Crystal bending,subgrain boundary development,and recrystallization in orthopyroxene during granulite-facies deformation

A prominent feature of a granulite-facies shear zone from the Hidaka Main Zone (Japan) is the folding of orthopyroxene (opx) porphyroclasts. Dislocation density estimated by transmission electron microscope (TEM) and chemical etching in homogeneously folded domains is too low to account for the amplitude of crystallographic bending, leading us to propose a model similar to “flexural slip” folding, where folded layers are micrometer-wide opx layers between thin planar clinopyroxene (cpx) exsolutions. Extension (compression) in the extrados (intrados) of the folded layer is accommodated by dislocations at the cpx–opx interfaces. Alternatively to distributed deformation, crystal bending also localizes in grain boundaries (GBs), mostly oriented close to the (001) plane and with various misorientation angles but misorientation axes consistently close to the b-axis. For misorientation up to a few degrees, GBs were imaged as tilt walls composed of regularly spaced (100)[001] dislocations. For misorientation angles of 7°, individual dislocations are no longer visible, but high-resolution TEM (HRTEM) observation showed the partial continuity of opx tetrahedral chains through the boundary. For 21° misorientation, the two adjacent crystals are completely separated by an incoherent boundary. In spite of these atomic-scale variations, all GBs share orientation and rotation axis, suggesting a continuous process of misorientation by symmetric incorporation of (100)[001] dislocations. In addition to the dominant GBs perpendicular to the (100) plane, boundaries at low angle with (100) planes are also present, incorporating dislocations with a component of Burgers vector along the a-axis. The two kinds of boundaries combine to delimit subgrains, which progressively rotate with respect to host grains around the b-axis, eventually leading to recrystallization of large porphyroclasts.     

Exsolution of Ca-clinopyroxene from orthopyroxene aided by deformation

Monoclinic calcium-poor shear-transformation lamellae and calcium-rich exsolution lamellae occur parallel to (100) in orthopyroxene. The formation of both structures from an orthopyroxene host involves a shear on (100) parallel to [001], with additional cation exchange in the exsolution case. The shear transformation involves a macroscopic simple shear angle of 13.3° (shear strain of 0.236) and produces a specific a-axis orientation with respect to the sense of shear; we have found that this orientation dominates in exsolution lamellae in kinked orthopyroxene, where the sense of shear is known. In undeformed orthopyroxene, there is generally no preferred sense of orientation of the monoclinic a axes. We advance a specific model for exsolution involving nucleation and growth by shear transformation combined with cation exchange, thus circumventing the classical nucleation barrier and permitting exsolution at lower solute supersaturations.     

The effect of Cr on the solubility of Al in orthopyroxene: experiments and thermodynamic modelling

The partitioning of chromium and aluminium between coexisting orthopyroxene and spinel in equilibrium with forsterite in the system MgO–Al₂O₃–SiO₂–Cr₂O₃ (MAS–Cr) has been experimentally determined as a function of temperature, pressure and Cr/(Cr + Al) ratio. Experiments were conducted at temperatures between 1300 and 1500 °C and at pressures from 5 to 54 kbar. Previous experimental results on the (Al, Cr)₂O₃ and Mg(Al, Cr)₂O₄ solid solutions have been combined with the present results plus relevant data from the CMAS system to derive a thermodynamic model for Al–Cr-bearing orthopyroxenes, spinels and corundum–eskolaite solid solutions. The orthopyroxene solid solution can be modelled within the accuracy of all experimental constraints as a ternary solid solution involving the components Mg₂Si₂O₆ ( E), MgAl₂SiO₆ (M) and MgCr₂SiO₆ (C), in which the activities are related to composition through the equations: The mole fractions are defined as where n _Al and n _Cr are the number of Al and Cr cations per orthopyroxene formula unit of six oxygens. These expressions reduce to one-site mixing for Mg₂Si₂O₆–MgAl₂SiO₆ orthopyroxenes in the Cr-free system, but are equivalent to two-site mixing for the exchange of Al and Cr between orthopyroxene and spinel, as required by the experimental data. We find W ^opx _EM =W ^opx _EC  = 20 kJ mol⁻¹ and W ^opx _MC =0. Received: 9 August 1999 / Accepted: 18 February 2000     

The effect of the basal-prism mechanism switch on fabric development during plastic deformation of quartzite

Blacic described a transition from basal 〈a〉 to prism 〈c〉 dislocation glide systems as temperature increased or strain-rate decreased in sequences of experiments involving deformation of single crystals of quartz. In this paper theoretical aspects of competition between these systems during plastic deformation are discussed. It is concluded that the basal-prism mechanism switch should have important consequences for the development of crystallographic fabrics during plastic deformation of quartzite, and the Taylor-Bishop-Hill analysis is used in an attempt to predict expected fabric transitions.     

