Non-Equilibrium Degassing and a Primordial Source for Helium in Ocean-Island Volcanism

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Non-Equilibrium Degassing and a Primordial Source for Helium in Ocean-Island Volcanism

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Title: Non-Equilibrium Degassing and a Primordial Source for Helium in Ocean-Island Volcanism
Author: Mukhopadhyay, Sujoy; Gonnermann, H. G.

Note: Order does not necessarily reflect citation order of authors.

Citation: Gonnermann, Helge M., and Sujoy Mukhopadhyay. 2007. Non-equilibrium degassing and a primordial source for helium in ocean-island volcanism. Nature 449: 1037-1040.
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Abstract: Radioactive decay of uranium and thorium produces He-4, whereas He-3 in the Earth's mantle is not produced by radioactive decay and was only incorporated during accretion-that is, it is primordial(1). He-3/He-4 ratios in many ocean-island basalts (OIBs) that erupt at hotspot volcanoes, such as Hawaii and Iceland, can be up to sixfold higher than in mid-ocean ridge basalts (MORBs). This is inferred to be the result of outgassing by melt production at mid-ocean ridges in conjunction with radiogenic ingrowth of He-4, which has led to a volatile-depleted upper mantle (MORB source) with low He-3 concentrations and low He-3/He-4 ratios(2-6). Consequently, high He-3/He-4 ratios in OIBs are conventionally viewed as evidence for an undegassed, primitive mantle source, which is sampled by hot, buoyantly upwelling deep-mantle plumes(3,6,7). However, this conventional model provides no viable explanation of why helium concentrations and elemental ratios of He/Ne and He/Ar in OIBs are an order of magnitude lower than in MORBs. This has been described as the 'helium concentration paradox'(8) and has contributed to a long-standing controversy about the structure and dynamics of the Earth's mantle. Here we show that the helium concentration paradox, as well as the full range of noble-gas concentrations observed in MORB and OIB glasses, can self-consistently be explained by disequilibrium open-system degassing of the erupting magma. We show that a higher CO2 content in OIBs than in MORBs leads to more extensive degassing of helium in OIB magmas and that noble gases in OIB lavas can be derived from a largely undegassed primitive mantle source.
Published Version: http://dx.doi.org/10.1038/nature06240
Other Sources: http://www.people.fas.harvard.edu/~mukhop/publications.htm
Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:3224717

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  • FAS Scholarly Articles [7495]
    Peer reviewed scholarly articles from the Faculty of Arts and Sciences of Harvard University
 
 

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