Carbonatite melt-peridotite interaction at 5.5-7.0 GPa: Implications for metasomatism in lithospheric mantle

Alexander G. Sokol, Alexey N. Kruk, Dimity A. Chebotarev, Yury N. Palyanov

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)

Abstract

Interaction between carbonatite melt and peridotite is studied experimentally by melting samples of interlayered peridotite-carbonatite-peridotite in graphite containers at 1200-1350 °C and 5.5-7.0 GPa in a split-sphere multianvil apparatus. Starting compositions are lherzolite and harzburgite, as well as carbonatite which may form in the upper part of a slab or in a plume-related source. Most experimental runs were of 150 h duration in order for equilibrium to be achieved.The interaction produced carbonatitic melts with low SiO2 (≤7 wt.%) and high alkalis. At 1200 °C, melt-peridotite interaction occurs through Mg-Ca exchange, resulting in elimination of orthopyroxene and crystallization of magnesite and clinopyroxene. At 1350 °C hybridization of the carbonatite and magnesite-bearing peridotite melts occurred with consumption of clinopyroxene and magnesite, and crystallization of orthopyroxene at MgO/CaO ≥ 4.3. The resulting peridotite-saturated melt has Ca# (37-50) depending on primary carbonatite composition. Compositions of silicate phases are similar to those of high-temperature peridotite but are different from megacrysts in kimberlites. CaO and Cr2O3 changes in garnet produced from the melt-harzburgite interaction at 1200 and 1350 °C perfectly match the observed trend in garnet from metasomatized peridotite of the Siberian subcontinental lithospheric mantle. K-rich carbonatite melts equilibrated with peridotite at 5.5-7.0 GPa and 1200-1350 °C correspond to high-Mg inclusions in fibrous diamond. Carbonatite melt is a weak solvent of entrained xenoliths and therefore cannot produce kimberlitic magma if temperatures are ~1350 °C on separation from the lithospheric peridotite source and ~1000 °C on eruption.

Original languageEnglish
Pages (from-to)66-79
Number of pages14
JournalLithos
Volume248-251
DOIs
Publication statusPublished - 1 Apr 2016

Keywords

  • Diamond formation
  • Experiment
  • Kimberlite
  • Magma
  • Mantle
  • Metasomatism

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