Ridge vent deposits

Hydrothermal Vent Deposits. Mid-Ocean Ridge Geochemistry and Petrology. 

Hydrothermal Vent Deposits. Hydrothermal Vent Fluids, Chemistry of. Mid-Ocean Ridge Geochemistry and Petroiogy. Nobie Gases and the Cryosphere. Tritium-Heiium Dating. 

F17 Deposition of marine sulfate via thermal vent reactions at midocean ridges 43 ... 

The isotopic composition of present day ocean water is more or less constant with 5-values close to 0%c. The isotopic composition of ancient ocean water is less well constrained, but stiU should not be removed from 0 by more than 1 or 2%c. Many volcanogenic massive sulfide deposits are formed in submarine environments from heated oceanic waters. This concept gains support from the recently observed hydrothermal systems at ocean ridges, where measured isotopic compositions of fluids are only slightly modified relative to 0%c. 8 0 and 5D-values of vent fluids are best understood in terms of sea water interaction with the ocean crust (Shanks 2001). 

Scott, 1997). Where these deposits are relatively large, such as at the TAG mound on the Mid-Atlantic Ridge, they resemble ancient volcanic-hosted massive sulphide (VMS) deposits like those presently found in ophiolites (Rona Scott, 1993 Humphris etal., 1995 Mills, 1995 Goulding etal., 1998 Scott, 1997). Some of the metals at hydrothermal vents are discharged as black smoke along with gases and other dissolved ions, and are expelled into plumes above and away from the vents (see Section 2.4). 

Layer-silicates Recent studies have also demonstrated the potential microbial influence on clay mineral (layer silicates) formation at hydrothermal vents. Bacterial cells covered (or completely replaced) with a Fe-rich silicate mineral (putative nontronite), in some cases oriented in extracellular polymers (as revealed by TEM analysis), were found in deep-sea sediments of Iheya Basin, Okinawa Trough (Ueshima Tazaki, 2001), and in soft sediments, and on mineral surfaces in low-temperature (2-50°C) waters near vents at Southern Explorer Ridge in the northeast Pacific (Fortin etal., 1998 Fig. 8.6). The Fe-silicate is believed to form as a result of the binding and concentration of soluble Si and Fe species to reactive sites (e.g. carboxyl, phosphoryl) on EPS (Ueshima Tazaki, 2001). Formation of Fe-silicate may also involve complex binding mechanisms, whereas metal ions such as Fe possibly bridge reactive sites within cell walls to silicate anions to initiate silicate nucleation (Fortin etal., 1998). Alt (1988) also reported the presence of nontronite associated with Mn- and Fe-oxide-rich deposits from seamounts on the EPR. The presence of bacteria-like filaments within one nontronite sample was taken to indicate that bacterial activity may have been associated with nontronite formation. Although the formation of clay minerals at deep-sea hydrothermal vents has not received much attention, it seems probable that based on these studies, biomineralisation of clay minerals is ubiquitous in these environments. 

Mills, R.A. (1995) Hydrothermal deposits and metalliferous sediments from TAG, 26°N Mid-Atlantic Ridge, in Hydrothermal Vents and Processes (eds L.M. Parson, C.L. Walker and D.R. Dixon), Geological Society Special Publication No. 87, pp. 121-132. 

---