EGU22-3367, updated on 06 Oct 2023
https://doi.org/10.5194/egusphere-egu22-3367
EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Melting relations of carbonates and trace element partitioning between carbonates and carbonate liquid in the Earth's upper mantle

Melanie J. Sieber1,2, Max Wilke2, Marcus Oelze2,3, Oona Appelt2, Franziska D.H. Wilke2, and Monika Koch-Müller2
Melanie J. Sieber et al.
  • 1University of Potsdam, Germany
  • 2German Research Centre for Geoscience (GFZ), Potsdam, Germany
  • 3Bundesanstalt für Materialprüfung und -forschung (BAM), Berlin, Germany

We examined the supra-solidus phase relations of the CaCO3-MgCO3 system and established trace element partition coefficient between carbonates and carbonate melt by conducting high pressure (6 and 9 GPa) and temperature (1300-1800 oC) experiments with a rocking multi-anvil press. It is well known that the major element composition of initial melts derived from low-degree partial melting of the carbonated mantle strongly depends on the melting relations of carbonates (e.g. 1, 2 and reference therein). Understanding the melting relations in the CaCO3-MgCO3 system is thus fundamental in assessing low-degree partial melting of the carbonated mantle. We show here to which extent the trace element signature of a pure carbonate melt can be used as a proxy for the trace element signature of mantle-derived CO2-rich melts such as kimberlites.

Our results support that, in the absence of water, Ca-Mg-carbonates are thermally stable along geothermal gradients typical at subduction zones. Except for compositions close to the endmembers (~Mg0-0.1Ca1-0.9CO3; Ca0-0.1Mg1-0.9CO3), Ca-Mg-carbonates will partially (to completely) melt beneath mid‑ocean ridges and in plume settings. Ca-Mg-carbonates melt incongruently to dolomitic melt and periclase above 1450 oC and 9 GPa making the CaCO3-MgCO3 a (pseudo-) ternary system as the number of components increases. Further, our results show that the rare earth element signature of a dolomitic melt in equilibrium with magnesite is similar to those of Group I kimberlites, namely that HREE are depleted relative to primitive mantle signatures. This implies that dolomite-magnesite solid solutions might be useful to approximate melting relations and melt compositions of low-degree partial melting of the carbonated mantle.

References

1  Yaxley, Ghosh, Kiseeva, Mallik, Spandler, Thomson, and Walter, CO2-Rich Melts in Earth, in Deep Carbon: Past to Present, Orcutt, Daniel, and Dasgupta, Editors. 2019, Cambridge University Press: Cambridge. p. 129-162.

2  Dasgupta and Hirschmann, The deep carbon cycle and melting in Earth's interior. Earth and Planetary Science Letters, 2010. 298 (1-2): p. 1-13.

How to cite: Sieber, M. J., Wilke, M., Oelze, M., Appelt, O., Wilke, F. D. H., and Koch-Müller, M.: Melting relations of carbonates and trace element partitioning between carbonates and carbonate liquid in the Earth's upper mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3367, https://doi.org/10.5194/egusphere-egu22-3367, 2022.