Acoustic anisotropy and microfabric development in accreted sediment from the Nankai Trough

Acoustic anisotropy and microfabric development in accreted sediment from the Nankai Trough
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南海海槽增生沉积物中的声学各向异性和微纤维发育

DOI：
10.2973/odp.proc.sr.131.121.1993
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发表时间：
1993
期刊：
--
影响因子：
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通讯作者：
E. Taylor
E. Taylor
中科院分区：
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文献类型：
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作者：
W. Brückmann;K. Moran;E. Taylor

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ODP 期间 808 站点南海海槽增生杂岩的完全穿透和滑脱 第 131 段提供了大量的结构观察和物理性质数据。本文讨论了可能的机制 这可能是在 808 号站点观察到的声学各向异性井下趋势不规则发展的原因。 通过数据缩减和筛选的各个步骤，古地磁重新定向程序应用于选定的物理组 属性数据集。这有助于将观测到的物理性质变化与大地构造框架相结合 位于南海海槽增生杂岩变形前缘。重建中使用了古地磁数据库 下四国盆地沉积序列的声速方向特性，除以 急剧滑脱形成增生部分和俯冲部分。 P 波速度各向异性源自该 420 米厚上部的古地磁定向样本 半远洋序列在平行和垂直于板块汇聚推断矢量的方向上显示最大值 （31°-315°）。在层序的俯冲部分没有发现纵波速度各向异性的优选方向。 平行于会聚向量的最大各向异性的优选方向也与真实方向一致 808 号站点中观察到的宏观到中尺度结构特征。微裂缝和微裂纹随着应力释放和 半石化沉积物岩心中垂直于最大水平应力的拉伸裂缝讨论为 观察到的各向异性模式发展的控制机制。
Complete penetration of frontal thrust and decollement of the Nankai Trough accretionary complex in Site 808 during ODP Leg 131 provided a wealth of structural observations and physical property data. In this paper possible mechanisms are discussed that could be responsible for the development of irregular downhole trends in acoustic anisotropy observed in Site 808. After various steps of data reduction and screening, a paleomagnetic reorientation procedure is applied to a selected group of physical property data sets. This facilitates the integration of the observed changes in physical properties with the geotectonic framework at the deformation front of the Nankai Trough accretionary complex. The paleomagnetic database was employed in the reconstruction of directional properties of acoustic velocities of the Lower Shikoku Basin sedimentary sequence, which is divided by a sharply defined decollement into an accreting and a subducting portion. P-wave velocity anisotropies derived from paleomagnetically oriented samples in the upper part of this 420-m-thick hemipelagic sequence show maximum values in the direction parallel and normal to the inferred vector of plate convergence (31O°-315°). No preferred orientation of P-wave velocity anisotropy is found in the subducting part of the sequence. The preferred direction of maximum anisotropy parallel to the convergence vector is also in accordance with the true direction of the observed macro- to mesoscale structural features in Site 808. Microfractures and microcracks forming as stress relief and tensile fractures in cores of semilithified sediment normal and perpendicular to the maximum horizontal stress are discussed as control mechanisms for the development of the observed anisotropy pattern.