The Role of Randomly Mixed-Layered Chlorite/Smectite in the Transformation of Smectite to Chlorite
The Role of Randomly Mixed-Layered Chlorite/Smectite in the Transformation of Smectite to Chlorite
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DOI：
10.1346/ccmn.1997.0450403
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发表时间：
1997-08
影响因子：
2.2
通讯作者：
Lori Bettison-Varga;I. Mackinnon
中科院分区：
文献类型：
--
作者：
Lori Bettison-Varga;I. Mackinnon
利用透射电子显微镜（TEM）研究了加州Point Sal蛇绿岩中热液蚀变玄武岩中的泡状和基质层状硅酸盐。填孔层状硅酸盐的结构特征是具有连贯的、相对厚的和无缺陷的14 - 14周期性晶体。基质层状硅酸盐在结构上的特征是：1）宽度高达200微米的随机取向晶体和2）宽度高达1000微米的更大、更连贯的晶体。小的微晶主要包含14-ε层和一些24-ε单元。大晶体显示随机夹层的蒙脱石/蒙皂石（C/S），平均约50%蒙脱石。在基质层状硅酸盐中，相邻的蒙皂石状层并不少见。电子探针分析表明，基质和泡状层状硅酸盐的Fe/Mg比值相当恒定，在某些TEM图像中还发现了水镁石状夹层的终止。由这些层终止所代表的转变机制是1）在蒙皂石夹层区域内生长水镁石状夹层和2）元素溶解和再沉淀以形成氧化物层。这两种机制都需要增加的体积，蒙脱石转化为蒙脱石。的数据，结合以前发表的报告，表明随机夹层C/S是一个亚稳相形成的微环境中，低水/岩比。在同一样品中，以较高的水/岩比为主的微环境中形成了亚氯酸盐。两种结构的结构（Mg#）中Mg的相对恒定的数量表明，在这两种微环境中的散装岩石组合物的层状硅酸盐的组合物的影响。
Vesicular and groundmass phyllosilicates in a hydrothermally altered basalt from the Point Sal ophiolite, California, have been studied using transmission electron microscopy (TEM). Pore-filling phyllosilicates are texturally characterized as having coherent, relatively thick and defect-free crystals of chlorite (14 Å) with occasional 24-Å periodicities. Groundmass phyllosilicates are texturally characterized as 1) randomly oriented crystals up to 200 Å in width and 2) larger, more coherent crystals up to 1000 Å in width. Small crystallites contain predominantly 14-Å layers with some 24-Å units. Large crystals show randomly interlayered chlorite/smectite (C/S), with approximately 50% chlorite on average. Adjacent smectite-like layers are not uncommon in the groundmass phyllosilicates. Electron microprobe analyses show that Fe/Mg ratios of both groundmass and vesicular phyllosilicates are fairly constant.Termination of brucite-like interlayers has been identified in some of the TEM images. The transformation mechanisms represented by these layer terminations are 1) growth of a brucite-like interlayer within smectite interlayer regions and 2) the dissolution and reprecipitation of elements to form chlorite layers. Both mechanisms require an increase in volume as smectite transforms to chlorite.The data, combined with that from previously published reports, suggest that randomly interlayered C/S is a metastable phase formed in microenvironments with low water/rock ratios. Chlorite forms in microenvironments in the same sample dominated by higher water/rock ratios. The relatively constant number of Mg’s in the structure (Mg#) of both structures indicates that in both microenvironments the bulk rock composition has influence over the composition of phyllosilicates.