Burst of high-temperature seawater injection throughout accreting oceanic crust: a case study in Oman ophiolite

Following the discovery of a high temperature (HT) (∼800 °C) and a very high temperature (1000 °C) hydrothermal alteration in the crust of the Oman ophiolite, a systematic structural and petrological study was conducted throughout the entire ophiolite, with supporting isotopic geochemistry. The published results showed that the crustal gabbros are extensively altered down to Moho by a large seawater flux, which was channelled through an identified recharge and discharge circuit. Microcracks, constituting the recharge system, propagated through the hot gabbros, accreting at the ridge and, in spite of their submillimetre width, provided the conduit for the large volume of seawater necessary for the observed alteration. Building on these results, we show here that these microcracks opened and were active over a time of a few tens of thousands years, while the newly accreted gabbros were drifting away from the ridge. Microcrack activity was highly episodic, with bursts of seawater ingression lasting a few days to a few weeks, followed by quiescence periods of a few tens of years. This model of HT, oceanic hydrothermal alteration has several implications concerning fast spreading oceanic ridges.