Experimental Constraints on He, Ne, and Ar Solubility in Serpentinite

Abstract:

Experiments have been performed to constrain the solubility of He, Ne, and Ar in natural samples of antigorite from three locations. Geochemical analyses of exhumed subduction zone material [1] and well gases [2] indicate that noble gases are recycled from the surface of the earth into the mantle. The mechanism by which uncharged atoms can be bound to a mineral and subsequently recycled remains unclear, but recent experimental work suggests that ring structures in silicate minerals are ideal sites for noble gases [3]. Serpentine contains such ring structures and is abundant in subducting slabs, providing significant potential for control of the recycling of noble gases. Experiments were performed in a cold seal pressure vessel at 350°C using a mix of equal parts He, Ne, and Ar as the pressure media (Brown University, USA). Pressures varied from 0.15 to 1.13 kbar total pressure and durations varied from 20 to 188 hours. Samples were analyzed by UV laser ablation, noble gas mass spectrometry (Open University, UK). He and Ne reached equilibrium during the experiments and both exhibit Henrian behavior. Data from the cleanest sample reduces the error by approximately an order of magnitude over previous work [3] and confirms that He is significantly more soluble (HC_He=6.05x10^-10 mol/g/bar) than Ne (HC_Ne=5.12x10^-12 mol/g/bar) in antigorite. Preliminary data from the cleanest sample suggests that Ar is more soluble than both He and Ne (HC_Ar=1.94x10^-10 mol/g/bar). This provides a mechanism for fractionation of noble gases during recycling.

1. Kendrick, M.A., Scambelluri, M., Honda, M., Phillips, D., Nature Geoscience, 4, 807-812, 2011

2. Holland, G., and Ballentine, C.J., Nature, 441, 186-191, 2006

3. Jackson, C.R.M., Parman, S.W., Kelley, S.P., Cooper, R.F., GCA, 159, 1-15, 2015