SILICA MINERALS IN THE EARLY STAGE OF DIAGENESIS
SILICA MINERALS IN THE EARLY STAGE OF DIAGENESIS
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成岩早期的硅矿物
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
S. Mizutani
中科院分区：
文献类型：
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作者：
S. Mizutani
总结
实验研究表明，在水热条件下，无定形二氧化硅通过方石英转化为石英。在对产物中石英进行定量分析的基础上，研究了反应温度对转化率的影响，并考虑了诱导期对石英含量的影响。这种转变是一个连续的反应，包括两个一级步骤，从无定形二氧化硅到低方石英和从低方石英到低石英。动力学数据，如速率常数和活化能。
在硅质沉积物中发现的二氧化硅的矿物学品种表明，这种转化可能发生在自然条件下。较年轻的矿床含有无定形二氧化硅或方石英，而较老的矿床则总是由石英组成。通过假设实验观察到的转化过程在自然界中成立，可以估计动力学数据。由于该过程取决于热历史，因此可以跟踪给定热历史模型的转变过程。计算结果与地质证据的一个例子进行了比较，并得出结论，硅的矿物学变化是由转化过程。
硅质矿物的带状分布与沸石矿物的带状分布明显对应，硅质的转化作用可能发生在成岩过程中。显然，几乎所有的成岩相都代表了最终平衡过程中的中间阶段。本文所描述的方石英阶段即属于其中之一，可与早期成岩阶段相对应。硅质矿物可作为了解成岩作用渐进变化的线索。
Summary
Experimental investigation shows that amorphous silica is converted into quartz through cristobalite under hydrothermal conditions. The rate of transformation, essentially dependent on the reaction temperature, was studied on the basis of quantitative analyses of quartz in the products, and the variation of quartz content was elucidated by taking the induction period into consideration. The transformation is a consecutive reaction involving two first-order steps, from amorphous silica to low-cristobalite and from low-cristobalite to low-quartz. Kinetic data such as the rate constants and the energy of activation are obtained.
Mineralogical varieties of silica found in siliceous deposits suggest that the transformation probably takes place under natural conditions. Younger deposits contain amorphous silica or cristobalite, whereas older ones are invariably composed of quartz. By assuming that the transformation process observed experimentally holds in nature, kinetic data can be estimated. Since the process depends upon the thermal history, it is possible to follow the transformation process for a given model of a thermal history. An example of computed results is compared with the geological evidence, and it is concluded that the mineralogical variation of silica is accounted for by the transformation process.
Zonal distribution of silica minerals apparently corresponds to that of zeolite minerals, and the transformation of silica is considered to occur during diagenesis. Evidently, almost all diagenetic facies represent intermediate stages on the way to the ultimate equilibrium. The cristobalite stage described in this paper belongs to one of these stages, and is referable to the early stage of diagenesis. It is suggested that silica minerals can be used as clues to understand a progressive change in diagenesis.