Evolution of helium isotopes in the Earth's mantle

Publication Type  Journal Article
Year of Publication  2005
Authors  Class, C.; Goldstein, S. L.
Journal Title  Nature
Volume  436
Issue  7054
Pages  1107-1112
Journal Date  Aug 25
ISBN Number  0028-0836
Accession Number  ISI:000231416600035
Key Words  he-3/he-4 ratios; oceanic basalts; volcanic-rocks; excess he-3; plumes; geochemistry; constraints; systematics; convection; model
Abstract  

Degassing of the Earth's mantle through magmatism results in the irreversible loss of helium to space, and high He-3/He-4 ratios observed in oceanic basalts have been considered the main evidence for a 'primordial' undegassed deep mantle reservoir. Here we present a new global data compilation of ocean island basalts, representing upwelling 'plumes' from the deep mantle, and show that island groups with the highest primordial signal ( high He-3/He-4 ratios) have striking chemical and isotopic similarities to mid-ocean-ridge basalts. We interpret this as indicating a common history of mantle trace element depletion through magmatism. The high He-3/He-4 in plumes may thus reflect incomplete degassing of the deep Earth during continent and ocean crust formation. We infer that differences between plumes and the upper-mantle source of ocean-ridge basalts reflect isolation of plume sources from the convecting mantle for similar to 1-2 Gyr. An undegassed, primordial reservoir in the mantle would therefore not be required, thus reconciling a long-standing contradiction in mantle dynamics.

Notes  

958AKTimes Cited:28Cited References Count:49

URL  <Go to ISI>://000231416600035
DOI  Doi 10.1038/Nature03930