Alteration of the Oceanic Lithosphere and Implications for Seafloor Processes

Three-quarters of global magmatism and one-quarter of global heat loss are associated with tectonomagmatic and hydrothermal processes governing oceanic lithosphere accretion and the aging of the lithosphere from ridge to trench. Hydrothermal reactions between seawater and oceanic lithosphere under zeolite to granulite facies conditions are linked with magmatic and deformation processes, but they differ in nature depending on spreading rates. Fast-spreading ridges with frequent eruptions have telescoped metamorphic gradients and short-lived hydrothermal systems. Less magmatically robust, slow-spreading ridges are commonly cut by normal faults that expose ultramafic rocks on the seafloor and sustain long-lived hydrothermal systems with distinct vent fauna and fluid compositions.