Nitrogen under Super-Reducing Conditions: Ti Oxynitride Melts in Xenolithic Corundum Aggregates from Mt Carmel (N. Israel)

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