构造物理化学条件对煤变质作用的控制

煤是对温度和压力等地质因素十分敏感的有机岩,各种构造-热事件控制下的物理化学条件,是促进煤岩演化的根本动力。本文对煤变质作用过程的研究现状进行了综述,着重讨论了煤岩在高煤阶-石墨演化阶段的控制因素、演化过程和演化机制。煤变质作用包括煤化作用阶段和石墨化作用阶段,共同构成一个连续的有机质演化过程,总体趋势是分子结构有序化、化学成分单一化,最终演变为以碳元素为主、三维有序结构的石墨。温度和压力(应力)是控制煤变质作用两大因素,在不同的演化阶段,这两大因素所起的作用和演变机理都有所差异。在低、中煤阶演化阶段,温度是煤化学结构演化的主要控制因素,为化学键断裂提供活化能,应力缩聚和应力降解则对煤化学结构演化具有催化作用。高煤阶-石墨化阶段的主要机制是导致基本结构单元BSUs之间相互联结使短程有序化范围增大的拼叠作用,构造应力在其中起到关键作用,BSUs定向和面网间距不断减小,促进大分子物理结构演化。加强煤变质作用的高级阶段-石墨演化过程的研究,将丰富和深化对煤-石墨物理化学结构完整演化序列的认识。煤系石墨成矿机制的高温高压模拟实验,则为煤变质作用构造物理化学条件研究提供了可行的技术手段。

Control of coal metamorphism by tectonic physicochemical conditions

Coal is an organic rock very sensitive to geological factors such as temperature and pressure, and the physicochemical conditions associated with various tectonic thermal events are the fundamental driving force promoting the evolution of coal. In this paper, the current research status of coal metamorphism is reviewed; the control factors and evolutionary process and mechanism of coal in the stage from high rank coal to graphite are emphatically discussed. Coal metamorphism includes coalification stage and graphitization stage, which together constitute a continuous organic matter evolution process. The general trend of evolution is chemical constituents progressively simplifying and structure ordering, finally the graphite with three-dimensional ordered structure is evolved. Temperature and pressure (shear stress) are two major factors controlling coal metamorphism, their functions and evolution mechanism are different in different evolution stages. In the low and middle rank evolution stage, temperature is the main controlling factor of coal chemical structure evolution, which provides activation energy for chemical bond fracture, while stress polycondensation and stress degradation have catalytic effect on chemical structure evolution. The main mechanism from the high rank coal to graphite is that the basic structural units (BSUs) are interconnected and the short-range ordering range is increased,structural stress plays a key role in the evolution of the physical structure of macromolecules, it will promote the physical structure evolution of macromolecules by the orientation arrangement of BSUs and the distance decrease of carbon layer. It will enrich and deepen the understanding of the complete evolution sequence of the physical and chemical structure of coal by strengthening the research on the stage from high rank coal to graphite, the high-temperature and high-pressure simulation experiment of the coal-based graphite forming mechanism provides a feasible technical means for the study of the physical and chemical conditions of coal metamorphism.