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On the criticality of return flows in viscous accretionary wedges and its implications for deep-crustal exhumation in subduction zones.

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Title: On the criticality of return flows in viscous accretionary wedges and its implications for deep-crustal exhumation in subduction zones.
Authors: Patsa, Ayan1 (AUTHOR), Mandal, Nibir1 (AUTHOR) nibir.mandal@jadavpuruniversity.in
Source: Solid Earth. 2026, Vol. 17 Issue 3, p573-600. 28p.
Subjects: Accretionary wedges (Geology), Subduction zones, Tectonic exhumation, Viscous flow, Fluid flow, Structural geology, Rheology
Abstract: In subduction zones, the accretionary wedges play a vital role in mediating the burial processes of incoming oceanic sediments and eventually their return pathways to the surface. A direction of the previous tectonic models invoked the standard corner flow theory, assuming a slab-parallel shear and a rigid, fixed overriding plate, to elucidate the crustal recycling processes in tectonic wedges. To deal with more complex subduction-collisional settings, where they have deformable overriding plates, and associate a horizontal slab migration (advance or rollback) component during subduction, we develop a generalized corner flow model to revisit the problem of return flow mechanics, providing a criticality analysis of the return flows as a function of the geometric, kinematic, and rheological conditions in accretionary wedges. A new set of analytical solutions is presented to evaluate the limiting conditions in which a wedge can set in significant return flows, leading to focused exhumation of the deep-crustal materials. The theoretical results suggest that, for moderate wedge-taper angles (∼30 °), the viscosity ratios (μr) between the overriding plate and the wedge ≥∼103 provide favourable tectonic settings for the return flow kinematics in accretionary wedges. Decrease in μr , or addition of slab roll back weakens the return flows, whereas slab advance greatly strengthens the return flows. The analytical solutions are also utilized to demonstrate reversals in the shear-sense patterns across the wedge. We expand this study by incorporating results from scaled laboratory experiments to evaluate applicability of the generalized theoretical model. It is shown from the theoretical model that the total pressure in the accretionary wedge dynamics becomes close to the lithostatic value when the rheological setting has low-viscosity (1019 Pa s) wedge materials. [ABSTRACT FROM AUTHOR]
Copyright of Solid Earth is the property of Copernicus Gesellschaft mbH and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: On the criticality of return flows in viscous accretionary wedges and its implications for deep-crustal exhumation in subduction zones.
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  Data: <searchLink fieldCode="JN" term="%22Solid+Earth%22">Solid Earth</searchLink>. 2026, Vol. 17 Issue 3, p573-600. 28p.
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  Data: <searchLink fieldCode="DE" term="%22Accretionary+wedges+%28Geology%29%22">Accretionary wedges (Geology)</searchLink><br /><searchLink fieldCode="DE" term="%22Subduction+zones%22">Subduction zones</searchLink><br /><searchLink fieldCode="DE" term="%22Tectonic+exhumation%22">Tectonic exhumation</searchLink><br /><searchLink fieldCode="DE" term="%22Viscous+flow%22">Viscous flow</searchLink><br /><searchLink fieldCode="DE" term="%22Fluid+flow%22">Fluid flow</searchLink><br /><searchLink fieldCode="DE" term="%22Structural+geology%22">Structural geology</searchLink><br /><searchLink fieldCode="DE" term="%22Rheology%22">Rheology</searchLink>
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  Data: In subduction zones, the accretionary wedges play a vital role in mediating the burial processes of incoming oceanic sediments and eventually their return pathways to the surface. A direction of the previous tectonic models invoked the standard corner flow theory, assuming a slab-parallel shear and a rigid, fixed overriding plate, to elucidate the crustal recycling processes in tectonic wedges. To deal with more complex subduction-collisional settings, where they have deformable overriding plates, and associate a horizontal slab migration (advance or rollback) component during subduction, we develop a generalized corner flow model to revisit the problem of return flow mechanics, providing a criticality analysis of the return flows as a function of the geometric, kinematic, and rheological conditions in accretionary wedges. A new set of analytical solutions is presented to evaluate the limiting conditions in which a wedge can set in significant return flows, leading to focused exhumation of the deep-crustal materials. The theoretical results suggest that, for moderate wedge-taper angles (∼30 °), the viscosity ratios (μr) between the overriding plate and the wedge ≥∼103 provide favourable tectonic settings for the return flow kinematics in accretionary wedges. Decrease in μr , or addition of slab roll back weakens the return flows, whereas slab advance greatly strengthens the return flows. The analytical solutions are also utilized to demonstrate reversals in the shear-sense patterns across the wedge. We expand this study by incorporating results from scaled laboratory experiments to evaluate applicability of the generalized theoretical model. It is shown from the theoretical model that the total pressure in the accretionary wedge dynamics becomes close to the lithostatic value when the rheological setting has low-viscosity (1019 Pa s) wedge materials. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: <i>Copyright of Solid Earth is the property of Copernicus Gesellschaft mbH and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.5194/se-17-573-2026
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      – Code: eng
        Text: English
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        PageCount: 28
        StartPage: 573
    Subjects:
      – SubjectFull: Accretionary wedges (Geology)
        Type: general
      – SubjectFull: Subduction zones
        Type: general
      – SubjectFull: Tectonic exhumation
        Type: general
      – SubjectFull: Viscous flow
        Type: general
      – SubjectFull: Fluid flow
        Type: general
      – SubjectFull: Structural geology
        Type: general
      – SubjectFull: Rheology
        Type: general
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      – TitleFull: On the criticality of return flows in viscous accretionary wedges and its implications for deep-crustal exhumation in subduction zones.
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            NameFull: Patsa, Ayan
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            NameFull: Mandal, Nibir
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            – D: 01
              M: 03
              Text: 2026
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              Y: 2026
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