J. Muñoz-Montecinos, S. Angiboust, C. Minnaert, A. Ceccato, L. Morales, J. Gasc, W. Behr
{"title":"中等深度俯冲洋幔中的流体驱动剪切不稳定性:西阿尔卑斯山元辉石的启示","authors":"J. Muñoz-Montecinos, S. Angiboust, C. Minnaert, A. Ceccato, L. Morales, J. Gasc, W. Behr","doi":"10.1029/2024GC011581","DOIUrl":null,"url":null,"abstract":"<p>Serpentinites are major carriers of volatiles in deep subduction zones, releasing most fluids in the 500–650°C range. Despite fundamental implications for mass transfer and intermediate-depth seismicity, the mechanical role of these fluids is unclear. To characterize the mechanical role of fluids at (ultra)high-pressure conditions, we perform a petro-structural analysis on olivine-rich veins from the Western Alps meta-ophiolite. Some veins formed through dilational and mixed dilational-shear fracturing without significant shear-related deformation. However, field and microstructural observations indicate transient shearing and dilational fracturing at high pore fluid pressures. These include: (a) foliated sheared veins; (b) newly formed olivine and Ti-clinohumite within mineral lineations coating sheared veins and shear bands; (c) Olivine and Ti-clinohumite mineral fibers sealing porphyroclasts; (d) mutual crosscutting relationships among dilational and shear features. Dilational veins prevail in low-strain areas, while sheared veins and shear bands dominate within high-strain zones toward the ultramafic sliver boundaries. These strain variations underscore the role of local stress regimes during serpentinite dehydration. Consequently, areas experiencing stronger shear stresses around large-scale blocks or mechanical weakening during fluid circulation are prone to draining overpressurized fluids. These interface-parallel and fracture-controlled pathways thus facilitate fluid escape from the dehydrating downgoing slab. Transient events of dilational fracturing and brittle-ductile shearing, along with strain localization in highly comminuted olivine-bearing sheared veins, may have resulted from strain rate bursts potentially related to (sub)seismic deformation. These observations are in line with geophysical data indicating high pore fluid pressures within the intermediate-depth seismicity region.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9000,"publicationDate":"2024-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011581","citationCount":"0","resultStr":"{\"title\":\"Fluid-Driven Shear Instabilities in the Subducted Oceanic Mantle at Intermediate Depths: Insights From Western Alps Meta-Ophiolites\",\"authors\":\"J. Muñoz-Montecinos, S. Angiboust, C. Minnaert, A. Ceccato, L. Morales, J. Gasc, W. Behr\",\"doi\":\"10.1029/2024GC011581\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Serpentinites are major carriers of volatiles in deep subduction zones, releasing most fluids in the 500–650°C range. Despite fundamental implications for mass transfer and intermediate-depth seismicity, the mechanical role of these fluids is unclear. To characterize the mechanical role of fluids at (ultra)high-pressure conditions, we perform a petro-structural analysis on olivine-rich veins from the Western Alps meta-ophiolite. Some veins formed through dilational and mixed dilational-shear fracturing without significant shear-related deformation. However, field and microstructural observations indicate transient shearing and dilational fracturing at high pore fluid pressures. These include: (a) foliated sheared veins; (b) newly formed olivine and Ti-clinohumite within mineral lineations coating sheared veins and shear bands; (c) Olivine and Ti-clinohumite mineral fibers sealing porphyroclasts; (d) mutual crosscutting relationships among dilational and shear features. Dilational veins prevail in low-strain areas, while sheared veins and shear bands dominate within high-strain zones toward the ultramafic sliver boundaries. These strain variations underscore the role of local stress regimes during serpentinite dehydration. Consequently, areas experiencing stronger shear stresses around large-scale blocks or mechanical weakening during fluid circulation are prone to draining overpressurized fluids. These interface-parallel and fracture-controlled pathways thus facilitate fluid escape from the dehydrating downgoing slab. Transient events of dilational fracturing and brittle-ductile shearing, along with strain localization in highly comminuted olivine-bearing sheared veins, may have resulted from strain rate bursts potentially related to (sub)seismic deformation. 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Fluid-Driven Shear Instabilities in the Subducted Oceanic Mantle at Intermediate Depths: Insights From Western Alps Meta-Ophiolites
Serpentinites are major carriers of volatiles in deep subduction zones, releasing most fluids in the 500–650°C range. Despite fundamental implications for mass transfer and intermediate-depth seismicity, the mechanical role of these fluids is unclear. To characterize the mechanical role of fluids at (ultra)high-pressure conditions, we perform a petro-structural analysis on olivine-rich veins from the Western Alps meta-ophiolite. Some veins formed through dilational and mixed dilational-shear fracturing without significant shear-related deformation. However, field and microstructural observations indicate transient shearing and dilational fracturing at high pore fluid pressures. These include: (a) foliated sheared veins; (b) newly formed olivine and Ti-clinohumite within mineral lineations coating sheared veins and shear bands; (c) Olivine and Ti-clinohumite mineral fibers sealing porphyroclasts; (d) mutual crosscutting relationships among dilational and shear features. Dilational veins prevail in low-strain areas, while sheared veins and shear bands dominate within high-strain zones toward the ultramafic sliver boundaries. These strain variations underscore the role of local stress regimes during serpentinite dehydration. Consequently, areas experiencing stronger shear stresses around large-scale blocks or mechanical weakening during fluid circulation are prone to draining overpressurized fluids. These interface-parallel and fracture-controlled pathways thus facilitate fluid escape from the dehydrating downgoing slab. Transient events of dilational fracturing and brittle-ductile shearing, along with strain localization in highly comminuted olivine-bearing sheared veins, may have resulted from strain rate bursts potentially related to (sub)seismic deformation. These observations are in line with geophysical data indicating high pore fluid pressures within the intermediate-depth seismicity region.
期刊介绍:
Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged.
Areas of interest for this peer-reviewed journal include, but are not limited to:
The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution
Principles and applications of geochemical proxies to studies of Earth history
The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them
The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales
Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets
The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets
Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.