Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution
Clay fabric intensity in natural and artificial fault gouges: Implications for brittle fault zone processes and sedimentary basin clay fabric evolution
复制标题
DOI：
10.1029/2008jb005866
复制
发表时间：
2009-05-13
影响因子：
3.9
通讯作者：
Marone, Chris
中科院分区：
文献类型：
--
作者：
Haines, Samuel H.;van der Pluijm, Ben A.;Marone, Chris
层状硅酸盐组构在断层泥中的作用是脆性断裂带的力学和水文行为中一个鲜为人知的组成部分。我们用X射线结构测角术对来自低角度滑脱断层(加利福尼亚州死亡谷区滑脱、内华达州红宝石山脉、加利福尼亚州西萨尔顿滑脱断层)和西班牙东北部帕拉莫拉逆冲断层的22个天然富粘土断层泥进行了90次组构强度测量。与其他地质环境中发现的富含层状硅酸盐的岩石相比，天然断层泥的粘土组构均匀较弱(随机分布倍数(MRD)=1.7-4.5，平均MRD=2.6)。天然泥中粘土组构强度并不随构造环境或泥中主要粘土矿物学的变化而显著变化。我们将这些天然样品与实验室合成粘土-石英混合物上测得的69种层状硅酸盐织物强度进行了比较。室内土样的粘土组构强度与天然泥相似(MRD=1.7~4.6)，但随剪应变和正应力的增加而系统增大。层状硅酸盐总量对粘土织物强度没有显著影响。剪切应变对于开发更坚固的织物非常重要；即使在高法向应力(150兆帕)下压缩，仅受压缩的样品也表现出均匀的弱织物(MRD=1.6-1.8)。在天然断层泥中发现的弱组构表明，如果各向异性和整体低断层渗透率允许孔隙流体压力升高和断层弱化，这种各向异性肯定是一种暂时的特征，不会被保留。我们的数据还强化了这样的观点，即沉积岩中粘土组构的发展主要是自生矿物生长的函数，而不是压实引起的颗粒旋转的函数。
The role of phyllosilicate fabrics in fault gouge is a poorly understood component of the mechanical and hydrologic behavior of brittle fault zones. We present 90 fabric intensity measurements using X-ray texture goniometry on 22 natural clay-rich fault gouges from low-angle detachment faults (Death Valley area detachments, California; Ruby Mountains, Nevada; West Salton Detachment Fault, California) and the Peramola thrust in NE Spain. Natural fault gouges have uniformly weak clay fabrics (multiples of a random distribution (MRD) = 1.7-4.5, average MRD = 2.6) when compared to phyllosilicate-rich rocks found in other geologic settings. Clay fabric intensities in natural gouges do not vary significantly either as a function of tectonic environment or of dominant clay mineralogy in the gouge. We compare these natural samples with 69 phyllosilicate fabric intensities measured in laboratory experiments on synthetic clay-quartz mixtures. Clay fabric intensities from laboratory samples are similar to those in natural gouges (MRD = 1.7-4.6), but increase systematically with increasing shear strain and normal stress. Total phyllosilicate content does not significantly affect clay fabric intensity. Shear strain is important for developing stronger fabrics; samples subjected solely to compression exhibit uniformly weak fabrics (MRD = 1.6-1.8) even when compressed at high normal stresses (150 MPa). The weak fabrics found in natural fault gouge indicate that if anisotropic and overall low fault zone permeability allow elevated pore fluid pressures and fault weakening, this anisotropy must be a transient feature that is not preserved. Our data also reinforce the idea that clay fabric development in sedimentary rocks is primarily a function of authigenic mineral growth and not of compaction-induced particle rotation.