TECTONICS/Hydrothermal Vents At Mid-Ocean Ridges 395 assemblage preserved in a small ophiolite-hosted deposit in central California is particularly interesting because it contains fossils of vestimentiferan worms, gastropods, and brachiopods, but no clam or mussel fossils In contrast, modern and Palaeozoic faunal assemblages described thus far include clams, mussels, and gastropods, but no brachiopods Does this mean that brachiopods have competed with molluscs for ecological niches at vents, and have moved in and out of the hydrothermal vent environment over time? Fossilization of organisms is a selective process that does not preserve all of the fauna that are present at vents Identification of fossils at the species level is often difficult, especially where microbes are concerned Notwithstanding, it is important to search for more examples of ancient fossil assemblages and to trace the fossil record of life at hydrothermal vents back as far as possible, to shed light on questions about how vent communities have evolved and about whether life on Earth might have originated at submarine hydrothermal vents Summary Hydrothermal activity is an integral aspect of seafloor accretion at mid-ocean ridges The circulating fluids and plumes facilitate thermal and chemical exchange between the oceans and the lithosphere, support life above and below the seafloor, and affect current flow and biological activity at mid-water depths The mineral deposits are valuable for their metals, for the role that they play in fostering hydrothermal vent ecosystems, for the clues that they hold to understanding spatial–temporal variability in hydrothermal vent systems, and as geological records of how life at hydrothermal vents has evolved Vent organisms exhibit novel biochemistry, genetics, taxonomy, physiology, symbiosis, and community dynamics From submarine hydrothermal systems, the insights gained about biogeochemical processes at high temperatures and pressures can be applied to biotechnology and to understanding life in inaccessible realms within Earth’s crust, or the potential for life on other planetary bodies As the complexities of hydrothermal systems on the mid-ocean ridge are unravelled through ongoing exploration and interdisciplinary studies, exciting applications of this knowledge are being discovered See Also Minerals: Sulphates; Sulphides Mining Geology: Hydrothermal Ores; Magmatic Ores Origin of Life Plate Tectonics Seamounts Tectonics: Mid-Ocean Ridges Further Reading Baker ET (1996) Geological indexes of hydrothermal venting Journal of Geophysical Research 101(B6): 13 741 13 753 Dilek Y, Moores E, Elthon D, and Nicolas A (eds.) (2000) Ophiolites and Oceanic Crust: New Insights from Field Studies and the Ocean Drilling Program Geological So ciety of America Memoir Boulder: Geological Society of America Haymon RM (1989) Hydrothermal processes and products on the Galapagos Rift and East Pacific Rise In: Winterer EL, Hussong DM, and Decker RW (eds.) The Geology of North America: The Eastern Pacific Ocean and Hawaii, vol N, pp 125 144 Boulder: Geological Society of America Haymon RM (1996) The response of ridge crest hydrother mal systems to segmented, episodic magma supply In: MacLeod CJ, Tyler P, and Walker CL (eds.) Tectonic, Magmatic, Hydrothermal, and Biological Segmentation of Mid Ocean Ridges, Special Publication, vol 118, pp 157 168 London: Geological Society Haymon R, Fornari D, Von Damm K, et al (1993) Volcanic eruption of the mid ocean ridge along the East Pacific Rise at 9 45 520 N: direct submersible observation of seafloor phenomena associated with an eruption event in April, 1991 Earth and Planetary Science Letters 119: 85 101 Humphris SE, Zierenberg RA, Mullineaux LS, and Thomson RE (eds.) (1995) Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions, Geophysical Monograph vol 91 Washington, DC: American Geophysical Union Kelley DS, Karson JA, Blackman DK, et al (2001) An off axis hydrothermal field near the Mid Atlantic Ridge at 30 N Nature 412: 145 149 Little CTS, Herrington RJ, Haymon RM, and Danelian T (1999) Early Jurassic hydrothermal vent community from the Franciscan Complex, San Rafael Mountains, California Geology 27: 167 170 Schrenk MO, Kelley DS, Delaney JR, and Baross JA (2003) Incidence and diversity of microorganisms within the walls of an active deep sea sulfide chimney Applied and Environmental Microbiology 69: 3580 3592 Shank TM, Fornari DJ, Von Damm KL, et al (1998) Tem poral and spatial patterns of biological community devel opment at nascent deep sea hydrothermal vents (9 50 N, East Pacific Rise) Deep Sea Research II 45: 465 515 Tivey MK, Stakes DS, Cook TL, Hannington MD, and Petersen S (1999) A model for growth of steep sided vent structures on the Endeavour Segment of the Juan de Fuca Ridge: results of a petrological and geochemical study Journal of Geophysical Research 104: 22 859 22 883 Von Damm KL (2000) Chemistry of hydrothermal vent fluids from 10 N, East Pacific Rise: ‘‘Time Zero’’ the immediate post eruptive period Journal of Geophysical Research 105: 11 203 11 222