What does it take to break up a supercontinent?

The forces that drive supercontinent breakup are commonly attributed to either the upward push of rising sub-continental mantle plumes and related mantle convection, or the drag force produced by retreating subduction systems along the margin of the supercontinent. The Earth Dynamics Research Group’s geodynamic modeling team recently published results of a new 4D model featuring a full analysis of these forces and an evaluation of the effect of pre-existing orogens in the lithosphere on the breakup process (Figure 1).

Figure 1. (a) A 3-D presentation of the thermal structures (yellow for hot upwellings; blue for cold downwellings) for the model of a supercontinent (shown with grey shade) with embedded orogens (two elongated zones defined by purple lines). (b) Non-dimensional residual temperature and velocity fields on a cross-section passing through the center of the supercontinent (O) and the two orogens. The continental blocks are highlighted by black lines, and arrows point to the preferential diversion of rising plumes (shown in yellow) to the orogens, causing break-up along the orogens. The non-dimensional second invariant of strain-rate at the surface is given in (c). Here (a) and (c) share the same view angle.

Our models suggest that in both homogeneous supercontinents (ones with no orogens) and supercontinents with embeded orogens, sub-supercontinent plume upwelling acts as the controlling factor on the extensional stress in the supercontinent interior, whereas subduction retreat mainly affects a zone along the margin of the supercontinent (Figure 2). Convection-induced shear stress at the bottom of the supercontinent is 1–2 orders of magnitude smaller than that of extensional stress on the lithosphere. In our two end-member models (with or without orogens), the breakup can be achieved for a supercontinent with orogens after the first surge in the extensional stress, leading to a plate-like break-up behaviour. For a hypothetical supercontinent without orogens, the rising plumes cause more diffused local thinning of the continental lithosphere before a breakup can be achieved in a less plate-like manner. Our work thus indicates that weak orogens play a critical role in determining the locations of continental rifting and the dispersal behaviour of supercontinent breakup.

Figure 2. Contrasting break-up behaviours between a supercontinent without orogens (a and c), and one with orogens (d and e). Red represents continental lithosphere and blue the sub-lithospheric mantle. (a) Velocity fields at 160-km depth for a model of a homogeneous supercontinent at the breakup time (t1). The gray area in (a) represents a ~2000-km-wide retreating trench. (b) The same model 50 Myr after the inception of subduction retreat. The green dot line in (b) denotes the supercontinent boundary at t1, and the area surrounded by white dash lines is where strain concentrates due to the subduction retreat. (c) Extensional stress distribution in the supercontinent along the arc ⏜OE in (a) at t1 + 50 Myr, where the purple dot line shows the bottom of the continental lithosphere. (d, e) Velocity fields at 160-km depth for model with an orogeny-embedded supercontinent at the breakup time (t1) and t1 + 50 Myr, respectively. (f) Extensional stresses for this model at t1 (top panel) and t1 + 50 Myr (bottom panel) on cross-section passing through arc ⏜(FF^' ) in (d) and (e). The black triangles in (f) mark the positions of orogens.

Contact person: Nan Zhang, Earth Dynamics Research Group, Curtin University.

Relevant publication:

Chuan Huang, Nan Zhang, Zheng‐Xiang Li, Min Ding, Zhuo Dang, Amaury Pourteau, Shijie Zhong. Modeling the Inception of Supercontinent Breakup: Stress State and the Importance of Orogens. Geochemistry, Geophysics, Geosystems (In Press; https://doi.org/10.1029/2019GC008538).