板岩遇水软化的微观结构及力学特性研究

通过偏光显微镜、电子扫描电镜、粉晶X射线衍射,测定板岩泡水过程中吸水率、润湿角的变化,不同浸泡时间下的矿物颗粒微观结构、孔隙度的变化,并通过三轴压缩实验,研究了板岩泡水后发生软化的过程与机理。研究表明：板岩在浸泡后吸水率受板岩内层理面的产状、密度等参数的影响而改变,随着泡水时间的增加,吸水率在最初两天内变化较大,后期变化不太明显;板岩内部矿物颗粒在浸泡过程中产生体积膨胀,胶结变得松散,颗粒膨胀的时间稍滞后于吸水率的变化过程;三轴压缩实验结果显示,板岩浸泡后发生软化,峰值抗压强度随着吸水率增加按负对数规律降低;微观结构分析及润湿角的降低趋势表明,随浸泡时间延长,矿物颗粒之间的毛细管力、表面张力降低,使得板岩内部黏结力降低,宏观上则体现为岩石发生软化;在垂直于层理面方向更易发生体积膨胀,因此岩石在浸泡后更易沿着层理面产生破坏。     

Geology and geochemistry of Iberian roofing slates

This article analyzes the geochemical and mineralogical composition of the roofing slate deposits of the Iberian Peninsula. Most roofing slate deposits are found on Middle and Upper Ordovician terrains, although there are also deposits in the Ediacaran, Cambrian and Devonian terrains. Samples of slate were taken in most of the active quarries of the Iberian Peninsula, and being analyzed by X-ray Diffraction and Fluorescence. Each lithotect or slate productive formation has its own specific proportions of major and trace elements, being able to differentiate between them by using these relationships. This fact is particularly interesting in geological exploration and prospecting, as it allows knowing exactly the slate lithotect, and also for restoration work in the architectural heritage, due to the ability of identifying the source of the original slate tiles.     

粉砂质板岩力学特性及各向异性特性

为研究鄂西北地区板岩的力学特性及各向异性特征,开展了志留系粉砂质板岩的单轴压缩和巴西劈裂试验,分析了试样的力学特性和各向异性特征以及在不同荷载作用下的变形破坏模式,揭示了不同破坏模式的力学机制,并通过数值分析研究了不同板理面角度板岩边坡破坏模式及力学机制。研究结果表明,粉砂质板岩中的板理面是影响岩体力学行为的弱面,使得粉砂质板岩表现出明显的各向异性的特征。在单轴压缩条件下,粉砂质板岩在垂直板理面方向比平行板理面方向更易变形,变形量更大;平行板理面方向加载时试样破坏类型为竖向劈裂型张拉破坏,其实质是压杆失稳;垂直板理面加载时试样的破坏类型为穿切板理面的劈裂型剪切破坏;所测得的力学参数各向异性也较明显。在劈裂荷载作用下,粉砂质板岩的破坏模式主要有张拉劈裂破坏和沿板理面剪切破坏两种,所得抗拉强度在平行板理面方向上最大,在垂直板理面方向上最小,两个方向上的抗拉强度均小于抗压强度。由于板理面间的抗拉强度极低,在受到与板理面呈小角度相交的劈裂荷载作用时,容易产生沿板理面的张拉劈裂或拉剪破坏,在实际工程中应尽量避免板理面间的受拉破坏和沿板理面的拉剪破坏。在边坡工程中,板理面倾向、倾角对边坡破坏模式及力学机制有较大影响,边坡防护治理需充分考虑这一影响。上述研究为粉砂质板岩区岩质边坡防护治理以及其他岩石工程设计与施工提供理论依据与技术基础。     

Conical fold terminations in the bannisdale slates of the english lake district

The structure of an area of Silurian rocks in the non-metamorphic Caledonides near Kendal, Cumbria (U.K.) is briefly described. The main folds are periclinal and die away in the southeast of the area. The uniform thickness of sandstone beds around folds shows that they deformed dominantly by buckling and only locally is flattening important. A model is developed to explain the conical attitude of bedding within the periclinal terminations. The model is erected on the basis of buckling alone and is developed to examine the effects of flattening. Inhomogeneity in buckling and flattening over the area is demonstrated using the model and discussed. The pattern of folding is compared to that predicted by earlier, published, experimental work.     

