# How to add mantle convection to a continental extension system

Hi all,
I’m a beginner of ASPECT. I want to simulate the influence of different rift formation mechanisms (Active rifting, Passive rifting, Combined model) on rift evolution. And I have basically understood continental_extension.prm in cookbooks. I want to know how to generate a steady-state mantle convection on this basis, which can create a stress field at the bottom of the lithosphere. What examples can I refer to? What boundary conditions, material models, or anything else do I need to change or add?

Hi Wang,

Thanks for posting this question to the forum. This is more of a general research question rather an ASPECT-specific one, but an interesting topic nonetheless.

To simulate how stresses at the base of the lithosphere drive rifting, as opposed to boundary velocities at the lithosphere, I can envision a few setups:

1. Use the two merged boxes geometry, where one “box” represents the lithosphere and the second represents the convecting mantle. The lateral walls of the lithosphere would have traction boundary conditions, allowing material to flow in and out. The convecting mantle “box” would have applied velocity boundary conditions that produce a convective cell with divergent flow in the model center.

2. Similar to 1, but start with free-slip on all sides, an initial thermal anomaly that creates two convection cells with upwelling at the center, and a highly rigid lithosphere such that no significant deformation occurs. Run that model until you reach a convective steady state, then change the properties of the lithosphere to allow failure and switch the lateral walls to traction BCs. I believe Kenni Petersen published some rifting studies where he first simulated mantle convection that reached steady, then initiated rifting (don’t recall the specific details).

3. Separately simulate mantle convection, and then apply stresses at the base of the lithosphere from those simulations to a continental extension simulation. This approach was used in the following recent paper: Coupled influence of tectonics, climate, and surface processes on landscape evolution in southwestern North America | Nature Communications

I suspect option 1 would be much easier to implement than option 2 and 3.

Cheers,
John

I think the second option is more suitable for my simulation needs. But I still don’t quite understand how to achieve the transformation of lithospheric properties. And I tried to set an initial thermal anomaly on a section of the bottom boundary but it didn’t work. How can I solve the problem? The model size is 1200 x 660 km.

Best,
Wang

``````  set Model name = function

subsection Function
set Variable names      = x,z
set Function constants  = H=540e6, h=120e6
set Function expression = if (z>=H, 273+1300/h*(h+H-z), 1573+270/H*(H-z)+if(x>=500 && x<=700 && z==0e6, 150, 0 ));
end
end
type or paste code here
``````

Hi Wang,

You could modify the lithospheric properties to not undergo significant deformation during the initial stages of convection by setting a very high cohesion value.

Regarding the thermal anomaly, my recommendation would be to look at some of the other examples in the ASPECT cookbooks (or published studies) and use these as a template.

Cheers,
John

Hi Jhon,
According to your suggestion, I tried to establish rift motion model and convection model respectively, and then combine them. Since this is my first time doing a simulation related to mantle convection I had some problems when I tried to create it.

1. When I add viscous flow law (composite) in the visco-plastic material model, it is difficult to generate convection. I’m not sure whether it is a problem with the parameter setting or what details are overlooked.

2. How to judge whether the mantle convection has reached the steady state?

Here is my prm file.
test_convection.prm (10.0 KB)

Best,
Wang

Hi Wang,

Regarding point 1, I unfortunately cant readily offer more input as this is not an area (process, parameter space) I spend much time working on these days. Others may chime in and it may be worth reading one the following papers:

Point - there are a few cookbooks and benchmarks in the repository/manual that specifically address the question. That material is a good place to start.

Cheers,
John

Hi Jhon，

Thank you for your help! I will read and learn the above content.

Best,
Wang