An internally consistent pressure calibration of geobarometers applicable to the Earth’s upper mantle using in situ XRD

Beyer, Christopher; Rosenthal, Anja; Myhill, Robert; Crichton, Wilson A.; Yu, Tony; Wang, Yanbin; Frost, Daniel J.

doi:10.1016/j.gca.2017.10.031

Cited by 9 publications

(5 citation statements)

References 56 publications

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“…Kusaba et al (1999) did not specify uncertainty for their values, so we adopted a value for s(P Kusaba ) of 0.2 GPa. This is comparable to uncertainty estimates of pressure calculated using in situ diffraction in comparable experiments (Beyer et al, 2018), although uncertainty in pressure and temperature measured by in situ diffraction in DIA-type multi-anvil apparatus can be greater than this (Farmer et al, 2020).…”

Section: Fitting Phase Equilibrium Results To the Thermodynamic Modelsupporting

confidence: 79%

The miscibility gap between the rock salt and wurtzite phases in the MgO–ZnO binary system to 3.5 GPa

Farmer,

O'Neill

2023

Eur. J. Mineral.

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Abstract. At ambient pressure, MgO crystallizes in the rock salt (B1) structure, whereas ZnO crystallizes in the wurtzite structure (B4). The asymmetric miscibility gap between these two structures in the MgO–ZnO binary system narrows with increasing pressure, terminating at the wurtzite-to-rock-salt phase transition in pure ZnO, which occurs at approximately 5 GPa at 1000 ∘C. Despite their essential simplicity, the pressure–temperature–composition (P–T–X) relations in the MgO–ZnO binary system have been sparsely studied experimentally, with disparate results that are inconsistent with available thermodynamic data. Here we report the experimental determination of the P–T–X relations of the miscibility gap from 940 to 1500 ∘C and 0 to 3.5 GPa, which we combine with calorimetric and equation-of-state data from the literature and on the transition in endmember ZnO, to build a thermodynamic model that resolves many of the inconsistencies. The model treats the rock salt phase as an ideal solution (no excess Gibbs free energy of mixing), while in the wurtzite phase the MgO component follows Henry's law and the ZnO component Raoult's law in the range of compositions accessed experimentally. However, there is an inconsistency between the partial molar volume of wurtzite-structured MgO deduced from this model and that inferred from lattice parameter measurements by X-ray diffraction in the quenched samples. This discrepancy may be caused by unquenchable disordering of some significant fraction of the substituting Mg2+ into normally vacant octahedral interstices of the wurtzite structure.

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Section: Fitting Phase Equilibrium Results To the Thermodynamic Modelsupporting

confidence: 79%

The miscibility gap between the rock salt and wurtzite phases in the MgO–ZnO binary system to 3.5 GPa

Farmer,

O'Neill

2023

Eur. J. Mineral.

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“…(2) Three majorite barometers of Collerson et al (2010), Wijbrans et al (2016), and Beyer and Frost (2017) were used to calculate the pressures, and compared with the experimental pressures. In most of the experiments, the calculated pressures with these barometers are within ±(1–1.5) GPa of the nominal run pressures, except for systematic underestimation of pressures for experiments conducted at 20 GPa (Figure S4), while the corrected Collerson barometer (Beyer et al, 2018; Collerson et al, 2010) can produce pressures within ±(1–1.5) GPa of the run pressures for experiments carried out at 20 GPa, except for one (R1008B). (3) The calculated pressures using these majoritic barometers produce a systematic trend, which are in accordance with previous studies of Kiseeva, Litasov, et al (2013) and Thomson et al (2016) (Figure S4).…”

