Melting of carbonate-bearing peridotite as a function of oxygen fugacity: implications for mantle melting beneath mid-ocean ridges

Goni Shahar, Yingwei Fei, Ronit Kessel*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

The depth of melting beneath mid-ocean ridges (MORs) controls the melt composition as well as its rheology. Since mantle melting below MORs is the main mechanism of mantle degassing and CO2 emission into the atmosphere and oceans, there is an increasing interest in understanding the sub-ridge mantle conditions leading to its melting. Here we study the effect of oxygen fugacity on melting of carbonate-bearing peridotite at 3 GPa. Two metal—metal-oxide buffers (RRO and IW) were used to influence the fO2 of the experimental charge. Using Ir–Fe alloy sliding redox sensors, the fO2 of the two sets of experiments was measured. The solidus at IW + 4.5 was found to be at 950 °C, while at IW + 2.5 melting initiated at 1150 °C. In both sets of experiments, near-solidus carbonatitic melts evolved to carbon-bearing silicate melts with increasing temperature. This study together with previous studies suggest that increasing fO2 of a carbonate-bearing peridotite results in lowering of its melting temperature. Extrapolating these solidi to higher pressures results in initiation of melting of a relatively oxidizing mantle at ~ 430 km while melting of a more reduced mantle will initiate at depth of ~ 320 km. Very low velocity anomalies in the sub-ridge mantle at depth may reflect the initiation of melting, triggered by the presence of carbonate in the mantle at 1–2 log units below QFM.

Original languageAmerican English
Article number83
JournalContributions to Mineralogy and Petrology
Volume176
Issue number10
DOIs
StatePublished - Oct 2021

Bibliographical note

Publisher Copyright:
© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

Keywords

  • HP-HT experiments
  • MORB
  • Oxygen fugacity
  • Sub-ridge mantle

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