Microstructures and their implications for faulting processes –Insights from DGLab core samples from the Gulf of Corinth

We have examined microstructures, mineralogical composition, geochemical alteration, and texture of four selected fault rock samples from the Deep Geodynamical Laboratory (DGLab) Gulf of Corinth project using optical microscopy, cathodoluminescence microscopy (CL), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements. The fault core is composed of red and gray clayey gouge material and surrounded by a damage zone of brecciated limestones. Pressure solution features, calcite veins and calcite clasts in the breccia and gouge material attest the presence of paleo-fluids and fluid-driven mass transfer during deformation. Differences in CL-colors between the matrix and calcite vein cement and inside the vein cement suggest repeated infiltration of fluids with different composition from various sources (formation water and meteoric water). Twin lamellae densities estimated in calcite veins are used as paleo-piezometer. The deduced differential stress is ∼140 ± 70 MPa for the older vein generation and appears to be higher than stress for the youngest veins (45 ± 23 MPa). In spite of the relatively small clay content in both samples, newly formed clay minerals have been observed in gray as well as red clayey gouge material. Differences between gray and red clay gouge material are found in fault rock composition, porosity and clay fabric. The proportion of chlorite in the red gouge is significantly less than that in the gray gouge whereas the initial porosity is significantly higher than in the gray gouge material. The detection of a well-oriented clay fabric in red clay gouge samples is unique in comparison to other major fault zones.     

龙门山飞仙关断层传播褶皱磁组构特征及构造意义

沿龙门山南段冲断前锋带飞仙关断层传播褶铍剖面钻取了270个磁组构定向岩芯样品,对其进行了磁性矿物与磁组构分析。通过等温剩磁和三轴热退磁实验确定了样品中的主要载磁矿物为赤铁矿。磁组构测试结果显示27个采样点的磁组构为中间组构与构造组构两种类型。通过对各点磁组构特征及各项磁组构参数进行详细分析,再结合断层传播褶皱运动学模型,得出断层传播褶皱形成过程中岩石应变及磁组构演化：断层扩展前的平行层缩短作用把原始的沉积组构改造成为中问组构;在断层扩展过程中,两翼地层的旋转抬升产生的简单剪切作用对地层磁化率各向异性产生影响,使得校正的磁化率各向异性度Pj值局部升高,以及在剪切变形强烈的区域形成构造磁组构。     

Clay fabrics in relation to the burial history of shales

Quantitative appraisal of compaction strain is essential for the study of the burial history of shales in sedimentary basins. The results of a preliminary fabric analysis of Westphalian and Zechstein shales in the Campine Basin (Belgium) show that clay fabric analysis, using an X-ray pole figure goniometer, is suitable for this purpose. Clay fabrics, in the range studied, are independent of depth and therefore cannot be used as depth indicators. This suggests that in the early stages of the burial history a stable clay fabric has to develop, which will basically remain unchanged during the subsequent burial history. The degree of clay particle preferred orientation not only reflects the compaction strain, but is also determined by mineralogical parameters: the presence of non-platy particles and the relative concentrations of the different clay minerals. This degree of preferred orientation furthermore determines the degree of fissility of the shales. These mineralogical factors limit the use of clay fabrics as truly quantitative strain markers. Their use as semi-quantitative strain markers remains advantageous, mainly because of the common occurrence of clay fabrics in the geological record. Moreover, the relative ease of measurement and the possibility of distinguishing compaction from tectonic strains favour the use of clay fabrics in the quantitative strain analysis of argillaceous rocks.     

