Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts
Frictional Properties of Simulated Chlorite Gouge at Hydrothermal Conditions: Implications for Subduction Megathrusts
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DOI：
10.1029/2018jb017205
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发表时间：
2019-05
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通讯作者：
Ayumi S. Okamoto;B. Verberne;A. Niemeijer;M. Takahashi;Ichiko Shimizu;T. Ueda;C. Spiers
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文献类型：
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作者：
Ayumi S. Okamoto;B. Verberne;A. Niemeijer;M. Takahashi;Ichiko Shimizu;T. Ueda;C. Spiers
绿泥石在俯冲带的震源深处富集，可能在控制大逆冲慢滑和突变破裂中起关键作用。然而，在与俯冲发震带相关的热液条件下，没有关于绿泥石（富）断层岩摩擦特性的资料。我们报告了在这种条件下进行的实验结果，使用由单晶斜氯石（Mg‐亚氯酸盐）制备的亚氯酸盐粉末，以及使用一堆单晶片进行的有限实验。在有效法向应力（σn）为100 ~ 400 MPa，孔隙流体压力（Pf）为50 ~ 220 MPa，温度(T)为22 ~ 600℃，阶梯驱替速率(v)为0.3 ~ 100 μm/s的条件下，进行了剪切实验。在T≤400°C时，摩擦系数（μ）为0.2-0.3，在500-600°C时为0.3-0.4，而（a‐b）值在除300°C外的几乎所有测试条件下均为正值。与600°C时孔隙率较低相比，在T≤300°C时剪切的沟槽微观结构显示出广泛的粉碎现象。单晶片叠片实验显示，在低位移（<3 mm）处μ≤0.008，随后发生硬化，显微组织提示沿（001）滑动、解理面折叠和撕裂以及凿泥的产生。我们的研究结果对俯冲带绿片岩相条件下巨型逆冲断层滑动的控制机制具有重要意义，并对剪切沟槽与层状硅酸盐单晶之间的应变调节机制有了新的认识。
Chlorite is abundant at hypocentral depths in subduction zones and is likely to play a key role in controlling megathrust slow slip and catastrophic rupture. However, no data exist on the frictional properties of chlorite(‐rich) fault rocks under the hydrothermal conditions relevant for the subduction seismogenic zone. We report results from experiments conducted under such conditions, using chlorite powders prepared from single crystal clinochlore (Mg‐chlorite), as well as limited experiments using a stack of single crystal sheets. Shear experiments were carried out at effective normal stresses (σn) of 100 to 400 MPa, pore fluid pressures (Pf) of 50 to 220 MPa, and at temperatures (T) of 22 to 600 °C, using stepped displacement rates (v) from 0.3 to 100 μm/s. The gouges are characterized by a coefficient of friction (μ) of 0.2–0.3 at T ≤ 400 °C and 0.3–0.4 at 500–600 °C, while (a‐b) values showed positive values for nearly all conditions tested, except at 300 °C. Microstructures of gouges sheared at T ≤ 300 °C show evidence for widespread comminution, compared with a lower porosity at 600 °C. Experiments using a stack of single crystal sheets showed μ ≤ 0.008 at low displacements (<3 mm) followed by hardening, while microstructures are suggestive of slip along (001), folding and tear of cleavage planes, and gouge production. Our results have important implications for the mechanisms controlling megathrust fault slip under greenschist facies conditions in a subduction zone and shed new light on the strain accommodation mechanisms within sheared gouges versus single crystals composed of phyllosilicates.