9:45 AM - 10:00 AM
[SIT06-04] Reaction between olivine and nitrogen at high pressure and high temperature
Keywords:nitrogen, mantle, olivine
San Carlos olivine or synthetic forsterite were loaded as a starting material in a diamond anvil cell with nitrogen in liquid state or compressed gas (180 MPa). After applying pressure at 5 GPa, a sample was heated using CO2 laser or fiber laser. X-ray diffraction patterns, SEM-EDS images, XPS spectra were obtained on the recovered samples.
XRD measurements on the recovered samples revealed the formation of enstatite (MgSiO3) suggesting the decomposition of Mg2SiO4 into MgSiO3 and MgO. This reaction is contrastive to the reaction occurring in H2 fluid (Shinozaki et al., 2013), Mg2SiO4 decomposed into SiO2 and MgO. Moreover, EDS mapping observations revealed that there are some Mg-rich (Si-depleted) spots.
XPS spectra shown in Fig. 1 revealed that nitrogen was detected from an olivine sample recovered from 5 GPa and 1700 K. Before Ar-sputtering, species assignable to NH4+ is dominant. Presumably, the sample surface is covered with adsorbed molecules. After Ar-sputtering, a broad band attributable to intrinsic nitrogen reacted with the mineral was observed. The present results suggest the formation of nitride species (N3-) in a mantle-derived silicate mineral. This study proposes nitride as a hidden nitrogen reservoir in the deep mantle.