Pseudotachylytes in an ancient accretionary complex and implications for melt lubrication during subduction zone earthquakes
Pseudotachylytes in an ancient accretionary complex and implications for melt lubrication during subduction zone earthquakes
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DOI：
10.1016/j.jsg.2006.10.012
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发表时间：
2007-04
影响因子：
3.1
通讯作者：
K. Ujiie;H. Yamaguchi;A. Sakaguchi;S. Toh
中科院分区：
文献类型：
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作者：
K. Ujiie;H. Yamaguchi;A. Sakaguchi;S. Toh
在日本西南部的岛曼托增生杂岩中发现的含假水杨酸断裂带是在发震深度的俯冲或底板时期发育的。伪石质出现在小于几毫米厚的狭窄的深色脉中，脉与源自石质岩的叶状碎裂岩紧密相连。伪羧酸盐的微观结构是由摩擦熔体的快速冷却导致的碎片堆积，玻璃支撑的纹理。透射电镜显示玻璃的存在，其中局部发育莫来石自面体微晶。伪石酸盐基体的组成和基体中未熔化颗粒和微晶石的特征表明，摩擦熔融发生在富含伊利石的滑移带，最低熔融温度为1100℃。摩擦熔体的粘度由伪羧酸盐基体组成以及未熔化晶粒的体积分数和长径比计算得到。1100℃下黏度为85 ~ 290Pas，在1m/s滑移速率下沿1 mm厚熔体层的剪切阻力为0.1 ~ 0.3 mpa。在富含伊利石的滑动带中，熔体层的形成可能引起较大的应力降，增加滑动速率，增强破裂扩展，这些因素共同影响着俯冲带的地震震级。
Pseudotachylyte-bearing fault zones, found in the Shimanto accretionary complex, southwest Japan, developed during subduction or underplating at seismogenic depths. The pseudotachylytes occur in narrow dark veins less than a few millimeters thick that are sharply bounded by foliated cataclasites that originated from a mélange. The microstructures of pseudotachylytes are represented by a fragment-laden, glass-supported texture resulting from the rapid cooling of the frictional melt. Transmission electron microscopy reveals the presence of glass in which euhedral microcrystals of mullite are locally developed. The compositions of the pseudotachylyte matrix and the characteristics of the unmelted grains and microlites in the matrix suggest that frictional melting occurred in an illite-rich slip zone with a minimum melting temperature of 1100°C. The viscosities of the frictional melt were calculated from the pseudotachylyte matrix composition as well as from the volume fraction and aspect ratio of the unmelted grains. The viscosities at 1100°C range from 85 to 290Pas, and the corresponding shear resistance along a 1-mm-thick melt layer at a slip rate of 1m/s was 0.1–0.3MPa. The formation of a melt layer in an illite-rich slip zone can possibly induce large stress drops, increase the slip rate and enhance rupture propagation, which together could affect the earthquake magnitude in a subduction zone.