The global mid-ocean ridge system spreads over a spectrum of rates, and oceanic crust formed at slow and ultra-slow spreading ridges (< 40 mm yr–1) differs from the more “ideal” layered structure formed at faster spreading ridges. Tectonic activity is more important at slower spreading ridges, resulting in local uplift and exposure of mantle peridotites that can be intruded by mafic melts and that are exposed in oceanic core complexes. Thus, hydrothermal activity at slow spreading ridges can range from mafic- to ultramafic-hosted systems that have different rock and fluid compositions; both of them can occur over a range of temperatures. Faulting can control the depth of hydrothermal circulation as well as the location of hydrothermal vents and deposits.

Alt, J. 2013. Review of Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges, edited by P.A. Rona, C.W. Devey, J. Dyment, and B.J. Murton. Oceanography 26(1):108–109, https://doi.org/10.5670/oceanog.2013.15.

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