黏土矿物与碱激发地聚物的相互作用机理

土体固化的核心问题之一就是使用适宜的固化剂固化黏土矿物。通过扫描电镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射(XRD)以及X射线光电子能谱(XPS)等试验方法,研究不同碱含量下碱激发地聚物固化的蒙脱石、伊利石和高岭土的微观结构、物质组成及物理化学反应过程,探究碱激发地聚物与黏土矿物之间的相互作用机理。研究结果表明:黏土矿物经碱激发地聚物固化后,由松散颗粒转变为块状致密结构;随着地聚物中碱含量的增加,Si、Al及Ca元素电子结合能下降;蒙脱石在衍射角为5°左右(001)峰形右移,层间距减小;蒙脱石吸附水含量减小,亲水能力下降,矿物活性被限制。     

一种求取碎屑岩储层中粘土总量的新方法

在实验分析的基础上,提出了一种新的求取碎屑岩储层中粘土总量的方法---二级抽提分离+非定向X射线衍射法,即首先用传统的抽提分离法分别提取出粒径小于10μm和10～64μm的微粒,然后用粒径小于10μm微粒的质量加上利用非定向X射线法测出的粒径在10～64μm微粒中粘土部分的质量,就得到该样品中粘土总量。并以WN油田碎屑岩储层为例,具体论述了该法的计算过程及其实际应用效果。研究结果表明,该法具有原理简单、精度高、理论性强、实际应用效果良好的优点,可作为求取沉积岩储层中粘土总量的可靠方法。     

Characteristics and implication of clay minerals in the northern and southern parts of the Chelung-pu fault, Taiwan

In this study, we report the characteristics of clay minerals present in the Chelung-pu fault in Taiwan. In the 1999 Chi-Chi earthquake, different slip motions were recorded along the Chelung-pu fault in the northern and southern parts of the fault. The characteristics of clay minerals present in the fault zones can be attributed to the differences in motion. We analyzed the shallow drill core samples obtained from the northern and southern sites penetrating the fault. The clay minerals identified in most of the samples from both the sites are smectite, illite, and chlorite. There are illite–smectite mixed layers with a high illite content and no chlorite–smectite mixed layer. In some samples, no smectite is detected. We also examined the iron content and symmetry of iron and magnesium in the silicate and hydroxide layers in chlorite. At the northern site, the total iron content in chlorite of gouge is larger than that of the host rocks. On the other hand, at the southern site, the total iron content varies widely. It is hypothesized that the smectite consumption and differences in the characteristics of chlorite may be controlled by the differences in the lithology, fluid chemistry, fluid temperature, or fault activities (heating or breakage) between the northern and southern sites.     

Shear zones in clay-rich fault gouge: A laboratory study of fabric development and evolution

Clay-rich fault rocks have long been recognized to host distinctive fabric elements, and fault rock fabric is increasingly thought to play a fundamental role in fault mechanical behaviour in the brittle regime. Although the geometries of fabric elements in fault gouges have been described for almost a century, the genesis and evolution of these elements during shear, and their links to bulk mechanical properties, remain poorly understood. We characterize the development and evolution of fabric elements with increasing shear in a variety of clay-rich experimental gouges over shear strains of <1 to >20 and at normal stresses of 2–150 MPa in the double-direct shear configuration. In addition to SEM observations of experiment products at a variety of shear strains, we quantified clay fabric intensity and the degree of grain size reduction using X-ray Texture Goniometry (XTG) and particle size distribution (PSD) measurements. We also measured P- and S-wave velocities during shear to further probe the evolution of shear fabric and gouge properties. We find that clay fabric elements develop in a systematic manner regardless of the gouge material. Riedel shears in the R₁ orientation and boundary-parallel shears are the dominant fabric elements. Riedel shears nucleate at layer margins and propagate into the layer shortly after reaching yield stress. Clay particles rotate into the P-orientation shortly after Riedels propagate through the layer. The Riedel shears are through-going, but are >10× thinner than similar zones observed in coarser granular materials. Our results suggest that the weakness of clay-rich fault gouge may be less a function of anisotropic crystal structure, as has been suggested previously, and more a consequence of very thin shear surfaces permitting deformation in clay-rich materials with minimal dilation or cataclasis. The very thin shear surfaces are a function of the fine grain size of the materials and possibly polymodal PSD's.     

