Effects of structural unconformity on development of volcanic rock fracture in Chepaizi area, Junggar Basin

Key words:  unconformity structure  fracture  volcanic rock  Chepaizi area  Carboniferous

Abstract:

The fractures of volcanic rock are studied in the Carboniferous Chepaizi area of Junggar Basin. Using drilling cores, thin section, conventional logging and image logging, the characteristics of the structural unconformity and the characterization of fracture in each structure are statistically analyzed. The results show that the structure of the Carboniferous top unconformity has a six-layer structure, which includes overlying rock, soil layer, hydrolysis zone, leached zone, broken-down zone Ⅰ, and broken-down zone Ⅱ from top to bottom. Under the unconformity, the characterization of the fractures in individual structures differs. The degree of fracture filling increases gradually from the leached zone, the hydrolysis zone, the broken-down zone Ⅰ, to the broken-down zone Ⅱ. The fracture development is the best in the leached zone, but downgrades gradually from the broken-down zone Ⅰ, the broken-down zone Ⅱ, to the hydrolysis zone, respectively. The characterization of the fractures in the structure is clearly related to volcanic rock, weathered leaching and argillazation. Basalt and andesitic basalt have well developed fractures, and account for a large proportion in the leached zone and the broken-down zone Ⅰ. Argillazation is less developed than weathered leaching in leached zone, where fractures are well developed.