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Structural control on chromitite deposits in ophiolites: the Oman case

By
Françoise Boudier
Françoise Boudier
1
Geosciences, University Montpellier II, Pl. Eugene Bataillon, 34095 Montpellier, France
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Ali Al-Rajhi
Ali Al-Rajhi
2
Directory General of Minerals, Ministry of Commerce & Industry, P.O. Box 550, Muscat, Sultanate of Oman
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Published:
January 01, 2014

Abstract

Chromitite genesis in ophiolites is indirectly related to spreading rate, controlling mantle fertility and depth of melt crystallization. The most favourable conditions for chromitite concentrations are found in ophiolites generated at moderate spreading rates, where the world's largest chromitite deposits reside. A huge extension of the Oman Ophiolite permits an overview of chromitite distribution in relation to ridge tectonics, yielding constraints on ophiolitic chromitite genesis. Chromite genesis requires large instantaneous melt delivery, coupled with increasing oxygen fugacity produced by hydrous fluids. Chromitites in the Oman Ophiolite reside either in the Moho Transition Zone or at depth in the mantle, along wide shear zones. Both locations are domains of large melt transfer. Thinner crust on top of mantle diapirs and large shear zones limiting propagating segments represent particular domains where seawater circulation at depth is favoured. The thermal structure of these domains may explain the preferential formation of Al-rich versus Cr-rich chromites. A frozen equilibrium with parent mid-ocean ridge basalt (MORB) in the Al-rich chromites could result from rapid cooling of chromitites formed close to the ridge axis. Alternatively, equilibrium with primitive melt and a variable oxidation state is explained here by fluid circulation along the shear zones, active during transition from spreading to detachment.

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Geological Society, London, Special Publications

Tectonic Evolution of the Oman Mountains

H. R. Rollinson
H. R. Rollinson
University of Derby, UK
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M. P. Searle
M. P. Searle
Oxford University, UK
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I. A. Abbasi
I. A. Abbasi
Sultan Qaboos University, Muscat, Oman
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A. I. Al-Lazki
A. I. Al-Lazki
Petroleum Development Oman, Oman
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M. H. Al Kindi
M. H. Al Kindi
Petroleum Development Oman, Oman
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Geological Society of London
Volume
392
ISBN electronic:
9781862396685
Publication date:
January 01, 2014

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