Clay fabrics in SAFOD core samples

Janssen, C.; Kanitpanyacharoen, Waruntorn; Wenk, Hans‐Rudolf; Wirth, Richard; Morales, Luiz F. G.; Rybacki, E.; Kienast, Markus; Dresen, Georg

doi:10.1016/j.jsg.2012.07.004

Cited by 27 publications

(33 citation statements)

References 41 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6e and f, white arrows; see also Holdsworth et al, 2011;Hadizadeh et al, 2012;Janssen et al, 2012). These phyllosilicates either show clay particles that are randomly oriented or they are aligned forming face-to-face particle contacts (black arrow in Fig.…”

Section: Dissolutioneprecipitation Processesmentioning

confidence: 86%

See 1 more Smart Citation

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

Janssen

Wirth

Wenk

et al. 2014

Journal of Structural Geology

Self Cite

View full text Add to dashboard Cite

a b s t r a c tThe microstructures, mineralogy and chemistry of representative samples collected from the cores of the San Andreas Fault drill hole (SAFOD) and the Taiwan Chelungpu-Fault Drilling project (TCDP) have been studied using optical microscopy, TEM, SEM, XRD and XRF analyses. SAFOD samples provide a transect across undeformed host rock, the fault damage zone and currently active deforming zones of the San Andreas Fault. TCDP samples are retrieved from the principal slip zone (PSZ) and from the surrounding damage zone of the Chelungpu Fault. Substantial differences exist in the clay mineralogy of SAFOD and TCDP fault gouge samples. Amorphous material has been observed in SAFOD as well as TCDP samples. In line with previous publications, we propose that melt, observed in TCDP black gouge samples, was produced by seismic slip (melt origin) whereas amorphous material in SAFOD samples was formed by comminution of grains (crush origin) rather than by melting. Dauphiné twins in quartz grains of SAFOD and TCDP samples may indicate high seismic stress. The differences in the crystallographic preferred orientation of calcite between SAFOD and TCDP samples are significant. Microstructures resulting from dissolutioneprecipitation processes were observed in both faults but are more frequently found in SAFOD samples than in TCDP fault rocks. As already described for many other fault zones clay-gouge fabrics are quite weak in SAFOD and TCDP samples. Clay-clast aggregates (CCAs), proposed to indicate frictional heating and thermal pressurization, occur in material taken from the PSZ of the Chelungpu Fault, as well as within and outside of the SAFOD deforming zones, indicating that these microstructures were formed over a wide range of slip rates.

show abstract

Section: Dissolutioneprecipitation Processesmentioning

confidence: 86%

“…11a and b) and randomly oriented (newly formed) clay particles ( Fig. 11c and d), dominating the fault matrix ("matrix fabric"; Janssen et al, 2012), in all samples of both groups. Faultrelated deformation on the particle scale is characterized by kinking and rotation of sheet silicates (Fig.…”

Section: Clay-gouge Fabricmentioning

confidence: 91%

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

Janssen

Wirth

Wenk

et al. 2014

Journal of Structural Geology

Self Cite

View full text Add to dashboard Cite

show abstract

“…Previous and on-going analyses of whole-rock core suggests the mechanical properties of the SDZ and CDZ are likely influenced by: (1) the presence of neo-mineralized clay coatings on interconnected fracture surfaces (HOLDSWORTH et al 2011;JANSSEN et al 2012;SCHLEICHER et al 2010SCHLEICHER et al , 2012; (2) formation of amorphous matter related to syndeformational fault lubrication RYBACKI et al 2010); (3) cataclasis and brittle microfracture, intense shearing and multi-phased veins related to episodic deformation events and transient fluid flow (BRADBURY et al 2011;MOORE and RYMER 2012;RYBACKI et al 2010); (4) pressure solution creep mechanisms Holdsworth et al 2011;MITTEMPHERGER et al 2011);and (5) presence and/or transformation of frictionally weak minerals within clay gouge such as saponite, talc, and/or serpentine (CARPENTER et al 2011;LOCKNER et al 2011;MOORE and RYMER 2007;MOORE and RYMER 2012). In this paper, we also document the presence of carbon-rich materials and distinct geochemical alteration signatures adjacent to and within the fault zone.…”

Section: W Ementioning

confidence: 99%

Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Bradbury

Davis

Shervais

et al. 2014

Pure Appl. Geophys.

