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Helium isotopes in ferromanganese crusts from the central Pacific Ocean

Geochimica et Cosmochimica Acta

By:
, , , , ,
DOI: 10.1016/j.gca.2006.05.015

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Abstract

Helium isotopes have been measured in samples of two ferromanganese crusts (VA13/2 and CD29-2) from the central Pacific Ocean. With the exception of the deepest part of crust CD29-2 the data can be explained by a mixture of implanted solar- and galactic cosmic ray-produced (GCR) He, in extraterrestrial grains, and radiogenic He in wind-borne continental dust grains. 4He concentrations are invariant and require retention of less than 12% of the in situ He produced since crust formation. Loss has occurred by recoil and diffusion. High 4He in CD29-2 samples older than 42 Ma are correlated with phosphatization and can be explained by retention of up to 12% of the in situ-produced 4He. 3He/4He of VA13/2 samples varies from 18.5 to 1852 Ra due almost entirely to variation in the extraterrestrial He contribution. The highest 3He/4He is comparable to the highest values measured in interplanetary dust particles (IDPs) and micrometeorites (MMs). Helium concentrations are orders of magnitude lower than in oceanic sediments reflecting the low trapping efficiency for in-falling terrestrial and extraterrestrial grains of Fe-Mn crusts. The extraterrestrial 3He concentration of the crusts rules out whole, undegassed 4–40 μm diameter IDPs as the host. Instead it requires that the extraterrestrial He inventory is carried by numerous particles with significantly lower He concentrations, and occasional high concentration GCR-He-bearing particles.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Helium isotopes in ferromanganese crusts from the central Pacific Ocean
Series title:
Geochimica et Cosmochimica Acta
DOI:
10.1016/j.gca.2006.05.015
Volume
70
Issue:
15
Year Published:
2006
Language:
English
Publisher:
Elsevier
Contributing office(s):
Coastal and Marine Geology Program
Description:
11 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geochimica et Cosmochimica Acta
First page:
3996
Last page:
4006
Number of Pages:
11
Other Geospatial:
Pacific Ocean