Stress And Topographic Evolution Under Lithospheric Faults Stretching

The extensional structure of lithosphere affects continental cracking,ocean formation,continental basin development and evolution.Continental lithosphere may form wide rifts,narrow rifts and nuclear complex extension under tensile stress.This process is mainly controlled by crustal thickness,elongation rate,lithospheric rheological properties,magmatism,and presents a fault system composed of faults with different dip angles and spacing.There have been many studies on extensional structures and single fault evolution,but the studies on fault systems formed by a few faults are relatively limited,and the importance of elastic properties on fault stretching process is not clear.In this paper,we combine the theoretical calculation with the semi-analytical solution and the numerical simulation.The fault topography and the elastic potential energy are calculated in combination with the simplified assumption of equal thickness or homogeneous lower crust.The theoretical form of the faults is thus determined by the principle of minimum energy.Two-dimensional models with viscoelastoplastic and viscoplastic properties are constructed to solve the Stokes fluid equation to simulate the fault evolution in a small scale lithosphere.Firstly,we study the influence of elastic properties on the fault stretching process.Our results show that the role of elasticity in the process cannot be ignored.Secondly,we study the formation of the second fault after healing of one mature fault.Depending on the initial state,the second fault may occur at the same location of the first fault,or it may occur on the hanging wall or footwall of the first fault.If the initial fault stretching distance is short,the second fault occurs on the hanging wall and close to the first fault.On the contrary,if the initial fault stretching distance is long and has gone through the isostatic equilibrium,the second fault tends to occur at a certain distance from the first fault on the footwall.The distance from the first fault depends on the elastic thickness and elastic modulus of the crust,the tensile amount of the first fault and other factors.Finally,we study the topographic features of the fault system with two adjacent faults.In the case of equal crustal thickness,the topographic structure is only controlled by the relative tensile extents of the two faults,which are mainly affected by friction,fault dip angle.When the dip angle is small,the tensile extent is relatively large.Our results provide important references for further understanding the evolution of dip angle,stress,and strain of a fault system under lithospheric stretching.