loading page

The Speciation and Coordination of a Deep Earth Carbonate-Silicate-Metal Melt
  • +1
  • Anne H. Davis,
  • Natalia Solomatova,
  • Andrew J. Campbell,
  • Razvan Caracas
Anne H. Davis
University of Chicago, Department of the Geophysical Sciences

Corresponding Author:ahdavis@uchicago.edu

Author Profile
Natalia Solomatova
École Normale Supérieure de Lyon
Author Profile
Andrew J. Campbell
University of Chicago
Author Profile
Razvan Caracas
French National Centre for Scientific Research (CNRS)
Author Profile


Ab initio molecular dynamics calculations on a carbonate-silicate-metal melt were performed to study speciation and coordination changes as a function of pressure and temperature. We examine in detail the bond abundances of specific element pairs and the distribution of coordination environments over conditions spanning Earth’s present-day mantle. Average coordination numbers increase continuously from 4 to 8 for Fe and Mg, from 4 to 6 for Si, and from 2 to 4 for C from 1 to 148 GPa (4,000 K). Speciation across all pressure and temperature conditions is complex due to the unusual bonding of carbon. With increasing pressure, C-C and C-Fe bonding increase significantly, resulting in the formation of carbon polymers, C-Fe clusters, and the loss of carbonate groups. The increased bonding of carbon with elements other than oxygen indicate that carbon begins to replace oxygen as an anion in the melt network. We evaluate our results in the context of diamond formation and of metal-silicate partitioning behavior of carbon. Our work has implications for properties of carbon and metal-bearing silicate melts, such as viscosity, electrical conductivity, and reactivity with surrounding phases.
Mar 2022Published in Journal of Geophysical Research: Solid Earth volume 127 issue 3. 10.1029/2021JB023314