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On spreading modes and magma supply at slow and ultraslow mid-ocean ridges.

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Title: On spreading modes and magma supply at slow and ultraslow mid-ocean ridges.
Authors: Cannat, Mathilde1 (AUTHOR) cannat@ipgp.fr, Sauter, Daniel2 (AUTHOR), Lavier, Luc3 (AUTHOR), Bickert, Manon1 (AUTHOR), Momoh, Ekéabino1 (AUTHOR), Leroy, Sylvie4 (AUTHOR)
Source: Earth & Planetary Science Letters. Aug2019, Vol. 519, p223-233. 11p.
Subjects: Mid-ocean ridges, Lithosphere, Volcanoes, Magmas, Plate tectonics, Hydrothermal alteration, Sea-floor spreading
Abstract: The ultraslow eastern Southwest Indian Ridge (SWIR) offers an opportunity to study the effect of magma supply on an ultraslow mid-ocean ridge starting from quasi-melt-free detachment-dominated spreading, and transitioning to volcanic spreading as one nears prominent axial volcanos. Detachments in the quasi-melt-free mode extend along-axis 60 to 95 km and have a lifetime of 0.6 to 1.5 myrs. They cut into their predecessor's footwall with an opposite polarity, causing part of the footwall lithosphere to experience further deformation, hydrothermal alteration, sparse magmatism and possibly thermal rejuvenation, in a hanging wall position. The accretion of the oceanic lithosphere in this context therefore occurs in two distinct stages over the lifetime of two successive detachment faults. We examine the transition from this nearly amagmatic detachment-dominated mode to the more common volcanic mode of spreading, showing that it occurs along-axis over distances ≤30 km. It involves a significant thinning of the axial lithosphere and a gradual decrease of the amount of tectonic displacement on faults, as the magmatic contribution to the divergence of the two plates increases. We develop a conceptual model of this transition, in which magma plays a double role: it fills the space between the diverging plates, thus reducing the need for displacement along faults, and it modifies the thermal state and the rheology of the plate boundary, affecting its thickness and its tectonic response to plate divergence. Based on a comparison of the ultraslow eastern SWIR, with the faster spreading Mid-Atlantic Ridge, we show that the activation of the volcanic, or of the detachment-dominated modes of spreading is connected with the volume of magma supplied per increment of plate separation, over a range of axial lithosphere thickness, and therefore over a range of the M ratio defined by (Buck et al., 2005) as the relative contribution of magma and faults to plate divergence (M is smaller, for a given volume of melt per increment of plate separation, if the plate is thicker). We therefore propose that M does not fully explain the variability in faulting styles observed at slow and ultraslow ridges and propose that rheological changes induced by magma also play a key role (melt itself is weak, hydrothermally altered gabbro-peridotite mixtures are weak, and melt heat sustains more vigorous hydrothermal circulation), resulting in contrasted potentials for strain localization, footwall flexure on faults and the development of detachment faults. • The Southwest Indian Ridge includes corridors of nearly amagmatic spreading. • New oceanic lithosphere there forms over lifetime of two successive detachment faults. • Nearly amagmatic corridors transition into more standard magmatic spreading in <30 km. • Melt supply impacts the thermal state and rheology of the axial lithosphere. • Melt supply is the main control on spreading mode at slow and ultraslow ridges. [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: On spreading modes and magma supply at slow and ultraslow mid-ocean ridges.
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  Data: &lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Cannat%2C+Mathilde%22&quot;&gt;Cannat, Mathilde&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;i&gt; cannat@ipgp.fr&lt;/i&gt;&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Sauter%2C+Daniel%22&quot;&gt;Sauter, Daniel&lt;/searchLink&gt;&lt;relatesTo&gt;2&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Lavier%2C+Luc%22&quot;&gt;Lavier, Luc&lt;/searchLink&gt;&lt;relatesTo&gt;3&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Bickert%2C+Manon%22&quot;&gt;Bickert, Manon&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Momoh%2C+Ek&#233;abino%22&quot;&gt;Momoh, Ek&#233;abino&lt;/searchLink&gt;&lt;relatesTo&gt;1&lt;/relatesTo&gt; (AUTHOR)&lt;br /&gt;&lt;searchLink fieldCode=&quot;AR&quot; term=&quot;%22Leroy%2C+Sylvie%22&quot;&gt;Leroy, Sylvie&lt;/searchLink&gt;&lt;relatesTo&gt;4&lt;/relatesTo&gt; (AUTHOR)
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  Data: &lt;searchLink fieldCode=&quot;JN&quot; term=&quot;%22Earth+%26+Planetary+Science+Letters%22&quot;&gt;Earth &amp; Planetary Science Letters&lt;/searchLink&gt;. Aug2019, Vol. 519, p223-233. 11p.
