Temperature [K]
1000 1500 2000 2500 3000 3500
Depth [km]
0 100 200 300 400 500 600
Solidii for different compositions
Fertile c=0.6 Depleted
A:#Temperature#[K]# B:#Mel2ng#age#[BY]#
C:#Basalt#frac2on# D:#206Pb/204Pb#
0.0 0.3 0.7 1.0 1.4#
1.7#
2.1#
2.5#
2.9 3.2#
3.6#
18.5#
18.2#
18.0#
17.8#
17.5#
17.2#
17.0#
16.8#
16.5#
16.2#
16.0#
1.0#
0.9#
0.8#
0.7#
0.6#
0.5#
0.4#
0.3#
0.2#
0.1#
0.0#
3000#
2730#
2460#
2190#
1920#
1650#
1380#
1110#
840#
570#
300#
Calcula&on Setup
Conclusions Mel&ng via par&cles
van Heck et al., GMD, in reviewReferences:
Van Heck, Davies, Ellio1, Porcelli, Global scale modeling of mel:ng and isotopic evolu:on of Earth’s mantle, GMD, under review.
Rudge, Mantle pseudo-isochrons revisited, EPSL, 2006
Stable for 3.5 Billion years Introduc&on
Tracking Radiogenic isotopes
DI31A-2553 Dynamic coupling of bulk chemistry, trace elements and mantle flow
Huw Davies, Hein van Heck, Andy Nowacki, James Wookey, Tim Ellio1, Don Porcelli
Cardiff University, Utrecht University, University of Leeds, University of Bristol, Oxford University
Comparing: temperature, mel&ng age composi&on and isotopic-ra&o.
Sketch illustra:ng how mel:ng separates a basal:c and depleted layer.
Le[: Example of composi:on separa:on, plate forma:on.
Blue: depleted composi:on
Yellow: enriched composi:on (c=0.2 vs c=0.6)
Red: core-mantle boundary.
Since we have to split and merge the par:cles. A[er an ini:al phase, the
number of par:cles stabilizes. On splibng/mergin, bulk composi:on is scaled to the mass of the par:cles, isotope abundance is simply added / divided.
We use a 3D-spherical finite element code (TERRA) to model convec:on. With par:cles to track bulk composi:on. To test our implementa:on we use a
simplified setup:
• Incompressible.
• Layered viscosity 3*1021,
increase by 30 at 660 km.
• Grid resolu:on 22 km.
• Max 35 par:cles per cell.
• “Plume-driven” mel:ng.
Add hea&ng and density
Comparison to analy&cal theory
(Rudge, EPSL, 2006)
Pseudo-isochron ages can be es:mated from: 1. the distribu:on of mel:ng ages in all of the mantle, 2. Pb-isotopes at
the surface / melt. Both agree in our model.
Basalt effec&ng density
Composi:onal surface layer at 2800 km depth.
Le[: Neutral (reference calcula:on).
Middle: Basalt 5% denser in the lower mantle (660 km onwards).
Right: Basalt 10% denser in the lower mantle (660 km onwards).
Plo1ed:
Heat produc:on via U, Th, and K.
Highly incompa:ble elements, so move with first produc:on of basalt.
100
10 50
*1016 40 30 20
Fully dynamical models that not only track the evolu:on of chemical heterogenei:es through the mantle, but also incorporate the effect of chemical heterogenei:es on the dynamics of mantle convec:on are now emerging. We extend our exis:ng numerical mantle convec:on code that can track fluid flow in 3D spherical geometry and tracks both bulk chemical components (basalt frac:on) and different trace elements. The chemical components frac:onate upon mel:ng when and where the solidus is crossed.
Now, the chemical informa:on will effect the flow of the fluid in the following ways: The bulk composi:on will link to density and the (radioac:ve) trace element abundance to heat produc:on.
• Mel:ng, isotope frac:ona:on and mixing benchmarked successfully using comparison to Rudge, 2006.
• Link between bulk chemistry and density works.
- High density of basalt creates bigger pools of basalt in the lowermost mantle.
• Tracking heat produc:on with par:cles works.
- Pa1ern of heat produc:on at surface follows basalt distribu:on - All aspects not fully tested.
On each par:cle we track the abundance of radiogenic
isotopes (U, Th, K) and their daughters (Pb, He, Ar). The heat produced by decay
can be linked to the temperature.