The use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones

The microstructures of turbiditic and hemipelagic muds and mudstones were investigated using a scanning electron microscope to determine whether there are microstructural features that can differentiate turbiditic from hemipelagic sedimentary processes. Both types of muddy deposits are, in general, characterized by randomly‐oriented clay particles. However, turbiditic muds and mudstones also characteristically contain aggregates of ‘edge‐to‐face’ contacts between clay particles with long‐axis lengths of up to 30 μm. Based on observations of the clay fabric of the experimentally‐formed muds settled from previously agitated muddy fluids, these types of aggregates, hereafter referred to as ‘aggregates of clay particles’, are interpreted as having been formed by the collision of component flocs in turbulent fluids. Furthermore, some aggregates of clay particles have ‘face‐to‐face’ contacts between clay particles; this is similar to face‐to‐face aggregates characteristically developed in fluid‐mud deposits that are commonly recognized only in turbiditic mudstones, indicating the possibility of a final stage of deposition under highly‐dense conditions, such as temporary fluid muds. In conjunction with earlier proposed lithofacies‐based and ichnofacies‐based criteria, aggregates of clay particles should be useful for the differentiation of turbiditic and hemipelagic muddy deposits, particularly with limited volumes of non‐oriented samples from deep‐water successions.     

贵州碳酸盐岩红土中的粘土矿物及其形成机理

本文运用Ｘ射线衍射、红外光谱、差热、透射电镜和扫描电镜等方法对贵州碳酸盐岩红土中的粘土矿物进行了系统研究。高岭石和０．７ｎｍ埃洛石是碳酸盐岩红土中的主要粘土矿物，其次为伊利石、蛭石、绿泥石、绿泥石／蛭石混层矿物，水铝英石和三水铝石等。     

粘土矿物特征与沉积环境关系的初步探讨

采取同一盆地中含有不同指相化石的泥岩和现代已知不同环境中的泥质沉积物样品分别作为海水、半咸水和淡水沉积的代表,进行电镜、X光衍射和差热分析。发现不同环境样品中粘土组构、粘土矿物组合和自生粘土矿物类型均不相同,这些差异可能主要是由不同环境中的不同水介质条件所引起的。因此,粘土矿物的这些特征有可能成为指相标志。     

沉积环境对降落火山灰蚀变作用的影响--以大青山晚古生代煤系为例

借助于X光衍射仪、透射电子显微镜(TEM)和扫描电子显微镜(SEM)等手段,较详细地揭示了内蒙大青山晚古生代(C2-P1)煤系中降落火山灰的蚀变特征,以此来论述沉积环境对火山灰蚀变作用的影响。泥炭沼泽环境中,降落火山灰以原地直接高岭石化为主,残留较多的火山玻屑和晶屑形态,并具斑状结构;非泥炭沼泽环境中,降落火山灰以异地凝胶化-多种粘土矿物化为主,微层理、微层面等沉积岩特征明显。火山灰降落的环境不同,其蚀变作用和蚀变产物亦不同。本文对加深煤系火山事件沉积的认识和研究煤系高岭岩的成因机理颇有意义。     

Microtextural investigation (SEM and TEM study) of phyllosilicates in a major thrust fault zone (Monte Perdido, southern Pyrenees): impact on fault reactivation

Thrusting fault zone in foreland basins are characterized by highly foliated zones generally enriched in phyllosilicates which can play a major role on the mechanical behaviour of the fault. In this context, investigations of synkinematic clay minerals permit to determine the origin of the fluid from which they precipitated as well as the mechanisms of deformation. Our study is focused on clay mineral assemblages (illite and chlorite) in a major thrust fault located in the Monte Perdido massif (southern Pyrenees), a shallow thrust that affects upper cretaceous-paleocene platform carbonates and lower Eocene marls and turbidites. It implied 3?km of displacement of the Monte Perdido thrust unit with respect to the underlying Gavarnie unit. In this area the cleavage development by pressure-solution is linked to the Monte Perdido and Gavarnie thrust activity. The core zone of the fault, about 6?m thick, consists of an interval of intensely deformed clay-bearing rocks bounded by major shear surfaces. The deformed sediment is markedly darker than the protolith. Calcite-quartz shear veins along the shear planes are abundant. Detailed SEM and TEM observations of highly deformed fault zone samples indicate that clay mineral enrichment in the core zone of the fault is not only related to passive increase by pressure-solution mechanism but that dissolution?Crecrystallization of phyllosilicates occurs during deformation. A mineral segregation is observed in the highly deformed zone. Newly formed 2M ₁ muscovite is present along the cleavage whereas IIb chlorite crystals fill S_V2 shear veins suggesting syntectonic growth of phyllosilicates in the presence of fluids in low-grade metamorphic conditions. These mineralogical reactions act as weakening processes and would favour Monte Perdido fault creeping.     

