Ultrafine spherical quartz formation during seismic fault slip: Natural and experimental evidence and its implications
Ultrafine spherical quartz formation during seismic fault slip: Natural and experimental evidence and its implications
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DOI：
10.1016/j.tecto.2015.09.008
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发表时间：
2015-11
期刊：
影响因子：
2.9
通讯作者：
L. Kuo;Yen-Fang Song;Che-Ming Yang;Sheng-rong Song;Chun-Chieh Wang;Jia‐Jyun Dong;J. Suppe;T. Shimamoto
中科院分区：
文献类型：
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作者：
L. Kuo;Yen-Fang Song;Che-Ming Yang;Sheng-rong Song;Chun-Chieh Wang;Jia‐Jyun Dong;J. Suppe;T. Shimamoto
在最近的工作中，假玄武玻璃内的主滑带（PSZ）的车笼埔断层（台湾）的测定，我们证明了摩擦熔融发生在1999年Mw7.6集集地震的浅层。因此，熔体的特性是至关重要的调查过程中控制动态断层力学地震滑动。本文对台湾车笼埔断层钻探工程（TCDP）所采粉砂岩进行了滑动速率为1.3m/s、正应力为1 MPa的岩石摩擦实验。在这里，我们的目标不仅是表征实验的假玄武玻璃和评估相关的摩擦行为，但也比较它与天然摩擦熔体TCDP。结果表明：（1）初始剪切应力的下降与低粘度熔体斑块的形成有关;（2）熔体在熔融后的剪切应力演化与摩擦流变学过程一致;（3）摩擦熔体的极低含水量可能导致滑移强化。特别是，最先进的原位同步加速器分析（X射线衍射和透射X射线显微镜）确定超细球形石英（USQ）颗粒（约10 nm至50 nm）的存在下，在玻璃状基质中，推测在高温下产生。我们的观察证实了岩石摩擦实验中形成的USQ颗粒确实存在于天然断层中。我们推测USQ是粉砂岩摩擦熔融的结果，代表了车笼埔断层最新的滑动带，并进一步推断粘性熔体可能在地壳浅部条件下终止地震滑动。
In recent works on the determination of pseudotachylyte within the principal slip zone (PSZ) of the Chelungpu fault (Taiwan), we demonstrated that frictional melting occurred at shallow depths during the 1999 Mw 7.6 Chi-Chi earthquake. Thus, the characteristics of melts are of paramount importance to investigate processes controlling dynamic fault mechanics during seismic slips. We conducted rock friction experiments on siltstone recovered from the Taiwan Chelungpu fault Drilling Project (TCDP) at a slip rate of 1.3 m/s and a normal stress of 1 MPa. Here we not only target to characterize experimental pseudotachylyte and evaluate the associated frictional behavior, but also compare it with natural frictional melts of TCDP. Our results show that (1) initial shear stress drop was related to the generation of low viscosity melt patches, (2) the evolution of shear stress in the postmelting regime was congruent with frictional melt rheology, and (3) the slip strengthening presumably resulted from the extremely low content of water of the frictional melt. In particular, the state-of-art of in situ synchrotron analyses (X-ray diffraction and Transmission X-ray Microscope) determine the presence of ultrafine spherical quartz (USQ) grains (~ 10 nm to 50 nm) in the glassy matrices presumably produced at high temperature. Our observations confirm that the USQ grains formed in rock friction experiments do occur in natural faults. We surmise the USQ is the result of frictional melting on siltstone and represents the latest slip zones of the Chelungpu fault, and further infer that the viscous melts may terminate seismic slips at shallow crustal conditions.