# Simple Subduction Model: 2D Cartesian#

*Contributed by Magali Billen*

This tutorial will present how to set up a subduction model structure intended for use in a mantle convection model. The model will use a 2D slice in a Cartesian geometry. The model will consist of 4 features:

A

`mantle layer`

with a uniform temperatureAn

`oceanic plate`

defining the overriding plate structureAn

`oceanic plate`

defining the sinking plate structure (along the model surface)A

`subducting plate`

defining the subducted portion of the sinking plate (the slab)

For each feature, we need to choose the geometry and we can define the temperature model and the composition model to delineate layers in the plates and slab.

For this tutorial, we will choose to use a simple temperature structure with a uniform
background temperature (i.e., no adiabat) and we will use the `plate model`

[8]
for temperature in the three plate related features. By using the same temperature model
for all three features, it is possible to have continuous temperatures across the feature
boundaries.

When building a new World Builder model for input to some other software, we recommend creating a grid file so you can check the construction of your model as you add in additional features by visualizing the model output created by gwb-grid using Paraview (or similar). A grid file has a specific structure defining the geometry, extent of the model region to visualize and the grid spacing. Choose a grid spacing that is sufficient to check the model is defined properly. For a 2D model only the information for the 2D grid of points needs to be indicated in the grid file. For this example, the full model domain is 8000 km long and 1600 km deep. The grid file for this example is:

```
# Grid File for creating vtk files to view in Paraview or Visit
grid_type = cartesian
dim = 2
compositions = 1
# domain of the grid (x and y are the surface, z is vertical with 0 at the bottom)
x_min = 0e3
x_max = 8000e3
z_min = 0e3
z_max = 1600e3
# grid properties
n_cell_x = 2000
n_cell_z = 400
```

## Root model information#

In the root model section we need to indicate the geometry (Cartesian). Even though we
only want a 2D model, World Builder starts from a 3-D space. Therefore, we also need to
define a 2-D cross section through the 3D World Builder space. The `cross section`

parameter defines the start and end locations for the cross section at the surface of
the model (z = 0). We choose to put the cross section at y = 0, and give the end
points of the cross section at x = 0 and x = 8000e3 m. The other physical parameters
are defined as reference values, which will be used by the feature temperature models
if the values are not entered separately.

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
```

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
52 }
53 ]
54}
```

### Feature Geometry, temperature and composition#

Because the World Builder defines features in 3D space, even though we want to define a 2D model, we still need to indicate some lateral extent for features in the y-direction. Any value can be chosen for this width, so we will center the cross section at y = 0, and let the y-direction extend from -100e3 m to 100e3 m.

#### Mantle Layer#

We start by defining the mantle layer to encompass all of the model domain. We don’t need to define a thickness for the mantle, but we need to define its lateral extent. This is done by assigning the x, y coordinates of the vertices of a polygon given in clockwise order. In this example, the polygon is a rectangle, so there are 4 pairs of coordinates provide. Because this is the first feature in the parameter file, features that follow and overlap with this layer will replace (by default) the existing value.

The reason we define a mantle layer is so we can set the background temperature to a u uniform value of 1573 K. The same value will be used as the bottom temperature in the plate models. A constant temperature mantle is a simplification, but is sometimes useful for testing ideas. A large model domain size is chosen to reduce the effects of the side boundaries, However, an even wider model is likely needed with a depth of only 1600 km. Alternatively, the box depth can be increased to 3000 km.

```
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
```

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
52 }
53 ]
54}
```

#### Oceanic Plates#

The geometry of the oceanic plates is defined by their lateral extent in the x direction and their depth in the z direction, again setting the y direction width to an arbitrary value:

Overriding plate extends from 0 to 3500e3 m in the x-direction.

Sinking plate extends from 3500e3 m to 8000e3 m in the x-direction.

In the z direction, the maximum depth of the plate is chosen to be deep enough to account for any changes in the plate temperature in depth. If too small a value is chosen, a sharp jump in temperature will be seen in the output. The down side to using a larger value is that it can take longer to needlessly assign values to additional grid points in the larger depth range. After defining the temperature model, by trial and error, we choose the maximum depth to be 200e3 m for the overriding plate and 300e3 m for the sinking plate.

For the temperature model we use the plate model: for plate ages less than about 80 my the half space [10] and plate models [8] are similar, but for older ages, the half space model over predicts the thickness of the lithosphere, based on bathymetric data. The temperature of the oceanic plates is calculated from the plate age, which is based on the location of the ridge for that plate and the spreading velocity. For this model we place the ridge for each plate at the box edges at x = 0 and x = 8000e3 m.

Finally, a composition field has also been included for the sinking plate. A thickness of 50e3 m is chosen so this layer can easily be seen in the example. This layer does not correspond to a geological feature, but can be used to refer to or show the initial location or thickness of the slab. The same approach can be used to define a crustal layer with a max depth/thickness of 8e3 m.

