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Georg Dresen - One of the best experts on this subject based on the ideXlab platform.

  • Clay fabrics in SAFOD Core Samples
    Journal of Structural Geology, 2012
    Co-Authors: C. Janssen, Erik Rybacki, Hans-rudolf Wenk, Richard Wirth, Waruntorn Kanitpanyacharoen, Luiz F. G. Morales, M. Kienast, Georg Dresen
    Abstract:

    With optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements, we analyzed clay microfabrics in ultracataclastic/gouge and cataclastic Core Samples obtained from the main bore hole of the San Andreas Fault observatory at depth (SAFOD). The analysis reveals a significant contrast between weak clay fabrics observed in the Core Samples with synchrotron X-ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope. TEM and SEM observations also show distinct zones of locally aligned and randomly oriented clay minerals. The lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks. The presence of weak fabrics in intensely strained ultracataclasites/fault gouges is attributed to 1) newly formed clay minerals that grew in many orientations, 2) folded and kinked clay minerals, and 3) clay particles that are wrapped around grains. In addition, the locally aligned clay particles may act as barriers to fluid flow, which in turn decrease porosity, expel intergranular pore fluids, and consequently, may increase fluid pressure.

  • nanoscale porosity in safod Core Samples san andreas fault
    Earth and Planetary Science Letters, 2011
    Co-Authors: C. Janssen, Erik Rybacki, Rudolf Naumann, Richard Wirth, Andreas Reinicke, H R Wenk, Georg Dresen
    Abstract:

    article i nfo With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured Core Samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10 − 21 -10 − 19 m 2 and 10 − 17 m 2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the Samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radiusN 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radiusb 50 nm) are typically observed in the extremely fine-grained matrix (grain sizeb 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/ desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V. All rights reserved.

  • Amorphous material in SAFOD Core Samples (San Andreas Fault): Evidence for crush‐origin pseudotachylytes?
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

  • amorphous material in safod Core Samples san andreas fault evidence for crush origin pseudotachylytes
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

C. Janssen - One of the best experts on this subject based on the ideXlab platform.

  • Clay fabrics in SAFOD Core Samples
    Journal of Structural Geology, 2012
    Co-Authors: C. Janssen, Erik Rybacki, Hans-rudolf Wenk, Richard Wirth, Waruntorn Kanitpanyacharoen, Luiz F. G. Morales, M. Kienast, Georg Dresen
    Abstract:

    With optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements, we analyzed clay microfabrics in ultracataclastic/gouge and cataclastic Core Samples obtained from the main bore hole of the San Andreas Fault observatory at depth (SAFOD). The analysis reveals a significant contrast between weak clay fabrics observed in the Core Samples with synchrotron X-ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope. TEM and SEM observations also show distinct zones of locally aligned and randomly oriented clay minerals. The lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks. The presence of weak fabrics in intensely strained ultracataclasites/fault gouges is attributed to 1) newly formed clay minerals that grew in many orientations, 2) folded and kinked clay minerals, and 3) clay particles that are wrapped around grains. In addition, the locally aligned clay particles may act as barriers to fluid flow, which in turn decrease porosity, expel intergranular pore fluids, and consequently, may increase fluid pressure.

  • nanoscale porosity in safod Core Samples san andreas fault
    Earth and Planetary Science Letters, 2011
    Co-Authors: C. Janssen, Erik Rybacki, Rudolf Naumann, Richard Wirth, Andreas Reinicke, H R Wenk, Georg Dresen
    Abstract:

    article i nfo With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured Core Samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10 − 21 -10 − 19 m 2 and 10 − 17 m 2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the Samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radiusN 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radiusb 50 nm) are typically observed in the extremely fine-grained matrix (grain sizeb 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/ desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V. All rights reserved.

  • Amorphous material in SAFOD Core Samples (San Andreas Fault): Evidence for crush‐origin pseudotachylytes?
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

  • amorphous material in safod Core Samples san andreas fault evidence for crush origin pseudotachylytes
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

Richard Wirth - One of the best experts on this subject based on the ideXlab platform.

  • Clay fabrics in SAFOD Core Samples
    Journal of Structural Geology, 2012
    Co-Authors: C. Janssen, Erik Rybacki, Hans-rudolf Wenk, Richard Wirth, Waruntorn Kanitpanyacharoen, Luiz F. G. Morales, M. Kienast, Georg Dresen
    Abstract:

    With optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements, we analyzed clay microfabrics in ultracataclastic/gouge and cataclastic Core Samples obtained from the main bore hole of the San Andreas Fault observatory at depth (SAFOD). The analysis reveals a significant contrast between weak clay fabrics observed in the Core Samples with synchrotron X-ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope. TEM and SEM observations also show distinct zones of locally aligned and randomly oriented clay minerals. The lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks. The presence of weak fabrics in intensely strained ultracataclasites/fault gouges is attributed to 1) newly formed clay minerals that grew in many orientations, 2) folded and kinked clay minerals, and 3) clay particles that are wrapped around grains. In addition, the locally aligned clay particles may act as barriers to fluid flow, which in turn decrease porosity, expel intergranular pore fluids, and consequently, may increase fluid pressure.

