Black smokers

Amorphous silica and barite precipitate simultaneously from white smoker in midoceanic ridge hydrothermal system (Edmond et al., 1979). It is inferred that amorphous silica precipitates in the chimney at a later stage than sulfides and sulfates (anhydrite and barite) which constitute chimneys from which black smoker is emerging. 

In these chimneys, coprecipitation of barite and amorphous silica is taking place from the solution characterized by lower temperatures and lower flow rate than the black smoker. 

Northeastern Lau Basin Papatua expedition site (15°17 S, 174"45 W) 2100 Axial region of northeasterly trending active spreading ridge of the northern Lau Basin. Dredged black smoker chimney samples. Wurtzite, pyrite, chalcopyrite, barite, and amorphous silica. Thin film of Mn-oxyhydroxide. 

Haymon, R.M. (1983) The growth history of hydrothermal black smoker chimneys. Nature, 301, 695-698. 

Macdonald, K.C., Becker, K., Spiess, F.N. and Ballard, R.D. (1980) Hydrothermal heat flux of the black smoker vents on the East Pacific Rise. Earth Planet. Sci. Lett., 48, 1-7. 

Of the major solids formed from melts, many, but not all, at equilibrium, the overwhelming influence is of cooperative interaction between ionic units of similar shape and size as we see in crystals. Trace elements apart from forming isolated minerals are fractioned in bulk oxides, for example, in particular orders as the melt solidifies, and this reduces the relative availability of some elements such as Cr and Ni (see Williams, and Williams and Frausto da Silva (1999) in Further Reading). Again the interaction of selective molten minerals and water creates extremely reactive environments and such environments still exist, especially in the deep sea black smokers (hydrothermal vents), around which particular mixed minerals form, which could also have been involved in prebiotic chemistry and are still involved in the peculiarities of life in these smokers . In Figure 1.6 we summarise... 

The interior zones - the core and the mantle - at high temperature interact very little with the surface, although here and there and now and then there is input to the surface from volcanoes and sea-floor black smokers . The surface also receives dust and debris from extra-terrestrial bodies and more rarely from more sizeable meteorites. 

Molten Rock (a) The magma is a constant flow carrying sediments downwards only for them to emerge in transformed states (b) Upwelling of minerals in the black smokers (also contributes to temperature) (c) Continental drift causes changes in environment... 

Seawater is circulated below the sea bed where it is heated by volcanic activity before being re-injected into the sea at high pressure and temperature. The pressure prevents water from boiling until the temperature reaches 725 K. The superheated water dissolves minerals from around the vent that then precipitate as the water temperature cools. This gives the vents their black smoker appearance. Many small molecules such as H2, H2S and Mn2+ do not precipitate but remain in their reduced formed and are available as electron donors. 

Location Mud holes geothermal power plants deep terrestrial oil fields Submarine hot springs vents or black smokers deep submarine oil fields... 

In this chapter, we develop geochemical models of two hydrothermal processes the formation of fluorite veins in the Albigeois ore district and the origin of black smokers, a name given to hydrothermal vents found along the ocean floor at midocean ridges. 

Where fluids discharge from hot springs and mix with seawater, they cool quickly and precipitate clouds of fine-grained minerals. The clouds are commonly black with metal sulfides, giving rise to the term black smokers. Some vents give off clouds of white anhydrite these are known as white smokers. Structures composed of chemical precipitates tend to form at the vents, where the hot fluids discharge into the ocean. The structures can extend upward into the ocean for several meters or more, and are composed largely of anhydrite and, in some cases, sulfide minerals. 

The chemical processes occurring within a black smoker are certain to be complex because the hot, reducing hydrothermal fluid mixes quickly with cool, oxidizing seawater, allowing the mixture little chance to approach equilibrium. Despite this obstacle, or perhaps because of it, we bravely attempt to construct a chemical model of the mixing process. Table 22.3 shows chemical analyses of fluid from the NGS hot spring, a black smoker along the East Pacific Rise near 21 °N, as well as ambient seawater from the area. 

Table 22.4. Minerals in samples taken above black smokers of the East Pacific Rise near 21 °N (Mottl and McConachy, 1990)...

The energetics depicted in this way are in accord with the microbial ecology observed at deep sea hydrothermal systems (e.g., Kelley el al., 2002 Huber el al., 2003 Schrenk et al, 2003). Sediments and black smoker walls invaded by hydrothermal fluids there contain sparse microbial populations of mostly thermophilic methanogens and sulfate reducers. Abundant populations of mesophilic aerobes dominated by sulfide reducers, in contrast, are found in the open ocean where hydrothermal fluids mix freely with seawater. 

I Black smoker chalcopyrite, n=16 Carbonaceous chondrites and iron meteorites, n=20... 

Figure 9. Compilation of 5 Cu (%o) values in various copper ores (redrawn from Larson et al. 2003). Source of data Marechal et al. (1999), Zhu et al. (2000), Larsen et al. (in press) for ores, Marechal et al. (1999) and Zhu et al. (2000) for black smokers. Luck et al. (2003) for meteorites.

Black smoker, at a depth of 2,500 m on the East Pacific Rise (by courtesy of John Baross, University of Washington)... 

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