Add to dashboard Cite

We studied gouge from an upper-crustal, lowoffset reverse fault in slightly overconsolidated claystone in the Mont Terri rock laboratory (Switzerland). The laboratory is designed to evaluate the suitability of the Opalinus Clay formation (OPA) to host a repository for radioactive waste. The gouge occurs in thin bands and lenses in the fault zone; it is darker in color and less fissile than the surrounding rock. It shows a matrix-based, P-foliated microfabric bordered and truncated by micrometer-thin shear zones consisting of aligned clay grains, as shown with broad-ion-beam scanning electron microscopy (BIB-SEM) and optical microscopy. Selected area electron diffraction based on transmission electron microscopy (TEM) shows evidence for randomly oriented nanometer-sized clay particles in the gouge matrix, surrounding larger elongated phyllosilicates with a strict P foliation. For the first time for the OPA, we report the occurrence of amorphous SiO 2 grains within the gouge. Gouge has lower SEM-visible porosity and almost no calcite grains compared to the undeformed OPA. We present two hypotheses to explain the origin of gouge in the Main Fault: (i) "authigenic generation" consisting of fluid-mediated removal of calcite from the deforming OPA during shearing and (ii) "clay smear" consisting of mechanical smearing of calcite-poor (yet to be identified) source layers into the fault zone. Based on our data we prefer the first or a combination of both, but more work is needed to resolve this. Microstructures indicate a range of deformation mechanisms including solution-precipitation processes and a gouge that is weaker than the OPA because of the lower fraction of hard grains. For gouge, we infer a more ratedependent frictional rheology than suggested from laboratory experiments on the undeformed OPA.

show abstract

Deformation in cemented mudrock (Callovo–Oxfordian Clay) by microcracking, granular flow and phyllosilicate plasticity: insights from triaxial deformation, broad ion beam polishing and scanning electron microscopy

Cited by 51 publications

References 87 publications

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

Grain-scale deformation mechanisms and evolution of porosity in experimentally deformed Boom Clay

Comment to the reviewers

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