2006 Fiscal Year Final Research Report Summary
Oversea Research on the Bou-Azzer Ophiolite (Morocco) of Proterozoic Age
| Project/Area Number |
16403010
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Kanazawa University |
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Principal Investigator |
ARAI Shoji Kanazawa University, Graduate School of Natural Science and Technology, Professor, 自然科学研究科, 教授 (20107684)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIWATARI Akira Kanazawa University, Graduate School of Natural Science and Technology, Professor, 自然科学研究科, 教授 (90184572)
MIYASHITA Sumio Niigata University, Graduate School of Natural Science and Technology, Professor, 自然科学研究科, 教授 (60200169)
MORISHITA Tomoaki Kanazawa University, Graduate School of Natural Science and Technology, Assistant Professor, 自然科学研究科, 助手 (80334746)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Bou-Azzer / ophiolite / Proterozoic / harzburgite / highly refractory character / Ni-bearing magnetite / Co ores |
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| Research Abstract |
The Bou-Azzer ophiolite, Morroco, of Proterozic age has been known to have a well-preserved ophiolite stratigraphy. It is significantly dismembered, being composed of peridotites, isotropic gabbro, dolerite dikes and volcanic rocks. The rocks are highly altered or metamorphosed. Completely serpentinized harzburgite with strong foliation comprises the mantle section of the ophiolite. Small amount of dunite and pyroxenite are concordant and discordant, respectively. Small concordant chromitite pods are not rare. Dunite is predominate near the contact with the gabbroic section, having frequent gabbroic bands. This lithology is equivalent to the Moho transition zone. Relic textures and spinel chemistry constrained initial lithology and chemical characteristics of the peridotites. The Cr# of spinet is >0.6 in harzburgite and >0.7 in chromitite, indicating a refractory character of the mantle section of the Bou-Azzer ophiolite. Late-intrusive wehrlite was found in the gabbroic rocks. Constituent rocks are basically similar to those in the Phanerozoic ophiolites, such as the Oman ophiolite, except for the refractory character of the mantle section. The highly refractory character of the mantle section may be one of characteristics of the Proterozoic ophiolite.
To be interesting, secondary clots or veins of magnetite (sometimes Ni-bearing) are common to the serpentinized harzburgite. Secondary chromian spinels with appreciable amounts of Mn, Co and Ni are occasionally found in harzburgite. These elements were expelled from olivine upon serpentinization because serpentine minerals are low in them relative to olivine. They are mobile and could precipitate to form magnetite clots/veins of were incorporated in chromian spinels. The mobility of these elements are possibly related to precipitation as ores (arsenides) (= Bou-Azzer Co ores) around the boundary of the ophiolitic serpentinite.
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