Abstract Details
(2020) Lengthscales of Mantle Volatile Heterogeneity
Matthews S, Shorttle O, Maclennan J, Rudge JF & Murton B
https://doi.org/10.46427/gold2020.1746
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02d: Room 1, Wednesday 24th June 05:30 - 05:33
Simon Matthews
View all 5 abstracts at Goldschmidt2020
View abstracts at 7 conferences in series
Oliver Shorttle View all 7 abstracts at Goldschmidt2020 View abstracts at 12 conferences in series
John Maclennan View all 3 abstracts at Goldschmidt2020 View abstracts at 17 conferences in series
John F. Rudge View abstracts at 3 conferences in series
Bramley Murton View abstracts at 8 conferences in series
Oliver Shorttle View all 7 abstracts at Goldschmidt2020 View abstracts at 12 conferences in series
John Maclennan View all 3 abstracts at Goldschmidt2020 View abstracts at 17 conferences in series
John F. Rudge View abstracts at 3 conferences in series
Bramley Murton View abstracts at 8 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by sylvie demouchy on Thursday 18th June 10:31
The temperature used for the water (hydrogen) diffusion model is very high 1800 °C. Which petrological evidence permits you to conclude to such high temperature in the system ? S. Demouchy
Thank you for the question. In our diffusion model, we are considering diffusion during transport of solid mantle material from the lower mantle to the upper mantle. Our own work (Matthews et al., 2016, G3) shows that petrological and geophysical observations suggest the Icelandic mantle has a potential temperature (Tp) of ~1480°C; i.e., the temperature if the mantle were allowed to upwell to the surface without chemical change. If mantle upwelling is adiabatic, or near-adiabatic, its temperature decreases during ascent (owing to expansion). Extrapolation of the adiabat downwards to the lower mantle would put the temperature well in excess of 2000°C (e.g. https://science.sciencemag.org/content/sci/343/6170/522/F4.large.jpg from Nomura et al., Science, 2014). If we were doing a more realistic version of the calculation, we would allow the temperature to vary with time, in addition to considering the changing pressure and mineral assemblage. Here I present an extremely simple version of the calculation to get a feeling for what the effects of diffusion might be, and on that basis I arbitrarily picked an intermediate temperature. The dashed lines on the figure show how our result changes if a temperature 100°C lower or higher is used instead.
The temperature used for the water (hydrogen) diffusion model is very high 1800 °C. Which petrological evidence permits you to conclude to such high temperature in the system ? S. Demouchy
Thank you for the question. In our diffusion model, we are considering diffusion during transport of solid mantle material from the lower mantle to the upper mantle. Our own work (Matthews et al., 2016, G3) shows that petrological and geophysical observations suggest the Icelandic mantle has a potential temperature (Tp) of ~1480°C; i.e., the temperature if the mantle were allowed to upwell to the surface without chemical change. If mantle upwelling is adiabatic, or near-adiabatic, its temperature decreases during ascent (owing to expansion). Extrapolation of the adiabat downwards to the lower mantle would put the temperature well in excess of 2000°C (e.g. https://science.sciencemag.org/content/sci/343/6170/522/F4.large.jpg from Nomura et al., Science, 2014). If we were doing a more realistic version of the calculation, we would allow the temperature to vary with time, in addition to considering the changing pressure and mineral assemblage. Here I present an extremely simple version of the calculation to get a feeling for what the effects of diffusion might be, and on that basis I arbitrarily picked an intermediate temperature. The dashed lines on the figure show how our result changes if a temperature 100°C lower or higher is used instead.
Submitted by Georg F. Zellmer on Wednesday 24th June 02:03
On your slide Iceland DM is less hydrated than Iceland EM, the righthand diagram is based on H2O/La. Is the x-axis H2O (ppmw), as stated, or is it H2O/La? If the former, I find it very intriguing that the plume component should have less H2O than the ambient upper mantle component. If you sampled along the Reykjanes ridge, would you expect H2O to increase away from Iceland? It seems counterintuitive...
On your slide Iceland DM is less hydrated than Iceland EM, the righthand diagram is based on H2O/La. Is the x-axis H2O (ppmw), as stated, or is it H2O/La? If the former, I find it very intriguing that the plume component should have less H2O than the ambient upper mantle component. If you sampled along the Reykjanes ridge, would you expect H2O to increase away from Iceland? It seems counterintuitive...
Submitted by Georg F. Zellmer on Wednesday 24th June 02:03
On your slide Iceland DM is less hydrated than Iceland EM, the righthand diagram is based on H2O/La. Is the x-axis H2O (ppmw), as stated, or is it H2O/La? If the former, I find it very intriguing that the plume component should have less H2O than the ambient upper mantle component. If you sampled along the Reykjanes ridge, would you expect H2O to increase away from Iceland? It seems counterintuitive...
On your slide Iceland DM is less hydrated than Iceland EM, the righthand diagram is based on H2O/La. Is the x-axis H2O (ppmw), as stated, or is it H2O/La? If the former, I find it very intriguing that the plume component should have less H2O than the ambient upper mantle component. If you sampled along the Reykjanes ridge, would you expect H2O to increase away from Iceland? It seems counterintuitive...
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