Sea-Floor Tectonics and Submarine Hydrothermal Systems

Abstract

The discovery of metal-depositing hot springs on the sea floor, and especially their link to chemosynthetic life, was among the most compelling and significant scientific advances of the twentieth century. More than 300 sites of hydrothermal activity and sea-floor mineralization are known on the ocean floor. About 100 of these are sites of high-temperature venting and polymetallic sulfide deposits. They occur at mid-ocean ridges (65%), in back-arc basins (22%), and on submarine volcanic arcs (12%). Although high-temperature, 350°C, black smoker vents are the most recognizable features of sea-floor hydrothermal activity, a wide range of different styles of mineralization has been found. Different volcanic substrates, including mid-ocean ridge basalt, ultramafic intrusive rocks, and more evolved volcanic suites in both oceanic and continental crust, as well as temperature-dependent solubility controls, account for the main geochemical associations found in the deposits. Although end-member hydrothermal fluids mainly originate in the deep volcanic basement, the presence of sediments and other substrates can have a large effect on the compositions of the vent fluids. In arc and backarc settings, vent fluid compositions are broadly similar to those at mid-ocean ridges, but the arc magmas also supply a number of components to the hydrothermal fluids.The majority of known black smoker vents occur on fast-spreading mid-ocean ridges, but the largest massive sulfide deposits are located at intermediate-and slow-spreading centers, at ridge-axis volcanoes, in deep backarc basins, and in sedimented rifts adjacent to continental margins. The range of deposit sizes in these settings is similar to that of ancient volcanic-associated massive sulfide (VMS) deposits. Detailed mapping, and in some cases drilling, indicates that a number of deposits contain 1 to 5 million tons (Mt) of massive sulfide (e.g., TAG hydrothermal field on the Mid-Atlantic Ridge, deposits of the Galapagos Rift, and at 13°N on the East Pacific Rise). Two sediment-hosted deposits, at Middle Valley on the Juan de Fuca Ridge and in the Atlantis II Deep of the Red Sea, are much larger (up to 15 and 90 Mt, respectively).In the western Pacific, high-temperature hydrothermal systems occur mainly at intraoceanic back-arc spreading centers (e.g., Lau basin, North Fiji basin, Mariana trough) and in arc-related rifts at continental margins (e.g., Okinawa trough). In contrast to the mid-ocean ridges, convergent margin settings are characterized by a range of different crustal thicknesses and compositions, variable heat flow regimes, and diverse magma types. These variations result in major differences in the compositions and isotopic systematics of the hydrothermal fluids and the mineralogy and bulk compositions of the associated mineral deposits. Intraoceanic back-arc basin spreading centers host black smoker vents that, for the most part, are very similar to those on the mid-ocean ridges. However, isotopic data from both the volcanic rocks and the sulfide deposits hig...

Evidence of a shallow water submarine hydrothermal field off Zannone Island from morphological and geochemical characterization: Implications for Tyrrhenian Sea Quaternary volcanism

“…Widespread hydrothermal activity occurs on the shallow flanks and in the breached calderas of numerous arc volcanoes in the Mediterranean Sea [Hannington et al, 2005, and reference therein]. The discovery of the Zannone hydrothermal field updates the record of seafloor hydrothermal systems of the Tyrrhenian Sea, supporting the evidence that extensional back-arc basins and their margins represent likely settings for hydrothermal venting.…”

Multiple hydrothermal sources along the south Tonga arc and Valu Fa Ridge

“…[36] Because they are commonly major aqueous ionic components of submarine vent fluids (as reviewed by Hannington et al [2005]), and have a long residence time in the water column making them resolvable analytically even as distant plumes [e.g., Klinkhammer and Bender, 1980;Boyle et al, 2005], Fe and Mn are useful tracers of seafloor venting. Enrichments in Fe were detected within all of the identified arc plumes ( (Table 1).…”

Diversity of biogenic minerals in low-temperature Si-rich deposits from a newly discovered hydrothermal field on the ultraslow spreading Southwest Indian Ridge

“…Since 1977, more than 200 seafloor vent fields have been investigated. Most interest in the mid-oceanic ridge has been focused on the hydrothermal activities in the fast, slow, and intermediate spreading ridges [Hannington et al, 2005]. The search for hydrothermal sites on the ridges, however, has been largely constrained to the ultraslow spreading ridge where full spreading rates are <2 cm yr −1 .…”