泥岩埋藏成岩过程中绿泥石的演化途径及意义

Chloritization Sequences in Mudstone during Diagenesis and Its Geological Significance

粘土矿物是泥质沉积岩重要的组成部分。在温度、压力、阳离子及水/岩比值等多种因素的共同作用下,埋藏成岩过程常常伴随着不同粘土矿物间的相互转化:蒙脱石、伊利石、高岭石和磁绿泥石等矿物均可发生绿泥石化。但各种矿物发生绿泥石化条件及反应机制不同,形成的绿泥石在化学成分及构型方面也有很大差异,通过X-射线衍射(XRD)、电子探针(EMPA)和高分辨率透射电子显微镜(HRTEM)等测试手段可识别出不同类型的绿泥石,区分不同转化序列并分析其转化机制。不同转化序列形成的绿泥石,不仅受温度的控制,还受阳离子类型和浓度的控制,在利用绿泥石作为地温计时需慎重;不同转化序列绿泥石化过程中都有水的参与,并伴有氢离子释放或消耗,这将会对有机质生烃产生影响。因此,关注泥岩埋藏成岩过程中绿泥石演化途径的差异,对拓宽绿泥石化的地质应用领域,特别是粘土矿物—有机质的协同作用具有重要的意义。

Clay minerals are important components of argillaceous sedimentary rocks. During the middle and late stages of diagenesis, a variety of minerals such as smectite, illite, kaolinite, and berthierine are prone to being converted to chlorite due to the combination of temperature, pressure, cation, water/rock ratio and other factors, resulting in increased chlorite content. However, because the chloritization conditions and reaction mechanisms of each mineral are different, chemical composition and configuration of chlorite varygreatly. Therefore, we can use XRD, EMPA and HRTEM to identify different types of chlorite, and further to distinguish differentconversion sequences and analyze their conversion mechanisms. Recognizing the multiple conversion sequences of chloritization canhelp study the influence of conversion sequence on the chemical composition of chlorite and further improve the application of chloritegeothermometer. In addition, in some of the conversion sequences, the chloritization process consumes water and releases hydrogen,while others consume hydrogen. And hydrocarbon generation is a process of deoxidation and hydrogenation. Therefore, the identification of different conversion sequences can provide a basis for the study of the influence of mineral evolution on the hydrocarbon generation.