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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Comparison of smectite- and illite-rich gouge frictional properties: application to the updip limit of the seismogenic zone along subduction megathrusts
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Comparison of smectite- and illite-rich gouge frictional properties: application to the updip limit of the seismogenic zone along subduction megathrusts

机译：富蒙皂石和伊利石的切屑摩擦特性的比较：沿俯冲巨推力作用于成地震带的上倾极限

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Along plate boundary subduction thrusts, the transformation of smectite to illite within fault gouge at temperatures of ～150 ℃ is one of the key mineralogical changes thought to control the updip limit of seismicity. If correct, this hypothesis requires illite-rich gouges to exhibit frictionally unstable (velocity-weakening) behavior. Here, we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay-rich gouges. We sheared 5-mm-thick layers of commercially obtained pure Ca-smectite, a suite of smectite-quartz mixtures, and natural illite shale (grain size ranging from 2 to 500 μm) in the double-direct shear geometry to shear strains of ～7-30 at room humidity and temperature. XRD analyses show that the illite shale contains dominantly clay minerals and quartz; within the clay-sized fraction (< 2 μm), the dominant mineral is illite. Thus, we consider this shale as an appropriate analog for fine-grained sediments incoming to subduction zones, within which smectite has been transformed to illite. We observe a coefficient of friction (μ) of 0.42 - 0.68 for the illite shale, consistent with previous work. Over a range of normal stresses from 5 to 150 MPa and sliding velocities from 0.1 to 200 μm/s, this material exhibits only velocity-strengthening behavior, opposite to the widely expected, potentially unstable velocity-weakening behavior of illite. Smectite sheared under identical conditions exhibits low friction (μ = 0.15 - 0.32) and a transition from velocity weakening at low normal stress to velocity strengthening at higher normal stress (> 40 MPa). Our data, specifically the velocity-strengthening behavior of illite shale under a wide range of conditions, do not support the hypothesis that the smectite-illite transition is responsible for the seismic-aseismic transition in subduction zones. We suggest that other depth- and temperature-dependent processes, such as cementation, consolidation, and slip localization with increased shearing, may play an important role in changing the frictional properties of subduction zone faults, and that these processes, in addition to clay mineralogy, should be the focus of future investigation.
机译：沿板块边界俯冲冲断作用，在〜150℃温度下，蒙脱石向伊利石的转变是控制地震活动上限值的重要矿物学变化之一。如果正确，则该假设需要富含伊利石的凿具表现出摩擦不稳定（速度减弱）行为。在这里，我们报告了旨在研究天然和合成富含粘土的凿子的摩擦性能的实验室实验。我们在双向剪切几何结构中剪切了5毫米厚的市售纯钙蒙脱石，一套蒙脱石-石英混合物和天然伊利石页岩（粒度范围为2至500μm），以剪切〜在室温和湿度下为7-30。 XRD分析表明，伊利石页岩主要含有粘土矿物和石英。在粘土大小的部分（<2μm）内，主要矿物是伊利石。因此，我们认为该页岩是进入俯冲带的细粒沉积物的合适模拟物，在该区域中，蒙脱石已转变为伊利石。我们发现伊利石页岩的摩擦系数（μ）为0.42-0.68，与先前的工作一致。在5到150 MPa的正应力范围和0.1到200μm/ s的滑动速度范围内，这种材料仅表现出速度增强行为，这与伊利石广泛预期的，潜在的不稳定的速度减弱行为相反。在相同条件下剪切的蒙脱石显示出低摩擦（μ= 0.15-0.32），并且从低法向应力下的速度减弱到高法向应力（> 40 MPa）下的速度增强过渡。我们的数据，特别是伊利石页岩在各种条件下的速度增强行为，并不支持蒙脱石-伊利石转变是俯冲带地震-地震转变的原因。我们建议其他与深度和温度有关的过程，例如胶结，固结和滑动局部化以及增加的剪切力，可能在改变俯冲带断层的摩擦特性方面起着重要作用，而且这些过程除了粘土矿物学外，应该是以后调查的重点。

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