A Mid‐Ocean Ridge Thermal Model: Constraints on the volume of axial hydrothermal heat flux

Abstract

The depth to the axial magma chamber at three oceanic spreading centers, as indicated by seismic reflection surveys, is greater than that predicted by conductive cooling thermal models of ridge crests. The additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust. A theoretical model for the temperature distribution at spreading centers, which includes distributed heat sources and sinks, is presented. By representing the hydrothermal heat loss as a series of heat sinks, the depths to the axial magma chamber at the East Pacific Rise at latitude 9øN., the southern Juan de Fuca Ridge, and the Lau Basin spreading center are modeled. Heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys. The thermal modeling indicates that the axial hydrothermal heat flux is between 7.1 x 10 6 and 13.8 x 10 6 MJ/m 2, or 10 to 20% of the total missing heat at the ridge axis, requiring extensive low-temperature circulation off axis. High-temperature vents that are spaced 1 km apart and are active between 4 and 10% of the time would account for the axial hydrothermal heat loss.

Mid‐ocean ridge magma chamber processes: Constraints from olivine zonation in lavas from the East Pacific Rise at 9°30′N and 10°30′N

“…[2] Axial magma chambers (AMCs) beneath mid-ocean ridges (MORs) are instrumental in building the oceanic crust [Sleep, 1975;Morton and Sleep, 1985;Wilson et al, 1988;Sinton and Detrick, 1992;Perfit and Chadwick, 1998]. As the major locus of magma cooling, crystallization, differentiation, and mixing, AMC processes are responsible for creating the layered oceanic crust, especially at ridges with axial highs [Carbotte et al, 1997[Carbotte et al, , 1998], where magmatic processes dominate crust formation.…”

Seawater strontium isotopes, oceanic anoxic events, and seafloor hydrothermal activity in the Jurassic and Cretaceous

“…Based on the Sr and Cl concentrations in these vent fluids, the marine Sr-isotopic mass balance implies an axial high-temperature fluid flux of 17 ϫ 10 13 kg/yr (Elderfield and Schultz, 1996). In contrast, the global ocean-ridge heat-flow anomaly (Stein and Stein, 1994) and the observed depth and geometry of mid-ocean-ridge magma chambers (Morton and Sleep, 1985;Wolery and Sleep, 1988) imply axial high-temperature fluid fluxes of only 3 (Ϯ1.5) ϫ 10 13 kg/yr (Elderfield and Schultz, 1996) or about a factor of six less than that implied by the Sr mass balance.…”

“…Over the long-term, hydrothermal activity is driven by ocean-crust production because heat brought to the surface by rising magma and released during crystallization drives hydrothermal circulation (Sleep and Wolery, 1978;Morton and Sleep, 1985). Most high-and intermediate-temperature hydrothermal systems are located in the area over the ridge-axis magma chamber.…”

Cooperation of upper and lower boundary-layer fractionations in a sheet-like intrusion: Composition and microstructure of the Aosawa dolerite sill in Yamagata Prefecture, northeastern Japan

“…Therefore, we argue that heat in the sill was basically transported through heat conduction but not thermal convection. The effective heat loss from the top of the intrusion is attributed to a hydrothermal system above the intrusion (Morton and Sleep, 1985). The reason why the final solidification site is located at two thirds of the way from the bottom, in spite of a faster cooling of the upper part than the lower part, may be either due to (1) subdued hydrothermal activities in a later stage of the solidification or, (2) suppression of the advancement of the upper boundary layer during the earlier stage of compositional convection, which is caused by the transportation of the fractionated melt from the lower boundary layer, or both.…”