Time‐Lapse Record of an Earthquake in the Dry Felsic Lower Continental Crust Preserved in a Pseudotachylyte‐Bearing Fault

Mancktelow, Neil S.; Camacho, Alfredo; Pennacchioni, Giorgio

doi:10.1029/2021jb022878

Cited by 12 publications

(15 citation statements)

References 132 publications

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“…Recently, Dunkel et al 16 reported textures indicative of seismic faulting in dry lower crustal rocks from the Lofoten Archipelago in the Northern Norwegian Caledonides, indicating very high (≥1 GPa) stress levels and therefore suggesting that the lower crust was strong, not weak 17 . Similar suggestions have been made also for other field areas where dry, lower-crustal lithologies occur 18,19 . For the Bergen Arcs of Western Norway, such high stress levels were recently demonstrated directly by the presence of highly overpressured frictional melts along lower crustal faults 20 .…”

supporting

confidence: 85%

“…With ongoing deformation, stresses build up until the yield stress is reached. Field observations demonstrate that this is followed by dynamic rupturing and highly localized seismic slip 19,39 . Associated wall rock damage allows fluid infiltration, metamorphic hydration reaction, and mechanical weakening of a 0.1-1 m wide zone of wall rocks 8 .…”

Section: Resultsmentioning

confidence: 99%

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Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

Jamtveit

Moulas

Kaus

2023

Preprint

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When continents collide, the Earth&#8217;s crust experiences structural and metamorphic transformations that control the geodynamic evolution of the orogen. Metamorphism of dry, lower crust requires fluid supply and produce mechanically weaker rocks. Metamorphism is often localized in shear-zones, which provide the available fluid pathways. Several field-based studies show that shear zone development is preceded by brittle faults, frequently portraying evidence for seismic slip rates and introduction of externally derived fluids. However, despite the extensive documentation of lower crustal metamorphism and associated deformation features, a unifying model coupling deformation to fluid migration and metamorphic reactions does not exist. Here, we present a visco-elasto-plastic model where the most pertinent features observed in transformed lower crust emerge from basic mechanical principles during the deformation of a coherent rock volume with associated fluid introduction. Characteristic features include a strikingly dynamic and heterogeneous pressure distribution in the reacting and deforming rock volumes. Lower crustal pressure variations may reach 1 GPa at any given depth. This will have first order effects on the pattern of fluid migration in the lower crust, and may also explain the apparent discrepancies between the relevant tectonic settings and petrologically-inferred burial depths. An additional petrological consequence of the positive pressure variations is the generation of fluid-undersaturated high-pressure assemblages. For common bulk-rock compositions that are observed in the Bergen Arcs (Norway), and for finite amounts of fluid, phase equilibria modelling results suggest that the quasi-isothermal pressurization will lead to the formation of H2O-undersaturated metamorphic rocks. These results highlight the importance of coupling between metamorphic reaction progress and deformation at high-grade conditions. &#160; &#160; Acknowledgements: This project was supported by a research award from the Alexander von Humboldt foundation to BJ, by ERC Advanced Grant Agreement n&#176;669972 to Jamtveit and ERC Consolidator Grant Agreement n&#176;771143 to Kaus from the European Union&#8217;s Horizon 2020 Research and Innovation Programme. Parts of this research were conducted using the supercomputer MOGON2 and/or advisory services offered by Johannes Gutenberg University Mainz (hpc.uni-mainz.de), which is a member of the AHRP (Alliance for High Performance Computing in Rhineland Palatinate, www.ahrp.info) and the Gauss Alliance e.V. Andrew Putnis and H&#229;kon Austrheim are acknowledged for numerous discussions. &#160; References: Moulas, E., Kaus, B., Jamtveit, B., 2022. Dynamic pressure variations in the lower crust caused by localized fluid-induced weakening. Communications Earth & Environment 3, 157. https://doi.org/10.1038/s43247-022-00478-7

