Constraining the cooling rate of the lower oceanic crust: a new approach applied to the Oman ophiolite

Knowledge of the cooling rate of newly formed lower oceanic crust is critical in constraining models of crustal accretion and hydrothermal circulation at mid-ocean ridges. In this study we calculate the cooling rate of the lower oceanic crust based on the closure temperature of down-temperature diffusive exchange of Ca from olivine to clinopyroxene in gabbros from the Oman ophiolite. Modelling of the closure temperatures shows that the cooling rates for the lower oceanic crust decrease with depth, changing rapidly in the upper third of the gabbros but more slowly in the lower two-thirds. There is several orders of magnitude variation in cooling rate between the top and bottom of the lower crust. The cooling rate versus depth profile closely matches that of a conductive cooling model, or a model in which conductive cooling is enhanced by a constant factor due to hydrothermal circulation.