Dynamic Evolution of Porosity in Lower-Crustal Faults During the Earthquake Cycle

Stephen Paul Michalchuk; Sascha Zertani; François Renard; Florian Fusseis; Alireza Chogani; Oliver Plümper; Luca Menegon

doi:10.1029/2023JB026809

Dynamic Evolution of Porosity in Lower-Crustal Faults During the Earthquake Cycle

Stephen Paul Michalchuk^*, Sascha Zertani, François Renard, Florian Fusseis, Alireza Chogani, Oliver Plümper, Luca Menegon

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Earthquake-induced fracturing of the dry and strong lower crust can transiently increase permeability for fluids to flow and trigger metamorphic and rheological transformations. However, little is known about the porosity that facilitates these transformations. We analyzed microstructures that have recorded the mechanisms generating porosity in the lower crust from a pristine pseudotachylyte (solidified earthquake-derived frictional melt) and a mylonitized pseudotachylyte from Lofoten, Norway to understand the evolution of fluid pathways from the coseismic to the post- and interseismic stages of the earthquake cycle. Porosity is dispersed and poorly interconnected within the pseudotachylyte vein (0.14 vol%), with a noticeably increased amount along garnet grain boundaries (0.25–0.41 vol%). This porosity formed due to a net negative volume change at the grain boundary when garnet overgrows the pseudotachylyte matrix. Efficient healing of the damage zone by fluid-assisted growth of feldspar neoblasts resulted in the preservation of only a few but relatively large interconnected pores along coseismic fractures (0.03 vol% porosity). In contrast, porosity in the mylonitized pseudotachylyte is dramatically reduced (0.02 vol% overall), because of the efficient precipitation of phases (amphibole, biotite and feldspars) into transient pores during grain-size sensitive creep. Porosity reduction on the order of >85% may be a contributing factor in shear zone hardening, potentially leading to the development of new pseudotachylytes overprinting the mylonites. Our results show that earthquake-induced rheological weakening of the lower crust is intermittent and occurs when a fluid can infiltrate a transiently permeable shear zone, thereby facilitating diffusive mass transfer and creep.

Original language	English
Article number	e2023JB026809
Number of pages	19
Journal	Journal of Geophysical Research: Solid Earth
Volume	128
Issue number	8
DOIs	https://doi.org/10.1029/2023JB026809
Publication status	Published - Aug 2023

Bibliographical note

Funding Information:
We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB‐SEM access was Granted by the European Plate Observing System—Netherlands ( www.EPOS-NL.nl ). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø.

Funding Information:
We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB-SEM access was Granted by the European Plate Observing System—Netherlands (www.EPOS-NL.nl). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø.

Publisher Copyright:
© 2023. The Authors.

Funding

We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB‐SEM access was Granted by the European Plate Observing System—Netherlands ( www.EPOS-NL.nl ). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø. We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB-SEM access was Granted by the European Plate Observing System—Netherlands (www.EPOS-NL.nl). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø.

Keywords

earthquake
fluid-rock interaction
lower crust
porosity
pseudotachylyte
shear zone

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10.1029/2023JB026809Licence: CC BY

JGR Solid Earth - 2023 - MichalchukFinal published version, 5.92 MBLicence: CC BY

Cite this

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title = "Dynamic Evolution of Porosity in Lower-Crustal Faults During the Earthquake Cycle",

abstract = "Earthquake-induced fracturing of the dry and strong lower crust can transiently increase permeability for fluids to flow and trigger metamorphic and rheological transformations. However, little is known about the porosity that facilitates these transformations. We analyzed microstructures that have recorded the mechanisms generating porosity in the lower crust from a pristine pseudotachylyte (solidified earthquake-derived frictional melt) and a mylonitized pseudotachylyte from Lofoten, Norway to understand the evolution of fluid pathways from the coseismic to the post- and interseismic stages of the earthquake cycle. Porosity is dispersed and poorly interconnected within the pseudotachylyte vein (0.14 vol%), with a noticeably increased amount along garnet grain boundaries (0.25–0.41 vol%). This porosity formed due to a net negative volume change at the grain boundary when garnet overgrows the pseudotachylyte matrix. Efficient healing of the damage zone by fluid-assisted growth of feldspar neoblasts resulted in the preservation of only a few but relatively large interconnected pores along coseismic fractures (0.03 vol% porosity). In contrast, porosity in the mylonitized pseudotachylyte is dramatically reduced (0.02 vol% overall), because of the efficient precipitation of phases (amphibole, biotite and feldspars) into transient pores during grain-size sensitive creep. Porosity reduction on the order of >85% may be a contributing factor in shear zone hardening, potentially leading to the development of new pseudotachylytes overprinting the mylonites. Our results show that earthquake-induced rheological weakening of the lower crust is intermittent and occurs when a fluid can infiltrate a transiently permeable shear zone, thereby facilitating diffusive mass transfer and creep.",

keywords = "earthquake, fluid-rock interaction, lower crust, porosity, pseudotachylyte, shear zone",

author = "Michalchuk, {Stephen Paul} and Sascha Zertani and Fran{\c c}ois Renard and Florian Fusseis and Alireza Chogani and Oliver Pl{\"u}mper and Luca Menegon",

note = "Funding Information: We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB‐SEM access was Granted by the European Plate Observing System—Netherlands ( www.EPOS-NL.nl ). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Troms{\o}. Funding Information: We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB-SEM access was Granted by the European Plate Observing System—Netherlands (www.EPOS-NL.nl). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Troms{\o}. Publisher Copyright: {\textcopyright} 2023. The Authors.",

year = "2023",

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language = "English",

volume = "128",

journal = "Journal of Geophysical Research: Solid Earth",

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T1 - Dynamic Evolution of Porosity in Lower-Crustal Faults During the Earthquake Cycle

