Complex phase distribution and seismic velocity structure of the transition zone: Convection model predictions for a magnesium-endmember olivine–pyroxene mantle

Jacobs, Michael; Berg, A. P. van den

doi:10.1016/j.pepi.2011.02.008

Cited by 16 publications

(10 citation statements)

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“…In our model thermophysical properties density ρ, thermal expansivity α and specific heat c P are computed from pressure-temperature tables based on a mineral physics model for the magnesium endmember for an olivine-pyroxene composition (Jacobs and van den Berg, 2011;Jacobs and de Jong, 2007). Further details of the computational methods are given in van den Berg et al (2010Berg et al ( , 1993 and Jacobs and van den Berg (2011).…”

Section: Results Of Numerical Modellingmentioning

confidence: 99%

“…Here we use a compressible model based on the anelastic liquid approximation (ALA). This allows us to use, in a selfconsistent way, a detailed description of the material properties, density, specific heat, and thermal expansivity, obtained from a mineral physics model based on minimization of free energy (Jacobs and van den Berg, 2011;Jacobs and de Jong, 2007;Connolly, 2005). The model of Jacobs and de Jong (2007) is based on lattice dynamics and it includes both a more detailed parameterization of the vibrational density of states (VDoS) than the Debye model and anharmonicity, constrained by experimental data.…”

Section: Introductionmentioning

confidence: 99%

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Small-scale mineralogical heterogeneity from variations in phase assemblages in the transition zone and D″ layer predicted by convection modelling

et al. 2011

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Small-scale heterogeneity in the deep mantle is concentrated in the upper-mantle transition zone (TZ), in the depth range 410-660 km and also at the bottom 250 km D" region. This encourages a more detailed investigation of the potential for seismic reflectivity imaging by modelling heterogeneous structures in mantle convection models including phase transitions of the TZ and D" regions. We applied finite elements with variable spacing near the boundary layers in 2-D cylindrical geometry that allow for sufficient spatial resolution. We investigated several models including an extended Boussinesq (EBA) model, focused on the D" region, and a compressible (ALA) model for the TZ region. The results for the D" region show typical lens-shaped structures of post-perovskite (PPV) embedded in the perovskite (PV) background mantle, where the thickness of the lenses, at 200-400 km, strongly depends on the Clapeyron slope of the PV-PPV transition. A second phase transition (double crossing) occurs in case the core temperature is higher than the intercept temperature T i . Our phase-dependent rheology results in contrasting effective viscosity between PV and PPV. Our model results reveal a distinctly clear mechanical weakening of the PPV lenses with about an order of magnitude lower viscosity. The shear wave-speed distributions computed from our convection results are strongly correlated with the heterogeneous distribution of the mineral phase. Gradients in the seismic wave-speed that are the target of seismological reflectivity imaging are clearly Small-Scale Mineralogical Heterogeneity from Variations in Phase Assemblages in the Transition Zone and D" Layer 161 revealed. The wave-speed results show a clear resolution of the top and bottom interfaces of the PPV lenses. Our ALA model for the TZ is based on a thermodynamical model for the magnesium endmember of an olivine-pyroxene mantle. The model predicts a much more complex distribution of mineral phases, compared to our D" results, in agreement with the greater number of mineral phases involved in the olivine-pyroxene phase diagram for the P, T conditions of the transition zone. Near cold downwelling flows representing subducting lithospheric slabs, where the local geotherm can differ by up to 1 000 K from the horizontal average, and small-scale lateral variations in the mineral phases can occur.

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Section: Results Of Numerical Modellingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Small-scale mineralogical heterogeneity from variations in phase assemblages in the transition zone and D″ layer predicted by convection modelling

et al. 2011

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“…Another application of this flexible interfacing facility in SEPRAN is the implementation of completely general material properties, density, thermal expansivity and specific heat, derived from separate self-consistent thermodynamic models, both from Ab initio and semi-empirical lattice dynamics methods (van den Jacobs and van den Berg, 2011;Umemoto et al, 2006). This set up allows us to include results from frontier mineral physics in our convection models applied to planetary mantles but it is also applicable in other possible application domains such as reactive transport in porous media and geothermal modelling where thermodynamic properties play a role that may be tabulated in P, T space.…”