```
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
```

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
52 }
53 ]
54}
```

#### Subducting Plate#

Here we illustrate how to define a generic slab profile by defining segments of the slab
extending sequentially deeper from the surface trench location, given by the `coordinates`

.
The shape of the slab is controlled by the length of each segment and the dip angle of the
segment, which can vary linearly along the length of each segment. Each segment also has
a `thickness`

, which has the same purpose as the max depth parameter for the oceanic plate
feature, and a `top truncation`

parameter, which sets the distance above the slab surface
over which the composition or temperature will also be calculated. Distances above the slab
are negative. The code block below illustrates how the parameters defining the segments are
input in the World Builder file.

```
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
```

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
52 }
53 ]
54}
```

Here we first add the compositional layer for visualization (above) of the location and
thickness of the slab. We chose segments of different lengths, some with constant dip angle
and others with variable dip. We keep the `thickness`

and `top truncation`

values constant.
The figure below also visually illustrates the parameters defining the segments.

The last step is to define the temperature structure of the slab. For this we choose the
temperature model `mass conserving`

and the `plate model`

option for `reference model name`

.
Similar to the plate model temperature structure for the oceanic plate, the temperature
structure depends on the age of the plate at the trench and subducting plate velocity.
The age of the plate at the trench is determined from the `ridge coordinates`

, and subducting
`plate velocity`

. The slab continues to get older with depth based on the length along the
slab surface and subducting plate velocity. For the mass conserving temperature model,
heating up of the slab and cooling down of the surrounding mantle depends on age,
subducting plate velocity and length of the slab. The parameter `min distance slab top`

has the same role as `top truncation`

and the parameter `max distance slab top`

has the
same role as `thickness`

.

```
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
```

```
1{
2 "version":"1.0",
3 "coordinate system":{"model":"cartesian"},
4 "cross section":[[0,0],[8000e3,0]],
5 "surface temperature":273, "potential mantle temperature":1573,
6 "thermal expansion coefficient":3.1e-5, "specific heat":1000, "thermal diffusivity":1.0e-6,
7 "features":
8 [
9 {"model":"mantle layer", "name":"mantle", "max depth":1600e3,
10 "coordinates":[[0,-100e3],[0,100e3],[8000e3,100e3],[8000e3,-100e3]],
11 "temperature models":[{"model":"uniform", "temperature":1573}]},
12 {"model":"oceanic plate", "name":"Overriding",
13 "min depth":0, "max depth":200e3,
14 "coordinates":[[0,-100e3],[0,100e3],[3500e3,100e3],[3500e3,-100e3]],
15 "temperature models":[ {"model":"plate model",
16 "min depth":-10e3, "max depth":300e3,
17 "top temperature":273, "bottom temperature":1573,
18 "spreading velocity":0.05,
19 "ridge coordinates": [[[0,-100e3],[0,100e3]]]}]
20 },
21 {"model":"oceanic plate", "name":"Subducting",
22 "min depth":0, "max depth":300e3,
23 "coordinates" :[[3500e3,100e3],[3500e3,-100e3],[8000e3,-100e3],[8000e3,100e3]],
24 "temperature models":[{"model":"plate model",
25 "min depth":0, "max depth":300e3,
26 "top temperature":273, "bottom temperature":1573,
27 "spreading velocity":0.03,
28 "ridge coordinates": [[[8000e3,-100e3],[8000e3,100e3]]]}],
29 "composition models":[
30 {"model":"uniform", "compositions":[0], "min depth":0, "max depth":100e3}]
31 },
32 {"model":"subducting plate", "name":"Slab",
33 "coordinates":[[3500e3,-100e3],[3500e3,100e3]],
34 "dip point":[0,0],"max depth":1000e3,
35 "segments":[{"length":200e3,"thickness":[300e3],"top truncation":[-50e3],"angle":[0,30]},
36 {"length":100e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[30,50]},
37 {"length":500e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,50]},
38 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[50,10]},
39 {"length":300e3, "thickness":[300e3],"top truncation":[-50e3], "angle":[10,10]}],
40 "composition models":[
41 {"model":"uniform", "compositions":[0], "max distance slab top":100e3}],
42 "temperature models":[{"model":"mass conserving",
43 "reference model name": "plate model",
44 "density":3300, "thermal conductivity":3.3,"adiabatic heating":false,
45 "spreading velocity":0.03,
46 "subducting velocity":0.03,
47 "ridge coordinates":[[[8000e3,-100e3],[8000e3,100e3]]],
48 "coupling depth":80e3,
49 "forearc cooling factor":20.0,
50 "taper distance":100e3,
51 "min distance slab top":-200e3, "max distance slab top":300e3}]
52 }
53 ]
54}
```

Three other parameters control details of the temperature structure:

the rate of heating is different where the slab is in contact with the overriding plate versus when it is in direct contact with the mantle. This change is controlled by the

`coupling depth`

parameter.the temperature of the forearc region depends on the duration of subduction and shielding of this region from the warmer mantle. The amount of additional cooling of the forearc is controlled by the

`forearc cooling factor`

. This is a unconstrained tuning parameter in this model. Typical values are in the range of 0-20.the down-dip end of the slab needs to smoothly transition into the surrounding mantle. To achieve this, the

`taper distance`

indicates the distance at which to start linearly tapering the slab temperature into the background temperature.

#### Experimenting with the Model#

Recommendations for things to experiment with (only vary one parameter at a time) - change the:

`max depth`

for the oceanic plate: make smaller until its too small`top truncation`

: make smaller until its too small`coupling depth`

: make deeper or shallower - how does temperature change`forearc cooling factor`

: make larger or smaller - how does temperature change`taper distance`

: make larger or smaller - how does slab tip change`spreading velocity`

for the overriding plate: make smaller - how does temperature change`spreading velocity`

for the sinking plate: make smaller - how does temperature change`plate velocity`

for the slab to match that of the sinking plate