Thermochemical Mantle Convection with Drifting Deformable Continents: Main Features of Supercontinent Cycle

摘要

We employ 2D Cartesian geometry model of thermochemical convection with non-Newtonian rheology and phase transitions, in the presence of floating deformable continents. Using a mantle model with continental crust, lithosphere and the material of the oceanic crust that can be subjected to eclogitization we study the stages of supercontinent cycle: assembly, evolution of supercontinent, its breakup and divergence of continents. Our results show that cold downgoing flows aggregate continents into a supercontinent. After its formation, the convection pattern changes: the subduction zones at the edges of the supercontinent and typical relatively narrow mantle plumes in the subcontinental mantle arise. The lifetime of the supercontinent is about 550 Ma. Typical velocities for continents before collision are 3-10 cm/year, for supercontinent 0.5-1.5 cm/year and after the breakup 4-8 cm/year. Despite the small mobility of the supercontinent, there is no significant warming up of the subcontinental mantle. The temperature anomaly under supercontinent is less than + 50 K and the superplume does not arise. We obtain that the phase transitions at 410 km and 660 km and the eclogitization of the subducted oceanic crust affects the supercontinent cycle significantly. Our results demonstrate certain irregularity of supercontinent cycle. The typical shear stresses in the mantle are less than 30 MPa; in the subduction zones and on the continent borders they are 100-250 MPa. Before the breakup maximum shear stress generated in the supercontinent can reach 200 MPa.