Abstract:

There are four tectonic forces controlling the dynamics of continental rifting basin: F1an adhesive traction force generated by the mantle convection from the bottom of lithosphere, F2a lateral push force generated by the relative movement of plates from the plate boundary, F3an isotropic force generated by expanding and shrinking of the lithosphere due to temperature changes, and F4a lithostatic force generated by the mass of the lithosphere. The stress within the crust is a function S(Fi) of these four variables，but the magnitude and direction of F1 and F2 effects the magnitude and direction of the principal stress in the triaxial stress unit. The condition of lithospheric stretching, i.e., the formation of normal fault in the crust, is to have the principal stress σ2σ3 plan in the stress function S(Fi) close to horizontal level, and direction of maximal principal stress σ1 close to vertical. That means the composition of forces between F1 and F2 should be tensile force. In the case of F1 and F2 are in same direction and F1>F2, or directions of F1 and F2 are perpendicular to each other and the minimal principal stress of the stressunit is in the xaxis, the crust could have arisen  normal rifting. If the direction of F1 and F2 is neither perpendicular nor parallel to each other and the minimal principal stress σ3 of the stressunit is not directional on the xaxis, the crust could have arisen oblique rifting. As the force generated by the mantle convection from the bottom of lithosphere to lithospheric interior decreases, and the extrusion force generated by movements of the plates from lateral boundary of lithosphere plate to lithospheric  interior increases, the principal stress of crusts stress state S(Fi) on the X and Y axis can exceed the principal stress on the Z axis, making σZ equivalent to σ2 in the triaxial stress state, the strikeslip fault could be arisen  in rifting basin. If the magnitude of principal stress of crust stress state S(Fi) on the XY plane exceeds the principal stress on the Z axis, then σZ is the equivalent of σ3, the thrust faults or inverted normal faults could be arisen  in rifting basin. Along with the gradually advancing process of the rifting, the  variation of tectonic forces F1 and F2, both in magnitude and direction, must have induced the changes of the stress state S(Fi), causing different structural characteristics of the rifting basin  appeared in  various stages of tectonic evolution.

Key words:  rifting basin, extensional structure, strikeslip structure, inverted structure, tectonic dynamics