Possible sub-arc origin of podiform chromitites |
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| Authors: | Shoji Arai Hisayoshi Yurimoto |
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| Institution: | Department of Earth Sciences, Kanazawa University, Kakuma, Kanazawa 920-11, Japan;Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152, Japan |
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| Abstract: | Abstract The sub-arc mantle condition possibly favors the formation of podiform chromitites. The Cr/(Cr + Al) atomic ratio (= Cr#) of their chromian spinel frequently is higher than 0.7, which is comparable with the range for arc-related primitive magmas. This almost excludes the possibility of their sub-oceanic origin, because both oceanic peridotites and MORB have chromian spinel with the Cr# < 0.6. Precipitation of chromitite and associated dunite enhances a relative depletion of high-field strength elements (HFSE) to large-ion lithophile elements (LILE), one of chemical characteristics of arc magmas, for the involved magma. This cannot alter completely, however, the MORB to the arc-type magma, especially for Ti and Zr. The presence of chromitite xenoliths, similar both in texture and in chemistry to podiform chromitites of some ophiolitic complexes, in some Cenozoic alkali basalts from the southwest Japan arc indicates directly that the upper mantle beneath the Japan arcs has chromitites. |
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| Keywords: | arc setting mantle-melt interaction podiform chromitites replacive dunite |
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