Mid-ocean ridge degassing

The oceanic crust is a source of CO2 when magma upwelling at mid-ocean ridges degasses and later is a sink when circulating sea water reacts with the sea floor at low temperatures. For simplicity, we assume that at first the basalt degasses completely and later, when the basalt is cool, CO2 is added to it by reaction with sea... 

Sarda, P., Graham, D. (1990) Mid-ocean ridge popping rocks Implications for degassing at ridge crests. Earth Planet. Sci. Lett., 97, 268-89. 

Dixon J. E. and Stolper E. M. (1995) An experimental study of water and carbon dioxide solubilities in mid-ocean ridge basaltic liquids 2. Applications to degassing. J. Petrol. 36,... 

Gerlach T. M. (1989) Degassing of carbon dioxide from basaltic magma at spreading centers 2. Mid-ocean ridge basalts. J. Voleanol Geotherm. Res. 39, 221. 

He with high He/" He ratios is often assumed to be stored in a mantle reservoir that has evolved approximately as a closed system for noble gases and has BSE parent nuclide concentrations. Since this reservoir must be isolated from degassing at mid-ocean ridges and subduction zones, it is often placed within the deeper, or lower mantle. Assigning the highest OIB He/" He ratios to this reservoir, a comparison between the total production of " He and the shift in He/ He from the initial terrestrial value to the present value provides an estimate of the He concentration in this reservoir ... 

Figure 7. Numerical models can be used to assess the variance in natural heat and helium fluxes without assuming steady state conditions, as well as to consider the effect of secular cooling on the convection rate. In similar models to those used to investigate the mixing and degassing of me and " He (van Keken and Ballentine 1998, van Keken and Ballentine 1999 see Fig. 8). van Keken, Ballentine et al. (2001) show that a model of whole mantle convection produces a large variance in the " He flux at mid ocean ridge analogues (a), but with much smaller variance in the heat flux extracted across the entire model surface (b). The variance in the combined ""He/heat ratio is dominated by the variance in the He flux, and matches the very low present day " He/heat ratio ( He...

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