Tectonically dewatered slates in the Ludlovian of the Lake District,England

Multiple siltstone dykes intruded parallel to cleavage in the Ludlovian argillites and graywackes of the Lake District throw new light on the origin of slaty cleavage. Pore pressures equalling lithostatic pressure developed during the Caledonian orogeny and caused tectonic dewatering of the partially lithified sediments. Slaty cleavage was initiated as an essentially planar structure by the intrusion of thin pelitic folia during the escape of the pore water. Cleavage folia and fold axial planes may have a common geometric relationship to the deforming stresses, but are independent of each other in origin. Continued deformation after tectonic dewatering refracted the cleavage by rotation of competent layers. Critical examination of evidence supporting traditional theories of slaty-cleavage formation shows that all observed relationships are compatible with the tectonic-dewatering theory.     

Mica beards in three slates: Morphology,formation and bearing on the strain history

Beards are intergrowths of mica, chlorite and quartz or feldspar on detrital grains in weakly metamorphosed sedimentary rocks. The three samples studied contain beards of mica and quartz (or feldspar). Their internal morphology shows a variation in mica orientation related to the external foliation (matrix). Formation occurred during foliation development with a syntaxial growth history. In three dimensions, the beards have oblate shapes, so that they are present in all planes cut parallel to the shortening direction. This indicates flattening strain conditions around the detrital grains during the beard formation.Bulk inhomogeneous shortening, resulting in an anastomosing foliation, can explain the local extension within the plane containing the fold axis and the shortening direction. Concurrently, an approximately constant lenght in the direction of the fold axis is maintained on a regional scale (plane strain). Volume loss probably plays an important role during the formation history.

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Zusammenfassung Glimmerbärte in schwach metamorphen Sedimenten sind syntektonische Verwachsungen von Glimmer, Chlorit, Quarz oder Feldspat auf detritischen Körnern. Die drei hier untersuchten Proben enthalten Bärte aus Hellglimmer und Quarz (oder Feldspat). Die Glimmerorientierung zeigt Variationen in Relation zum umgebenden Schieferungsgefüge (Matrix). Die Bildung der Bärte fand mit syntaxialem Wachstum während der Schieferung statt. Dreidimensional haben die Bärte eine abgeplattete Gestalt, so daß sie in allen Schnittlagen parallel zur Verkürzungsrichtung zu beobachten sind. Dies weist auf plättende Verformung um detritische Körner während der Bildung der Bärte hin.Bulk inhomogeneous shortening führt zu einem linsigen Schieferungsgefüge und kann bei gleichzeitiger Annahme einer nicht volumenkonstanten Deformation als Erklärung für die im Korngefüge beobachtete Dehnung parallel zur Faltenachse herangezogen werden. Im regionalen Maßstab wird aber eine konstante Länge in Richtung der Faltenachse und damit ebene Deformation angenommen.

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Résumé Les barbes de mica sont des intercroissances de quartz (ou feldspath) et de mica sur des grains détritiques dans les roches sédimentaires peu métamorphisées. Elles ont été étudiées dans trois échantillons. Leur morphologie interne montre une variation dans l'orientation du mica en relation avec la schistosité externe (matrice). Leur formation s'est produite pendant le développement de la schistosité, avec une histoire de croissance «syntaxiale». Les barbes ont une forme oblongue en trois dimensions, de sorte qu'elles sont visibles dans toutes les sections parallèles à la direction de raccourcissement. Cela indique, pendant la formation des barbes, l'existence d'un aplatissement autour des grains détritiques.Le raccourcissement non homogène, qui entraîne une foliation anastomosée peut être invoqué, conjointement à une déformation avec perte de volume, pour expliquer l'allongement que présente localement la microstructure parallèlement à l'axe des plis. A l'échelle régionale, toutefois, on admet la constance de la longuer selon la direction des axes et, partant, le caractère plan de la déformation.

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, (Glimmerbärte). Glimmerbärte ( ). — . Glimmerbärte . Glimmerbärte , , . Bulk inhomogeneous shortening , , , . .

