ORCID Profile
0000-0002-1074-3815
Current Organisation
University of Leeds
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Publisher: American Physical Society (APS)
Date: 22-01-2013
Publisher: Cambridge University Press (CUP)
Date: 10-12-2009
DOI: 10.1017/S0022112009991583
Abstract: We investigate thermally driven convection in a rotating spherical shell subject to inhomogeneous heating on the outer boundary, extending previous results to more rapid rotation rates and larger litudes of the boundary heating. The analysis explores the conditions under which steady flows can be obtained, and the stability of these solutions, for two boundary heating modes: first, when the scale of the boundary heating corresponds to the most unstable mode of the homogeneous problem second, when the scale is larger. In the former case stable steady solutions exhibit a two-layer flow pattern at moderate rotation rates, but at very rapid rotation rates no steady solutions exist. In the latter case, stable steady solutions are always possible, and unstable solutions show convection rolls that cluster into nests that are out of phase with the boundary anomalies and remain trapped for many thermal diffusion times.
Publisher: American Geophysical Union (AGU)
Date: 04-2021
DOI: 10.1029/2020JE006726
Abstract: Modeling the planetary heat transport of small bodies in the early Solar System allows us to understand the geological context of meteorite s les. Conductive cooling in planetesimals is controlled by thermal conductivity, heat capacity, and density, which are functions of temperature ( T ). We investigate if the incorporation of the T ‐dependence of thermal properties and the introduction of a nonlinear term to the heat equation could result in different interpretations of the origin of different classes of meteorites. We have developed a finite difference code to perform numerical models of a conductively cooling planetesimal with T ‐dependent properties and find that including T ‐dependence produces considerable differences in thermal history, and in turn the estimated timing and depth of meteorite genesis. We interrogate the effects of varying the input parameters to this model and explore the nonlinear T ‐dependence of conductivity with simple linear functions. Then we apply non‐monotonic functions for conductivity, heat capacity, and density fitted to published experimental data. For a representative calculation of a 250 km radius pallasite parent body, T ‐dependent properties delay the onset of core crystallization and dynamo activity by ∼40 Myr, approximately equivalent to increasing the planetary radius by 10%, and extend core crystallization by ∼3 Myr. This affects the range of planetesimal radii and core sizes for the pallasite parent body that are compatible with paleomagnetic evidence. This approach can also be used to model the T ‐evolution of other differentiated minor planets and primitive meteorite parent bodies and constrain the formation of associated meteorite s les.
Publisher: Elsevier BV
Date: 08-2011
Publisher: American Geophysical Union (AGU)
Date: 17-11-2022
DOI: 10.1029/2022GL100692
Abstract: Earth's core has produced a global magnetic field for at least the last 3.5 Gyrs, presently sustained by inner core (IC) growth. Models of the core with high thermal conductivity suggest potentially insufficient power available for the geodynamo prior to IC formation ∼1 Ga. Precipitation of silicon from the liquid core might offer an alternative power source for the ancient magnetic field, although few estimates of the silicon partition coefficient exist for conditions of the early core. We present the first ab initio determination of the silicon partition coefficient at core‐mantle boundary conditions and use these results to confirm a thermodynamic description of partitioning that is integrated into a model of coupled core‐mantle thermal evolution. We show that models including precipitation of silicon can satisfy constraints of IC size, mantle convective heat flux, mantle temperature and a persistent ancient geodynamo, and favor an oxygen poor initial core composition.
Publisher: Wiley
Date: 27-09-2010
DOI: 10.1002/CPE.1593
Publisher: Wiley
Date: 24-11-2020
Publisher: Elsevier BV
Date: 05-2014
Publisher: Wiley
Date: 02-2021
Publisher: Elsevier BV
Date: 09-2023
Publisher: American Physical Society (APS)
Date: 23-06-2021
Publisher: Oxford University Press (OUP)
Date: 28-09-2011
Publisher: Elsevier BV
Date: 02-2013
Publisher: California Digital Library (CDL)
Date: 07-04-2023
DOI: 10.31223/X5BT0S
Abstract: We examine magnesium and potassium solubility in liquid Fe mixtures, representative of Earth’s core composition, in equilibrium with liquid silicate mixtures representative of an early magma ocean. Our study is based on the calculation of the chemical potentials of MgO and K2O in both phases, using density functional theory. For MgO, we also study stability against precipitation of the solid phase. We use thermal evolution models of the core and mantle to assess whether either radiogenic heating from 40K decay or Mg precipitation from the liquid core can resolve the new core paradox by powering the geodynamo prior to inner core formation. Our results on K show that concentrations in the core are likely to be small and the effect of 40K decay on the thermal evolution of the core is minimal, making it incapable of sustaining the early geodynamo alone. Our results also predict small concentrations of Mg in the core although these might be sufficient to power the geodynamo prior to inner core formation, depending on the process by which it is transported across the core mantle boundary.
