Formation process of a silica gel layer along a fault in chert
Formation process of a silica gel layer along a fault in chert
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沿燧石断层的硅胶层形成过程
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
A. Miyake
中科院分区：
文献类型：
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作者：
A. Tsutsumi;A. Miyake
以前的实验研究已经证明，硅质物质中的断层在相对较低的滑动速度(V>；0.01 mm/S)下发生[Goldsby and Tullis，2002；Di Toro et al.，2004；Hayashi and TsutSumi，2010]，在这种条件下，由于温度较低，转变反应(如熔融、分解等)无法进行。硅质岩石中硅胶(水合无定形二氧化硅)层的形成被认为是导致这种弱化行为的可能原因[Goldsby和Tullis，2002]。然而，关于石英岩中断层上摩擦生成物质的信息却很有限。为了更好地了解硅质材料中的断裂带过程，我们对硅质岩样品进行了中速摩擦实验，并对断裂面材料进行了透射电子显微镜(TEM)研究。摩擦试验是在中等速度(V=104 mm/S)和1.5 Mpa的低法向应力下进行的。正如Hayashi和TsutSumi(2010)初步报告的那样，在形成0.1毫米厚的断层泥层的同时，硅质岩样品中的断层减弱。断层表面的扫描电子显微镜观察表明，断层表面由光滑部分和粗糙部分组成，光滑部分可能对应于玻璃光泽区域。在表面光滑的部分，与滑动方向垂直排列的棒状颗粒(长1至5微米，直径∼0.5微米)，可能表明它们在实验过程中被滚动[Hayashi and TsutSumi，2010]。这些粒子被称为“卷”。A聚焦离子束(FIB)系统。制作了断层表面的横截面，以便用透射电子显微镜观察轧辊和衬底的界面。在准备过程中，我们注意了切割方向；轧辊的切割垂直于其长轴。透射电子显微镜观察揭示了实验生成的硅质岩中断层表面材料的以下特征：(1)光滑的断层表面由几百纳米厚的无定形二氧化硅层组成。(2)轧辊存在于光滑的断层表面，与无定形二氧化硅层接触。(3)轧辊由无定形二氧化硅制成。透射电子显微镜观察的结果表明，在光滑的断层表面观察到的轧辊是通过消耗薄的无定形二氧化硅层而形成的。Hayashi和TsutSumi(2010)表明，断层泥由水化的无定形二氧化硅和石英颗粒组成。断层表面形成的几百纳米厚的薄无定形二氧化硅层可能是水合无定形断层泥材料(硅胶层)的候选来源。
Previous experimental studies have demonstrated that fault weakening in siliceous material occurred at relatively low slip velocities (V > 0.01 mm/s) [Goldsby and Tullis, 2002; Di Toro et al., 2004; Hayashi and Tsutsumi, 2010], under which conditions transformation reactions (e.g., melting, decomposition, etc) are unable to proceed because of low temperatures. Formation of a silica gel (hydrated amorphous silica) layer within a siliceous rock has been suggested for a possible cause of the weakening behavior [Goldsby and Tullis, 2002]. However, there exists only limited information on the frictionally generated material on faults in quartz-rocks. To get a better understanding of fault zone process in siliceous material, we have performed intermediate-velocity friction experiments on chert samples and have performed transmission electron microscope (TEM) studies of the fault surface material. Friction experiments were performed on chert at intermediate velocity (V = 104 mm/s) and at low normal stress of 1.5 MPa. As has been reported preliminary in Hayashi and Tsutsumi (2010), fault weakening in chert samples occurred in association with the formation of a 0.1-mm-thick fault gouge layer. SEM observations on the fault surfaces revealed that the fault surfaces consisted of smooth and rough parts, with the smooth parts probably corresponding to the area with vitreous luster. On the smooth part of the surfaces, rod-shaped particles ( 1 to 5 µ m long with a diameter of ∼ 0.5 µ m), aligned perpendicular to the sliding direction, probably indicating that they were rolled during the experiment [Hayashi and Tsutsumi, 2010]. These particles have been termed “rolls” . The a focused ion beam (FIB) system. Cross-sections of the fault surface were prepared so that rolls and the substrata interface could be observed using TEM. During the preparation, we paid attention to the cutting direction; rolls were cut perpendicular to their long axes. TEM observations revealed the following characteristics of the experimentally generated fault surface material in chert: (1) the smooth fault surface consist of several hundred-nm-thick amorphous silica layer. (2) Rolls exist on the smooth fault surface and are in contact with the amorphous silica layer. (3) Rolls are made of amorphous silica. The result from TEM observation implies that the rolls observed on the smooth fault surface are formed via a process of consuming the thin amorphous silica layer. Hayashi and Tsutsumi (2010) showed that the fault gouge consists of a mixture of hydrated amorphous silica and quartz grains. The thin, several hundred-nm-thick amorphous silica layer formed on the fault surface would be a likely candidate for the source of the hydrated amorphous gouge material (silica gel layer).