Deformation and fluid pressure variation during initiation and evolution of the plate boundary décollement zone in the Nankai accretionary prism
Deformation and fluid pressure variation during initiation and evolution of the plate boundary décollement zone in the Nankai accretionary prism
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DOI：
10.1029/2002jb002314
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发表时间：
2003-08
影响因子：
--
通讯作者：
K. Ujiie;T. Hisamitsu;A. Taira
中科院分区：
文献类型：
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作者：
K. Ujiie;T. Hisamitsu;A. Taira
[1]南开吸积棱镜区木户地区的板块边界滑脱带记录了受时间流体压力变化影响的变形和固结史。微观结构观察和化学分析表明，滑脱带起源于以自生粘土粒间胶结作用为特征的多孔粘土沉积层。微观组织的横切关系表明，滑脱带记录了两次压实变形。早期压实变形涉及多孔胶结结构的破坏，可能是由流体压力波动引起的。后期压实变形主要表现为黏土颗粒沿滑面组的旋转和孔隙崩塌，形成了黏土颗粒的择优取向区。与上覆棱柱沉积物的压实趋势相比，这些压实变形导致滑脱带内的堆积密度显著增加。压实变形后的流体压力升高导致滑脱带内的超固结状态，形成充满流体的膨胀裂缝。在逆冲下沉积的顶部，堆积密度突然减小，但没有胶结作用的微观结构证据。扩张裂缝和欠胶结逆冲下沉积物中的流体是滑脱带及其下方流体压力升高的潜在来源，导致增生棱柱与逆冲下沉积物发生机械解耦。Muroto地区的断层-流体相互作用可能适用于其他汇聚的板块边缘，在这些板块边缘，与扩张脊的俯冲或热的年轻洋壳相关的高温增强了成岩作用和胶结作用。
[1] The plate boundary decollement zone in the Muroto region of the Nankai accretionary prism records deformation and consolidation histories that have been affected by temporal changes in fluid pressure. Microstructural observations and chemical analysis demonstrate that the decollement zone initiated in an interval of porous clayey sediments characterized by cementation due to intergranular bonding of authigenic clays. Crosscutting relations of microstructures indicate that the decollement zone records two compactive deformations. The early compactive deformation involved destruction of porous cemented structure, probably caused by fluid pressure fluctuation. The late compactive deformation was characterized by clay-particle rotation and porosity collapse along the sets of slip surfaces, resulting in zones of preferred orientation of clay particles. These compactive deformations led to significantly higher bulk densities within the decollement zone compared to the compaction trend of the overlying prism sediments. Elevated fluid pressure following compactive deformations induced an overconsolidated state within the decollement zone, with fluid-filled dilatant fractures. Bulk density abruptly decreases at the top of the underthrust sediments, but there is no microstructural evidence for cementation. Fluids in the dilated fractures and underconsolidated underthrust sediments are potential sources for the elevated fluid pressure in and below the decollement zone, resulting in mechanical decoupling of the accretionary prism from underthrust sediments. The fault-fluid interactions in the Muroto region may be applicable to other convergent plate margins where high temperature associated with the subduction of a spreading ridge or hot, young oceanic crust enhances diagenesis and cementation.