The structural evolution character of different types of coal metamorphism and its geological significance

Abstract：Based on the importance of structural evolution character of coal and its geological significance in studying coalification, the deformed coals of different types of metamorphism under the special environment were investigated using X-ray diffraction, electron paramagnetic resonance, Fourier transformation infrared microspectroscopy and high-resolution transmission electron microscope. The results show that the three different types of coal metamorphism showed remarkable systemic differences, and the differences were obvious among the regional metamorphic coal and another two kinds. The superimposing tectonic stress due to high tem- perature of the environment resulted in the decrease of the lamellae spacing （d002） of the basic structural unit （BSU）, increase of the BSU diameter （La） and the BSU stack height （Lc） and the orientation increase of the BSU. Under the experimental conditions, the d002 of tectonic thermal metamorphic coal decreased 0. 012 nm compared to the other two types of coal. How- ever, the average values of La and Lc were nearly 2 times and 3 times to those of the other two types of coal, respectively. The tectonic stress not only affects physical coalification, but also leads to changes in chemical structures and compositions of organic micromolecules in coal, which suggests the leading effect to the structural evolution of coal.