The interaction of slab-derived silicic fluid and harzburgite – Metasomatism in the sub cratonic lithospheric mantle

Amit Meltzer*, Ronit Kessel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Understanding the interaction between fluids and the depleted peridotite is essential in deciphering the geochemical and mineralogical variability of the sub-continental lithospheric mantle (SCLM). High-density fluid (HDF) inclusions trapped in diamonds during their formation in the SCLM are potential metasomatic agents. In this study, experiments were performed on a harzburgite + silicic fluid system at an 80:20 rock:fluid ratio (bulk 5 wt% H2O and 3 wt% CO2), simulating the infiltration of a slab-derived silicic fluid into the SCLM. Experiments were performed at 3–6 GPa and 900–1200 °C on a rocking multi-anvil apparatus, conditions corresponding to the deep SCLM. The fluid and melt compositions were directly determined using the cryogenic LA-ICP-MS technique. The metasomatized peridotite consisted of olivine, clinopyroxene, phlogopite, orthopyroxene, amphibole, and magnesite. The H2O-CO2-saturated solidus in this system is located between 900–1000 °C at 3 GPa and between 1000–1100 °C at 4–6 GPa. The fluids at all pressures are alkali-rich. With increasing temperature and crossing the solidus, the melts evolve towards the initial silicic fluid composition. Together with previous studies on various peridotite + H2O ± CO2 systems, the results presented here suggest a positive correlation between the bulk alkali/volatile ratio and the solidus temperatures. An increase in this parameter and in the mantle fertility (i.e., Ca#) increases the near-solidus isobaric melt production rate. The experimental fluid compositions found in this study are similar to saline HDFs. We propose a scenario where the percolation of a slab-derived silicic fluid into the depleted cratonic peridotite leads to the formation of near-solidus saline fluids. Such sequence of metasomatic events was reported from fluid inclusions in diamonds from several localities in the Kaapvaal craton in South Africa (e.g., De Beers, Finsch, Voorspoed).

Original languageAmerican English
Pages (from-to)103-119
Number of pages17
JournalGeochimica et Cosmochimica Acta
Volume328
DOIs
StatePublished - 1 Jul 2022

Bibliographical note

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • High-pressure high-temperature experiments
  • Metasomatized peridotites
  • Saline high-density fluids
  • Sub-cratonic mantle lithology

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