Microstructures in subglacial and proglacial sediments: understanding faults,folds and fabrics,and the influence of water on the style of deformation

Macroscopic field and micromorphological studies have been carried out on subglacially and proglacially deformed glacigenic sequences at a number of sites throughout Scotland, UK. Examination of microstructures (folds, faults, hydrofractures, plasmic fabrics) aided understanding of the deformation histories preserved in the sediments, but a similar range of structures were developed in both Subglacial and Proglacial settings. Discrimination between Subglacial and Proglacial deformation was only possible when micromorphological data was used in conjunction with larger-scale field observations. Variations in lithology and water content were controlling factors influencing the style and apparent intensity of deformation recorded. Changes in pore-water content and pressure during deformation can lead to liquefaction and hydrofracturing, with early-formed structures locally controlling the pattern of water escape. Liquefaction can also lead to homogenisation of the sediments and the destruction of earlier deformation structures, even at relatively low strains. Beds or zones of liquefied sand and silt may form highly ‘lubricated’ detachments within the sediment pile, resulting in a marked reduction in the amount of shear transmitted to underlying units. A multidisciplinary approach, involving sedimentological, geomorphological, stratigraphical and structural field observations, combined with micromorphological analysis, is recommended to confidently unravel the glacitectonic history and depositional environment of most deformed glacigenic sedimentary sequences.     

低含水量粘土的加载速率效应与蠕变变形

通过对低含水量藤森粘土(Fujinomori clay)试样的单向固结试验,研究了低含水量粘土的加载速率效应与蠕变变形。所采用的藤森粘土土样有湿润(含水量小于15%)、风干(含水量小于4.5%)与烘干(含水量小于1%)3种。试验中,应变率逐步改变,同时进行了蠕变及加、卸载试验以及小幅度的循环加载试验。试验结果表明:湿润土样、风干土样与烘干土样都有明显的加载速率效应与蠕变变形;在大范围的卸载-重复加载过程中,蠕变变形会由卸载初期的正变形逐步发展为后期的负变形,在这个发展过程中存在着中性点(即蠕变为零,或者无蠕变的点);藤森粘土的加载速率效应随含水量的降低有所降低,即湿润藤森土样的加载速率效应更明显。     

盐渍土水-热场耦合效应与盐胀变形试验

为了研究西北干旱地区盐渍土在自然气候条件下的水-热场变化特征与盐胀变形规律,在4.5 m深试验坑内埋设了若干套竖向变形观测设备、含水率和温度传感器,对坑内不同深度土层的温度场、水分场和盐胀变形随季节性变化状况进行了为期1 a的动态监测和分析研究。结果表明：0.6 m以上土层相较于其他土层对气候温度变化的响应更加积极、温差变化幅值也更大,且土层间的温差幅值随降温期的不断深入而增大;土体含水率变化主要受降水、蒸发和温度梯度的耦合影响, 0.4 m以上土层水分的变化幅度较其他土层而言更为显著,土层水分迁移沿深度方向表现出分带现象;盐胀变形主要受温度和水分迁移的影响,盐胀变形主要发生在距地表1.0 m土层深度内,主要发展时间在当年11月至次年2月之间。     

