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1.
Shyh‐Lung Hwang Pouyan Shen Hao‐Tsu Chu Tzen‐Fu Yui Yoshiyuki Iizuka Hans‐Peter Schertl 《Journal of Metamorphic Geology》2019,37(8):1079-1098
Metamorphic garnet commonly contains needle‐like rutile inclusions as well as equant rutile inclusions that surround quartz inclusions and range in size from submicrometer to nanometer. Although the origin of these equant rutile inclusions, that is, exsolution or non‐exsolution, has important implications for petrological and tectonic processes, the crystallographic characteristics of these inclusions have rarely been studied because of the small sizes and analytical difficulties involved. Here, we report the crystallographic characteristics pertinent to the genetic origin of minute equant rutile inclusions in cloudy, nearly spherically shaped garnet domains with Ti‐depleted compositions surrounding quartz inclusions in ultrahigh‐pressure garnet from several diamondiferous Erzgebirge quartzofeldspathic gneissic rock samples. TEM analyses show that the equant rutile crystals in cloudy garnet domains are partially bounded by the low‐energy {100}rt ± {110}rt ± {101}rt facets and have rather random crystallographic orientation relationships (CORs) with the garnet host, with preferential alignment of low‐energy lattice planes, for example, {100}rt//{112}grt, for some rutile crystals. Although the rather random CORs are unlikely to be attributed to solid‐state exsolution subjected to the stringent topotactic garnet lattice constraints, the characteristic subhedral {100}rt ± {110}rt ± {101}rt crystal forms of rutile can be rationalized by a metasomatic dissolution‐reprecipitation mechanism via a fluid phase. In this scenario, the quartz+fluid inclusions in garnet were first subjected to decompression microcracking during rock exhumation, followed by dissolution of Ti‐bearing garnet matrix at the crack tips or along the crack surfaces and subsequent reprecipitation of rutile, apatite, gahnite, akdalaite, and Ti‐depleted garnet. The rapid coalescence between rutile and garnet crystals in fluid or direct attachment of rutile crystals onto the dissolving crack surfaces would then yield the rather random CORs as reported here. These results, along with previous work on rutile needles, indicate rather diverse genesis of rutile inclusions in various crystal forms, thus shedding light on the controversial exsolution origin for other inclusion suite/microstructure in minerals. 相似文献
2.
利用偏光显微镜对经历不同高温循环作用后的细粒大理岩进行观测,通过统计微裂纹长度、开度、数量等参数,探讨不同加热循环次数后岩样内微裂纹的扩展规律。结果表明,（1）经历不同热循环次数作用的岩样,微裂纹的数量和长度均不同,未经热处理岩样内颗粒致密,胶结较好,内部无明显的微裂纹。经历4次热循环作用后岩样内微裂纹发育明显,以晶界裂纹为主,开度和长度均显著增加。岩样经历16次热循环作用后开度持续增大,为55 µm,是4次热循环的4倍;（2）对不同热循环处理后岩样内部发育微裂纹的方向进行了统计,发现微裂纹无明显的方向性,还表明细观切片的取样位置对微裂纹的发育影响不大;（3）线性裂纹密度随热循环次数的增加而增大,经历16次热循环作用后岩样的线性裂纹密度是没有经历热处理岩样的21倍。 相似文献
3.
花岗岩宏观尺度疲劳破坏是由于细观尺度微裂纹的萌生、发育和贯通引起的,所以对处于细观尺度的微裂纹特征进行量化分析,对于理解花岗岩的动力特性有一定的意义。首先利用RMT-150B多功能全自动刚性岩石伺服试验机,采用振幅为10 MPa,频率分别为0.01、0.02、0.05、0.10、0.20、0.50、1.00 Hz的正弦循环荷载作为动力扰动,对海南昌江花岗岩试样进行单轴循环荷载试验。然后,利用扫描电镜（SEM）拍摄得到花岗岩的大量细观结构图片,运用数字图像技术获取微裂纹的细观几何信息,从方位角、长度、宽度和面积对不同荷载频率相应的花岗岩细观尺度微裂纹特征进行量化分析。研究结果表明,随着循环荷载频率的增加,微裂纹方位角发育离散性增加,而其统计均值则在某一区间内波动;微裂纹长度的发育则较快,而仅当荷载频率达到1 Hz时,宽度才有一定的发展,同时,能量耗散的方式也发生一定的变化。 相似文献
4.
鉴于试验砂岩内摩擦角较大及峰后脆性强的特点,选用颗粒流程序PFC2D中的cluster单元进行模拟,在常规三轴压缩试验校正的基础上得到一组能够真实反映砂岩宏观力学行为的细观参数,模拟了砂岩两种卸围压路径,结果表明其峰值强度随初始轴向应力的增大而不断增大,其规律与试验相同。选取了两种卸围压路径微裂纹数目随应力-应变的演化趋势进行分析,结果表明卸围压对试样造成的损伤较加轴压大,同时初始轴向应力增大一定程度上增加了试样承受破坏的能力。通过对不同应力路径裂纹两侧位移场的分析可知卸围压会造成颗粒在横向产生位移不连续,导致试样破坏。 相似文献
5.
