Mantle source provinces beneath the Northwestern USA delimited by helium isotopes in young basalts

D. W. Graham, Mary Reid, B. T. Jordan, A. L. Grunder, W. P. Leeman, J. E. Lupton

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

We report new He, Nd and Sr isotope results for basalts from the northwestern United States. The new 3He/4He results for olivine phenocrysts in basalts from the eastern Snake River Plain (SRP), the Owyhee Plateau (OP) and the Oregon High Lava Plains (HLP), together with published He isotope data for Yellowstone and the Cascades volcanic arc, delineate distinct mantle sources for each of these sub-provinces. All basalts from the eastern SRP (8 Quaternary localities plus 1 Miocene locality) have 3He/4He ratios higher than observed in normal mid-ocean ridge basalts, but overlapping with ranges observed in hotspot-related oceanic islands. For a lateral distance of some 400 km along the SRP, 3He/4He ranges from ~ 11 RA in the west to > 19 RA adjacent to Yellowstone. Such high ratios have not been observed elsewhere in the western U.S., and are consistent with the presence of a mantle plume. The lateral gradient in 3He/4He suggests that the proportion of plume-derived He decreases westward, but this interpretation is complicated by possible addition of crustal helium during open-system crystal fractionation in some SRP basaltic magmas. Although crustal contamination may modulate 3He/4He in basalts along the SRP, the effect is not strong and it does not obscure the elevated 3He/4He mantle source signature. In contrast, young basalts from the HLP and the OP have 3He/4He values of 8.8-9.3 RA, within the range for mid-ocean ridge basalts; these data reflect a shallow asthenospheric source with no discernible influence from the Yellowstone hotspot. Basalts from Newberry volcano have slightly lower 3He/4He (7.6-8.3 RA), within the range for other Cascades arc lavas (7.0-8.4 RA). Three alternative explanations are possible for the origin of the high 3He/4He signature along the SRP: (1) multi-component mixing of (a) magmas and/or CO2-rich fluids derived from plume mantle having high 3He/4He, (b) continental lithosphere having low 3He/4He, and (c) shallow asthenospheric mantle (MORB source); (2) a mantle plume beneath Yellowstone that has an unusual combination of He, Nd and Sr isotope characteristics; or (3) a continental lithospheric mantle that experienced ancient enrichment of 3He relative to (U + Th). The isotope relations between He-Nd and He-Sr, along with other considerations, generally favor the first explanation, but the other possibilities cannot be ruled out at the present time.

Original languageEnglish (US)
Pages (from-to)128-140
Number of pages13
JournalJournal of Volcanology and Geothermal Research
Volume188
Issue number1-3
DOIs
StatePublished - Nov 20 2009

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helium isotope
Helium
helium isotopes
alluvial plain
plains
mantle source
Isotopes
basalt
Earth mantle
rivers
Rivers
mantle plume
mid-ocean ridge basalt
isotope
plumes
isotopes
lava
mid-ocean ridges
hot spot
plateau

Keywords

  • helium isotopes
  • High Lava Plains
  • mantle plume
  • Snake River Plain
  • Yellowstone

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Mantle source provinces beneath the Northwestern USA delimited by helium isotopes in young basalts. / Graham, D. W.; Reid, Mary; Jordan, B. T.; Grunder, A. L.; Leeman, W. P.; Lupton, J. E.

In: Journal of Volcanology and Geothermal Research, Vol. 188, No. 1-3, 20.11.2009, p. 128-140.

Research output: Contribution to journalArticle

Graham, D. W. ; Reid, Mary ; Jordan, B. T. ; Grunder, A. L. ; Leeman, W. P. ; Lupton, J. E. / Mantle source provinces beneath the Northwestern USA delimited by helium isotopes in young basalts. In: Journal of Volcanology and Geothermal Research. 2009 ; Vol. 188, No. 1-3. pp. 128-140.
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AU - Graham, D. W.

AU - Reid, Mary

AU - Jordan, B. T.

AU - Grunder, A. L.

AU - Leeman, W. P.

AU - Lupton, J. E.