广东河台金矿田糜棱岩磁组构对剪切带变形与成矿的约束

河台金矿田是广东省内规模最大的金矿,由于金矿床都产于糜棱岩带中,因而被认为是典型的与剪切带有关的金矿。然而,对于Au矿化与剪切带变形条件之间的关系目前仍不十分清楚。高村和云西是河台金矿田两个代表性的金矿床,分别受ML11和ML9两条剪切带的控制。本文在对两条剪切带中的含矿和无矿糜棱岩的变形特征进行野外调查和室内岩（矿）相学观察的基础上,分别开展岩石磁学和磁化率各向异性（AMS）特征研究。糜棱岩x- T曲线显示了磁黄铁矿的居里温度,结合磁滞回线、等温剩磁（IRM）以及矿相学特征,表明河台金矿田糜棱岩几乎不含磁铁矿,载磁矿物主要为黑云母和磁黄铁矿,但是磁黄铁矿的贡献要远大于黑云母。两条糜棱岩带中不含矿糜棱岩的平均磁化率Km＜500×10-6 (SI)、磁化率各向异性度Pj、椭球体形状参数T、磁面理F和磁线理L没有明显差别。并且形成两条剪切带的主应力方向也近于一致,最大主应力方向σ1（K3）为近水平NNW- SSE向,最小主应力σ3（K1）为NEE- SWW向,倾伏角较缓。运动学涡度Wk值也近似,在0. 12~0. 65之间,小于0. 71。上述特征暗示两条含金剪切带都是在印支期NNW- SSE向近水平的强烈挤压作用下形成的,其中发育的糜棱岩为S型和SL型构造岩,具有强烈压扁的特征,并且在剪切变形过程中纯剪切作用所占的比重要明显大于简单剪切。然而,两条剪切带中含矿糜棱岩与无矿糜棱岩的AMS特征有明显的区别。含矿糜棱岩的K1近于直立,且Km＞500×10-6 (SI)和Pj值都明显大于无矿糜棱岩。因此,糜棱岩的变形强度与含矿性具有一定的正相关关系,而在燕山期叠加的脆韧性变形使得最大磁化率主轴（即最小主应力轴）变陡,更有利于热液的运移和最终成矿。     

Calcite fabrics around folds as indicators of deformation history

In the Morcles nappe (lowermost Helvetic nappe in western Switzerland) two phases of folding have been established. In this article the relationship between the calcite fabrics present in folded limestones and the folding history is analysed. Calcite fabrics around the first- and second-phase folds are related to the second phase of deformation. The following fabric patterns have been found. (1) The fabric geometry around a second-phase fold from the most internal part of the inverted limb of the nappe (locality Saillon) can be related to an overall simple shear deformation sequence, the sense of shear being related to the last advance of the Morcles nappe over the underlying autochthonous sedimentary cover of the Aiguilles Rouges massif. (2) In more external parts of the inverted limb (locality Petit Pré) the fabrics around a second-phase fold are interpreted as indicating a change in the deformation history from simple shear to a strain regime which can account for shortening along the first-phase cleavage by the formation of buckle folds. This change in the local strain regime could be related to a ‘locking’ of the frontal folds of the nappe during the last overthrust shear movements. (3) In the normal limb of the nappe the fabrics around a late second-phase kink fold (locality Neimia) are earlier than the folding event and appear to be rotated passively by the fold. (4) The fabrics around a first-phase fold (locality La Routia) are later than the folding event and overprint the fold.     

The effect of experimental deformation on the graphitization of Pennsylvania anthracite

“Hard” carbon-based Pennsylvania anthracite was deformed in the steady-state at high temperatures and pressures in a series of coaxial and simple shear experiments designed to constrain the role of shear strain and strain energy in the graphitization process. Graphitization did not occur in coaxially deformed anthracite. Nonetheless, dramatic molecular ordering occurs at T 700°C, with average bireflectance values (%) increasing from 1.68 at 700°C to 6.36 at 900°C. R_omin is lowest and bireflectance is highest in zones of high strain (e.g., kink bands) at all temperatures.In anthracite samples deformed in simple shear over the 600°–900°C range at 1.0 GPa, average R_omax (%) values increase up to 11.9, whereas average bireflectance (%) values increase up to 10.7. Bireflectance increases with increasing shear strain and locally exceeds 12.5%. Graphitization occurs in several anthracite sample deformed in simple shear at 900°C. X-ray diffraction and transmission electron microscopy confirms the presence of graphite with d₀₀₂=0.3363 nm. These data strongly suggest that shear strain is the dominant factor responsible for the natural transformation of anthracite to graphite at temperatures far below the 1600°C required for graphitization of other hard carbons in earlier hydrostatic heating experiments at 0.5 GPa pressure.     