Publisher: Elsevier BV
Date: 08-2008
Publisher: Elsevier BV
Date: 07-2023
Publisher: American Geophysical Union (AGU)
Date: 21-03-2013
DOI: 10.1002/GRL.50186
Publisher: California Digital Library (CDL)
Date: 14-07-2023
DOI: 10.31223/X59W86
Abstract: Pallasite meteorites contain evidence for vastly different cooling timescales: rapid cooling at high temperatures (K/yrs) and slow cooling at lower temperatures (K/Myrs). Pallasite olivine also shows contrasting textures ranging from well-rounded to angular and fragmental, and some s les record chemical zoning. Previous pallasite formation models have required fortuitous changes to the parent body in order to explain these contrasting timescales and textures, including late addition of a megaregolith layer, impact excavation, or parent body break-up and recombination. We investigate the timescales recorded in Main Group Pallasite meteorites with a coupled multiscale thermal diffusion modelling approach, using a 1D model of the parent body and a 3D model of the metal-olivine intrusion region, to see if these large-scale changes to the parent body are necessary. We test a range of intrusion volumes and aspect ratios, metal-to-olivine ratios, and initial temperatures for both the background mantle and the intruded metal. We find that the contrasting timescales, textural heterogeneity, and preservation of chemical zoning can all occur within one simple ellipsoidal segment of an intrusion complex. These conditions are satisfied in 13% of our randomly generated models (2200 model runs), with small intrusion volumes (with a mean radius ≲100 m) and colder background mantle temperatures (≲1200 K) favourable. Large rounded olivine can be explained by a previous intrusion of metal into a hotter mantle, suggesting possible repeated bombardment of the parent body. We speculate that the formation of pallasitic zones within planetesimals may have been a common occurrence in the early Solar System, as our model shows that favourable pallasite conditions can be accommodated in a wide range of intrusion morphologies, across a wide range of planetesimal mantle temperatures, without the need for large-scale changes to the parent body. We suggest that pallasites represent a late stage of repeated injection of metal into a cooling planetesimal mantle, and that heterogeneity observed in micro-scale rounding or chemical zoning preservation in pallasite olivine can be explained by erse cooling rates in different regions of a small intrusion.
Publisher: ACM
Date: 18-06-2021
Publisher: California Digital Library (CDL)
Date: 26-03-2023
DOI: 10.31223/X50M2C
Publisher: California Digital Library (CDL)
Date: 17-06-2022
DOI: 10.31223/X5H34M
Abstract: Earth's core has produced a global magnetic field for the last 4 Gyrs, presently sustained by inner core growth.Models of the core with high thermal conductivity suggest potentially insufficient power available for the geodynamo prior to inner core formation ~1 Ga.Precipitation of SiO2 from the liquid core might offer an alternative power source for the magnetic field before inner core growth, however, no estimates of partition coefficient exist for conditions of the early core.We present the first determination of the silicon partition coefficient at core-mantle boundary conditions and use these results to build a thermodynamic model that is integrated into a model of coupled core-mantle thermal evolution.We show that models including precipitation of silicon can satisfy constraints of inner core size, mantle convective heat flux, mantle temperature and a persistent ancient geodynamo whilst those excluding fail.Successful power from precipitation favours an oxygen poor initial core composition.
Publisher: Springer Science and Business Media LLC
Date: 11-04-2012
DOI: 10.1038/NATURE11031
Abstract: The Earth acts as a gigantic heat engine driven by the decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing (as the solid inner core grows), and on chemical convection (due to light elements expelled from the liquid on freezing). The power supplied to the geodynamo, measured by the heat flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent experimental and theoretical difficulties. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles--unlike previous estimates, which relied on extrapolations. The mixtures of iron, oxygen, sulphur and silicon are taken from earlier work and fit the seismologically determined core density and inner-core boundary density jump. We find both conductivities to be two to three times higher than estimates in current use. The changes are so large that core thermal histories and power requirements need to be reassessed. New estimates indicate that the adiabatic heat flux is 15 to 16 terawatts at the CMB, higher than present estimates of CMB heat flux based on mantle convection the top of the core must be thermally stratified and any convection in the upper core must be driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted, and future models of mantle evolution will need to incorporate a high CMB heat flux and explain the recent formation of the inner core.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
No related grants have been discovered for Christopher Davies.