Fluid focusing and back-reactions in the uplifted shoulder of the Rhine rift system: a clay mineral study along the Schauenburg Fault zone (Heidelberg, Germany)

A retrograde sequence of fluid-controlled, low-temperature mineral reactions has been preserved along an east-west striking, dextral-oblique-slip fault in the uplifted Rhine Graben shoulder. This fault (the Schauenburg Fault, near Heidelberg), juxtaposes Permian rhyolite against Carboniferous (Variscan) granite and shows syn- or post-rift displacement of the north–south trending, eastern boundary fault of the rift basin. Both mineral texture and rock fabric indicate that the fault forms a site of high rock permeability and fluid flow, and records the exhumation and fluid-rock history of the rift shoulder since the Mesozoic. The reaction sequence and mineral compositions of the clay minerals within the cataclasite, and adjacent granite and rhyolite lithologies, document progressively decreasing fluid temperatures, with back-reactions of pure 2M₁ illite to 1M_d (R3) illite-smectite, and eventually smectite and kaolinite assemblages. Compositional variations are attributed to Tertiary to Recent fluid flushing of the fault zone associated with rift flank uplift, and with progressive dilution of the electrolyte-rich, acidic to neutral hydrothermal brines by down-flowing electrolyte-poor, meteoric waters.     

湖南郴州枞树板铅锌矿X光组构分析

作者通过对湖南郴州枞树板铅锌矿围岩及含矿构造带岩石的X光岩组分析,认为在构造变形过程中,原岩粒度越细,对变形的反映越敏感。在相同的变形条件下,较细的变质砂岩石的石英定向组构比较粗的变质砂岩内明显,板岩和粉砂质板岩的定向组构最明显。枞树板地区近EW向褶皱变形组构表现强烈,近SN向褶皱变形组构较弱。矿化热液的蚀变作用破坏了岩石中早期褶皱变形组构,但铅锌矿脉内的石英没有明显的生长组构,说明在矿化和含矿石英脉成生过程中没有明显的张性充填结晶表现,而是一种以交代为主的矿化形式。这与从其它地质地球化学研究取得的关于本     

Adsorption capacity and mineralogical and physico-chemical characteristics of Shuwaymiyah palygorskite (Oman)

In this paper, Shuwaymiyah palygorskite in the Sultanate of Oman has been characterized mineralogically by X-ray diffraction (XRD) and electron microscopy, chemically by oxide compositions, structural formulae, and cation exchange capacity (CEC), and physically by specific surface area and adsorption isotherms. Batch adsorption studies were performed to evaluate the adsorption performance of methylene blue (MB) basic dye on the local clay mineral. The quantitative XRD analysis indicates that the purity of some selected samples of palygorskite clay is very high (about 70% of the clay minerals are palygorskite and 30% kaolinite). The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly support this conclusion. The adsorption equilibrium revealed that Shuwaymiyah palygorskite clay can uptake up to 51 mg of MB per 1 g mass of clay. MB adsorption is best fitted by Langmuir isotherm, and a pseudo-second-order kinetic model can be efficiently used to predict the kinetic of adsorption of MB by the palygorskite. The results obtained from these laboratory-scale adsorption tests indicate the promising adsorption capability of the Omani palygorskite.     

