Transmission Electron Microscopic Study of the Kaolinitization of Muscovite
Transmission Electron Microscopic Study of the Kaolinitization of Muscovite
复制标题
白云母高岭石化的透射电镜研究
DOI：
10.1346/ccmn.1991.0390101
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发表时间：
1991
影响因子：
2.2
通讯作者：
D. Peacor
中科院分区：
文献类型：
--
作者：
W. Jiang;D. Peacor
通过透射和分析电子显微镜（TEM 和 AEM）对产自新西兰布莱顿奥塔哥片岩的水热高岭土化白云母进行了研究，以确定蚀变机制并比较二八面体云母和三八面体云母的反应物-产物关系。白云母是具有白云母组成的初级变质相。它以有序的两层和三层多型体形式出现，颗粒厚度可达 30 μm。高岭石呈层状分布，每层厚度约为 100–600 Å，与白云母或类蒙脱石层状层交替出现。大多数高岭石在堆积顺序上是高度无序的，尽管也存在单层多型体，以相对厚的层顺序出现。高岭石和白云母之间的相界总是平行于 001 晶格条纹，没有应变对比；即，沿层不存在过渡。高岭石和白云母的 00l 和 11l 反射列的平行性意味着地轴共生。还存在类似蒙脱石的相，以波状层的形式出现，其局部具有周期性对比，这可能反映了伊利石/蒙脱石的 R1 排序。这种材料似乎是白云母的直接“沿层”蚀变产物。电子衍射数据和晶格条纹图像表明高岭石与云母相具有一定的规律性交替；即，云母层被大致相等数量的高岭石层分隔开。类似的长程周期性也出现在高岭石层组内的对比变化中。数据共同表明，蚀变界面是自我延续的，并且一旦在晶体边缘或应变区域的 2:1 层中开始，蚀变就会沿着层快速进行，没有可观察到的垂直于层的分量。他们还表明，蒙皂石可能是在白云母热液高岭土化过程中形成的中间相。在先前对同一样品中黑云母蚀变的研究中，通常观察到“沿层”过渡边界，并且没有检测到第二个中间产物相，这意味着蚀变机制与反应物和产物之间的化学差异之间存在关系。
Hydrothermally kaolinitized muscovite from the Otago schist of Brighton, New Zealand, has been studied by transmission and analytical electron microscopy (TEM and AEM) to determine the mechanism of alteration and to compare reactant-product relations for di- and trioctahedral micas. The muscovite is a primary metamorphic phase having a phengitic composition. It occurs as well-ordered, two- and three-layer polytypes, in grains as thick as 30 μm. Kaolinite occurs as packets of layers, each about 100–600 Å thick, which alternate with packets of muscovite or smectite-like layers. Most of the kaolinite is highly disordered in stacking sequence, although a one-layer polytype is also present, occurring as relatively thick sequences of layers. Phase boundaries between kaolinite and muscovite are invariably parallel to the 001 lattice fringes with no strain contrast; i.e., no transitions exist along layers. Parallelism of 00l and 11l reflection rows of both kaolinite and muscovite implies a topotaxial intergrowth. A smectitelike phase is also present, occurring as packets of wavy layers, which locally have periodic contrast that may reflect R1 ordering of illite/smectite. This material appears to be a direct, “along-layer” alteration product of muscovite. Electron diffraction data and lattice-fringe images imply that kaolinite alternates with micaceous phase(s) with some regularity; i.e., micaceous layers are separated by approximately equal numbers of kaolinite layers. Similar long-range periodicity occurs in contrast variations within packets of kaolinite layers.The data collectively suggest that the alteration interface was self-perpetuating and that alteration proceeded rapidly along layers once it initiated in 2:1 layers at crystal edges or strained areas, with no observable component normal to the layers. They also suggest that smectite may have formed as an intermediate phase during the hydrothermal kaolinitization of muscovite. In the previous study of alteration of biotite in the same sample, “along-layer” transition boundaries were commonly observed, and a second, intermediate product phase was not detected, implying a relation between the alteration mechanisms and the chemical differences between reactants and products.