Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges
Abstract Aseismic megathrust slip downdip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. We examined exhumed subduction mélanges on Kyushu, Japan, which de...
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| Format: | Article |
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Wiley
2022-08-01
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| Series: | Geochemistry, Geophysics, Geosystems |
| Online Access: | https://doi.org/10.1029/2022GC010569 |
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| author | Kohtaro Ujiie Kazuya Noro Norio Shigematsu Åke Fagereng Naoki Nishiyama Christopher J. Tulley Haruna Masuyama Yasushi Mori Hiroyuki Kagi |
| author_facet | Kohtaro Ujiie Kazuya Noro Norio Shigematsu Åke Fagereng Naoki Nishiyama Christopher J. Tulley Haruna Masuyama Yasushi Mori Hiroyuki Kagi |
| author_sort | Kohtaro Ujiie |
| collection | DOAJ |
| description | Abstract Aseismic megathrust slip downdip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. We examined exhumed subduction mélanges on Kyushu, Japan, which deformed at ∼370–500°C under greenschist to epidote‐amphibolite facies conditions, comparable to warm‐slab environments. The mélanges recorded fluid release and viscous shear localization associated with metasomatic reactions between juxtaposed metapelitic and metabasaltic rocks. Metasomatic reactions caused albitization of metapelite, resulting in depth‐dependent changes to megathrust rheology. In a mélange deformed at ∼370°C, very fine grained reaction products (metasomatic albite) facilitated grain boundary diffusion creep at stresses of ∼45 MPa, less than those in the surrounding metabasalt. Mineralogical and chemical changes during metasomatic reactions, and their field content, imply an onset of albite metasomatism at ∼350°C. Albite metasomatism therefore potentially contributed to decreased megathrust strength around the inferred thermally controlled base of the seismogenic zone. In a mélange deformed near the mantle wedge corner at ∼500°C, metasomatic reactions promoted local quartz vein formation and localized viscous shear at slow slip strain rates, during which the coarse‐grained metasomatic albite behaved as relatively rigid blocks in a viscous matrix. We suggest that albite metasomatism can facilitate changes in a megathrust slip mode with depth and may explain why slip mode changes from creep to SSEs with tremor with increasing depth. |
| format | Article |
| id | doaj-art-9bca72cb7ee14ca8a004122dfe1100d5 |
| institution | DOAJ |
| issn | 1525-2027 |
| language | English |
| publishDate | 2022-08-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj-art-9bca72cb7ee14ca8a004122dfe1100d52025-08-20T03:17:54ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-08-01238n/an/a10.1029/2022GC010569Megathrust Shear Modulated by Albite Metasomatism in Subduction MélangesKohtaro Ujiie0Kazuya Noro1Norio Shigematsu2Åke Fagereng3Naoki Nishiyama4Christopher J. Tulley5Haruna Masuyama6Yasushi Mori7Hiroyuki Kagi8Graduate School of Science and Technology University of Tsukuba Tsukuba JapanGraduate School of Science and Technology University of Tsukuba Tsukuba JapanGeological Survey of Japan National Institute of Advanced Industrial Science and Technology Tsukuba JapanSchool of Earth and Environmental Sciences Cardiff University Cardiff UKGeological Survey of Japan National Institute of Advanced Industrial Science and Technology Tsukuba JapanSchool of Earth and Environmental Sciences Cardiff University Cardiff UKGraduate School of Science and Technology University of Tsukuba Tsukuba JapanKitakyushu Museum of Natural History and Human History Kitakyushu JapanGeochemical Research Center Graduate School of Science University of Tokyo Tokyo JapanAbstract Aseismic megathrust slip downdip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. We examined exhumed subduction mélanges on Kyushu, Japan, which deformed at ∼370–500°C under greenschist to epidote‐amphibolite facies conditions, comparable to warm‐slab environments. The mélanges recorded fluid release and viscous shear localization associated with metasomatic reactions between juxtaposed metapelitic and metabasaltic rocks. Metasomatic reactions caused albitization of metapelite, resulting in depth‐dependent changes to megathrust rheology. In a mélange deformed at ∼370°C, very fine grained reaction products (metasomatic albite) facilitated grain boundary diffusion creep at stresses of ∼45 MPa, less than those in the surrounding metabasalt. Mineralogical and chemical changes during metasomatic reactions, and their field content, imply an onset of albite metasomatism at ∼350°C. Albite metasomatism therefore potentially contributed to decreased megathrust strength around the inferred thermally controlled base of the seismogenic zone. In a mélange deformed near the mantle wedge corner at ∼500°C, metasomatic reactions promoted local quartz vein formation and localized viscous shear at slow slip strain rates, during which the coarse‐grained metasomatic albite behaved as relatively rigid blocks in a viscous matrix. We suggest that albite metasomatism can facilitate changes in a megathrust slip mode with depth and may explain why slip mode changes from creep to SSEs with tremor with increasing depth.https://doi.org/10.1029/2022GC010569 |
| spellingShingle | Kohtaro Ujiie Kazuya Noro Norio Shigematsu Åke Fagereng Naoki Nishiyama Christopher J. Tulley Haruna Masuyama Yasushi Mori Hiroyuki Kagi Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges Geochemistry, Geophysics, Geosystems |
| title | Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges |
| title_full | Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges |
| title_fullStr | Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges |
| title_full_unstemmed | Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges |
| title_short | Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges |
| title_sort | megathrust shear modulated by albite metasomatism in subduction melanges |
| url | https://doi.org/10.1029/2022GC010569 |
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