Hydrothermal convection systems

Fig. 13.2 Model showing a seawater hydrothermal convection system above a subaxial magma chamber at an oceanic spreading center. Radius of a typical convection cell is about 3-5 km. Depth of the magma chamber usually varies between 1.5 and 3.5 km (see text for details).

Off-axis hydrothermal circulation is responsible for 70% of the convectively driven heat flow from hydrothermal systems. This circulation is thought to occur on the flanks of the mid-ocean ridges and rises at temperatures on the order of 20 to 54°C. The... 

Recirculation of fluid by convection ( multipass flow) is another possible regime (cf. Etheridge etal, 1983). While convection is widely recognized in shallow hydrothermal systems, the conventional wisdom is that permeability is too small in the deep crust to allow the downward penetration of fluid necessary for convection (cf. Walther and Orville, 1982 England and Thompson, 1984 Hanson, 1997 Manning and Ingebritsen, 1999). Nonetheless, study of active mountain belts in New Zealand and Pakistan has shown that shallow fluids can penetrate to at least mid-cmstal levels near the brittle-ductile transition (cf. Koons and Craw, 1991 Templeton etal, 1998 Poage et al, 2000). For example, fluid... 

While most studies of seafloor hydrothermal systems have focused on the currently active plate boundary ( 0-1 Ma crust), pooled heat-flow data from throughout the world s ocean basins (Figure 1) indicate that convective heat loss from the oceanic lithosphere actually continues in crust from 0-65 Ma in age (Stein et al, 1995). Indeed, most recent estimates would indicate that hydrothermal circulation through this older (1-65 Ma) section, termed flank fluxes, may be responsible for some 70% or more of the total hydrothermal heat loss associated with spreading-plate boundaries—either in the form of warm (20-65 °C) altered seawater, or as cooler water, which is only much more subtly chemically altered (Mottl, 2003). 

Bischoff JL, Rosenbauer RJ (1989) Salinity variations in submarine hydrothermal systems by layered double-diffusive convection. J Geol 97 613-623... 

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