Evolutionary model of oblique rift basins-Study of Central African Rifts

English Abstract:

The geometry of oblique-rifting basin has relationship with the acute angle – α-between the rift trend and trend of tensile stress. In this study, we simulated the formation of oblique-rifting basin by Particle Flow Code 3-Dimensions-(PFC 3D) and drew a comparison between the simulation results and the evolutional models of Doba basin, Doseo basin and Salamat basin in Central African Rifts. The main theory of PFC 3D is based on the Discrete Element Method (DEM) which a whole model framework is established by applying different parameters to the every particles in the model.

There are two big-model sets in this study, Model-set1 and Model-set2. Model-set1: The model is divided into two blocks according to the rift trend. Both blocks are applied two tensile stresses parallel to the y-axis. Model-set2: Set the plate below the model. The plate is divided into two plates according to the rift trend. A fixed -tensile velocity parallel to the y-axis is applied to the both plates. The α is set at 90°, 75°, 60° and 45° in both model-sets. The study results indicated that 1. The en echelon faults in the rifting basins are sub-vertical to the trend of tensile stress. 2. The density of en echelon faults in rift basins decrease gradually when α is close to 45°. 3. By comparison with the α value of the Central African Rifts, we reckon that the α of the Doba Basin, Doseo Basin and Salamat Basin are 60°, 60° and 75°, respectively. 4. The Doba basin- wide and shallow- is a mesoscale rift basin, while the Doseo basin and the Salamat basin- narrow and deep- are megascale rift basins. We proposed that the petroleum systems of Doba basin and Doseo-Salamat basin are different.