Diagenetic controls on the evolution of fault-zone architecture and permeability structure: Implications for episodicity of fault-zone fluid transport in extensional basins
Diagenetic controls on the evolution of fault-zone architecture and permeability structure: Implications for episodicity of fault-zone fluid transport in extensional basins
复制标题
DOI：
10.1130/b31443.1
复制
发表时间：
2017-03
影响因子：
4.9
通讯作者：
Randolph T. Williams;L. Goodwin;P. Mozley
中科院分区：
文献类型：
--
作者：
Randolph T. Williams;L. Goodwin;P. Mozley
成岩作用明显地改变了沉积物的力学性质和水文性质。然而，随着时间的推移，这些变化对断裂带中发育的构造的分布和类型的影响，以及它们对断裂带流体流动的影响，以前没有系统地研究过。探讨了成岩作用对拉张盆地同沉积正断层切割的初始未岩化砂力学和水文性质的影响。现场、微观结构和地球化学数据记录了最初连续流体流过10米宽的上盘损伤带的成岩记录。在这一区域，颗粒流动产生的初始变形记录为由颗粒形状优选取向定义的叶理作用，并由随后沉淀的、充填孔隙的方解石胶结物保存。方解石脉在相对较窄（距离断层核心≤5米）的较老损伤带段内横切了先前胶结的片理砂岩，证明了向幕式流体流动的过渡。与颗粒流的广泛记录不同，脉体仅限于重叠断层段之间的映射中继带附近，以及推断的部分覆盖的中继带。静脉显微结构记录了重复的裂缝打开和闭合。角砾岩带脉体δ 13c值高达+6.0‰，表明含co2和/或ch4的流体脱气。这些数据共同表明，相对较早的损伤区胶结强化和硬化了叶状损伤区，影响了脆性裂缝的局部化和接力区的流体流动。研究结果突出了正断层发育过程中变形和流体流动特征和轨迹的系统变化，为预测正断层在伸展盆地发育过程中如何圈闭或输送流体提供了依据。
Diagenesis demonstrably changes both the mechanical and hydrologic properties of sediments. However, the effect of these changes on the distribution and types of structures that develop in fault zones over time, and their impact on fault-zone fluid flow has not previously been systematically investigated. We explored the impact of diagenesis on the mechanical and hydrologic properties of initially unlithified sand cut by a syndepositional normal fault in an extensional basin. Field, microstructural, and geochemical data document a diagenetic record of initially continuous fluid flow through a hanging-wall damage zone up to 10 m wide. In this zone, initial deformation via particulate flow is recorded by a foliation defined by a grain shape preferred orientation, preserved by subsequently precipitated, pore-filling calcite cement. A transition to episodic fluid flow is demonstrated by calcite veins that crosscut the previously cemented, foliated sandstone within relatively narrow (≤5 m from the fault core) segments of the older damage zone. Unlike the widespread record of particulate flow, veins are restricted to the vicinity of a mapped relay zone between overlapping fault segments, and an inferred, partially covered relay zone. Vein microstructures record repeated fracture opening and sealing. Veins in breccia zones have δ 13 C values as high as +6.0‰, suggesting degassing of CO 2 - and/or CH 4 -charged fluids. These data collectively suggest that relatively early damage zone cementation strengthened and stiffened the foliated damage zone, affecting the localization of brittle fractures and fluid flow in relay zones. Our results highlight systematic changes in the character and locus of deformation and fluid flow during the development of normal faults and provide a basis for predicting how these structures may act to trap or transmit fluids during the development of extensional basins.