The influence of MORB and harzburgite composition on thermo-chemical mantle convection in a 3-D spherical shell with self-consistently calculated mineral physics

Nakagawa, Takashi; Tackley, P. J.; Deschamps, Frédéric; Connolly, J. A. D.

doi:10.1016/j.epsl.2010.05.026

Cited by 126 publications

(142 citation statements)

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“…Foley and Becker 2009;Nakagawa et al 2010;Rolf and Tackley 2011;Tackley 2000a,b;van Heck and Tackley 2008). However, compared to the global models presented here, they all lack realistic single-sided subduction-a key feature of global mantle convection observed on Earth.…”

Section: Discussionmentioning

confidence: 99%

Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface

Crameri

Tackley

2016

Prog. in Earth and Planet. Sci.

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Subduction initiation is a key in understanding the dynamic evolution of the Earth and its fundamental difference to all other rocky planetary bodies in our solar system. Despite recent progress, the question about how a stiff, mostly stagnant planetary lid can break and become part in the global overturn of the mantle is still unresolved. Many mechanisms, externally or internally driven, are proposed in previous studies. Here, we present the results on subduction initiation obtained by dynamically self-consistent, time-dependent numerical modelling of mantle convection. We show that the stress distribution and resulting deformation of the lithosphere are strongly controlled by the top boundary formulation: A free surface enables surface topography and plate bending, increases gravitational sliding of the plates and leads to more realistic, lithosphere-scale shear zones. As a consequence, subduction initiation induced by regional mantle flow is demonstrably favoured by a free surface compared to the commonly applied, vertically fixed (i.e. free-slip) surface. In addition, we present global, three-dimensional mantle convection experiments that employ basal heating that leads to narrow mantle plumes. Narrow mantle plumes impinging on the base of the plate cause locally weak plate segments and a large topography at the lithosphere-asthenosphere boundary. Both are shown to be key to induce subduction initiation. Finally, our model self-consistently reproduces an episodic lid with a fast global overturn due to the hotter mantle developed below a former stagnant lid. We conclude that once in a stagnant-lid mode, a planet (like Venus) might preferentially evolve by temporally discrete, global overturn events rather than by a continuous recycling of lid and that this is something worth testing more rigorously in future studies.

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Section: Discussionmentioning

confidence: 99%

Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface

Crameri

Tackley

2016

Prog. in Earth and Planet. Sci.

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“…This constitutes another possible source of chemical heterogeneity at the bottom of the mantle (e.g. Nakagawa et al 2010). Furthermore, this recycled MORB may interact with the reservoirs of dense primordial material and modify the thermochemical structure of the lower mantle and its dynamics.…”

Section: O N C L U D I N G Discussionmentioning

confidence: 99%

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Deschamps

Tackley

2014

Geophysical Journal International

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S U M M A R YLarge-scale chemical lateral heterogeneities are inferred in the Earth's lowermost mantle by seismological studies. We explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time, by using similar analysis in 3-D spherical geometry. In this study, we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle, including the chemical density contrast between the primordial dense material and the regular mantle material (buoyancy ratio), thermal and chemical viscosity contrasts, volume fraction of primordial dense material and the Clapeyron slope of the phase transition at 660 km depth. We find that most of the findings from the 3-D Cartesian study still apply to 3-D spherical cases after slight modifications. Varying buoyancy ratio leads to different flow patterns, from rapid upwelling to stable layering; and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle. Chemical viscosity contrasts in a reasonable range have a second-order role in modifying the stability of the dense anomalies. The volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts, but has significant effects on calculations with intermediate and small thermal viscosity contrasts. The volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast. An endothermic phase transition at 660 km depth acts as a 'filter' allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle.

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“…After that study was published, many followed a similar approach, either tracking preset heterogeneities (e.g. Davies, 2002;Zhong and Hager, 2003;Nakagawa and Tackley, 2004), or having the chemical heterogeneities emerge via melting during the calculation at fixed melting zones (Walzer and Hendel, 1999;Davies, 2002;Huang and Davies, 2007a, b, c), moving melting zones that follow force-balanced plates or imposed plate motions (Brandenburg and van Keken, 2007a, b;Brandenburg et al, 2008), or freely moving melting location via a melting phase diagram (De Smet et al, 1998;Van Thienen et al, 2004;Xie and Tackley, 2004a, b;Nakagawa et al, 2009Nakagawa et al, , 2010.…”

Section: Introductionmentioning

confidence: 99%

Global-scale modelling of melting and isotopic evolution of Earth's mantle: melting modules for TERRA

et al. 2016

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Abstract. Many outstanding problems in solid-Earth science relate to the geodynamical explanation of geochemical observations. Currently, extensive geochemical databases of surface observations exist, but satisfying explanations of underlying mantle processes are lacking. One way to address these problems is through numerical modelling of mantle convection while tracking chemical information throughout the convective mantle.We have implemented a new way to track both bulk compositions and concentrations of trace elements in a finiteelement mantle convection code. Our approach is to track bulk compositions and trace element abundances via particles. One value on each particle represents bulk composition and can be interpreted as the basalt component. In our model, chemical fractionation of bulk composition and trace elements happens at self-consistent, evolving melting zones. Melting is defined via a composition-dependent solidus, such that the amount of melt generated depends on pressure, temperature and bulk composition of each particle. A novel aspect is that we do not move particles that undergo melting; instead we transfer the chemical information carried by the particle to other particles. Molten material is instantaneously transported to the surface layer, thereby increasing the basalt component carried by the particles close to the surface and decreasing the basalt component in the residue.The model is set to explore a number of radiogenic isotopic systems, but as an example here the trace elements we choose to follow are the Pb isotopes and their radioactive parents. For these calculations we will show (1) the evolution of the distribution of bulk compositions over time, showing the buildup of oceanic crust (via melting-induced chemical separation in bulk composition), i.e. a basalt-rich layer at the surface, and the transportation of these chemical heterogeneities through the deep mantle; (2) the amount of melt generated over time; (3) the evolution of the concentrations and abundances of different isotopes of the trace elements (U, Th, K and Pb) throughout the mantle; and (4) a comparison to a semi-analytical theory relating observed arrays of correlated Pb isotope compositions to melting age distributions (Rudge, 2006).

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The influence of MORB and harzburgite composition on thermo-chemical mantle convection in a 3-D spherical shell with self-consistently calculated mineral physics

Cited by 126 publications

References 46 publications

Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface

Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Global-scale modelling of melting and isotopic evolution of Earth's mantle: melting modules for TERRA

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