Tectonic mélange as fault rock of subduction plate boundary

Kimura, Gaku; Yamaguchi, Asuka; Hojo, Megumi; Kitamura, Yujin; Kameda, J.; Ujiie, Kohtaro; Hamada, Yohei; Hamahashi, Mari; Hina, Shoko

doi:10.1016/j.tecto.2011.08.025

Cited by 115 publications

(121 citation statements)

References 66 publications

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“…Details of the internal structure of SISZ and the physical conditions prevailing therein are inevitably speculative, but are constrained by geophysical observations and the structural characteristics of analogous exhumed thrust zones. Mélange formations so typical of exhumed SISZ (Fagereng 2011;Kimura et al 2012) are of particular interest because of the likelihood of extreme stress and competence (i.e. tensile strength) heterogeneity within such formations .…”

Section: Tensile Overpressure Compartments Along Subduction Interfacesmentioning

confidence: 99%

Tensile overpressure compartments on low-angle thrust faults

Sibson

2017

Earth Planets Space

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Hydrothermal extension veins form by hydraulic fracturing under triaxial stress (principal compressive stresses, σ 1 > σ 2 > σ 3 ) when the pore-fluid pressure, P f , exceeds the least compressive stress by the rock's tensile strength. Such veins form perpendicular to σ 3 , their incremental precipitation from hydrothermal fluid often reflected in 'crackseal' textures, demonstrating that the tensile overpressure state, σ 3 ′ = (σ 3 − P f ) < 0, was repeatedly met. Systematic arrays of extension veins develop locally in both sub-metamorphic and metamorphic assemblages defining tensile overpressure compartments where at some time P f > σ 3 . In compressional regimes (σ v = σ 3 ), subhorizontal extension veins may develop over vertical intervals <1 km or so below low-permeability sealing horizons with tensile strengths 10 < T o < 20 MPa. This is borne out by natural vein arrays. For a low-angle thrust, the vertical interval where the tensile overpressure state obtains may continue down-dip over distances of several kilometres in some instances. The overpressure condition for hydraulic fracturing is comparable to that needed for frictional reshear of a thrust fault lying close to the maximum compression, σ 1 . Under these circumstances, especially where the shear zone material has varying competence (tensile strength), affecting the failure mode, dilatant fault-fracture mesh structures may develop throughout a tabular rock volume. Evidence for the existence of fault-fracture meshes around low-angle thrusts comes from exhumed ancient structures and from active structures. In the case of megathrust ruptures along subduction interfaces, force balance analyses, lack of evidence for shear heating, and evidence of total shear stress release during earthquakes suggest the interfaces are extremely weak (τ < 40 MPa), consistent with weakening by nearlithostatically overpressured fluids. Portions of the subduction interface, especially towards the down-dip termination of the seismogenic megathrust, are prone to episodes of slow-slip, non-volcanic tremor, low-frequency earthquakes, very-low-frequency earthquakes, etc., attributable to the activation of tabular fault-fracture meshes at low σ 3 ′ around the thrust interface. Containment of near-lithostatic overpressures in such settings is precarious, fluid loss curtailing mesh activity.© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Tensile Overpressure Compartments Along Subduction Interfacesmentioning

confidence: 99%

Tensile overpressure compartments on low-angle thrust faults

Sibson

2017

Earth Planets Space

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“…Although the mélanges have a chaotic appearance on various scales, one commonly observed feature is a systematic repetition of disrupted ocean-floor stratigraphy; that is, a pile of ocean-floor basalt, pelagic to hemipelagic sediments, and trench-fill terrigenous sediments (Kimura and Mukai 1991;Hashimoto and Kimura 1999;Ikesawa et al 2005). On the basis of detailed structural observations in the Mugi mélange, Kimura et al (2012) proposed a model where the mélange was underplated together with a duplex structure that was in the process of formation. Slab-shaped basaltic rocks often occur at the base of each horse in such duplex structures, suggesting a décol-lement step-down into the oceanic crust.…”

Section: Geological Background and Analyzed Samplesmentioning

confidence: 99%

“…The study areas include the upper sections of the Mugi mélange (MGUB), the lower sections of the Mugi mélange (MGLB) (Ikesawa et al 2005;Kimura et al 2012), the Kure mélange (KRB) (Mukoyoshi et al 2006), the Okitsu mélange (OKB) Sakaguchi 1999), and the Makimine mélange (MKB) (Fig. 1).…”