The effect of protective pillars on the deformation of mine shafts

Summary Mine shafts have traditionally been protected by leaving the ore in the immediate surroundings of the shafts in place as a pillar. Empirical rules are used to determine the dimensions of these protective pillars. The face element principle introduced by Salamon has been used to compute functions which express the influence of mining in a horizontal seam on the rock mass above it. Values have been calculated for the tilt, distortion, horizontal and vertical strain, curvature, and vertical stress along a shaft for various values of Poisson's ratio, seam depth, pillar radius, mining geometry, and closure over the mined area. The results are compared with those obtained using empirical ideas, particularly the angle of draw concept in determining pillar size. It appears that the depth of the seam is of major significance and that no pillar is needed for the protection of a shaft when the mined seam is beyond a certain depth. On the other hand it is possible, at all depths, to replace the protective action of a shaft pillar by other mining schemes. A significant amount of information which has been published on experience gained during the mining of shaft pillars tends to indicate that in many mines shaft pillars are excessively large.

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Zusammenfassung Schachtsicherheitspfeiler, die den Schacht vor Abbaueinwirkungen schützen sollen, werden gewöhnlich aufgrund von Erfahrungswerten bemessen.Die durch den Abbau in einem Flöz flacher Lagerung verursachten Einwirkungen auf einen saigeren Schacht sind hier nach dem Flächenelement-Prinzip ermittelt, wie Salamon es einführte. Entlang der Schachtsäule wurden die Schiefstellung, Verschiebung, horizontale und vertikale Dehnung, Krümmung und vertikale Spannung berechnet. Dabei wird der Einfluß der Querdehnungszahl, der Flöztiefe, des Pfeilerradius, der Form des Abbaufeldes und der Konvergenz im Flöz betrachtet. Diese Ergebnisse werden mit empirischen Regeln verglichen. Dabei ergab sich, daß die Tiefe des Flözes erhebliche Bedeutung hat und daß zum Schutze des Schachtes kein Pfeiler benötigt wird, wenn das abgebaute Flöz unterhalb einer bestimmten Teufe liegt. Auf der anderen Seite ist es für alle Tiefen möglich, den Schutz des Schachtes durch den Sicherheitspfeiler ersetzende geeignete Abbaumethoden zu gewährleisten.Manche Veröffentlichungen lassen erkennen, daß Schachtsicherheitspfeiler oft unnötig groß bemessen sind.

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Résumé En général la protection des puits est accomplie par l'abandon d'une partie du gisement, le stot de puits. Les dimensions des stots sont déterminées par des méthodes empiriques.Dans cette étude c'est la méthode proposée par Salamon qui est employée; il s'agit du calcul de l'influence de l'extraction d'un élément de taille sur les morts terrains supérieurs. Cette méthode permet de calculer les déformations, la pente, la distorsion, la courbure et les tensions le long du puits. L'influence de la profondeur de la couche, de la convergence, de l'aire exploitée, du diamètre du stot de protection et des caractéristiques mécaniques du terrain ont été considérées.Les résultats indiquent l'importance particulière de la profondeur du gisement. En effet, au-delà d'une certaine profondeur un stot de protection devient superflu. D'autre part l'influence de l'aire exploitée et de la convergence dans cette région sont telles qu'il est toujours possible de remplacer l'action protectrice du stot par une protection equivalente fournie par l'emploi d'un schèma d'exploitation bien choisi.Le nombre de cas où une exploitation partielle ou entière du stot de puits a eu lieu et où son influence sur la colonne du puits a été décrite est suffisant pour permettre d'affirmer qu'en général les dimensions du stot de puits sont trop importantes.

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With 11 Figures     

Heterogeneous deformation recorded by magnetic fabrics in the Pyrenean Axial Zone