  • nanoscale porosity in safod Core Samples san andreas fault
    Earth and Planetary Science Letters, 2011
    Co-Authors: C. Janssen, Erik Rybacki, Rudolf Naumann, Richard Wirth, Andreas Reinicke, H R Wenk, Georg Dresen
    Abstract:

    article i nfo With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured Core Samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10 − 21 -10 − 19 m 2 and 10 − 17 m 2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the Samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radiusN 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radiusb 50 nm) are typically observed in the extremely fine-grained matrix (grain sizeb 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/ desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V. All rights reserved.

  • Amorphous material in SAFOD Core Samples (San Andreas Fault): Evidence for crush‐origin pseudotachylytes?
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

  • amorphous material in safod Core Samples san andreas fault evidence for crush origin pseudotachylytes
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

Erik Rybacki - One of the best experts on this subject based on the ideXlab platform.

  • Clay fabrics in SAFOD Core Samples
    Journal of Structural Geology, 2012
    Co-Authors: C. Janssen, Erik Rybacki, Hans-rudolf Wenk, Richard Wirth, Waruntorn Kanitpanyacharoen, Luiz F. G. Morales, M. Kienast, Georg Dresen
    Abstract:

    With optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements, we analyzed clay microfabrics in ultracataclastic/gouge and cataclastic Core Samples obtained from the main bore hole of the San Andreas Fault observatory at depth (SAFOD). The analysis reveals a significant contrast between weak clay fabrics observed in the Core Samples with synchrotron X-ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope. TEM and SEM observations also show distinct zones of locally aligned and randomly oriented clay minerals. The lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks. The presence of weak fabrics in intensely strained ultracataclasites/fault gouges is attributed to 1) newly formed clay minerals that grew in many orientations, 2) folded and kinked clay minerals, and 3) clay particles that are wrapped around grains. In addition, the locally aligned clay particles may act as barriers to fluid flow, which in turn decrease porosity, expel intergranular pore fluids, and consequently, may increase fluid pressure.

  • nanoscale porosity in safod Core Samples san andreas fault
    Earth and Planetary Science Letters, 2011
    Co-Authors: C. Janssen, Erik Rybacki, Rudolf Naumann, Richard Wirth, Andreas Reinicke, H R Wenk, Georg Dresen
    Abstract:

    article i nfo With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured Core Samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10 − 21 -10 − 19 m 2 and 10 − 17 m 2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the Samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radiusN 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radiusb 50 nm) are typically observed in the extremely fine-grained matrix (grain sizeb 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/ desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V. All rights reserved.

  • Amorphous material in SAFOD Core Samples (San Andreas Fault): Evidence for crush‐origin pseudotachylytes?
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

  • amorphous material in safod Core Samples san andreas fault evidence for crush origin pseudotachylytes
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

Rudolf Naumann - One of the best experts on this subject based on the ideXlab platform.

  • nanoscale porosity in safod Core Samples san andreas fault
    Earth and Planetary Science Letters, 2011
    Co-Authors: C. Janssen, Erik Rybacki, Rudolf Naumann, Richard Wirth, Andreas Reinicke, H R Wenk, Georg Dresen
    Abstract:

    article i nfo With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured Core Samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10 − 21 -10 − 19 m 2 and 10 − 17 m 2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the Samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radiusN 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radiusb 50 nm) are typically observed in the extremely fine-grained matrix (grain sizeb 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/ desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V. All rights reserved.

  • Amorphous material in SAFOD Core Samples (San Andreas Fault): Evidence for crush‐origin pseudotachylytes?
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.

  • amorphous material in safod Core Samples san andreas fault evidence for crush origin pseudotachylytes
    Geophysical Research Letters, 2010
    Co-Authors: C. Janssen, Erik Rybacki, Helga Kemnitz, Hans-rudolf Wenk, Rudolf Naumann, Richard Wirth, Georg Dresen
    Abstract:

    [1] Several types of amorphous material in ultracataclastic Core Samples recovered from 3194 m and 3294 m depth of the main bore hole of the San Andreas Fault Observatory at Depth are identified and described with transmission electron microscopy and scanning electron microscopy. We observed (1) amorphous material on a slickenside surface, (2) glassy bands contained in an ultracataclastic matrix and (3) amorphous rims surrounding quartz or feldspar clasts. Chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix. We suggest that all amorphous material was formed by comminution of clasts (crush-origin pseudotachylytes) rather than by melting (melt-origin pseudotachylytes). The observed amorphous phases may act as lubricating layers that reduce friction in the San Andreas Fault.