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

Single crystals of paragenetic garnet (gt), omphacite (cpx) and kyanit e (ky) were isolated from an eclogite xenolith from the Zagadochnaya k imberlite, Yakutia (grospydite Z13) and studied by polarized FTIR-micr ospectrometry in the OH valence vibrational region and by microprobe a nalyses. 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 v ery likely caused by vibrations of tetrahedral (OH)44- clusters replac ing SiO44- tetrahedra. Cpx shows one strong, but weakly pleochroic ban d at 3464 cm-1 (halfwidth ca. 160 cm-1) and a weak satellite band cent ered at 3620 cm-1 with a distinct pleochroism. Ky OH spectra exhibit t wo 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 i n the unpolarized spectra defect-hydroxyl contents in the three coexis ting minerals were estimated and found near 0.0X wt% H2O. The distribu tion scheme of hydrogen in the paragenetic minerals was evaluated to b e c(ky) < c(cpx) << c(gt).