Geology Reference
In-Depth Information
15
4000
(b)
(a)
Core (
T
)
C
14
Plates (
Q
)
S
3000
Lower Mantle (
T
)
Heat gen (
Q
)
L
R
13
Plumes (
Q
)
2000
C
Upper Mantle (
T
)
Total
U
12
1000
Inner core radius
Thermal dissipation
0
11
0
1
2
3
4
0
1
2
3
4
Time, Gyr
Time, Gyr
Figure B.1. The thermal evolution of Figure 9.1 including core-related results
(long-dashed, thin lines). (a) The radius of the inner core. (b) Thermal dissipation
in the core (lower curve) and total dissipation (upper curve) including dissipation
from compositional convection driven by crystallisation of the inner core.
mantle material. The result would be a core considerably hotter than the mantle, even at
the core-mantle boundary. In the present model, the lower mantle starts at the same
temperature as the core, but the mantle cools very quickly, so a large temperature
difference is soon established.
B.3 Numerical thermal evolution model
The results shown in Figures 9.2 and 9.3 are Case 5 of Davies [156], where full details can
be found. The most relevant inputs and outputs are shown in Table B.3. This model is not
tailored as closely to fit observed heat flows, and they are a little higher than either the
model of Figure 9.4 or the observed values. Nevertheless, the model demonstrates
basically similar behaviour of the numerical and parametrised models.
B.4 Basalt tracers
Material of basaltic composition is represented in the numerical convection models by
tracers. The tracers each carry a small mass anomaly, corresponding to the different
density of the basaltic component at depth relative to average mantle. Tracers are advected
with the mantle flow using a fourth-order Runge-Kutta algorithm [139, 156, 203].
As fluid rises through the depth of the solidus, melting is simulated by removing
tracers and placing them in a thin crustal layer. This simulates pressure release melting,
and leaves a layer of fluid depleted of tracers, simulating the depleted residue of the
oceanic crust source. The depleted layer is less dense than surrounding material
containing heavy tracers.
To calculate the depth of the solidus, the mantle is presumed to be heterogeneous
in major element composition. Since eclogite has a lower solidus temperature than
peridotite, the depth at which first melting occurs will be controlled by the eclogite. The
