Premium
Micro‐X‐ray absorption near edge structure determination of Fe 3+ /Σ Fe in omphacite inclusion within garnet from D abie eclogite, E ast‐ C entral C hina
Author(s) -
Terabayashi Masaru,
Matsui Takashi,
Okamoto Kazuaki,
Ozawa Hiroaki,
Kaneko Yoshiyuki,
Maruyama Shigenori
Publication year - 2013
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/iar.12017
Subject(s) - omphacite , xanes , eclogite , analytical chemistry (journal) , electron microprobe , geology , absorption (acoustics) , mineralogy , crystallography , spectral line , materials science , chemistry , paleontology , physics , chromatography , astronomy , subduction , composite material , tectonics
The F e K ‐edge micro‐X‐ray absorption near edge structure ( XANES) spectra of omphacite included within garnet from the Dabie eclogites, east‐central C hina, were measured to estimate the oxidation state of iron in omphacite. The micro‐ XANES analyses of omphacite inclusions within garnet yield higher Fe 3+ /Σ Fe ratios of 0.18 to 0.59 than those of 0.00 to 0.31 calculated by charge balance from electron microprobe analyses. The estimated temperatures of garnet‐clinopyroxene pairs from 10 eclogites using Fe 3+ and Fe 2+ contents calculated by charge balance are 603 to 1078° C except one sample. The temperatures calculated using micro‐ XANES ‐measured Fe 3+ and Fe 2+ contents are 530–918° C except one sample. Along the north–south cross‐section in the study area, the estimated temperatures based on the charge balance calculation of Fe 3+ tend to be identical or higher than temperatures estimated based on the calculation of Fe 3+ using the XANES technique. Seven of the micro‐ XANES measurements give approximate temperatures from 500° C to 700° C , and three of the measurements give temperatures of more than 800° C . Those three samples contain higher XG rs corresponding to the distribution coefficient of garnet‐clinopyroxene pairs. The pressure and temperature results estimated by the garnet‐clinopyroxene‐phengite geothermobarometers are mostly in subsolidus conditions, suggesting that there is no extensive melting in eclogite. The present study represents a new temperature calibration based on Fe 3+ estimates in omphacite inclusion within garnet based on the XANES analysis, which is taken into account.