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Reaction products between high-temperature hydrothermal solution/uppermost mantle peridotite or lowermost crustal gabbro have been reported along Wadi Fizh of the northern Oman ophiolite; they are named as mantle diopsidite' and crustal diopsidite' respectively (Figure 1).The mantle diopsidite contains Cr-rich minerals like chromite, Cr-rich diopside (<2.5 wt per cent cr2o3) and cr-bearing grossular (><7.0 wt per cent cr2o3). the chromites are varied in shape in the mantle diopsidite, euhedral to anhedral chromite grains contain globular inclusions of grossular and chlorite, and film-like chromite veinlets branch off from partially dissolved coarse chromite grains. in the crustal diopsidite, fine chromite grains are included in oscillatory-zoned skeletal uvarovite, especially in its high-cr zones. the uvarovites are rich in rare earth elements (rees). direct laser ablation - inductively coupled plasma - mass spectrometer (la-icp-ms) analysis of the primary fluid inclusions detected na, but not k.our detailed studies of wadi fizh diopsidites clarify that the high-temperature hydrothermal solution dissolves chromite grains at the uppermost mantle section and precipitates hydrothermal chromite at the lowermost crust section. in addition, rees were mobilised in the hydrothermal solution together with cr. the hydrothermal solution involved in the diopsidite formation is assumed to have been rich in nacl, and could mobilise appreciable amounts of cr and ree.citation:akizawa, n, arai, s and tamura, a, 2015. chromium and rare earth elements mobility by sodium-bearing high-temperature hydrothermal solution - an example from mantle diopsidite and crustal diopsidite, in proceedings pacrim 2015 congress, pp 291-296 (the australasian institute of mining and metallurgy: melbourne).>