很低级变质作用研究及其在沉积盆地中的应用

A study of the very low_grade metamorphism and its application to the sedimentary basin

很低级变质岩石在沉积盆地中分布广泛。在成岩-低级变质作用演化过程中,随着变质程度的增加,油气、煤的演化阶段也会发生相应的变化。因此,很低级变质作用与石油、天然气、煤等能源矿产关系密切。本文系统总结了很低级变质作用研究的几个方面及其新进展,包括很低级变质带的划分、粘土矿物地质温压计、变质作用p_T_t轨迹及其在沉积盆地中的应用等等,并结合实例初步探讨了川西北若尔盖坳陷三叠系的很低级变质作用。研究表明,对沉积盆地中很低级变质作用的研究,对于划分成岩-变质界限,明确盆地的热成熟阶段,恢复盆地古地温、古构造史以及指导油气勘探等,都具有十分重大的理论和实际意义。

Very low-grade metamorphic rocks are widely spread in the sedimentary basin. During the diagenetic to low-grade metamorphic process, the evolution stage of petroleum and coal would undergo corresponding changes with the increasing metamorphic grade. Thus, the very low- grade metamorphism has close relationship with oil,gas, coal and other energy mineral resources. This paper first summarizes some aspects of this problem and the new progress in the study of very low-grade metamorphism, such as the dividing of very low-grade metapelitic zones,geothermobarometry on clay minerals, metamorphic p-T-t path and their application to the sedimentary basin, and then preliminarily discusses the Triassic very low-grade metamorphism in the Zoigê depression, northwest Sichuan.Studies show that the research on diagenetic to very low- grade metamorphism in the sedimentary basin has great theoretical and practical significance in dividing the boundary between diagenesis and metamorphism, determining the stage of basin maturity, recovering the paleotemperature and paleotectonic history and, on such a basis, guiding oil and gas exploration.