Investigating the controls on fault rock distribution in normal faulted shallow burial limestones, Malta, and the implications for fluid flow
Investigating the controls on fault rock distribution in normal faulted shallow burial limestones, Malta, and the implications for fluid flow
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DOI：
10.1016/j.jsg.2018.05.024
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发表时间：
2018-09
影响因子：
3.1
通讯作者：
Andy P. Cooke;Q. Fisher;E. Michie;G. Yielding
中科院分区：
文献类型：
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作者：
Andy P. Cooke;Q. Fisher;E. Michie;G. Yielding
在露头观察到的碳酸盐岩断层岩的空间分布和组构往往具有高度的非均质性。因此，断层岩样的岩石物理性质可能不能代表断裂带的整体封闭能力。通过量化马耳他几个断裂带的断裂岩分布(即断裂岩厚度和断裂岩连续性)，并与浅埋灰岩进行对比，研究了断裂带结构、变形机制和断裂岩分布之间的关系。显微构造分析结果表明，与致密碳酸盐中经常观察到的裂隙碎屑岩不同，高孔隙度(>；15%)以颗粒为主的灰岩是通过颗粒尺度变形而变形的。低孔隙度(<；15%)以颗粒为主的灰岩和以泥晶为主的高孔隙度的灰岩通过伸展破裂和角砾化以更均匀的方式变形。断层岩石连续性估计表明，在所研究的层序中，需要50-200 m的位移才能形成连续的低渗透碎裂岩薄板。然而，当存在分布的损伤区时，可能需要更大的位移，在该区域中，应变被容纳在多个滑动面上。这项工作突出了碳酸盐断裂岩在承载数十米位移的断裂带内分布和组构的非均质性，以及在估计碳酸盐赋存断裂带的封闭能力时考虑断层岩厚度和连续性的重要性。
The spatial distribution and fabric of carbonate fault rocks observed at outcrop are often highly heterogeneous. Therefore, petrophysical properties of fault rock samples may not be representative of the overall sealing capacity of the fault zone. By quantifying the fault rock distributions (i.e. fault rock thickness and fault rock continuity) of several fault zones in Malta, juxtaposing shallow burial limestones, this work investigates the relationship between fault zone architecture, deformation mechanisms, and fault rock distribution. Results from microstructural analyses indicate that high porosity (>15%) grain-dominated limestones deform via grain scale deformation, as opposed to fracture-derived cataclasites often observed in tight carbonates. Low porosity (<15%) grain-dominated limestones and high porosity micrite-dominated limestones deform in a more distributed manner, through extensional fracturing and brecciation. Fault rock continuity estimates suggest displacements of 50–200 m are required to form a continuous low-permeability cataclasite veneer in the studied sequence. However, greater displacements may be required when a distributed damage zone is present, in which strain is accommodated over multiple slip surfaces. This work highlights the heterogeneity in the distribution and fabric of carbonate fault rocks within fault zones hosting tens of meters displacement, and the importance of considering fault rock thickness and continuity when estimating the sealing capacity of a carbonate-hosted fault zone.