View full text Add to dashboard Cite

Abstract-We examine the fine-scale variations in mineralogical composition, geochemical alteration, and texture of the faultrelated rocks from the Phase 3 whole-rock core sampled between 3,187.4 and 3,301.4 m measured depth within the San Andreas Fault Observatory at Depth (SAFOD) borehole near Parkfield, California. This work provides insight into the physical and chemical properties, structural architecture, and fluid-rock interactions associated with the actively deforming traces of the San Andreas Fault zone at depth. Exhumed outcrops within the SAF system comprised of serpentinitebearing protolith are examined for comparison at San Simeon, Goat Rock State Park, and Nelson Creek, California. In the Phase 3 SAFOD drillcore samples, the fault-related rocks consist of multiple juxtaposed lenses of sheared, foliated siltstone and shale with blockin-matrix fabric, black cataclasite to ultracataclasite, and sheared serpentinite-bearing, finely foliated fault gouge. Meters-wide zones of sheared rock and fault gouge correlate to the sites of active borehole casing deformation and are characterized by scaly clay fabric with multiple discrete slip surfaces or anastomosing shear zones that surround conglobulated or rounded clasts of compacted clay and/or serpentinite. The fine gouge matrix is composed of Mgrich clays and serpentine minerals (saponite ± palygorskite, and lizardite ± chrysotile). Whole-rock geochemistry data show increases in Fe-, Mg-, Ni-, and Cr-oxides and hydroxides, Fe-sulfides, and C-rich material, with a total organic content of [1 % locally in the fault-related rocks. The faults sampled in the field are composed of meters-thick zones of cohesive to non-cohesive, serpentinite-bearing foliated clay gouge and black fine-grained fault rock derived from sheared Franciscan Formation or serpentinized Coast Range Ophiolite. X-ray diffraction of outcrop samples shows that the foliated clay gouge is composed primarily of saponite and serpentinite, with localized increases in Ni-and Cr-oxides and C-rich material over several meters. Mesoscopic and microscopic textures and deformation mechanisms interpreted from the outcrop sites are remarkably similar to those observed in the SAFOD core. Microscale to meso-scale fabrics observed in the SAFOD core exhibit textural characteristics that are common in deformed serpentinites and are often attributed to aseismic deformation with episodic seismic slip. The mineralogy and whole-rock geochemistry results indicate that the fault zone experienced transient fluid-rock interactions with fluids of varying chemical composition, including evidence for highly reducing, hydrocarbon-bearing fluids.

show abstract

“…Fault gouge is composed of mineral fragments, typically including quartz, feldspar, and phyllosilicates resulting from comminution and alteration reactions. Some of the phyllosilicates are authigenic, suggesting an environment with aqueous components (Gratier et al, 2011;Janssen et al, 2012). In SAFOD material we also find extensively fractured quartz cataclasites, such as the sample studied here (hole E, run 1, section 6, Dressen, at 3141 m; www.earthscope.org/science /data/data-access/safod-data/) that stems from the Great Valley Formation in the damage zone, ~50 m from the currently active southwest deforming zone (e.g., Zoback et al, 2011, their figures 3 and 5).…”

Section: Introductionmentioning

confidence: 99%

Residual stress preserved in quartz from the San Andreas Fault Observatory at Depth

Chen¹,

Kunz

Tamura

et al. 2015

Geology

Self Cite

View full text Add to dashboard Cite

We report on measurements of residual stress up to 300 MPa with a microfocused synchrotron X-ray beam in quartz fragments in a cataclasite from the damage zone of the San Andreas fault, California (USA). Samples were extracted from the San Andreas Fault Observatory at Depth drill core at a depth of 2.7 km. Stresses were derived from lattice distortions observed on Laue diffraction images. These stresses are distributed nonhomogeneously at the micron scale and are much higher than bulk-rock strengths of fault gouge, suggesting different processes at the microscopic and macroscopic scales. Our results indicate that residual lattice strain in quartz is a potential paleopiezometer to estimate stress in deformed rocks.

show abstract

Clay fabrics in SAFOD core samples

Cited by 27 publications

References 41 publications

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

Faulting processes in active faults – Evidences from TCDP and SAFOD drill core samples

Composition, Alteration, and Texture of Fault-Related Rocks from Safod Core and Surface Outcrop Analogs: Evidence for Deformation Processes and Fluid-Rock Interactions

Residual stress preserved in quartz from the San Andreas Fault Observatory at Depth

Contact Info

Product

Resources

About