Structural control on chromitite deposits in ophiolites: the Oman case
Published:January 01, 2014
Françoise Boudier, Ali Al-Rajhi, 2014. "Structural control on chromitite deposits in ophiolites: the Oman case", Tectonic Evolution of the Oman Mountains, H. R. Rollinson, M. P. Searle, I. A. Abbasi, A. I. Al-Lazki, M. H. Al Kindi
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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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Tectonic Evolution of the Oman Mountains
The Oman Mountains contain one of the world's best- exposed and best-understood fold–thrust belts and the largest, best-exposed and most intensively studied ophiolite complex on Earth. This volume presents new international research from authors currently active in the field focusing on the geology of the Oman Mountains, the foreland region, the carbonate platforms of Northern and Central Oman and the underlying basement complex. In addition there is a particular focus on geoconservation in the region. The volume is divided into three main sections that discuss the tectonics of the Arabian plate using insights from geophysics, petrology, structural geology, geochronology and palaeontology; the petrology and geochemistry of the Oman Ophiolite and the sedimentary and hydrocarbon systems of Oman, drawing on the geophysics, structure and sedimentology of these systems. The volume is enhanced by numerous colour images provided courtesy of Petroleum Development Oman.