Raman spectroscopic characteristics of magnesiochromite: A case study from chromitite of the Muslim Bagh Ophiolite, Pakistan
Keywords:
Raman spectrometry, magnesiochromite, OphiolitesAbstract
The studied multi-textural magnesiochromite from the Muslim Bagh Ophiolite shows narrow ranges in contents (wt%) of Cr2O3 (52.9–56.5), Al2O3 (10.5–12.6), FeOt (16.1–19.7), MgO (12.5–14.8), and TiO2 (0.10–0.8), which are consistent with values of typical ophiolitic chromitites of boninitic to arc-related affinity. Two morphological types (Type I and II) are recognized in the studied magnesiochromite. Spectral bands of both morphological types could be grouped into three band clusters (P1, P2, and P3). P1 contains peaks at Raman shifts from 371 to 607 cm-1, P2 from 650 to 743 cm-1, and P3 from 1106 to 1558 cm-1. In P1 and P2, four characteristic peaks that occur at ~693 cm-1, ~605 cm-1, ~548 cm-1, and ~474 cm-1 could be assigned to ν1(A1g), ν3(F2g), ν4(F2g), and ν2(Eg) vibrational modes. An unassigned peak of low intensity was found at ~725 cm-1 in Type I, and high-intensity peaks were found at ~741 and ~743 cm-1 in Type IIa and IIb. These bands have been interpreted to be related to the high-Cr nature of the studied chromites. The difference in band intensity is attributed to variations in crystal orientation caused by crystallization and textural arrangement during or after plastic mantle deformation. Presently, EBSD is a well-established method for detection of the crystallographic orientations, but these results highlight the potential of Raman spectroscopy as a preliminary approach for determining the orientation of magnesiochromite in ophiolitic chromitites, if geochemical compositional variability can be adequately constrained.
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