The effect of CO2 on the water-saturated solidus of K-poor peridotite between 4 and 6 GPa

Omri Dvir, Ronit Kessel*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

The effect of various amounts of CO2 on the solidus of H2O–CO2-bearing peridotite was examined by determining the composition of H2O–CO2-bearing fluids and melts in equilibrium with garnet peridotite at 4–6 GPa and 900–1100 °C. Two capsules were placed in a rocking multi-anvil apparatus in each experiment. Both capsules contained a fertile peridotite with 10 wt% H2O, one with 1 (CLZ1) and the other with 5 wt% CO2 (CLZ5). In both capsules a diamond trap was placed on one end of the capsule as a fluid/melt trap. The H2O and CO2 content in the fluid or melt trapped in between the diamonds were measured using the quartz-tube-system technique by releasing the volatiles through infrared gas analyzer. The total dissolved solids in these phases were determined using the cryogenic laser-ablation – inductive couple plasma – mass spectrometry technique. The residual lherzolite consists of olivine, orthopyroxene, ±clinopyroxene, garnet, and ±magnesite as carbonate phase. The solidus of CLZ1 peridotite was located between 900 and 1000 °C at 4 GPa and between 1000 and 1100 °C at 5 and 6 GPa. CLZ5 peridotite melts below 900 °C at 4 GPa and between 900 and 1000 °C at 5 and 6 GPa. The results demonstrate a decrease in melting temperature of hydrous peridotite at pressures between 4 and 6 GPa with increasing amount of CO2. The H2O–CO2-bearing fluids found in this study at 900–1000 °C are similar in composition to low-Mg carbonatitic to silicic high-density fluids found in fluid inclusions in diamonds. With increasing temperature, the melts approach type II kimberlites. We propose that H2O–CO2-induced partial melting of metasomatized garnet lherzolite at 4–6 GPa is a possible origin for group II kimberlites.

Original languageAmerican English
Pages (from-to)184-200
Number of pages17
JournalGeochimica et Cosmochimica Acta
Volume206
DOIs
StatePublished - 1 Jun 2017

Bibliographical note

Publisher Copyright:
© 2017 Elsevier Ltd

Keywords

  • CO
  • Carbonate melts
  • HO
  • High-pressure experiments
  • Hydrous carbonate solidus
  • Hydrous melts
  • Kimberlites
  • Mantle peridotite

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