Coseismic ultramylonites: An investigation of nanoscale viscous flow and fault weakening during seismic slip
Coseismic ultramylonites: An investigation of nanoscale viscous flow and fault weakening during seismic slip
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同震超糜棱岩：地震滑动过程中纳米级粘性流和断层弱化的研究
DOI：
10.1016/j.epsl.2019.03.042
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发表时间：
2019
影响因子：
5.3
通讯作者：
Pozzi G
中科院分区：
文献类型：
--
作者：
Pozzi G
由于热激活机制的启动，断层在地震传播过程中变弱，这取决于岩石类型。最近的实验工作表明，碳酸盐赋存的断层是由具有超糜棱岩结构的纳米颗粒集合体中的粘性流动所润滑的。然而，超糜棱岩的脆弱性质往往阻碍了对在这种极端条件(应变率高达104)下工作的结构和变形机制的公正表征，到目前为止，对这些结构和变形机制的研究仍然很少。我们探索了高速(S−1的1.4m)碳酸盐赋存断层中同震超糜棱岩的形成、演化和变形机制，在旋转装置上进行了位移控制剪切实验。用扫描电子显微镜和透射电子显微镜分析了显微组织，用电子背散射衍射(EBSD)技术研究了详细的晶体组构。力学数据表明，实验断层的强度随滑移而动态衰减，遵循四个阶段的特征演化；每个阶段都与特征织构有关。显微结构观察表明，当断层较强时，脆性过程占主导地位(摩擦系数为0.6)。在孪生和晶体塑性的帮助下，崩解作用形成了一个极其粉碎的剪切带(平均颗粒尺寸∼200 nm)。随着断层开始减弱，剪切力集中在定义明确的主滑移带内。在这里，热激活的晶粒度敏感(GSS)和不敏感(GSI)蠕变机制在控制断层强度方面与脆性过程竞争。GSI机制在滑移区产生强烈的单斜晶体择优取向，而相邻位置的织构和晶体取向不会从前一变形阶段演化。在瞬时弱化阶段结束时，滑移带已达到稳定的厚度(30μm)，并显示出纳米颗粒的超糜棱岩结构。与前一阶段相比，同震超糜棱岩中晶体择优取向的强度降低，这是由于粒度敏感蠕变机制逐渐占优势所致。随着实验断层的再次加强，在减速到停止时，超糜棱岩可能会被脆性变形部分改造。我们的研究结果表明，在同震超糜棱岩的滑移带和相邻的狭窄失活层中，镜像表面所处的瞬时微观结构的结晶取向被保留下来。这表明EBSD技术可以有效地用于确定实验断层和潜在的天然断层中同震超糜棱岩的变形机制及其在地震滑动过程中的演化。
Faults weaken during the propagation of earthquakes due to the onset of thermally-activated mechanisms, which vary depending on the rock type. Recent experimental work suggests that carbonate-hosted faults are lubricated by viscous flow in nano-granular aggregates having ultramylonitic textures. However, their frail nature has often hindered unbiased characterisation of the textures and deformation mechanisms operating at such extreme conditions (strain rates as high as 104), which remain so far poorly investigated and understood.We explore the formation, evolution and deformation mechanisms of coseismic ultramylonites in carbonate-hosted faults generated during high velocity (1.4 m s−1), displacement-controlled shear experiments in a rotary apparatus. Microstructures were analysed using integrated SEM and TEM imaging while detailed crystallographic fabrics were investigated using the electron back-scattered diffraction (EBSD) technique.Mechanical data show that the strength of the experimental fault decays dynamically with slip, according to a characteristic four stage evolution; each stage is associated with characteristic textures. Microstructural observations show that brittle processes dominate when the fault is strong (friction coefficients >0.6). Cataclasis, aided by twinning and crystal plasticity, operates forming an extremely comminuted shear band (mean grain size ∼200 nm). As the fault starts weakening, shear localises within a well-defined principal slip zone. Here, thermally-activated grain size sensitive (GSS) and insensitive (GSI) creep mechanisms compete with brittle processes in controlling fault strength. GSI mechanisms produce strong monoclinic crystallographic preferred orientations in the slip zone, while textures and crystallographic orientations in adjacent locations do not evolve from the previous deformation stage. By the end of the transient weakening stage, the slip zone has reached a steady state thickness (30 μm) and shows a nanogranular ultramylonitic texture. The intensity of the crystallographic preferred orientation in the coseismic ultramylonite is reduced compared to the previous stage, due to grainsize sensitive creep mechanisms becoming gradually more dominant. As the experimental fault re-strengthens, upon deceleration to arrest, the ultramylonite may be partially reworked by brittle deformation.Our findings show that the crystallographic orientations of transient microstructures are preserved in the slip zone of coseismic ultramylonites and in narrow, adjacent deactivated layers, where mirror-like surfaces are located. This shows that EBSD techniques can usefully be employed to determine the deformation mechanisms of coseismic ultramylonites and their evolution during earthquake slip in both experimental and, potentially, natural faults.
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影响因子：
5.8
作者：
G. Pozzi;N. Paola;S. Nielsen;R. Holdsworth;L. Bowen
通讯作者：
G. Pozzi;N. Paola;S. Nielsen;R. Holdsworth;L. Bowen
低温（150–350°C）下自然变形的泥晶灰岩的延性变形机制
DOI：
10.1144/gsl.sp.1990.054.01.23
发表时间：
1990
期刊：
Geological Society, London, Special Publications
影响因子：
--
作者：
M. Burkhard
通讯作者：
M. Burkhard
通过方向分布函数进行织物分析
影响因子：
2.9
作者：
H. Bunge
通讯作者：
H. Bunge
影响因子：
3.5
作者：
H. Wenk;C. S. Venkitasubramanyan;D. Baker;F. J. Turner
通讯作者：
F. J. Turner
挖掘出的类似发震碳酸盐岩逆冲断层的断层结构和变形机制。
影响因子：
3.1
作者：
T. Tesei;C. Collettini;C. Viti;M. Barchi
通讯作者：
M. Barchi