Numerical modelling of trace element fractionation during diffusion controlled crystallization

Wright, C. J.; McCarthy, T. S.; Cawthorn, R. Grant

doi:10.1016/0098-3004(83)90007-9

Cited by 10 publications

(5 citation statements)

References 11 publications

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“…Here we have chosen a value of 200 which is consistent with f O2 within one log unit of QFM 20,26,28,29 . Previous models resorted to diffusive addition of Cr from convecting layers above [10][11][12]14,15,53 . Considering diffusive supply from a reservoir of fixed size to the crystallizing magnetite, Wright et al 53 and McCarthy et al 14 found that to fit the measured profiles for a fixed value of the Cr diffusion coefficient D Cr-melt in the melt, the rate of crystal accumulation had to be arbitrarily constrained by the observed compositions.…”

Section: Discussionmentioning

confidence: 99%

“…Previous models resorted to diffusive addition of Cr from convecting layers above [10][11][12]14,15,53 . Considering diffusive supply from a reservoir of fixed size to the crystallizing magnetite, Wright et al 53 and McCarthy et al 14 found that to fit the measured profiles for a fixed value of the Cr diffusion coefficient D Cr-melt in the melt, the rate of crystal accumulation had to be arbitrarily constrained by the observed compositions. The rate of crystal accumulation implied by the model would require as much as 3 Myr to crystallize the 1 m thick MML 15 .…”

Section: Discussionmentioning

confidence: 99%

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Magnetite layer formation in the Bushveld Complex of South Africa

Yao

Mungall

2022

Nat Commun

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The great economic significance of layered mafic-ultramafic intrusions like the Bushveld Complex of South Africa results from the existence within them of some layers highly concentrated in valuable elements. Here we address the origins of the Main Magnetite Layer, a globally important resource of Fe-Ti-V-rich magnetite. Previous models of in situ fractional magnetite crystallization require frequent ad hoc adjustments to the boundary conditions. An alternative model incorporating compositional convection near the top of the pile and infiltration of the pile from beneath by migrating intercumulus melt fits observations without any adjustments. Lateral variations in Cr concentration formerly held as indisputable evidence for in situ crystallization can be accommodated better by models of reactive melt infiltration from below. The choice of models has pivotal ramifications for understanding of the fundamental processes by which crystals accumulate and layers form in layered intrusions.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Magnetite layer formation in the Bushveld Complex of South Africa

Yao

Mungall

2022

Nat Commun

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show abstract

“…The choices of model parameters and boundary conditions may reflect the robustness and reliability of these forward models. Previous models resorted to diffusive addition of Cr from convecting layers above [10][11][12][14][15]46 . Considering diffusive supply from a reservoir of fixed size to the crystallizing magnetite Wright et al 46 and McCarthy et al 14 found that, to fit the measured profiles for a fixed value of the Cr diffusion coefficient D in the melt, the rate of crystal accumulation had to be arbitrarily constrained by the observed compositions.…”

Section: Discussion and Comparison With Previous Workmentioning

confidence: 99%

“…Previous models resorted to diffusive addition of Cr from convecting layers above [10][11][12][14][15]46 . Considering diffusive supply from a reservoir of fixed size to the crystallizing magnetite Wright et al 46 and McCarthy et al 14 found that, to fit the measured profiles for a fixed value of the Cr diffusion coefficient D in the melt, the rate of crystal accumulation had to be arbitrarily constrained by the observed compositions. The rate of crystal accumulation implied by the model would require as much as 3 Myr to crystallize the 1 m thick MML 15 .…”

Section: Discussion and Comparison With Previous Workmentioning

confidence: 99%

Magnetite layer formation in the Bushveld Complex of South Africa

Yao

Mungall

2021

Preprint

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The great economic significance of layered mafic-ultramafic intrusions like the Bushveld Complex of South Africa results from the existence within them of some layers highly concentrated in valuable elements. Here we address the origins of the Main Magnetite Layer, a globally important resource of Fe-Ti-V-rich magnetite. Previous models of in situ fractional magnetite crystallization require frequent ad hoc adjustments to the boundary conditions. An alternative model of rapid deposition of loose piles of magnetite crystals followed by compositional convection near the top of the pile and infiltration of the pile from beneath by migrating intercumulus melt fits observations without any adjustments. The data admit both explanations, but the latter model, with the fewest unconstrained interventions, is preferable. The choice of models has pivotal ramifications for understanding of the fundamental processes by which crystals accumulate and layers form in layered intrusions.

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“…Chemical exchanges have been examined on chemical bases through simple chemical reactions and evolution, using trace elements for instance (Wright et al, 1983). Further developments apply to specific minerals, e.g.…”

Section: The Eulerian Approachmentioning

confidence: 99%