A kilometre-scale highly refractory harzburgite zone in the mantle section of the northern Oman Ophiolite (Fizh Block): implications for flux melting of oceanic lithospheric mantle
2014
We report the major element compositions of constituent minerals in 278 harzburgites and of 101 whole rocks from the northern
Fizh mantle section in the northern Oman Ophiolite to investigate the formation and evolution of oceanic lithospheric mantle.
Olivine Fo varies from 90 to 92 whereas spinel Cr# (= Cr/(Cr+Al) atomic ratio) varies from 0.15 to 0.78. The Cr# of spinels
in a large number of harzburgites exceeds 0.6, which is the upper bound for abyssal peridotites. In the northern Fizh mantle
section, highly refractory harzburgites with spinel Cr# greater than 0.7 are distributed in a 3-km-wide band along a NW–SE-striking
shear zone. We infer a two-stage depletion process in the northern Fizh mantle section. In the first stage, asthenospheric
mantle was partially melted beneath a mid-ocean ridge, producing a harzburgitic residual column. In the second stage during
detachment of oceanic lithosphere an H 2 O-rich fluid, released from the metamorphic sole due to thermal metamorphism of altered oceanic crust, extensively infiltrated
the northern Fizh mantle section where the ridge segment boundary region was previously located. The residual harzburgites
were subjected to flux melting, resulting in a highly refractory harzburgite zone with spinel Cr# greater than 0.7.
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