AU - Michalchuk, Stephen Paul

AU - Zertani, Sascha

AU - Renard, François

AU - Fusseis, Florian

AU - Chogani, Alireza

AU - Plümper, Oliver

AU - Menegon, Luca

N1 - Funding Information: We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB‐SEM access was Granted by the European Plate Observing System—Netherlands ( www.EPOS-NL.nl ). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø. Funding Information: We gratefully thank Melanie Finch and Bruce Yardley for their constructive reviews that improved the manuscript, and Yves Bernabe for editorial handling. Funding for this study was received from the UK Natural Environment Research Council (NERC project “The Geological Record of the Earthquake Cycle in the Lower Crust,” Grant NE/P001548/1 to LM) and from the University of Oslo. The Research Council of Norway is acknowledged for support to the Goldschmidt Laboratory national infrastructure (project number 295894). FIB-SEM access was Granted by the European Plate Observing System—Netherlands (www.EPOS-NL.nl). SZ acknowledges funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation; Grant 461241592). This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant 101019628 BREAK to FR), and an ERC starting Grant (Grant 852069 nanoEARTH to OP). Amicia Lee and the SEM staff are thanked for support during the acquisition of the EBSD data at the University of Tromsø. Publisher Copyright: © 2023. The Authors.

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N2 - Earthquake-induced fracturing of the dry and strong lower crust can transiently increase permeability for fluids to flow and trigger metamorphic and rheological transformations. However, little is known about the porosity that facilitates these transformations. We analyzed microstructures that have recorded the mechanisms generating porosity in the lower crust from a pristine pseudotachylyte (solidified earthquake-derived frictional melt) and a mylonitized pseudotachylyte from Lofoten, Norway to understand the evolution of fluid pathways from the coseismic to the post- and interseismic stages of the earthquake cycle. Porosity is dispersed and poorly interconnected within the pseudotachylyte vein (0.14 vol%), with a noticeably increased amount along garnet grain boundaries (0.25–0.41 vol%). This porosity formed due to a net negative volume change at the grain boundary when garnet overgrows the pseudotachylyte matrix. Efficient healing of the damage zone by fluid-assisted growth of feldspar neoblasts resulted in the preservation of only a few but relatively large interconnected pores along coseismic fractures (0.03 vol% porosity). In contrast, porosity in the mylonitized pseudotachylyte is dramatically reduced (0.02 vol% overall), because of the efficient precipitation of phases (amphibole, biotite and feldspars) into transient pores during grain-size sensitive creep. Porosity reduction on the order of >85% may be a contributing factor in shear zone hardening, potentially leading to the development of new pseudotachylytes overprinting the mylonites. Our results show that earthquake-induced rheological weakening of the lower crust is intermittent and occurs when a fluid can infiltrate a transiently permeable shear zone, thereby facilitating diffusive mass transfer and creep.

AB - Earthquake-induced fracturing of the dry and strong lower crust can transiently increase permeability for fluids to flow and trigger metamorphic and rheological transformations. However, little is known about the porosity that facilitates these transformations. We analyzed microstructures that have recorded the mechanisms generating porosity in the lower crust from a pristine pseudotachylyte (solidified earthquake-derived frictional melt) and a mylonitized pseudotachylyte from Lofoten, Norway to understand the evolution of fluid pathways from the coseismic to the post- and interseismic stages of the earthquake cycle. Porosity is dispersed and poorly interconnected within the pseudotachylyte vein (0.14 vol%), with a noticeably increased amount along garnet grain boundaries (0.25–0.41 vol%). This porosity formed due to a net negative volume change at the grain boundary when garnet overgrows the pseudotachylyte matrix. Efficient healing of the damage zone by fluid-assisted growth of feldspar neoblasts resulted in the preservation of only a few but relatively large interconnected pores along coseismic fractures (0.03 vol% porosity). In contrast, porosity in the mylonitized pseudotachylyte is dramatically reduced (0.02 vol% overall), because of the efficient precipitation of phases (amphibole, biotite and feldspars) into transient pores during grain-size sensitive creep. Porosity reduction on the order of >85% may be a contributing factor in shear zone hardening, potentially leading to the development of new pseudotachylytes overprinting the mylonites. Our results show that earthquake-induced rheological weakening of the lower crust is intermittent and occurs when a fluid can infiltrate a transiently permeable shear zone, thereby facilitating diffusive mass transfer and creep.

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Dynamic Evolution of Porosity in Lower-Crustal Faults During the Earthquake Cycle

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Bibliographical note

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Keywords

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