Section: Sepran Applications To Geodynamical Problemsmentioning

confidence: 99%

“…This set up allows us to include results from frontier mineral physics in our convection models applied to planetary mantles but it is also applicable in other possible application domains such as reactive transport in porous media and geothermal modelling where thermodynamic properties play a role that may be tabulated in P, T space. For these compressible models we apply an anelastic liquid approximation as described in (Jacobs and van den Berg, 2011). For the Stokes equation an integrated method is applied retaining velocity and pressure as the degrees of freedom (dof).…”

Section: Sepran Applications To Geodynamical Problemsmentioning

confidence: 99%

SEPRAN: A versatile finite-element package for a wide variety of problems in geosciences

2015

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Numerical modelling of geological processes, such as mantle convection, flow in porous media, and geothermal heat transfer, has become quite common with the increase in computing and the availability of usable software. Today modelling these dynamical processes entails the solving of the governing equations involving the mass, momentum, energy and chemical transport. These equations represent partial differential equations and must be solved on powerful enough computers because they require sufficient spatial and temporal resolution to be useful. We describe here the salient and outstanding features of the SE-PRAN software package, developed in the Netherlands, as a case study for a robust and user-friendly software, which the geological community can utilize in handling many thermal-mechanical-chemical problems found in geology, which will include geothermal situations, where many types of partial differential equations must be solved at the same time with thermodynamical input parameters. KEY WORDS: SEPRAN, finite element package, geodynamic and planetary modelling, geothermal, groundwater flow.

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“…Numerical models have looked at mechanical properties of mantle materials and their effects on the deformation of slabs in the upper mantle and transition zone [e.g., Schmeling et al , 1999; van Hunen et al , 2002, 2004; Běhounková and Čížková , 2008; Schmeling et al , 2008; Billen , 2010], their descent into the lower mantle [e.g., Christensen , 1996; Čížková et al , 2002; Enns et al , 2005; Billen and Hirth , 2007; Běhounková and Čížková , 2008; Yoshioka and Naganoda , 2010] and the surface expression of the subduction process [e.g., Christensen , 1996; King , 2001; Tosi et al , 2009; Krien and Fleitout , 2008; Faccenna et al , 2009; Quinquis et al , 2011]. Numerical studies have emphasized the importance of viscosity variations within the slab and in the ambient mantle [ Čížková et al , 2002; Stein et al , 2004; Billen and Hirth , 2005; Quinteros et al , 2010] and demonstrated effects associated with phase transitions [ Jacobs and van den Berg , 2011; Bina and Kawakatsu , 2010; Marton et al , 2005, 1999]. On the other hand, numerical models of subduction usually consider thermal diffusivity to be constant throughout the model domain.…”

Section: Introductionmentioning

confidence: 99%

The effect of variable thermal diffusivity on kinematic models of subduction

et al. 2012

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[1] We examine the influence of variable thermal properties on the thermal state of a subducting slab in the upper mantle and the transition zone by combining a kinematic slab model with models of thermal conductivity. Thermal diffusivity and conductivity models for major mantle minerals in the MgO-SiO 2 system are developed based on experimental measurements on these minerals at high pressure and temperature. The models show significantly higher thermal conductivity for stishovite and clinopyroxene compared to the Mg 2 SiO 4 polymorphs and majorite garnet. In our subduction model we consider scenarios with a differentiated slab (basalt-harzburgite-pyrolite) in a pyrolite mantle and uniform composition for both the slab and the mantle (pyrolite or a pure Mg 2 SiO 4 -based system). The role of highly conductive pyroxene is examined by taking it into account in some models and replacing it in others with majorite garnet. This choice has a strong influence on the thermal state of the slab, shifting the depth of the À1000 K temperature anomaly by as much as 100 km. This is caused by faster cooling of the plate at the surface and thermal insulating effects once subducted. Temperature differences between models with variable thermal diffusivity and those with constant parameters can reach $125 K, i.e. 10% of total thermal anomalies of the slab relative to an average geotherm. Taking into account the stable mineral phases we evaluate density variations between different models and find that variable thermal diffusivity results in a modest increase of negative buoyancy of the slab.

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Complex phase distribution and seismic velocity structure of the transition zone: Convection model predictions for a magnesium-endmember olivine–pyroxene mantle

Cited by 16 publications

References 55 publications

Small-scale mineralogical heterogeneity from variations in phase assemblages in the transition zone and D″ layer predicted by convection modelling

Small-scale mineralogical heterogeneity from variations in phase assemblages in the transition zone and D″ layer predicted by convection modelling

SEPRAN: A versatile finite-element package for a wide variety of problems in geosciences

The effect of variable thermal diffusivity on kinematic models of subduction

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