Plastic deformation of wadsleyite: III. Interpretation of dislocations and slip systems

 Linear anisotropic elasticity has been applied to interpret the dislocation stability and ease of slip in wadsleyite. It is shown that wadsleyite is very isotropic from the elastic point of view. The influence of crystal chemistry and bonding on the choice of the slip plane is discussed. It is shown that slip is predominantly achieved on planes that do not shear Si–O bonds. It is suggested that dissociation of dislocations is essential in determining the ease of slip among the various slip systems. Received: 15 July 2002 / Accepted: 14 February 2003 Acknowledgements High-pressure experiments were performed at the Bayerisches Geoinstitut under the EU IHP – Access to Research Infrastructures Programme (Contract no. HPRI-1999-CT-00004 to D.C. Rubie). Enlightening discussions with A. Coujou and J. Rabier are gratefully acknowledged.     

Reaction-induced weakening of plagioclase–olivine composites

The localisation of strain into natural ductile shear zones is often associated with the occurrence of metamorphic reactions. In order to study the effects of solid–solid mineral reactions on plastic deformation of rocks, we have investigated the shear deformation of plagioclase–olivine composites during the reaction plagioclase + olivine → orthopyroxene + clinopyroxene + spinel (± garnet). Microstructures of plagioclase–olivine composites were studied after shear deformation experiments in a Griggs apparatus. Experiments were performed on anorthite–forsterite (An–Fo) and labradorite–forsterite (Lab–Fo) composites at 900 °C, confining pressures between 1000–1600 MPa and with constant shear strain rates of 5 × 10⁻⁵ s⁻¹.In absence of reaction, Lab–Fo composites are stronger than pure olivine and labradorite end-members that deform with a high temperature plasticity mechanism. Lab–Fo composites strain–harden due to the inhibition of extensive recrystallisation by interphase boundaries.In An–Fo composites, the reaction induces strain weakening by a switch from dislocation creep to grain size sensitive deformation mechanisms through the development of fine-grained (size < 0.5 μm) polyphase reaction products. Interconnecting layers of reaction products accommodate most of the applied strain by grain size sensitive creep. Recovery processes are pronounced during syndeformational reaction: original anorthite and olivine dynamically recrystallise by subgrain rotation and bulging recrystallisation. Presumably, the dynamic recrystallisation is caused by reduced stress conditions and partitioning of strain and strain rates between the new reaction products and the relict An–Fo grains. The results of our experiments are in good agreement with natural observations of shear localisation in the lower crust and upper mantle, and imply that anhydrous mineral reactions can be important causes for localisation of deformation.     

Coupled deformation-diffusion effects on water-level changes due to propagating creep events

Water-well-level fluctuations associated with episodic creep are studied using a coupled deformation-diffusion solution for the pore pressure produced by a plane-strain shear dislocation moving steadily at a speedV in a linear elastic, saturated porous medium. For largeVr/2c, wherer is distance from the dislocation andc is diffusivity, the solution approaches the form of the uncoupled elastic solution used by Wesson (1981) to analyze water-level changes due to creep events. The differences between the two solutions are significant within 10 diffusion lengths (20c/V) from the fault plane. More specifically, the pore pressure predicted by the coupled solution reverses sign behind the dislocation and is much smaller in magnitude than that predicted by the uncoupled solution. For an undrained Poisson ratio of 0.3, Skempton's coefficient of 0.8 and a shear modulus of 30 GPa, the coupled solution predicts a peak pore-pressure change of 13.7 kPa (137 mbar) per millimeter of slip forV=1 km/day andc=1.0 m²/sec. The spectrum of the coupled solution is limited to a band of frequencies, centered at a value proportional toV and approximately inversely proportional to the distance from the observation point to the fault plant. Thus, close to the fault plane the frequency band occupied by the coupled solution may lie above the range at which water wells can respond. The coupled solution is used in interpreting the same creep-associated water-level change observed by Johnson (1973) and modeled by Wesson (1981) using the uncoupled solution. Although there are uncertainties in properties of the rock material and in the speed of the creep event, the coupled solution predicts a water-level change comparable in magnitude to the observed change.     

