| Iron Distribution in High P-T Garnets from Sittampundi
Granulites, and its Geochemical Implications |
SACHINATH MITRA AsoK KuMAR SAMANTA AND S. ANNADVRA
Pages : 16-19
DOI : 10.1080/0371750X.1997.10804782 |
| Abstract |
| Garnets from high P-T granulite field of Sittampundi, Tamil
Nadu were investigated by 57Fe Miissbauer spectroscopy. The
room temperature (298 K) three-band spectra, which have
been splitted to two doublets, reveal Fe1+ ions to be exclusively
located at dodecahedral site (IS = 1.303-1.389 mm/s; QS =
3.423-3.822 mm/s) and Fel+ at tetrahedral site (IS = 0.006-
0.163 mm/s; QS = 0.520-0.663 mm/s). The Fe 3+/l:Fe ratios vary
between 0.073 and 0.150, which indicate its formation at high
P-T field. The high values of QS of tetrahedral FeJ+ suggest
that the occupied site is very regular with little distortion. The
fairly broad line-width (FWHM, 0.455-0.596 mm/s) of Fe 3+
doublet may arise from a substitution of some tetrahedral Si by
(OH)- group. The strong partition and ordering of Fe l+ and
Fe 3+ in dodecahedral and tetrahedral sites, having octahedral
sites totally free from iron, suggest in a strong measure of slow
cooling and recrystallization of garnet through decompression.
The presence of tetrahedral Fe J+ strongly depicts the existence
of octahedral Si, amounting to an excess of saturation value for
tetrahedral sites by Si + Fe J+ ions together at these sites. |
| Full text : Subscribe to Download Full Text |
| [Go Back] |
|
