Origin of wehrlite cumulates in the Moho transition zone of the Neoproterozoic Ras Salatit ophiolite,Central Eastern Desert,Egypt: crustal wehrlites with typical mantle characteristics |
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| Authors: | Email author" target="_blank">Hisham?A?GahlanEmail author Shoji?Arai Fawzy?F?Abu El-Ela Akihiro?Tamura |
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| Institution: | (1) Department of Geology, Faculty of Science, Assiut University, Assiut, 71516, Egypt;(2) Department of Earth Sciences, Kanazawa University, Kakuma Kanazawa, 920-1192, Japan |
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| Abstract: | Ultramafic cumulates, mainly crustal true wehrlites, were discovered and described in the mantle–crust transition zone (MTZ)
and the extremely lower layered gabbro sequence of the Ras Salatit ophiolite, Central Eastern Desert, Egypt. They form either
boudinaged lensoidal tabular bodies or interdigitated layers often concordant with the planolinear fabrics of the Ras Salatit
ophiolite rocks. The contact between wehrlites and the host MTZ dunite or layered gabbro is razor sharp, lobate and/or sinuous,
without chilled margins or any visible deformations. The Ras Salatit wehrlites are orthopyroxene-free and composed mainly
of olivine and clinopyroxene. They are texturally equilibrated and show a characteristic poikilitic texture. Crystallization
order of the Ras Salatit wehrlites is olivine/spinel followed by clinopyroxene with the absence of plagioclase. Olivine and
clinopyroxene of the Ras Salatit wehrlites are compositionally uniform and conspicuously high in Mg#, mostly around 0.93 and
0.92, respectively. Moreover, the clinopyroxene shows low Ti and Al contents coupled with marked depletion in LILE. The calculated
melt in equilibrium with clinopyroxene from the Ras Salatit wehrlites is largely similar to lavas from the Izu-Bonin forearc.
Given the above characteristics, the Ras Salatit wehrlites were produced by crystal accumulation from a hydrous depleted basaltic/tholeiitic
melt corresponding to temperatures between 1,000 and 1,100°C at the oceanic crustal pressure (~2 kbar). The involved hydrous
tholeiitic melt has been probably formed by fluid-assisted partial melting of a refractory mantle source (similar to the underlying
harzburgites) in a somewhat shallow sub-arc environment. |
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