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supporting

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

Jamtveit

Moulas

Kaus

2023

Preprint

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“…Interpretations of pulverization of single grains have recently accumulated from microstructural studies of lower crustal earthquakes in both naturally and experimentally deformed rocks (Austrheim et al., 2017; Incel et al., 2019; Petley‐Ragan et al., 2019; B. R. Song et al., 2020; Soda & Okudaira, 2018). Minerals observed to undergo pulverization‐style fragmentation include plagioclase (Pittarello et al., 2008; Soda & Okudaira, 2018; B. R. Song et al., 2020), garnet (Austrheim et al., 2017; Incel et al., 2019; Manktelow et al., 2022; Petley‐Ragan et al., 2019; B. R. Song et al., 2020) and diopside (Petley‐Ragan et al., 2019). In the Nusfjord samples, orthopyroxene is the only mineral to show microstructures compatible with pulverization style fragmentation, although on a centimeter‐scale the wider anorthosite is intensely fractured in places.…”

Section: Discussionmentioning

confidence: 99%

“…Such stress magnitudes prior to rupture have been implied by field characterization of pseudotachylyte‐bearing faults (Campbell et al., 2020) and, perhaps more commonly, are also associated with deformation linked to coseismic loading once rupture propagation has initiated (e.g., Anderson et al., 2021). This microstructural record of progressive and transient stress variation throughout the earthquake cycle (Anderson et al., 2021; Bestmann et al., 2012; Brückner & Trepmann, 2021; Campbell & Menegon, 2019; Johnson et al., 2021; Mancktelow et al., 2022; Petley‐Ragan et al., 2019) offers an under‐explored opportunity to further constrain deformation mechanisms and conditions associated with both prerupture stress amplification and coseismic rupture within the lower crust.…”

Section: Introductionmentioning

confidence: 99%

High Stress Deformation and Short‐Term Thermal Pulse Preserved in Pyroxene Microstructures From Exhumed Lower Crustal Seismogenic Faults (Lofoten, Norway)

Campbell

Menegon

2022

JGR Solid Earth

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Relocations of earthquakes, the study of focal mechanisms, and increased recognition of the geological signature of earthquakes recorded in exhumed lower crustal settings have promoted various models for nucleating seismic rupture within otherwise typically viscous deformation conditions. Many of these models require stress amplification or transfer, whether driven by local rheological heterogeneities across a shear zone network (Campbell

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“…Under lower crustal conditions, most rock-forming minerals such as quartz and feldspars deform by ductile creep, which can obscure microstructures associated with seismic events (Kirkpatrick and Rowe, 2013). Garnet, notably, is considered mechanically and chemically stable under elevated temperatures and commonly preserves microstructures related to seismicity (e.g., Mancktelow et al, 2022;Trepmann and Stöckhert, 2002). Although garnet is not the most predominant mineral in the lower crust, it becomes increasingly important with depth constituting a large modal proportion in metamorphosed rocks (up to 50%; Villaseca et al, 1999) and is assumed to play a significant role in crustal strengthening (e.g., Ingrin and Madon, 1995;Jin et al, 2001;Ji et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

A new mechanism for brittle failure in garnets

Dubosq¹,

Camacho²,

Gault³

2023

Preprint

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Garnet is a high-strength mineral and preserves structures that can consequently be used to understand the flow strength and evolution of stress within the lower crust. Yet, the deformation mechanisms at the brittle¬-ductile transition of garnet remain ambiguous. Here, we study garnet porphyroclasts from an eclogite facies mylonite (central Australia) to investigate the mechanisms by which garnet is deformed under relatively dry, lower crustal conditions. Electron backscatter diffraction analysis reveals bands of small, relatively strain-free garnet with scattered orientations, outlined by polygonal to lobate high-angle grain boundaries cross-cutting the garnet porphyroclasts. Atom probe tomography of a high-angle grain boundary shows Fe enrichment in the form of planar and equally spaced arrays of Fe-rich nanoclusters. Our experiments demonstrate Fe segregation along grain boundaries of garnet, resulting in the nucleation of Fe-rich nanoclusters that can act as barriers for migrating dislocations which leads to strain-hardening that facilitates mechanical failure. The occurrence of strain-hardening in garnet potentially contributes to crustal strengthening that can lead to seismicity at depths.

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Time‐Lapse Record of an Earthquake in the Dry Felsic Lower Continental Crust Preserved in a Pseudotachylyte‐Bearing Fault

Cited by 12 publications

References 132 publications

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

Dynamic Pressure Variations in the Lower Crust Caused by Localized Fluid-Induced Weakening

High Stress Deformation and Short‐Term Thermal Pulse Preserved in Pyroxene Microstructures From Exhumed Lower Crustal Seismogenic Faults (Lofoten, Norway)

A new mechanism for brittle failure in garnets

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