发震断裂带内黏土矿物的纳微米变形

断层泥是发震断裂最显著的物质标志之一,它保留着许多断层活动的信息.在野外宏观调查和显微视域观察基础上,利用SEM技术,从纳微米尺度,研究发震断裂带内黏土矿物的组合形态和变形样式,并对一些问题进行深入分析和讨论.黏土矿物在断层粘滑滑移过程中,出现定向排列,在正交偏光显微镜下表现为平行排列的消光带.在SEM视域下,可以观察到片状黏土矿物的定向排列,同时可以清晰地识别多次断层粘滑滑移事件.在断层泥中发现的蠕变滑移现象,带有普遍性.在显微视域下,黏土矿物表现为波状消光带.在SEM视域下,可以观察到片状黏土矿物的褶皱变形、流动变形、绕砾滑动、撕裂变形等.鉴于在同一个视域内,可以同时观察到粘滑滑移标志和蠕变滑移标志,通过分析其先后关系,发现蠕变滑移发生于粘滑滑移之前,对应于断层的亚失稳阶段的运动.      

岩石电子背散射衍射（EBSD）组构分析及应用

电子背散射衍射（EBSD）技术是现代构造地质学与显微构造分析领域一项崭新的技术,它与现代高分辨率扫描电子显微镜和能谱分析设备结合,可以对块状样品中微米或纳米级尺度的颗粒进行晶体结构分析, 从而使微观结构、微区成分与结晶学数据结合起来,能够更精细地对比研究矿物和岩石显微构造,为岩石显微构造分析开辟了一个全新的领域。分析了EBSD技术的基本原理、系统构成、样品制备和工作程序。介绍了石英组构测量,极细粒物质（微角砾岩）的组构特点,二轴晶矿物（角闪石）的组构、变形机制和金属硫化物组构分析的应用实例,对于应用EBSD系统开展研究存在的一些问题进行了讨论。     

A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault

The San Andreas Fault zone in central California accommodates tectonic strain by stable slip and microseismic activity. We study microstructural controls of strength and deformation in the fault using core samples provided by the San Andreas Fault Observatory at Depth (SAFOD) including gouge corresponding to presently active shearing intervals in the main borehole. The methods of study include high-resolution optical and electron microscopy, X-ray fluorescence mapping, X-ray powder diffraction, energy dispersive X-ray spectroscopy, white light interferometry, and image processing.The fault zone at the SAFOD site consists of a strongly deformed and foliated core zone that includes 2–3 m thick active shear zones, surrounded by less deformed rocks. Results suggest deformation and foliation of the core zone outside the active shear zones by alternating cataclasis and pressure solution mechanisms. The active shear zones, considered zones of large-scale shear localization, appear to be associated with an abundance of weak phases including smectite clays, serpentinite alteration products, and amorphous material. We suggest that deformation along the active shear zones is by a granular-type flow mechanism that involves frictional sliding of microlithons along phyllosilicate-rich Riedel shear surfaces as well as stress-driven diffusive mass transfer. The microstructural data may be interpreted to suggest that deformation in the active shear zones is strongly displacement-weakening. The fault creeps because the velocity strengthening weak gouge in the active shear zones is being sheared without strong restrengthening mechanisms such as cementation or fracture sealing. Possible mechanisms for the observed microseismicity in the creeping segment of the SAF include local high fluid pressure build-ups, hard asperity development by fracture-and-seal cycles, and stress build-up due to slip zone undulations.     

北京市中关村地区大气降尘的来源与垂向分布特征

利用光学和电子显微镜、X射线衍射仪以及同步辐射X射线荧光对北京市中关村地区大气降尘的粒度分布、颗粒物微观形貌特征、矿物组成及化学元素组成等方面进行分析研究。粒度分析表明中关村地区大气降尘随着相对高度的增加,粗颗粒物逐渐减少。大气降尘的颗粒物形貌可以分为粒状、柱状单矿物,圆球状飘珠和不规则粒状集合体3种类型。矿物组成及化学元素组成的分析显示中关村地区大气降尘的污染物主要来自自然扬尘、建筑扬尘、燃煤、汽车尾气等污染源。