New Thermodynamic Models and Calculated Phase Equilibria in NCFMAS for Basic and Ultrabasic Compositions through the Transition Zone into the Uppermost Lower Mantle

Holland, T. J. B.; Hudson, Neil F. C.; Powell, Roger; Harte, B.

doi:10.1093/petrology/egt035

Cited by 70 publications

(103 citation statements)

References 86 publications

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“…The most recent experimental estimates for the Clapeyron slope, G, of the ringwoodite to postspinel transition are between -0.5 and -2.0 MPa/K (Hirose, 2002;Fei et al, 2004;Katsura et al, 2004;Litasov et al, 2005;Stixrude and Lithgow-Bertelloni, 2011). At the lowest temperatures (below 900-1400 °C [Stixrude and Lithgow-Bertelloni, 2011;Holland et al, 2013]), the also strongly endothermic transition (G between -2 and -5 MPa/K) from ringwoodite through akimotoite to bridgmanite and magnesiowüstite may further contribute to the slab's phase buoyancy (Faccenda and Dal Zilio, 2017).…”

Section: Endothermic Phase Transitionmentioning

confidence: 99%

Subduction-transition zone interaction: A review

et al. 2017

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTAs subducting plates reach the base of the upper mantle, some appear to flatten and stagnate, while others seemingly go through unimpeded. This variable resistance to slab sinking has been proposed to affect long-term thermal and chemical mantle circulation. A review of observational constraints and dynamic models highlights that neither the increase in viscosity between upper and lower mantle (likely by a factor 20-50) nor the coincident endothermic phase transition in the main mantle silicates (with a likely Clapeyron slope of -1 to -2 MPa/K) suffice to stagnate slabs. However, together the two provide enough resistance to temporarily stagnate subducting plates, if they subduct accompanied by significant trench retreat. Older, stronger plates are more capable of inducing trench retreat, explaining why backarc spreading and flat slabs tend to be associated with old-plate subduction. Slab viscosities that are ~2 orders of magnitude higher than background mantle (effective yield stresses of 100-300 MPa) lead to similar styles of deformation as those revealed by seismic tomography and slab earthquakes. None of the current transition-zone slabs seem to have stagnated there more than 60 m.y. Since modeled slab destabilization takes more than 100 m.y., lower-mantle entry is apparently usually triggered (e.g., by changes in plate buoyancy). Many of the complex morphologies of lower-mantle slabs can be the result of sinking and subsequent deformation of originally stagnated slabs, which can retain flat morphologies in the top of the lower mantle, fold as they sink deeper, and eventually form bulky shapes in the deep mantle.

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Section: Endothermic Phase Transitionmentioning

confidence: 99%

Subduction-transition zone interaction: A review

et al. 2017

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“…Two Juina-5 clinopyroxenes also have elevated sodium contents that are indicative of eclogitic material at high pressure (Kiseeva et al 2013). NAL and CF phases are not stable minerals in peridotite but are known to be important components of eclogite at deep transition zone or lower mantle conditions (Ricolleau et al 2010;Holland et al 2013). The widespread occurrence of SiO 2 inclusions also suggests that the Juina-5 diamonds formed in a silica-rich protolith.…”

Section: Subducted Source Of Isotopically Light Carbonmentioning

confidence: 99%

Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

Thomson

Kohn²,

Bulanova

et al. 2014

Contrib Mineral Petrol

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interpreted as evidence of diamond growth from abiotic organic carbon added to the oceanic crust during hydrothermal alteration. The bulk isotopic composition of the oceanic crust, carbonates plus organics, is equal to the composition of mantle carbon (−5 ‰), and we suggest that recycling/mixing of subducted material will replenish this reservoir over geological time. Several exposed, syngenetic inclusions have bulk compositions consistent with former eclogitic magnesium silicate perovskite, calcium silicate perovskite and NAL or CF phases that have reequilibrated during their exhumation to the surface. There are multiple occurrences of majoritic garnet with pyroxene exsolution, coesite with and without kyanite exsolution, clinopyroxene, Fe or Fe-carbide and sulphide minerals alongside single occurrences of olivine and ferropericlase. As a group, the inclusions have eclogitic affinity and provide evidence for diamond formation at pressures extending to Earth's deep transition zone and possibly the lower mantle. It is observed that the major element composition of inclusions and isotopic compositions of host Juina-5 diamonds are not correlated. The diamond and inclusion compositions are intimately related to subducted material and record a polybaric growth history across a depth interval stretching from the lower mantle to the base of the lithosphere. It is suggested that the interaction of slabderived melts and mantle material combined with subsequent upward transport in channelised networks or a buoyant diapir explains the formation of Juina-5 diamonds. We conclude that these samples, despite originating at great mantle depths, do not provide direct information about the ambient mantle, instead, providing a snapshot of the Earth's deep carbon cycle. Keywords Diamonds · Sub-lithospheric mantle · Carbon cycle · SubductionAbstract Forty-one diamonds sourced from the Juina-5 kimberlite pipe in Southern Brazil, which contain optically identifiable inclusions, have been studied using an integrated approach. The diamonds contain <20 ppm nitrogen (N) that is fully aggregated as B centres. Internal structures in several diamonds revealed using cathodoluminescence (CL) are unlike those normally observed in lithospheric samples. The majority of the diamonds are composed of isotopically light carbon, and the collection has a unimodal distribution heavily skewed towards δ 13 C ~ −25 ‰. Individual diamonds can display large carbon isotope heterogeneity of up to ~15 ‰ and predominantly have isotopically lighter cores displaying blue CL, and heavier rims with green CL. The light carbon isotopic compositions are Communicated by O. Müntener. Electronic supplementary materialThe online version of this article

