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Does subduction-induced mantle flow drive backarc extension?

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Title: Does subduction-induced mantle flow drive backarc extension?
Authors: Chen, Zhihao1 zhihao.chen@monash.edu, Schellart, Wouter P.1, Strak, Vincent1, Duarte, João C.1
Source: Earth & Planetary Science Letters. May2016, Vol. 441, p200-210. 11p.
Subjects: Subduction zones, Paleoseismology, Regolith, Particle image velocimetry, Stereoscope
Abstract: Backarc extension is a characteristic feature of many narrow subduction zones. Seismological and geochemical studies imply the occurrence of mantle flow around the narrow subducting slabs. Previous 3D models suggested that backarc extension is related to subduction-induced toroidal mantle flow. The physical viability of this mechanism, however, has never been tested using laboratory-based geodynamic models. In this work, we present dynamic laboratory models of progressive subduction in three-dimensional (3D) space that were carried out to test this mechanism. To achieve this, we have used a stereoscopic Particle Image Velocimetry (sPIV) technique to map simultaneously overriding plate deformation and 3D subduction-induced mantle flow underneath and around an overriding plate. The results show that the strain field of the overriding plate is characterized by the localization of an area of maximum extension within its interior (at 300–500 km from the trench). The position of maximum extension closely coincides (within ∼2 cm, scaling to 100 km) with that of the maximum trench-normal horizontal mantle velocity and velocity gradient measured at a scaled depth of 15–25 km below the base of the overriding plate, and the maximum horizontal gradient of the vertical mantle velocity gradient. We propound that in narrow subduction zones backarc extension in the overriding plate is mainly a consequence of the trench-normal horizontal gradients of basal drag force at the base of the overriding plate. Such shear force gradients result from a horizontal gradient in velocity in the mantle below the base of the lithosphere induced by slab rollback. Calculations based on our models indicate a tensional horizontal trench-normal deviatoric stress in the backarc region scaling to ∼28.8 MPa, while the overriding plate trench-normal stress resulting from the horizontal component of the trench suction force is about an order of magnitude smaller, scaling to ∼2.4–3.6 MPa. [ABSTRACT FROM AUTHOR]
Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. 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: Does subduction-induced mantle flow drive backarc extension?
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  Data: <searchLink fieldCode="AR" term="%22Chen%2C+Zhihao%22">Chen, Zhihao</searchLink><relatesTo>1</relatesTo><i> zhihao.chen@monash.edu</i><br /><searchLink fieldCode="AR" term="%22Schellart%2C+Wouter+P%2E%22">Schellart, Wouter P.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Strak%2C+Vincent%22">Strak, Vincent</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Duarte%2C+João+C%2E%22">Duarte, João C.</searchLink><relatesTo>1</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Earth+%26+Planetary+Science+Letters%22">Earth & Planetary Science Letters</searchLink>. May2016, Vol. 441, p200-210. 11p.
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  Data: <searchLink fieldCode="DE" term="%22Subduction+zones%22">Subduction zones</searchLink><br /><searchLink fieldCode="DE" term="%22Paleoseismology%22">Paleoseismology</searchLink><br /><searchLink fieldCode="DE" term="%22Regolith%22">Regolith</searchLink><br /><searchLink fieldCode="DE" term="%22Particle+image+velocimetry%22">Particle image velocimetry</searchLink><br /><searchLink fieldCode="DE" term="%22Stereoscope%22">Stereoscope</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: Backarc extension is a characteristic feature of many narrow subduction zones. Seismological and geochemical studies imply the occurrence of mantle flow around the narrow subducting slabs. Previous 3D models suggested that backarc extension is related to subduction-induced toroidal mantle flow. The physical viability of this mechanism, however, has never been tested using laboratory-based geodynamic models. In this work, we present dynamic laboratory models of progressive subduction in three-dimensional (3D) space that were carried out to test this mechanism. To achieve this, we have used a stereoscopic Particle Image Velocimetry (sPIV) technique to map simultaneously overriding plate deformation and 3D subduction-induced mantle flow underneath and around an overriding plate. The results show that the strain field of the overriding plate is characterized by the localization of an area of maximum extension within its interior (at 300–500 km from the trench). The position of maximum extension closely coincides (within ∼2 cm, scaling to 100 km) with that of the maximum trench-normal horizontal mantle velocity and velocity gradient measured at a scaled depth of 15–25 km below the base of the overriding plate, and the maximum horizontal gradient of the vertical mantle velocity gradient. We propound that in narrow subduction zones backarc extension in the overriding plate is mainly a consequence of the trench-normal horizontal gradients of basal drag force at the base of the overriding plate. Such shear force gradients result from a horizontal gradient in velocity in the mantle below the base of the lithosphere induced by slab rollback. Calculations based on our models indicate a tensional horizontal trench-normal deviatoric stress in the backarc region scaling to ∼28.8 MPa, while the overriding plate trench-normal stress resulting from the horizontal component of the trench suction force is about an order of magnitude smaller, scaling to ∼2.4–3.6 MPa. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. 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: 10.1016/j.epsl.2016.02.027
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        Text: English
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        PageCount: 11
        StartPage: 200
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      – SubjectFull: Subduction zones
        Type: general
      – SubjectFull: Paleoseismology
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      – SubjectFull: Regolith
        Type: general
      – SubjectFull: Particle image velocimetry
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      – SubjectFull: Stereoscope
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      – TitleFull: Does subduction-induced mantle flow drive backarc extension?
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            NameFull: Chen, Zhihao
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            NameFull: Schellart, Wouter P.
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            NameFull: Strak, Vincent
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            NameFull: Duarte, João C.
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            – D: 01
              M: 05
              Text: May2016
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              Y: 2016
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