Lithospheric strength and stress revisited: Pruning the Christmas tree

Wang, K.; Ellis, Susan

doi:10.1016/j.epsl.2022.117771

Cited by 8 publications

(5 citation statements)

References 47 publications

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“…We have also not included any visco-elastic effects [e.g. Kusznir, 1991;Ellis and Wang, 2022] and assume that the deflection of the lithosphere can be modelled by static loading. Visco-elasticity has the effect of introducing time-dependence to the stress distribution following the application of a load, such that stresses associated with past episodes of loading can remain 'frozen in' to the lithosphere.…”

Section: Modelling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

“…Visco-elasticity has the effect of introducing time-dependence to the stress distribution following the application of a load, such that stresses associated with past episodes of loading can remain 'frozen in' to the lithosphere. Ellis and Wang [2022] showed that the time-scale for the change in stress state within the cold, elastic portion of cratonic lithosphere following a change in horizontal loading is on the order of ∼5-10 Myrs.…”

Section: Modelling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

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Lower-Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

Wimpenny,

Craig,

Blackwell

2023

Preprint

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Earthquakes beneath the foreland basins of the Andes and Tibet follow a simple pattern, with normal-faulting events from 0--20 km depth and reverse-faulting events from 30--50 km depth. The switch in faulting style with depth suggests that the elastic stresses generated by flexure within these forelands are large enough to break faults, with opposite senses of horizontal strain either side of a neutral fibre in the mid-crust. In this study, we document a 31 km-deep Mw 5.2 normal-faulting earthquake in the forelands of the Algerian Atlas Mountains near Biskra. The Biskra earthquake is of interest, as it indicates that the lower crust of the Atlas forelands is seismogenic and in extension at the same depth that the Tibetan and Andean forelands are in compression. In order to match the shape of the gravity anomaly and the depth of normal faulting in the Algerian foreland, we find that models of lithospheric flexure require the neutral fibre to be >35 km deep in places and at least the top 5--10 km of the lithospheric mantle supports elastic stresses without yielding. The differences in the depth-extent of normal-faulting earthquakes between the forelands of Tibet, the Andes and the Algerian Atlas can be explained solely by differences in the buoyancy forces acting between these mountain ranges and their lowlands that place the foreland lithosphere into varying amounts of net compression. The upper mantle beneath cratonic foreland lithosphere may therefore support bending stresses of the order of 10's of MPa, likely because it is cool and the strain rates associated with bending are low.

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Section: Modelling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

Section: Modelling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

Lower-Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

Wimpenny,

Craig,

Blackwell

2023

Preprint

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“…We have also not included any visco‐elastic effects (e.g., Kusznir, 1991; Ellis & Wang, 2022) and assume that the deflection of the lithosphere can be modeled by static loading. Visco‐elasticity has the effect of introducing time‐dependence to the stress distribution following the application of a load, such that stresses associated with past episodes of loading can remain “frozen in” to the lithosphere.…”

Section: Modeling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

“…Visco‐elasticity has the effect of introducing time‐dependence to the stress distribution following the application of a load, such that stresses associated with past episodes of loading can remain “frozen in” to the lithosphere. Ellis and Wang (2022) showed that the time‐scale for the change in stress state within the cold, elastic portion of cratonic lithosphere following a change in horizontal loading is on the order of ∼5–10 Myrs. Given that the Atlas and its forelands have been undergoing shortening and loading in the current tectonic configuration throughout the Cenozoic, and given that we are not trying to derive the values of the loads but rather the stresses within the plate, then we believe it is reasonable to model the loads using a static approximation (see also Monsalve et al., 2009).…”

Section: Modeling Of the Stresses In The Atlas Forelandmentioning

confidence: 99%

Lower‐Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

Wimpenny,

Craig,

Blackwell

2023

JGR Solid Earth

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Earthquakes beneath the foreland basins of the Andes and Tibet are rare but follow a simple pattern, with normal faulting from 0 to 20 km depth and reverse‐faulting from 30 to 50 km depth. The switch in faulting style with depth suggests that the stresses generated by foreland flexure are large enough to break faults, with opposite senses of horizontal strain either side of a neutral surface in the mid‐crust. In this study, we document a 31 km‐deep Mw 5.2 normal‐faulting earthquake in the forelands of the Algerian Atlas Mountains near Biskra. The Biskra earthquake is of interest, as it indicates that the lower crust of the Atlas forelands is in extension at the same depth that the Tibetan and Andean forelands are in compression. In order to match the gravity anomalies and the depth of normal faulting near Biskra, we find that models of lithospheric flexure require the neutral surface to be >35 km deep and at least the top 5–10 km of the lithospheric mantle supports elastic bending stresses. The differences in the pattern of earthquakes between the forelands of Tibet, the Andes and the Algerian Atlas can be explained by differences in the buoyancy forces acting between these mountain ranges and their lowlands that place the forelands into varying amounts of net compression. Our results suggest the upper mantle beneath cratonic foreland lithosphere may therefore support bending stresses of the order of 10s of MPa, likely because it is cool and the strain rates associated with bending are low.

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“…In this model, the lithosphere is assumed to be a single uniform layer with an upper brittle part that follows a law of static friction (i.e., Byerlee's law) and a lower ductile part that follows a viscous flow law (Byerlee, 1978;Wang, 2021). In truth, the lithosphere consists of multiple layers where brittle and ductile behaviour alternate (e.g., Bürgmann and Dresen, 2008;Kohlstedt et al, 1995;Ellis and Wang, 2022). Other more sophisticated forms of the strength profile for the continental lithosphere have been proposed including the well-known "jelly sandwich" and "crème brûlée" models (Burov and Watts, 2006;Jackson, 2002).…”

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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Lithospheric strength and stress revisited: Pruning the Christmas tree

Cited by 8 publications

References 47 publications

Lower-Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

Lower-Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

Lower‐Crustal Normal Faulting and Lithosphere Rheology in the Atlas Foreland

A new mechanism for brittle failure in garnets

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