Systematic variation of shear-induced physical properties and fabrics in the Miura–Boso accretionary prism: The earliest processes during off-scraping
Systematic variation of shear-induced physical properties and fabrics in the Miura–Boso accretionary prism: The earliest processes during off-scraping
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DOI：
10.1016/j.epsl.2006.01.049
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发表时间：
2006-04
影响因子：
5.3
通讯作者：
Yuzuru Yamamoto
中科院分区：
文献类型：
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作者：
Yuzuru Yamamoto
通过测量日本中部Miura-Boso吸积棱镜的孔隙率、孔隙尺寸分布和磁化率各向异性（AMS），阐明了浅层吸积棱镜的变形与物理性质和结构变化之间的相互关系。根据变形模式，陆上脱刮体实例从下到上可分为三部分：叠瓦状逆冲，对应于一个脱刮带；在脱刮体下部的推力单元；以及在刮除体的顶部的上相干单元。即使在特定的岩性中，这三个部分的物理性质和结构也各不相同。这些观测结果反映了每个构造单元在浅层剥落和增生过程中的个体应变历史。在增生之前，沉积物经历了垂直压实作用。当水平挤压应力随后开始使沉积物变形时，前兆剪切扰动了先前的压实结构，并伴随着在数十至数百米厚的区域内普遍存在的孔隙度减少。孔隙度降低是由大孔隙塌陷引起的，导致了不透水的超固结层的发育，其下方不可避免的高孔隙流体压力控制了随后的结垢带的位置。沿叠瓦状逆冲带在dsamement区内的位移发生在已产生高流体压力的超固结层下方。在这里，与叠瓦状逆冲平行的平坦构造，以及与断层运动相关的孔隙度和孔径进一步减小。这些发现暗示了沉积物在被纳入dsamacement带之前的不可恢复的断裂前应变信息，并表明通过颗粒重排和孔隙缩小而形成的过固结带是对增生棱镜浅部（特别是在岩性均质物质中）随后的大变形（即在dsamacement带内）的重要控制。
The interrelations between deformation and variations in the physical properties and fabrics of a shallow-level accretionary prism have been clarified using measurements of porosity, pore-size distribution, and the anisotropy of magnetic susceptibility (AMS) within the Miura–Boso accretionary prism, central Japan. Based on the mode of deformation, this onland example of an off-scraped body can be divided into three parts from bottom to top: imbricate thrusts corresponding to a décollement zone; a thrust unit in the lower part of the off-scraped body; and an upper coherent unit in the top part of the off-scraped body. Physical properties and fabrics are quite variable in each of the three parts, even within a particular lithology. These observations reflect each structural unit's individual strain history during shallow off-scraping and accretion. Prior to the accretion, the sediments underwent vertical compaction. When horizontal compressional stresses subsequently began to deform the sediments, precursory shear disturbed the previous compaction fabric accompanied by a pervasive porosity decrease over a zone several tens to hundreds of meters in thickness. The porosity decrease occurred by large pore collapse, which led to the development of an impermeable over-consolidated horizon and inevitable high pore fluid pressures below that controlled the position of the subsequent décollement zone. Displacement along imbricate thrusts within the décollement zone took place just below the over-consolidated horizon where high fluid pressure had been generated. Here, a flattening fabric parallel to the imbricate thrust and associated further porosity and pore size reductions occurred in association with the fault movement. These findings imply unrecoverable pre-fractured strain information of sediments before being included in the décollement zone and suggest that the precursory formation of an over-consolidated zone via grain rearrangement and pore size reduction is an essential control on subsequent large deformation (i.e., within a décollement zone) in the shallow part of an accretionary prism, especially within lithologically homogeneous material.