     

Mineralogical and geochemical alteration of low-grade metamorphic black slates due to oxidative weathering

Low-grade metamorphic black slates of Silurian and Lower Devonian ages (from the Thüringisches Schiefergebirge in Germany) were investigated to identify mineralogical and geochemical alterations that occur during the oxidative weathering black slates.The slates exhibit an intense total organic carbon decrease (>90 wt%) due to oxidative weathering. The organic matter in black slate consists mainly of non-pyrolysable material with only minor portions of pyrolysable material. In contrast to the non-pyrolysable organic matter, the concentration of pyrolysable organic matter is not decreased during weathering. Heating experiments have yielded information about a potential protection of pyrolysable organic matter against weathering, which is probably caused by a structural configuration or the intergrowth of organic matter and illite.The slates consist mainly of illite. Iron oxide (goethite) and phosphate encrustations were formed on slate surfaces as a result of oxidative and acid weathering of both iron sulfide and monazite. Kaolinite often occurs as an older encrustation beneath the iron oxide encrustations. Encrustations of iron oxide and phosphate are major sinks for trace elements, released during oxidative weathering.     

不同含水条件下板岩力学实验研究与理论分析

以南水北调西线的板岩为研究对象,进行了不同泡水条件下的三轴压缩实验,通过引入相对吸水率的定义,分析了吸水率变化对岩石强度、弹性模量及泊松比等力学参数的影响,并从微观的角度分析了试样发生变化的机理,得出如下结论：(1)板岩在泡水后三轴抗压强度发生降低,最大降低辐度达46 %左右,抗压强度随相对吸水率的变化可以用函数式来有效的描述;(2)在泡水后,板岩的弹性模量与泊松比随着吸水率的增大而增大,但由于板岩自身各向异性明显,规律性不是特别明显,只能近似用关系式来模拟;(3)理论分析证实：实际泡水条件下的岩样,在受力挤压后,会经历排水与不排水两种过程,随着吸水率的提高,弹性模量与泊松比增大,验证了实验结果;(4)利用微观力学模型初步证实：泡水后板岩颗粒的吸水性与颗粒间毛细管力的减小是造成板岩泡水后发生软化的原因。     

The stratigraphy and tectonics of the Skiddaw slates and the relationship of the overlying borrowdale volcanic series in part of the Lake District

The Skiddaw Slates consist of eight formations with the substantial thickness of about 30,000 ft. This geosynclinal sequence is of Arenig age though the highest formation may continue into the Lower Llanvirn. The polyphase tectonics of the Skiddaw Slates and the relationship of the overlying Borrowdale Volcanic Series are discussed. It is concluded that the Caledonian tectonic history of this part of Britain contains two paroxysms of orogenic activity. In addition to the orthodox end-Silurian orogenesis there was also an intra-Lower Ordovician orogenic episode which took place towards the close of the Llanvirn. During the earlier tectonic climax the Skiddaw Slates were deformed by two phases of folding. Their structure is, therefore, largely of pre-Borrowdale age and bears little relation to that of the overlying cover. After this dual deformation the slaty basement was truncated by erosion and is separated from the overlying Borrowdale Volcanic Series by an angular unconformity. Only the end-Silurian folding affects the volcanic superstructure and the younger Lower Palaeozoic sequence.     

Do reduction spots predate finite strain? A magnetic diagnosis of Cambrian slates in North Wales

The purple Cambrian slates of North Wales contain green-colored, irregular patches drawn out along cleavage and the more familiar ellipsoidal reduction spots that are parallel to cleavage. Because parallelism of pre-strain ellipsoids could only be produced by extremely high strain, we reject the hypothesis that these are strain markers. Here, we use magnetic methods to resolve this argument. The magnetic analysis reveals that the magnetic fabric of purple slate differs from the green variety of the slate only in the oxidation state, and indicates that the reduction process postdates cleavage. This suggests that the shape of reduction spots reflects the anisotropy of diffusion during reduction, not finite strain and alignment of an initially ellipsoidal object in the slates.     

A Note on Robust Estimates

It is well known that the mean can be an unsatisfactory estimator of a true value if data are a poor approximation to a normal distribution or are too few in number for a normal distribution to be adequately delineated. Unfortunately, this knowledge is not always implemented in the evaluation of analytical data. The median may be used occasionally because it is recognised to be less affected by discrepent data. However, there are other 'robust' estimators which can be better than the simple median. This note complements a previous paper by the writer (1).