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“…Experimental data are shown as red closed symbols Ito et al 1998;Kubo et al 2000;Walter et al 2004). Data set values are shown as purple closed symbols Lithgow-Bertelloni 2005, 2011;Holland et al 2013). Red and blue lines correspond, respectively, to elastic models for the MgSiO 3 -AlAlO 3 and MgSiO 3 -MgAlO 2.5 v 0.5 binaries Fig.…”

Section: Discussionmentioning

confidence: 99%

“…It is the dominant mineral in the Earth's lower mantle, playing a key role in determining the seismic velocities and density structure of the deep mantle from the 660 km discontinuity until its breakdown to the CaIrO 3 -type post-perovskite structure a few hundred kilometers above the core-mantle boundary (Murakami et al 2004 (Litasov et al 2004;Holland et al 2013). The four most important Dachs and Geiger (2006) endmembers of bridgmanite are, therefore, MgSiO 3 , FeSiO 3 , AlAlO 3 , and FeAlO 3 , although MgSiO 3 is the only endmember which is stable in the bridgmanite structure (Wicks and Duffy 2016).…”

Section: The Bridgmanite Solid Solutionmentioning

confidence: 99%

“…This is true both of disordered models appropriate at high temperatures (Stixrude and Lithgow-Bertelloni 2011;Holland et al 2013) and of models including order-disorder (e.g., Carpenter 1988;Ghiorso 1990;Putnis 1992;Salje 1993;Holland and Powell 1996;Ghiorso and Evans 2002;Holland and Powell 2006). In these models, parameter values describing interaction energies are typically either constant, or linear functions of pressure and temperature.…”

Section: Introductionmentioning

confidence: 99%

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The elastic solid solution model for minerals at high pressures and temperatures

Myhill

2018

Contrib Mineral Petrol

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Non-ideality in mineral solid solutions affects their elastic and thermodynamic properties, their thermobaric stability, and the equilibrium phase relations in multiphase assemblages. At a given composition and state of order, non-ideality in minerals is typically modelled via excesses in Gibbs free energy which are either constant or linear with respect to pressure and temperature. This approach has been extremely successful when modelling near-ideal solutions. However, when the lattice parameters of the solution endmembers differ significantly, extrapolations of thermodynamic properties to high pressures using these models may result in significant errors. In this paper, I investigate the effect of parameterising solution models in terms of the Helmholtz free energy, treating volume (or lattice parameters) rather than pressure as an independent variable. This approach has been previously applied to models of order-disorder, but the implications for the thermodynamics and elasticity of solid solutions have not been fully explored. Solid solution models based on the Helmholtz free energy are intuitive at a microscopic level, as they automatically include the energetic contribution from elastic deformation of the endmember lattices. A chemical contribution must also be included in such models, which arises from atomic exchange within the solution. Derivations are provided for the thermodynamic properties of n-endmember solutions. Examples of the use of the elastic model are presented for the alkali halides, pyroxene, garnet, and bridgmanite solid solutions. Elastic theory provides insights into the microscopic origins of non-ideality in a range of solutions, and can make accurate predictions of excess enthalpies, entropies, and volumes as a function of volume and temperature. In solutions where experimental data are sparse or contradictory, the Helmholtz free energy approach can be used to assess the magnitude of excess properties and their variation as a function of pressure and temperature. The formulation is expected to be useful for geochemical and geophysical studies of the Earth and other planetary bodies.

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New Thermodynamic Models and Calculated Phase Equilibria in NCFMAS for Basic and Ultrabasic Compositions through the Transition Zone into the Uppermost Lower Mantle

Cited by 70 publications

References 86 publications

Subduction-transition zone interaction: A review

Subduction-transition zone interaction: A review

Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

The elastic solid solution model for minerals at high pressures and temperatures

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