Seismic slip record in carbonate-bearing fault zones: An insight from high-velocity friction experiments on siderite gouge
Seismic slip record in carbonate-bearing fault zones: An insight from high-velocity friction experiments on siderite gouge
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DOI：
10.1130/g24106a.1
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发表时间：
2007-12
期刊：
影响因子：
5.8
通讯作者：
R. Han;T. Shimamoto;J. Ando;J. Ree
中科院分区：
文献类型：
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作者：
R. Han;T. Shimamoto;J. Ando;J. Ree
摩擦熔融形成的假玄武岩是过去发震断层滑动的唯一明确证据。我们在含菱铁矿的泥层上进行的高速摩擦实验中发现，摩擦加热引起的矿物分解也可以沿着地壳浅断层留下古地震事件的证据，而不是假玄武岩。在模拟菱铁矿或菱铁矿、方解石和石英混合物的模拟断层泥上进行了室内干燥试验，初始温度为0.6~1.3 Mpa，地震滑动速率为1.3~2.0m/S，经CO2测量、X射线衍射分析和透射电子显微镜证实，均表现出明显的滑移弱化现象，菱铁矿分解为纳米晶磁铁矿和CO2气体。这种减弱是由于超细分解产物在地震滑动速率下的低摩擦强度造成的。剪切过程中磁铁矿的形成使断层泥颜色变为黑色，磁化率增加了几个数量级。这些变化可以在天然断裂带中识别出来，台湾车龙铺断裂带的黑色断层泥可能就是这样一个例子。因此，我们的结果表明，地壳浅层断层的热分解不仅是动态断层弱化的重要同震过程，也是留下地震滑动记录的重要同震过程。
Pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip. We report from high-velocity friction experiments on siderite-bearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte. Experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite, calcite, and quartz, initially at room temperature, under normal stresses of 0.6–1.3 MPa and at seismic slip rates of 1.3–2.0 m/s. In all cases, gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and CO 2 gas, as confirmed by CO 2 measurement, X-ray diffraction analyses, and transmission electron microscopy. The weakening was caused by the low frictional strength of ultrafine decomposition products at seismic slip rates. Magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude. Those changes can be recognized in natural fault zones, and black gouge in the Chelungpu fault zone in Taiwan is perhaps such an example. Thus our results suggest that thermal decomposition in shallow crustal faults can be an important co-seismic process not only for dynamic fault weakening, but also for leaving seismic slip records.