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Control of Fault Weakening on the Structural Styles of Underthrusting-Dominated Non-Cohesive Accretionary Wedges

Bauville, Arthur and Mikito, Furuichi and Gerbault, Muriel Control of Fault Weakening on the Structural Styles of Underthrusting-Dominated Non-Cohesive Accretionary Wedges. (2020) JGR solid earth, 125 (3). 1-27. ISSN 2169-9356

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Official URL: https://doi.org/10.1029/2019JB019220

Abstract

Underthrusting is a typical process at compressive margins responsible for nappe stacking and sediment subduction. In nature, underthrusting is often associated with weak basal faults, although static mechanical analysis (critical taper theory) suggests that weak basal faults promote accretion while strong basal faults promote underthrusting. We perform mathematical analyses and numerical simulations to determine whether permanent fault weakening promotes or inhibits underthrusting. We investigate the control of permanent fault weakening on the dynamics of a strong-based ( (1 − λ ∗ b )μ b ≈ (1 − λ ∗ )μ ) non-cohesive wedge ( μ and μ b are internal and basal friction, respectively). We control the wedge material strength by a spatially constant fluid overpressure factor ( λ ∗ ), and fault strength by a plastic strain weakening factor ( χ ). First, we use the critical taper theory to determine a mechanical mode diagram that predicts structural styles. Then, we perform numerical simulations of accretionary wedge formation to establish their dynamical structural characteristics. We determine a continuum of structural styles between three end-members which correspond to the theoretical mechanical mode transitions. Style 1 is characterized by thin tectonic slices and little to no underthrusting. Style 2 shows thick slices, nappe stacking, and shallow gravity-driven tectonics. Style 3 displays the complete underthrusting of the incoming sediments, that are exhumed when they reach the backstop. We conclude that in the condition of an initially strong wedge base, permanent fault weakening promotes underthrusting. Thus, this contribution enlightens the control of the dynamic evolution of material properties on the formation of subduction channels, slope instabilities, and antiformal nappe stacks.

Item Type:Article
HAL Id:hal-03174355
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
French research institutions > Institut de Recherche pour le Développement - IRD (FRANCE)
Other partners > Japan Agency for Marine-Earth Science and Technology - JAMSTEC (JAPAN)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
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Japanese Society for the Promotion of Science - JSPS - Swiss National Science Foundation - SNF
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Deposited On:19 Mar 2021 09:25

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