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

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
J. Muñoz-Montecinos, S. Angiboust, C. Minnaert, A. Ceccato, L. Morales, J. Gasc, W. Behr
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引用次数: 0

摘要

蛇纹岩是深俯冲带挥发物的主要载体,在500-650°C范围内释放出大部分流体。尽管这些流体对传质和中深层地震具有重要影响,但其力学作用尚不清楚。为了描述流体在(超)高压条件下的力学作用,我们对来自西阿尔卑斯山元沸石的富橄榄石矿脉进行了岩石结构分析。一些矿脉是通过扩张和扩张-剪切混合断裂形成的,没有明显的剪切变形。然而,实地观察和微观结构观察表明,在高孔隙流体压力下会出现瞬时剪切和扩张断裂。这些现象包括(a)叶状剪切脉;(b)新形成的橄榄石和钛clinohumite矿物线包裹剪切脉和剪切带;(c)密封斑岩的橄榄石和钛clinohumite矿物纤维;(d)扩张和剪切特征之间的相互交叉关系。低应变区主要是扩张矿脉,而高应变区的剪切矿脉和剪切带则以超基性斜长岩边界为主。这些应变变化凸显了蛇绿岩脱水过程中局部应力机制的作用。因此,大尺度岩块周围剪应力较强或流体循环过程中机械应力减弱的区域容易排出超压流体。因此,这些界面平行和断裂控制的通道有利于流体从脱水下行板块中排出。扩张性断裂和脆-韧性剪切的瞬时事件,以及高度粉碎的含橄榄石剪切矿脉中的应变局部化,可能是由可能与(次)地震变形有关的应变率爆发引起的。这些观察结果与地球物理数据一致,表明中深地震区内的孔隙流体压力很高。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Fluid-Driven Shear Instabilities in the Subducted Oceanic Mantle at Intermediate Depths: Insights From Western Alps Meta-Ophiolites

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.

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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
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.
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