PY - 2009/11/20

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N2 - We report new He, Nd and Sr isotope results for basalts from the northwestern United States. The new 3He/4He results for olivine phenocrysts in basalts from the eastern Snake River Plain (SRP), the Owyhee Plateau (OP) and the Oregon High Lava Plains (HLP), together with published He isotope data for Yellowstone and the Cascades volcanic arc, delineate distinct mantle sources for each of these sub-provinces. All basalts from the eastern SRP (8 Quaternary localities plus 1 Miocene locality) have 3He/4He ratios higher than observed in normal mid-ocean ridge basalts, but overlapping with ranges observed in hotspot-related oceanic islands. For a lateral distance of some 400 km along the SRP, 3He/4He ranges from ~ 11 RA in the west to > 19 RA adjacent to Yellowstone. Such high ratios have not been observed elsewhere in the western U.S., and are consistent with the presence of a mantle plume. The lateral gradient in 3He/4He suggests that the proportion of plume-derived He decreases westward, but this interpretation is complicated by possible addition of crustal helium during open-system crystal fractionation in some SRP basaltic magmas. Although crustal contamination may modulate 3He/4He in basalts along the SRP, the effect is not strong and it does not obscure the elevated 3He/4He mantle source signature. In contrast, young basalts from the HLP and the OP have 3He/4He values of 8.8-9.3 RA, within the range for mid-ocean ridge basalts; these data reflect a shallow asthenospheric source with no discernible influence from the Yellowstone hotspot. Basalts from Newberry volcano have slightly lower 3He/4He (7.6-8.3 RA), within the range for other Cascades arc lavas (7.0-8.4 RA). Three alternative explanations are possible for the origin of the high 3He/4He signature along the SRP: (1) multi-component mixing of (a) magmas and/or CO2-rich fluids derived from plume mantle having high 3He/4He, (b) continental lithosphere having low 3He/4He, and (c) shallow asthenospheric mantle (MORB source); (2) a mantle plume beneath Yellowstone that has an unusual combination of He, Nd and Sr isotope characteristics; or (3) a continental lithospheric mantle that experienced ancient enrichment of 3He relative to (U + Th). The isotope relations between He-Nd and He-Sr, along with other considerations, generally favor the first explanation, but the other possibilities cannot be ruled out at the present time.

AB - We report new He, Nd and Sr isotope results for basalts from the northwestern United States. The new 3He/4He results for olivine phenocrysts in basalts from the eastern Snake River Plain (SRP), the Owyhee Plateau (OP) and the Oregon High Lava Plains (HLP), together with published He isotope data for Yellowstone and the Cascades volcanic arc, delineate distinct mantle sources for each of these sub-provinces. All basalts from the eastern SRP (8 Quaternary localities plus 1 Miocene locality) have 3He/4He ratios higher than observed in normal mid-ocean ridge basalts, but overlapping with ranges observed in hotspot-related oceanic islands. For a lateral distance of some 400 km along the SRP, 3He/4He ranges from ~ 11 RA in the west to > 19 RA adjacent to Yellowstone. Such high ratios have not been observed elsewhere in the western U.S., and are consistent with the presence of a mantle plume. The lateral gradient in 3He/4He suggests that the proportion of plume-derived He decreases westward, but this interpretation is complicated by possible addition of crustal helium during open-system crystal fractionation in some SRP basaltic magmas. Although crustal contamination may modulate 3He/4He in basalts along the SRP, the effect is not strong and it does not obscure the elevated 3He/4He mantle source signature. In contrast, young basalts from the HLP and the OP have 3He/4He values of 8.8-9.3 RA, within the range for mid-ocean ridge basalts; these data reflect a shallow asthenospheric source with no discernible influence from the Yellowstone hotspot. Basalts from Newberry volcano have slightly lower 3He/4He (7.6-8.3 RA), within the range for other Cascades arc lavas (7.0-8.4 RA). Three alternative explanations are possible for the origin of the high 3He/4He signature along the SRP: (1) multi-component mixing of (a) magmas and/or CO2-rich fluids derived from plume mantle having high 3He/4He, (b) continental lithosphere having low 3He/4He, and (c) shallow asthenospheric mantle (MORB source); (2) a mantle plume beneath Yellowstone that has an unusual combination of He, Nd and Sr isotope characteristics; or (3) a continental lithospheric mantle that experienced ancient enrichment of 3He relative to (U + Th). The isotope relations between He-Nd and He-Sr, along with other considerations, generally favor the first explanation, but the other possibilities cannot be ruled out at the present time.

KW - helium isotopes

KW - High Lava Plains

KW - mantle plume

KW - Snake River Plain

KW - Yellowstone

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