A new model for describing induced anisotropic damage in brittle rocks is proposed. Although phenomenological, the model is based on physical grounds of micromechanical analysis. Induced damage is represented by a second rank tensor, which is related to the density and orientation of microcracks. Damage evolution is related to the propagation condition of microcracks. The onset of microcrack coalescence leading to softening behaviour is also considered. The effective elastic compliance of the damaged material is obtained from a specific form of Gibbs potential. Irreversible damage‐related strains due to residual opening of microcracks after unloading are also captured. All the model's parameters could be determined from conventional triaxial compression tests. The proposed model is applied to a typical brittle rock. Comparison between test data and numerical simulations shows an overall good agreement. The proposed model is able to describe the main features related to induced microcracks in brittle geomaterials. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
6.
萝卜纹是田黄的重要鉴定特征。本文通过岩石薄片、X射线衍射分析和电子探针分析等手段,确定萝卜纹的组成矿物为伊利石;萝卜纹的成因为田黄的原岩受到构造应力作用后产生了显微裂隙,次生的伊利石填充了显微裂隙;显微裂隙中的伊利石与岩石中的主要矿物迪开石光学性质差别较大而呈丝缕状(萝卜纹)。 相似文献
7.
煤岩组合体在静力压缩下的宏观变形受界面效应影响,与煤、岩单体存在显著差异。在岩石单体材料的有效介质模型基础上进行改进,考虑了煤岩组合体的构成特征,提出一种适用于不同类型的煤岩组合体的裂前宏观弹性模型。模型参数基于轴向裂纹应变确定,均可从试验曲线获得,方法简单方便。通过现有文献的数据验证,表明了模型的合理性、有效性和普适性。对模型参数进行讨论,结果表明：（1）在煤岩组合体的裂前阶段,煤岩组合体裂纹差异可以忽略;（2）模型通过对煤岩组合体基质进行解耦,反映了界面效应对煤岩组合体弹性性能的影响;（3）模型中岩体基质的有效占比随着煤体比例的提高显著下降;（4）存在岩体与煤体弹性模量的最佳比值,使岩体基质的有效占比最大。模型可为矿井支护方案设计与材料选择提供一种新的思路。 相似文献
8.
红黏土失水易收缩开裂而诱发工程灾害,为抑制或缓减红黏土的收缩特征,添加4%偏高岭土和5%石灰改善其水敏性。按照最优含水率制备压实试样,养护180 d后抽真空饱和,脱湿到预定含水率,随后开展收缩、无侧限抗压强度、吸力和孔隙分析等试验。结果表明,压实红黏土随着含水率降低,其无侧限抗压强度呈现先增大后减少的变化规律,这是脱湿导致的红黏土衍生微裂隙,进而引起结构性损伤所致。红黏土掺入石灰,尤其是掺入石灰-偏高岭土后,虽然脱湿也会引起强度减小,但接近完全干燥时,其强度又会增大。由此说明,偏高岭土协同石灰可以更加有效地抑制红黏土收缩效应,提高其整体强度。究其原因,是偏高岭土含有大量无定形硅、铝氧化物,且呈现边-面“搭接”的独特结构形态,使其能够快速捕获氢氧化钙溶液中的钙离子,在红黏土团（颗）粒间形成了胶结性水化物。 相似文献
9.
以凌海花岗岩为研究对象,进行了一系列常规三轴高压试验,研究了花岗岩的变形特点及脆性演化规律。基于试验结果,分析了不同围压下的全应力-应变曲线,探讨了静态应变采集试验中花岗岩表面变形特点、峰前损伤规律及其与裂隙扩展的关系,总结了动态采集试验中典型的裂纹扩展模式,并基于改进的峰后能量平衡法评价岩石的脆性。研究结果表明：多应变片静态采集三轴试验中岩样不同位置变形规律差异明显,压缩应变较大的区域往往是裂隙产生、扩展的位置;动态应变采集三轴试验中识别了3种典型的裂隙扩展模式,且与应力加载方式存在一定联系;在70 MPa围压范围内,岩样都表现出明显的脆性破坏特征,其脆性指数随围压增加呈现出先减小后增加再减小的变化趋势。该研究成果对进一步开展其他硬岩的变形破坏机制研究和地下工程的稳定性分析具有一定参考价值。 相似文献
10.
Fracture toughness measurements under static loading conditions have been carried out in Barre and Lac du Bonnet granites.
An advanced AE technique has been adopted to monitor real-time crack initiation and propagation around the principal crack
in these tests to understand the processes of brittle failure under tension and related characteristics of the resulting fracture
process zone. The anisotropy of Mode I fracture toughness has been investigated along specific directions. Microcrack density
and orientation analysis from thin section studies have shown these characteristics to be the primary cause of the observed
variation in fracture toughness, which is seen to vary between 1.14 MPa.(m)1/2 and 1.89 MPa.(m)1/2 in Barre granite. The latter value represents the case in which the crack is propagated at right angles to the main set of
microcracks. The creation of a significant fracture process zone surrounding the propagating main crack has been confirmed.
Real-time imaging of the fracture process and formation of fracture process zone by AE techniques yielded results in very
good agreement with those obtained by direct optical analysis. 相似文献