Experimental and observational constraints on the mechanical behaviour in the toes of accretionary prisms
Experimental and observational constraints on the mechanical behaviour in the toes of accretionary prisms
复制标题
对吸积棱柱趾部机械行为的实验和观测约束
DOI：
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发表时间：
1990
期刊：
影响因子：
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通讯作者：
D. Karig
中科院分区：
文献类型：
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作者：
D. Karig
摘要将土力学原理和沉积物变形实验结果与深海钻探现场观测的物理性质相结合，可以分析增生棱柱体趾部多孔沉积物的力学行为。孔隙度是唯一被广泛收集的物理性质，即使这些数据通常也没有得到充分的分析。在对孔隙度反弹、岩性变化和缺乏代表性取样进行校正后，孔隙度数据必须从空间描述或欧拉描述转换为拉格朗日描述，拉格朗日描述遵循特定沉积物元素在通过棱柱趾移动时的行为。这种方法表明，沉积物元素紧凑的变形过程中的棱柱趾，强烈的南开棱镜和小安的列斯群岛少得多。压实应力路径是韧性的，有证据表明，大部分变形，至少在南开趾，是这种类型的。然而，在扩散构造上和沿着主要断层上，也存在非常强的脆性变形成分。这种脆性叠加是根据实验解释的，实验表明，如果破坏后的变形与σm′的减小有关，则已经处于韧性破坏状态的沉积物将发生脆性剪切。这种σm′的降低可能发生在孔隙压力波动期间的棱柱体趾部。持续性脆性断层被模拟为孔隙度和孔隙压力高于周围沉积物的区域，这种情况是由从棱柱体更深处沿断层流动的流体维持的。流体从断层向外扩散可能是造成脆性破坏的广泛区域的原因，其特征是鳞片状粘土。
Abstract The mechanical behaviour of porous sediments in the toes of accretionary prisms can be analyzed by combining the principles of soil mechanics and the results of experimental sediment deformation with the in-situ physical properties observed from deep sea drilling. Porosity is the only physical property that has been extensively collected and even these data have generally been inadequately analysed. After correction for porosity rebound, variations due to lithology, and lack of representative sampling, porosity data must be converted from a spatial or Eulerian description to a Lagrangian description, which follows the behaviour of a given sediment element as it moves through the prism toe. Such an approach shows that sediment elements compact during deformation in prism toes; strongly in the Nankai prism and much less so in the Lesser Antilles. Compactive stress paths are ductile, and there is evidence that much of the deformation, at least in the Nankai toe, is of this type. Nevertheless, there is also a very strong component of brittle deformation, both on diffuse structures and along the major faults. This brittle overprint is explained in the light of experiments as showing that sediments already at a state of ductile failure will shear brittlely if post-failure deformation is associated with a decrease in σm′. Such reduction of σm′ probably occurs in prism toes during fluctuations of pore pressure. Persistent brittle faults are modelled as zones in which porosity and pore pressure are higher than in the surrounding sediments, a condition maintained by fluid channelled up the faults from deeper in the prism. Outward diffusion of fluid from the faults may be responsible for broad zones of brittle failure, characterized by scaly clay.