Nitrogen under super-reducing conditions: Ti oxynitride melts in xenolithic corundum aggregates from Mt Carmel (n. Israel)

William L. Griffin*, Sarah E. M. Gain, Martin Saunders, Olivier Alard, Jeremy Shaw, Vered Toledo, Suzanne Y. O'reilly

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Titanium oxynitrides (Ti(N,O,C)) are abundant in xenolithic corundum aggregates in py-roclastic ejecta of Cretaceous volcanoes on Mount Carmel, northern Israel. Petrographic observa-tions indicate that most of these nitrides existed as melts, immiscible with coexisting silicate and Fe-Ti-C silicide melts; some nitrides may also have crystallized directly from the silicide melts. The TiN phase shows a wide range of solid solution, taking up 0–10 wt% carbon and 1.7–17 wt% oxygen; these have crystallized in the halite (fcc) structure common to synthetic and natural TiN. Nitrides coexisting with silicide melts have higher C/O than those coexisting with silicate melts. Analyses with no carbon fall along the TiN–TiO join in the Ti–N–O phase space, implying that their Ti is a mixture of Ti3+ and Ti2+, while those with 1–3 at.% C appear to be solid solutions between TiN and Ti0.75O. Analyses with >10 at% C have higher Ti2+/Ti3+, reflecting a decrease in fO2. Oxygen fugacity was 6 to 8 log units below the iron–wüstite buffer, at or below the Ti2O3–TiO buffer. These relation-ships and coexisting silicide phases indicate temperatures of 1400–1100 °C. Ti oxynitrides are prob-ably locally abundant in the upper mantle, especially in the presence of CH4–H2 fluids derived from the deeper metal-saturated mantle.

Original languageEnglish
Article number780
Pages (from-to)1-15
Number of pages15
JournalMinerals
Volume11
Issue number7
DOIs
Publication statusPublished - Jul 2021

Bibliographical note

Copyright the Author(s) 2021. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

Keywords

  • titanium nitrides
  • oxynitrides
  • methane–hydrogen fluids
  • mantle mineralogy
  • reducing conditions
  • Mt Carmel

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