Rate-and-state friction of epidote gouge under hydrothermal conditions and implications for the stability of subducting faults under greenschist metamorphic conditions

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
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Abstract

Epidote is a common hydrous mineral present in subduction zones subject to greenschist metamorphic conditions – and potentially an important control on the fault stability-instability transition observed under greenschist facies. We explore controls on this transition through shear experiments on simulated epidote gouge at temperatures of 100–500 °C, effective normal stresses of 100–300 MPa and pore fluid pressures of 30–75 MPa. We use rate-and-state friction to define these controls of temperature, effective stress and pore fluid pressure on gouge stability. Experimental results indicate that the epidote gouge is frictionally strong (μ ∼ 0.73) and the frictional strength is insensitive to variations in temperature or pressure. With increasing temperature, the epidote gouge exhibits a first transition from velocity-strengthening to velocity-weakening at sub-greenschist conditions (T < 100 °C) before transitioning to velocity-strengthening under greenschist metamorphic conditions (T > 300 °C). Elevating the pore fluid pressure or decreasing the effective stress promotes unstable sliding. The transition in gouge rheology at varied temperatures and pressures is explained by the competition between granular flow-induced gouge dilation and pressure solution-induced gouge compaction. Our results demonstrate that the rate-and-state frictional stability of epidote gouges support the potential for a fault stability-instability-stability transition for subduction under greenschist metamorphic conditions.

热液条件下的表土刨蚀作用的速率和状态摩擦及其对绿泥石变质条件下俯冲断层稳定性的影响
表土是受绿泥石变质条件影响的俯冲带中常见的含水矿物--可能是绿泥石面下观察到的断层稳定性-不稳定性转变的重要控制因素。我们通过在温度为 100-500 °C、有效法向应力为 100-300 兆帕和孔隙流体压力为 30-75 兆帕的条件下对模拟的表土冲沟进行剪切实验,来探索这种转变的控制因素。我们利用速率与状态摩擦来确定温度、有效应力和孔隙流体压力对缺口稳定性的控制。实验结果表明,辉绿岩气刨的摩擦强度很高(μ ∼ 0.73),而且摩擦强度对温度或压力的变化不敏感。随着温度的升高,在亚绿泥石条件下(T < 100 °C),表石质水门槽沟表现出速度增强到速度减弱的过渡,然后在绿泥石变质条件下(T > 300 °C)过渡到速度增强。提高孔隙流体压力或降低有效应力会促进不稳定滑动。在不同的温度和压力下,冲沟流变学的转变是由粒状流引起的冲沟扩张和压力溶液引起的冲沟压实之间的竞争造成的。我们的研究结果表明,在绿泥石变质条件下,表土沟的速率-状态摩擦稳定性支持了断层稳定性-不稳定性-稳定性过渡的可能性。
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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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