Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmdi53a1692w&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #DI53A-1692
Other
0545 Modeling (4255), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5418 Heat Flow, 5430 Interiors (8147), 8147 Planetary Interiors (5430, 5724, 6024)
Scientific paper
The possibility of time dependent layering, partial or otherwise, in Earth's mantle provides a mechanism, which could introduce periodicity into Earth's thermal evolution. The implications for deep Earth science would be significant. In the 3D spherical geometry modelling work presented here, the 660 km phase boundary was manipulated to induce layering to varying degrees. The time evolution of models that pass through various stages of full layering, partial layering and whole mantle convection is presented. Significant periodic time dependence emerges in the surface heat flux as model cases move into a partially layered regime. Previous work demonstrates cold upper mantle 'avalanches' into the lower mantle (Tackley et al. 1994), we confirm the existence of these avalanches and find evidence for the opposite process, a pulse of hot material entering the upper mantle from below. Such a process has been predicted for a partially layered mantle using parameterized models (Davies 1995). As far as we know, this process has not previously been demonstrated in 3D spherical geometry modelling. Should conditions within Earth's mantle be suitable for such processes to occur, the thermal evolution of the planet could show significant variation beyond secular and radioactive cooling trends. The resulting moderation of heat flux over time could resolve problems with projecting mantle temperature back in time with parameterized models (Butler and Peltier 2002). Additionally, periodic heat pulses into the upper mantle could promote increased melt extraction at certain times in Earth history. This provides a mechanism that could produce the phases of increased melting observed in some geochemical studies. Butler, S. L., and Peltier, W. R., 2002, Thermal evolution of Earth: Models with time-dependent layering of mantle convection which satisfy the Urey ratio constraint: J. Geophys. Res., v. 107, p. doi: 10.1029/20000JB000018. Davies, G. F., 1995, Punctuated tectonic evolution of the Earth: Earth Planet. Sci. Lett., v. 136, p. 363-379. Tackley, P. J., Stevenson, D. J., Glatzmaier, G. A., and Schubert, G., 1994, Effects of multiple phase transitions in a three dimensional spherical model of convection in Earth's mantle: J. Geophys. Res., v. 99, p. 15877-15901.
Davies John J.
Wolstencroft M.
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