SINGLE CRYSTAL INFRARED SPECTRA IN THE RANGE OF OH FUNDAMENTALS OF PARAGENETIC GARNET, OMPHACITE AND KYANITE IN AN EKLOGITIC MANTLE XENOLITH

Abstract

Single crystals of paragenetic garnet (gt), omphacite (cpx) and kyanite (ky) were isolated from an eclogite xenolith from the Zagadochnaya kimberlite, Yakutia (grospydite Z13) and studied by polarized FTIR-microspectrometry in the OH valence vibrational region and by microprobe analyses. The coexisting minerals are homogeneous with respect to major and minor elements and have compositions near gross49pyr26alm20uvar4 (gt), jad45dio47hed6kos2 (cpx) and ky>97. Single crystal spectra show one v(OH)-band for gt at 3630 cm-1 (halfwidth ca. 100 cm-1) which is very likely caused by vibrations of tetrahedral (OH)44- clusters replacing SiO44- tetrahedra. Cpx shows one strong, but weakly pleochroic band at 3464 cm-1 (halfwidth ca. 160 cm-1) and a weak satellite band centered at 3620 cm-1 with a distinct pleochroism. Ky OH spectra exhibit two sets of weak sharp pleochroic bands, a triplet, characteristic for high pressure ky, at 3439, 3410, 3387 cm-1 and a doublet at 3279, 3264 cm-1 (halfwidths ca. 10 cm-1). From integral and linear absorbances in the unpolarized spectra defect-hydroxyl contents in the three coexisting minerals were estimated and found near 0.0X wt% H2O. The distribution scheme of hydrogen in the paragenetic minerals was evaluated to be c(ky) < c(cpx) << c(gt).