Section: Geological Background and Analyzed Samplesmentioning

confidence: 99%

Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

Kameda

Inoué

Tanikawa

et al. 2017

Earth Planets Space

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The alteration and dehydration of predominantly basaltic subducting oceanic crustal material are thought to be important controls on the mechanical and hydrological properties of the seismogenic plate interface below accretionary prisms. This study focuses on pillow basalts exposed in an ancient accretionary complex within the Shimanto Belt of southwest Japan and provides new quantitative data that provide insight into clay mineral reactions and the associated dehydration of underthrust basalts. Whole-rock and clay-fraction X-ray diffraction analyses indicate that the progressive conversion of saponite to chlorite proceeds under an almost constant bulk-rock mineral assemblage. These clay mineral reactions may persist to deep crustal levels (~320 °C), possibly contributing to the bulk dehydration of the basalt and supplying fluid to plate-boundary fault systems. This dehydration can also cause fluid pressurization at certain horizons within hydrous basalt sequences, eventually leading to fracturing and subsequent underplating of upper basement rock into the overriding accretionary prism. This dehydration-induced breakage of the basalt can explain variations in the thickness of accreted basalt fragments within accretionary prisms as well as the reported geochemical compositions of mineralized veins associated with exposed basalts in onland locations. This fracturing of intact basalt can also nucleate seismic rupturing that would subsequently propagate along seismogenic plate interfaces.© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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“…The Mugi mélange is exposed along the southeastern coast of Shikoku Island and is composed of six repeated thrust sheets (units 1 to 6) bounded by north-dipping thrusts (Shibata et al 2008;Figure 1b,c). Each unit preserves the original ocean-floor trench stratigraphy, suggesting that the Mugi mélange was an underplated thrust-sheet package that was accreted beneath an ancient accretionary prism during the latest Cretaceous to earliest Paleocene (Onishi and Kimura 1995;Ikesawa et al 2005;Kitamura et al 2005;Shibata et al 2008;Kimura et al 2011). The Mugi mélange contains disrupted pillows and massive basalts, hemipelagic shale, pelagic red shale, and sandstone lenses enclosed in a sheared argillaceous matrix with scaly fabric (Figure 1b).…”

Section: Geological Settingmentioning

confidence: 99%

“…Tectonic mélanges often include slabs or fragments of oceanic basalt, the presence of which can be explained by décollement step-down and subsequent underplating of the downgoing mélange, in addition to movement of the upper part of the basement into the overriding plate (Kimura and Ludden 1995;Kimura et al 2011). Ikesawa et al (2005) identified fault rocks such as cataclasites and ultracataclasites at the base of a section of incorporated basalt and argued that fracturing of basalt is a seismogenic process.…”

Section: Implications For Seismogenesis At Subduction Zonesmentioning

confidence: 99%

Quartz deposition and its influence on the deformation process of megathrusts in subduction zones

et al. 2014

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We present a quantitative examination of the liberation and subsequent deposition of silica at the subduction zone plate interface in the Mugi mélange, an exhumed accretionary complex in the Shimanto Belt of southwest Japan. Frequency and thickness measurements indicate that mineralized veins hosted in deformed shales make up approximately 0.4% of the volume of this exposure. In addition, whole-rock geochemical evidence suggests that the net volume of SiO 2 liberated from the mélange at temperatures of < 200°C was as much as 35%, with up to 40% of the SiO 2 loss related to the smectite-illite (S-I) conversion reaction, and the rest attributable to the pressure solution of detrital quartz and feldspar. Kinetic modeling of the S-I reaction indicates active liberation of SiO 2 at approximately 70°C to 200°C, with peak SiO 2 loss at around 100°C, although these estimates should be slightly shifted toward lower temperature conditions based on X-ray diffraction (XRD) analyses of mixed-layer S-I in the Mugi mélange. The onset of pressure solution was not fully constrained, but has been documented to occur at around 150°C in the study area. The deposition in deformed shales of quartz liberated by pressure solution and the S-I reaction is probably linked to seismogenic behavior along the plate interface by (1) progressively enhanced velocity-weakening properties, which are favorable for unstable seismogenic faulting, including very-low-frequency earthquakes and (2) increasing intrinsic frictional strength, which leads to a step-down of the plate boundary décollement into oceanic basalt.

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Tectonic mélange as fault rock of subduction plate boundary

Cited by 115 publications

References 66 publications

Tensile overpressure compartments on low-angle thrust faults

Tensile overpressure compartments on low-angle thrust faults

Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

Quartz deposition and its influence on the deformation process of megathrusts in subduction zones

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