Magnetic fabrics studies (AMS) are a useful tool in order to describe the distribution of deformation in orogenic areas where conventional techniques are difficult to apply, especially due to the lack of proper strain markers. In the present study, AMS and structural analysis are used to define the distribution of deformation in the Central Axial and Nogueres Zones, an area of strong structural changes (i) in the geometry of the antiformal stack defining the Pyrenean Axial Zone and (ii) the distribution of Alpine cleavage. The studied rocks are Lower-Middle Triassic red beds that crop out in three different stacked thrust units (Bielsa, Nogueres and Orri). Primary sedimentary fabrics are preserved in the uppermost thrust units (Nogueres Zone), but a high percentage of the sampling sites shows an overprint of Alpine compression on magnetic fabrics, with the magnetic lineation mostly parallel to the tectonic grain defined by compressional structures and the magnetic foliation showing different orientations between the poles to cleavage and bedding. The development of compressional fabrics strongly depends on the structural position of the sites, and two deformation gradients can be inferred: the southern margin of the Axial Zone (Orri and Bielsa units) shows strong internal deformation, increasing towards the North; farther north (in the restored cross-section), deformation is in general terms lower, but increases towards the basal thrust of the Nogueres Zone. The heterogeneous distribution of Alpine internal deformation indicates a preferred development of cleavage in the Variscan basement and overlying units of the southern margin of the Axial Zone (mainly in the Orri unit), that could be partly controlled by the tectonic load resulting from the stacking of thrust sheets.     

油页岩开发地下水资源影响预测与评价

以吉林省汪清县罗子沟油页岩开发为实例．根据参数的确定、地下水资源的估算、坑道排水量的计算、矿坑排水最大水位降的预测．对矿坑排水量进行评价,再运用地下水资源补给模数、潜水调节量及疏干体积法验证排水量的计算．从而达到研究油页岩的开发对地下水资源的影响和评价的目的。     

The effect of ductile deformation on the kinetics and mechanisms of the aragonite-calcite transformation

Abstract The effect of ductile deformation (dislocation creep) on the kinetics of the aragonite-calcite transformation has been studied at 1 atm (330° C and 360° C) and 900-1500 MPa (500° C) using undeformed and either previously or simultaneously deformed samples (500° C and a strain rate of 10^-6 s). Deformation enhances the rate of the transformation of calcite to aragonite, but decreases the rate of transformation of aragonite to calcite. The difference results from a dependence of transformation rate on grain size, coupled with a difference in the accommodation mechanisms, climb versus recry-stallization, of these minerals during dislocation creep. Dislocation climb is relatively easy in calcite and thus plastic strain results in high dislocation densities without significant grain size reduction. The rate of transformation to aragonite is enhanced primarily because of the increase in nucleation sites at dislocations and subgrain boundaries. In aragonite, on the other hand, dislocation climb is difficult and thus plastic strain produces extensive dynamic recry-stallization resulting in a substantial grain size reduction. The transformation of aragonite is inhibited because the increase in calcite nucleation sites at dislocations and/or new grain boundaries is more than offset by the inability of calcite to grow across high angle grain boundaries. Thus the net effect of ductile deformation by dislocation creep on the kinetics of polymorphic phase transformations depends on the details of the accommodation mechanism.     

The development of orientated symplectites during deformation

Abstract Orientated symplectites have been observed in deformed granulite facies metabasic rocks from the Ivrea-Verbano zone in northern Italy. The area underwent lower crustal extension, accommodated by movement on localized high- T shear zones. In areas of relatively low strain, such as at the margins of shear zones, symplectites of orthopyroxene, plagioclase and spinel have formed. The symplectites are vermiform and orientated parallel to the main foliation and in the regional stretching direction. The reaction was synkinematic with the deformation, and only developed in potentially dilatant grain boundaries in the rock. It was presumably inhibited in grain boundaries subjected to higher normal stress due to the relatively large volume increase involved in the reaction.
The observations support the interpretation that the deformation was related to regional extension under high- T granulite facies conditions, the symplectites forming as a result of decreasing pressure.     

The effect of deformation on the TitaniQ geothermobarometer: an experimental study

