(Table 1) Wet and dry density and porosity of mudstone at DSDP 84 holes@en

Vein structure and related small fractures in muddy sedimentary Oligocene to Miocene rocks of Sites 568 and 569 have been analyzed to study the deformation and tectonics of the Middle America Trench landward slope area off Guatemala. These veins are filled with fine, clayey materials and essentially developed as extensional fracture cleavages perpendicular to the minimum principal compressive stress axis. Three stages are recognized; early stage fractures parallel to bedding (probably caused by bedding parallel slip), abundant fractures highly oblique or perpendicular to bedding, and veins formed at various angles during tilting. Most of the veins show drag or rotation features, which mostly show downdip sliding and probably occurred during stages of large-scale folding related to faulting or draping of the middle Trench slope area. Veins are concentrated only in the middle part of the Trench landward slope of the late Oligocene to middle Miocene sections, where high sedimentation rates and possible normal faulting and folding caused by local uplift of the basement occurred. This may indicate that the veins required rapid sediment consolidation, which caused abnormal lithification针对危地马拉近海中美海沟（Middle America Trench）陆坡区域的变形特征与构造演化开展研究，本次研究对568、569站位的泥质沉积渐新世（Oligocene）至中新世（Miocene）岩石中的脉体构造及相关小型断裂展开分析。这些脉体由细粒黏土质物质充填，本质上为垂直于最小主压应力轴的伸展断裂劈理。本次研究识别出三期脉体形成阶段：早期阶段的断裂与层理平行（推测由顺层滑移作用引发）、大量与层理呈高角度斜交或垂直的断裂，以及倾斜过程中形成的多角度脉体。多数脉体显示拖曳或旋转特征，整体呈现沿倾向滑动的迹象，其形成大概率与海沟中部陆坡区域因断层作用或披覆构造引发的大规模褶皱阶段相关。脉体仅集中分布于晚渐新世（late Oligocene）至中中新统（middle Miocene）地层的海沟陆坡中部区域，该区域具备高沉积速率，且存在因基底局部隆升引发的正断层与褶皱作用。该分布特征表明，脉体的形成依赖于快速的沉积物固结成岩作用，即异常成岩作用。