Tectonic Characteristics And Evolution Of Changling Rift Basin

It can be concluded through the analysis of fracture geometry’s features as the following: rift and fracture of Chang Ridge mainly run NNW, NNE and nearly SN; fracture separation increases from upper strata to lower strata in sequence, and dip angle of fault decreases; the vertical is controlled by different structural systems; on the basis of fracture geometry, the formation and evolution process of the fracture and the deformation mechanism are analyzed. According to the growth index section, growth deformation intensity (horizontal elongation of section), the structural evolution history determining the fracture activity period, by analyzing the fracture and deformation mechanism of each period, it can be obtained that Huoshiling deposition period, Shahezi deposition period, Yingcheng deposition period, Quantou later deposition period-Qingshankou early deposition period, Yaojia deposition period, the first and the second stretches of Nen River deposition period, Nen River later deposition period, Mingshui later deposition period, Paleogene System later period are all the main activity periods of fracture formation. Stretch and deformation are the major activities in Huoshiling deposition period, Shahezi deposition period, Yingcheng deposition period, stretch and twisting deformation in Quantou later deposition period-Qingshankou early deposition period, Yaojia deposition period, the first and the second stretches of Nen River deposition period, and inversion and deformation in Nen River later deposition period, Mingshui later deposition period, Paleogene System later period. Finally six types of fracture system are divided:fracture in rift period (Ⅰ type), fracture in depression period (Ⅱ type), fracture in inversion period (Ⅲ type), fracture formed in rift period and continuously active in depression period (Ⅰ-Ⅱ type), fracture formed in rift period and continuously active in both depression and inversion periods (Ⅰ-Ⅱ-Ⅲ type) and fracture formed structurally in rift period and continuously active in inversion period (Ⅱ-Ⅲ type). Formation in rift period (Ⅰ type), rift period and continuously active in depression period (Ⅰ-Ⅱ type) and rift period and continuously active in both depression and inversion periods (Ⅰ-Ⅱ-Ⅲ type) has close relations with rift growth and natural gas aggregation. Through the research on fracture activity methods, fracture of continuously active in several periods controls the growth of. inheritance rift and is the main type of controlled rift fracture. Meanwhile the controlled rift fracture has the features of segmented growth. Before the Shahezi deposition, each controlled rift fracture takes on segmented features and joins together into a controlled rift fracture in Shahezi deposition period. An the growth points of the fracture segmentation, lateral fault folds are multiply formed, which are the sites beneficial to deep gas enrichment. Half-graben structures controlled by shovel-style normal fault control are major rift type of Chang Ridge. At the same period half-grabens combine and arrange in multiple ways. Rift Period underwent the initial rift period of Huoshiling, the strong rift period of Shahezi and the rift-shrinking period of Yingcheng. Half-grabens of all periods have stacked relation of two categories, inheritance and coherence. After experiencing stretch deformation in early period, stretch and twisting deformation in mid-period and the inversion deformation in late period, tectonic deformation of the same period (under the same stress) produces corresponding tectonic styles, mainly including3styles, stretch tectonic style, magma diapir style and inversion style. Ultimately the paper analyzes the formation mechanism of Chang Ridge’s rift evolution, and suggests that Chang Ridge successively underwent lithospheric thinning stretch caused by post-orogenic lithospheric delamination. In the late period mantle lithosphere generated strong thinning effects and led to the stretch deformation of level tension. Stretch deformation of two periods was accompanied by strong volcanism. At the same time because of the change of Isawa Nagi plate slanting to the subduction direction; it generally resulted in the sinistral twist characteristics for Songliao Basin.