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Published July 9, 1993 | public
Journal Article

Helium-3 from the Mantle: Primordial Signal or Cosmic Dust?


Helium-3 in hotspot magmas has been used as unambiguous evidence for the existence of a primordial, undegassed reservoir deep in the Earth's mantle. However, a large amount of helium-3 is delivered to the Earth's surface by interplanetary dust particles (IDPs). Recycling of deep-sea sediments containing these particles to the mantle, and eventual incorporation in magma, can explain the high helium-3/helium-4 ratios of hotspot magmas. Basafts with high helium-3/helium-4 ratios may represent degassing of helium introduced by ancient (probably 1.5 to 2.0 billion years old) pelagic sediments rather than degassing of primordial lower mantle material brought to the surface in plumes. Influx of IDPs can also explain the neon and siderophile compositions of mantle samples.

Additional Information

© 1993 American Association for the Advancement of Science. I thank H. Craig for stimulating my interest in the elusive primordial source. He has unselfishly provided me with information and preprints for some years and, more recently, opinions on the present thesis. C. Allegre, T. Staudacher, and P Sarcia provided background material. I thank R. Pepin, D. Graham, M. Kurz, and S. Hart for helpful discussions and D. Graham, R. Carlson, E Stolper, D. Burnett, and F. Fanale for comments on the manuscript. K. Farley provided important information and a constructive review. This research was almost supported by grants from the National Science Foundation and the National Aeronautics and Space Administration. I acknowledge support from E. McMillan and J. McMillan. Contribution number 5223, Division of Geological and Planetary Sciences, California Institute of Technology.

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