Section: Resultsmentioning

confidence: 76%

Decarbonation of Stagnant Slab in the Mantle Transition Zone

2020

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Phase relations of carbonated basalts have been investigated at 13–20 GPa and 1200–1600°C, to model the decarbonation process of stagnant slab in the mantle transition zone (MTZ). Two synthetic mixes with CO2 contents of 2.5 wt% (PC‐a) and 5.0 wt% (PC‐b) were used as the starting materials. The estimated solidus was ~1350°C at the top of the MTZ (~13–15 GPa), which declined to ~1250°C for pressures of above ~15–16 GPa for both mixes. The average slab geotherms are lower than the obtained solidus, creating a carbonate‐bearing stagnant slab, followed by decarbonation of stagnant slab with increased residence time. Dehydration of stagnant oceanic lithosphere could induce decarbonation of the upper oceanic crust for temperatures below the solidus of carbonated basalts. The resulting carbonate melt is highly reactive with the ambient mantle, producing a carbonated domain in the MTZ or at the top of the 410‐km seismic discontinuity. A portion of carbonate melt could ascend to shallow depth because of low density and low viscosity and bring oceanic crust signatures into the source of some volcanoes after complex interactions with the surrounding mantle. On the example of Eastern Asia, decarbonation of stagnant slab is inferred to be a possible prerequisite for the formation of the big mantle wedge and triggered the intraplate volcanoes of Eastern Asia.

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“…Such refinement may be realized through experiments equilibrating rock salt + wurtzite assemblages with the pressure independently determined using in situ X-ray diffraction (e.g. Beyer et al, 2018). Confirmation of the pressure and temperature of the wz-rs univariant transition in endmember ZnO through in situ monitoring would also be most valuable, as the calibration of Farmer and O'Neill (2023) is quite sensitive to their selection of the results of Kusaba et al (1999).…”

Section: Discussionmentioning

confidence: 99%

The use of MgO–ZnO ceramics to record pressure and temperature conditions in the piston–cylinder apparatus

Farmer,

O'Neill

2024

Eur. J. Mineral.

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Abstract. The factors affecting the calibration of pressure in the piston–cylinder and other solid-media apparatus are so multifaceted and complex as to challenge existing approaches. Here we demonstrate how MgO–ZnO ceramics may be used in piston–cylinder assemblies to routinely record the pressure–temperature conditions experienced by samples in each run. The miscibility gap between rock-salt- and wurtzite-structured phases in the binary system MgO–ZnO is well suited for this purpose as it is capable of recording pressure and/or temperature in situ with a typical sensitivity to pressure of ± 0.02 GPa (1 standard deviation) if temperature is known, or variations in temperature around a sample of ∼ 10 °C assuming pressure is constant. MgO–ZnO ceramics can simply replace the widely used MgO surrounding samples under most conditions, since they are almost as inert chemically as MgO and have similar mechanical properties. As a demonstration, we apply the method to a redetermination of the quartz–coesite univariant phase transition in the piston–cylinder, using different assembly materials, sizes, and pressure–temperature path protocols. Continuous monitoring of piston travel during the entirety of each run helps reveal the differences in behaviour of the apparatus under these variables. We show that several assumptions about the behaviour of the piston–cylinder apparatus are ill-founded, that there may be a discrepancy of ∼ 10 % in pressure between otherwise identical experiments conducted using slightly different experimental protocols, and that the effects of the various options for assembly materials are complex, depending on the pressure–temperature path of the experiment throughout its duration. We have also used the sensitivity of the miscibility gap to temperature to map the temperature distribution in two dimensions surrounding a platinum capsule in a piston–cylinder experiment. The routine inclusion of the ceramic in piston–cylinder assemblies would provide an archive of actual experimental P–T conditions experienced by samples.

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An internally consistent pressure calibration of geobarometers applicable to the Earth’s upper mantle using in situ XRD

Cited by 9 publications

References 56 publications

The miscibility gap between the rock salt and wurtzite phases in the MgO–ZnO binary system to 3.5 GPa

The miscibility gap between the rock salt and wurtzite phases in the MgO–ZnO binary system to 3.5 GPa

Decarbonation of Stagnant Slab in the Mantle Transition Zone

The use of MgO–ZnO ceramics to record pressure and temperature conditions in the piston–cylinder apparatus

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