We performed high strain (up to 47 %) axial compression experiments on natural quartz single crystals with added rutile powder (TiO₂) and ~0.2 wt% H₂O to investigate the effects of deformation on the titanium-in-quartz (TitaniQ) geothermobarometer. One of the objectives was to study the relationships between different deformation mechanisms and incorporation of Ti into recrystallized quartz grains. Experiments were performed in a Griggs-type solid-medium deformation apparatus at confining pressures of 1.0–1.5 GPa and temperatures of 800–1,000 °C, at constant strain rates of 1 × 10^?6 or 1 × 10^?7 s^?1. Mobility of Ti in the fluid phase and saturation of rutile at grain boundaries during the deformation experiments are indicated by precipitation of secondary rutile in cracks and along the grain boundaries of newly recrystallized quartz grains. Microstructural analysis by light and scanning electron microscopy (the latter including electron backscatter diffraction mapping of grain misorientations) shows that the strongly deformed quartz single crystals contain a wide variety of deformation microstructures and shows evidence for subgrain rotation (SGR) and grain boundary migration recrystallization (GBMR). In addition, substantial grain growth occurred in annealing experiments after deformation. The GBMR and grain growth are evidence of moving grain boundaries, a microstructure favored by high temperatures. Electron microprobe analysis shows no significant increase in Ti content in recrystallized quartz grains formed by SGR or by GBMR, nor in grains grown by annealing. This result indicates that neither SGR nor moving grain boundaries during GBMR and grain growth are adequate processes to facilitate re-equilibration of the Ti content in experimentally deformed quartz crystals at the investigated conditions. More generally, our results suggest that exchange of Ti in quartz at low H₂O contents (which may be realistic for natural deformation conditions) is still not fully understood. Thus, the application of the TitaniQ geothermobarometer to deformed metamorphic rocks at low fluid contents may not be as straightforward as previously thought and requires further research.     

地表移动与变形的环境影响与预测

矿山开采会引发地表移动与变形。应用概率积分法对吉林省汪清县罗子沟油页岩矿区进行在矿区服务期满43年内有关地表下沉、倾斜、曲率、水平移动和水平变形的预测,以便在采矿过程中有所依据,以避免造成地表的破坏。     

铝离子对黑云母溶解/转化的制约及机制研究

采用X 射线衍射、傅里叶红外光谱、热重分析、透射电子显微镜和穆斯堡尔谱等手段,研究了 Al3+对黑云母溶解/转化过程的影响,重点分析了不同Al3+浓度作用下黑云母转化产物的矿物学特征及黑云母转化机制.结果显示,Al3+通过水解作用产生质子,加速黑云母片层的溶解及转化.当Al3+浓度较低时(0.01～0.10mol/L),Al3+水解产生的较少量质子对黑云母片层结构溶解有一定促进作用,转化产物以蛭石、水黑云母和绿泥石为主,优先溶出的Fe 聚集成核,同时吸附溶出的Si,形成具有核壳结构的球形纳米颗粒和结晶良好的赤铁矿.当Al3+浓度较高时(0.30～0.60mol/L),Al3+水解产生大量质子,显著加速黑云母结构溶解,黑云母转化产物主要为高岭石和弱结晶的铁氧化物.Al3+能明显改变黑云母的溶解速率及转化产物,从而影响黑云母的风化过程.     

The solubility of alumina in orthopyroxene coexisting with garnet

The solubility of alumina in complex orthopyroxenes crystallised in equilibrium with garnet has been determined over the pressure-temperature range 8–30 Kb and 800–1250° C. The results are in good agreement with predictions made using the simple thermodynamic model of Wood and Banno (1973). The model has been refined using a combination of the new data on orthopyroxenes of about En₆₀Fs₄₀ (with variable calcium content) and previously published data on more magnesian systems. Given analyses of coexisting Orthopyroxene and garnet in natural assemblages it is possible to calculate a P-T curve for the rock which should, in most cases, be accurate to within 2 or 3 kbar.     

The simulation of fabric development during plastic deformation and its application to quartzite: the influence of deformation history

The effect of deformation history on the development of crystallographic preferred orientation in quartzities has been simulated using a computer program based on the Taylor-Bishop-Hill analysis. Model quartzities with different combinations of glide systems have been subjected to various coaxial and non-coaxial deformation histories. It is possible to obtain information from the fabrics that develop during simple histories; for example, the location of the axis of extension is generally associated with a pole free area on a c-axis plot, and progressive axial shortening, plane strain and axial shortening produce characteristic fabrics. In progressive simple shear the fabric skeleton becomes asymmetric relative to the sense of shear and a-axes preferentially align in the flow plane parallel to the flow direction. However, this example illustrates that the fabric orientation and characteristics are controlled by the kinematic framework and bear only an indirect relationship to the finite strain accumulated to that point in the history.The imprint of the closing stages of deformation limits to some degree the use of crystallographic fabrics as a tool for structural geologists, but in favourable circumstances data can be obtained concerning characteristics of the deformation history, on the scale of the hand-specimen, for the last part of this history.