著者

ABBOU-KEBIR Khadidja ARAI Shoji HASSAN AHMED Ahmed CEULENEER Georges

出版者

一般社団法人 日本鉱物科学会

雑誌

Journal of mineralogical and petrological sciences (ISSN:13456296)

巻号頁・発行日

vol.106, no.5, pp.235-245, 2011-10-01

参考文献数

45

被引用文献数

3

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Enigmatic dunitic veins and veinlets crosscutting a podiform chromitite ore body discovered in Wadi Rajmi, northern Oman ophiolite, display a peculiar characteristic of being almost or completely spinel-free. Olivines show an evolution trend from the spinel-free dunites (Fo_93-94 and 0.4 wt% NiO) to the spinel-bearing dunites (Fo_91-93 and 0.2-0.3 wt% NiO). The Cr/(Cr + Al) of chromian spinel grains increases from 0.6 to 0.8, accompanied by a slight increase in Fe³⁺ ratio, and the Fo content of olivine decreases in the spinel-bearing dunites. A high-Mg magma, initially undersaturated with chromian spinel, precipitated the spinel-free dunites. Once the spinel saturation of the melt was attained by fractionation, the spinel-bearing dunites precipitated. The initial magma was possibly komatiitic in nature, which was produced at an early stage of detachment of the oceanic lithosphere that formed the Oman ophiolite.