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The geochemistry of mantle chromitites from the northern part of the Oman ophiolite: inferred parental melt compositions

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Abstract

Chromitites from a single section through the mantle in the Oman ophiolite are of two different types. Low-cr# chromitites, of MORB affinity are found in the upper part of the section, close to the Moho. High-cr# chromitites, with arc affinities are found deeper in the mantle. Experimental data are used to recover the compositions of the melts parental to the chromitites and show that the low-cr# chromitites were derived from melts with 14.5–15.4 wt% Al2O3, with 0.4 to 0.9 wt% TiO2 and with a maximum possible mg# of 0.76. In contrast the high-cr# chromitites were derived from melts with 11.8–12.9 wt% Al2O3, 0.2–0.35 wt% TiO2 and a maximum melt mg# of 0.785. Comparison with the published compositions of lavas from the Oman ophiolite shows that the low-cr# chromitites may be genetically related to the upper (Lasail, and Alley) pillow lava units and the high-cr# chromitites the boninites of the upper pillow lava Alley Unit. The calculated TiO2–Al2O3 compositions of the parental chromitite magmas indicate that the high-cr# chromitites were derived from high-Ca boninitic melts, produced by melting of depleted mantle peridotite. The low-cr# chromitites were derived from melts which were a mixture of two end-members—one represented by a depleted mantle melt and the other represented by MORB. This mixing probably took place as a result of melt–rock reaction.

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Acknowledgments

This research was funded by a research grant from Sultan Qaboos University—grant number IG/SCI/ETHS/04. Stuart Kearns, University of Bristol is thanked for his generous assistance with the microprobe analysis, and Francoise Boudier and Adolphe Nicolas are thanked for introducing the author to the Oman ophiolite in the field. The comments of two anonymous reviewers helped in greatly improving this manuscript.

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  1. Department of Earth Sciences, Sultan Qaboos University, Box 36, Postal Code 123, Al-Khodh, Muscat, Sultanate of Oman

    Hugh Rollinson

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  1. Hugh Rollinson
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Correspondence to Hugh Rollinson.

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Communicated by C. Ballhaus

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Rollinson, H. The geochemistry of mantle chromitites from the northern part of the Oman ophiolite: inferred parental melt compositions. Contrib Mineral Petrol 156, 273–288 (2008). https://doi.org/10.1007/s00410-008-0284-2

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