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  Data: The ultraslow eastern Southwest Indian Ridge (SWIR) offers an opportunity to study the effect of magma supply on an ultraslow mid-ocean ridge starting from quasi-melt-free detachment-dominated spreading, and transitioning to volcanic spreading as one nears prominent axial volcanos. Detachments in the quasi-melt-free mode extend along-axis 60 to 95 km and have a lifetime of 0.6 to 1.5 myrs. They cut into their predecessor&#39;s footwall with an opposite polarity, causing part of the footwall lithosphere to experience further deformation, hydrothermal alteration, sparse magmatism and possibly thermal rejuvenation, in a hanging wall position. The accretion of the oceanic lithosphere in this context therefore occurs in two distinct stages over the lifetime of two successive detachment faults. We examine the transition from this nearly amagmatic detachment-dominated mode to the more common volcanic mode of spreading, showing that it occurs along-axis over distances ≤30 km. It involves a significant thinning of the axial lithosphere and a gradual decrease of the amount of tectonic displacement on faults, as the magmatic contribution to the divergence of the two plates increases. We develop a conceptual model of this transition, in which magma plays a double role: it fills the space between the diverging plates, thus reducing the need for displacement along faults, and it modifies the thermal state and the rheology of the plate boundary, affecting its thickness and its tectonic response to plate divergence. Based on a comparison of the ultraslow eastern SWIR, with the faster spreading Mid-Atlantic Ridge, we show that the activation of the volcanic, or of the detachment-dominated modes of spreading is connected with the volume of magma supplied per increment of plate separation, over a range of axial lithosphere thickness, and therefore over a range of the M ratio defined by (Buck et al., 2005) as the relative contribution of magma and faults to plate divergence (M is smaller, for a given volume of melt per increment of plate separation, if the plate is thicker). We therefore propose that M does not fully explain the variability in faulting styles observed at slow and ultraslow ridges and propose that rheological changes induced by magma also play a key role (melt itself is weak, hydrothermally altered gabbro-peridotite mixtures are weak, and melt heat sustains more vigorous hydrothermal circulation), resulting in contrasted potentials for strain localization, footwall flexure on faults and the development of detachment faults. • The Southwest Indian Ridge includes corridors of nearly amagmatic spreading. • New oceanic lithosphere there forms over lifetime of two successive detachment faults. • Nearly amagmatic corridors transition into more standard magmatic spreading in &lt;30 km. • Melt supply impacts the thermal state and rheology of the axial lithosphere. • Melt supply is the main control on spreading mode at slow and ultraslow ridges. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Data: &lt;i&gt;Copyright of Earth &amp; 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&#39;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.&lt;/i&gt; (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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    Identifiers:
      – Type: doi
        Value: 10.1016/j.epsl.2019.05.012
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 11
        StartPage: 223
    Subjects:
      – SubjectFull: Mid-ocean ridges
        Type: general
      – SubjectFull: Lithosphere
        Type: general
      – SubjectFull: Volcanoes
        Type: general
      – SubjectFull: Magmas
        Type: general
      – SubjectFull: Plate tectonics
        Type: general
      – SubjectFull: Hydrothermal alteration
        Type: general
      – SubjectFull: Sea-floor spreading
        Type: general
    Titles:
      – TitleFull: On spreading modes and magma supply at slow and ultraslow mid-ocean ridges.
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            NameFull: Cannat, Mathilde
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            NameFull: Sauter, Daniel
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            NameFull: Lavier, Luc
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            NameFull: Bickert, Manon
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            NameFull: Momoh, Ekéabino
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              M: 08
              Text: Aug2019
              Type: published
              Y: 2019
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              Value: 519
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            – TitleFull: Earth & Planetary Science Letters
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