计算分层介质中位错点源静态位移场的广义反射、透射系数矩阵和离散波数方法

本文将计算合成地震图的广义反射、透射系数矩阵和离散波数方法应用于静态问题,给出了分层介质中位错点源产生的静态位移场的计算方法。该方法保留了反射、透射矩阵方法的原有优点,通过将数值结果与解析解的对比表明,该方法具有较高的数值精度,可用于研究地震断层活动造成的地表形变。     

断层走滑不均匀性对地面变形的影响

根据塞积群理论导出了走滑断层两端点固定时位移场随位置的不均匀分布解析表示关系,分析和讨论了断层上不同位置的位移场分布特征, 采用新导出的断层滑动不均匀分布公式对地面的水平位移场和垂直位移场进行了数值模拟计算,并与传统的Okada 位错模型在理论和计算结果上进行了对比分析.理论和计算结果分析表明：断层滑动不均匀分布公式是Okada位错模型在一定条件下理论上的扩展,而Okada位错模型是走滑不均匀公式的零阶近似;断层滑动不均匀分布公式与Okada 位错模型计算的地面位移场在走滑方向、垂直于断层走向和垂直于地面方向的近场变形差异最大在50%至65%之间,而最小差异在1%以内.     

钢结构管道穿越西山断层安全性分析

根据乌鲁木齐市西山发震断层的有关资料,针对西山地区两种主要地层岩土工程数据,利用有限元理论,采用大型通用有限元分析软件ANSYS对天然气管线穿越西山断层的反应进行了分析和研究。通过分析穿越断层地下管线的应力与变形情况,得出了在使用年限内钢结构管道以粉土层为地基持力层和覆土材料将处于安全状态的结论。     

微粒对多晶冰及冰川流变行为的影响——(Ⅰ)基于位错的弛豫模型

为量化冰及冰川在流变过程中位错密度随流变应力的变化,发展了一个基于位错的非线性弛豫模型.模型的计算表明：在冰的指数蠕变阶段,滞弹性试验所形成的应力/应变滞后环的宽度与面积随流变应力的增加呈线性增加,位错密度随流变应力的增加呈平方增加;在冰的线性蠕变阶段,滞弹性试验所形成的应力/应变滞后环的宽度、面积和位错密度保持不变.     

半无限空间中剪切断层错动产生的应力场——(一)走向滑动断层

给出了半无限空间中任意倾角的走向滑动剪切断层错动产生的应力场的一套严密的解析表达式 .对前人所做的该方面的工作进行了检验和回顾 ,重新对公式进行了严密的数学推导 ,给出了正确的结果 ,使得这一套公式更加完善和可靠 .     

橄榄石集合体中与位错蠕变相伴随的粒间滑动

为了研究橄榄岩位错蠕变过程中粒间滑动所起的作用,对经脱水干燥的橄榄石集合体试件进行了一系列的变形试验。三轴压缩蠕变试验在T=1473K、P=200和400MPa条件下使用一台高分辨率气体介质变形装置进行,每个试件在介于100~250MPa之间的不同应力水平下变形,得到的应变率介于10^-4 ~10^-6S^-1之间。随着差应力的增加,得到扩散蠕变到位错蠕变的过渡,在位错蠕变域,易滑动体系在~50MPa和颗粒尺寸为15μm时伴随粒间滑动。这一粒径敏感蠕变域由应力指数3.2±0.1和粒径指数1.8±0.2来刻划。将这一流动律与其他扩散和位错蠕变结果进行对比,表明本文得出的流动律可应用于粒度小于100μm和差应力大于20MPa时的岩石流动。因此,与粒间滑动相伴的位错蠕变可能是上地幔岩石圈剪切带变形局部化的主要变形机制。     

压力对橄榄石流变性的影响

本文给出细粒橄榄石集合体在位错蠕变域中压力效应的实验结果。对干燥、人工合成的橄榄石集合体进行了三轴压缩实验,试验在一台高分辨率的气体介质试验机上进行。典型的常载荷蠕变试验温度为1473K或1523K,围压为400MPa、200MPa、400MPa、200MPa。当差压力和温度给定时,试件在400MPa围压下,变形速度较200MPa围压下要慢。实验得出的细粒橄榄石集合体在位错蠕变域中的活化体积值为(23±3)×10~(-6)m~3/mol。最后,对实验结果在地幔动力学中的应用进行了讨论。