Resolving lithospheric and sub-lithospheric contributions to helium isotope variations in basalts from the southwestern US

Mary Reid, David W. Graham

Research output: Contribution to journalArticle

66 Citations (Scopus)

Abstract

The 3He/4He ratios of continental basalts and their peridotitic xenoliths delimit the (U + Th)/3He evolution of continental lithospheric mantle, but their interpretation is complicated by the potential for differential mobility of He with respect to lithophile elements. In this study we report 3He/4He ratios of 5.5-7.7 RA for olivines separated from young basalts in the southwestern US. Helium isotope ratios are lowest in samples that exhibit Th and Pb isotope evidence for derivation from an enriched source in the lithospheric mantle that has remained unmodified since ∼ 1.7 Ga. There is a strong, positive correlation between 3He/4He and ∈Nd in southwestern US lavas, suggesting a time-integrated affinity between light rare earth- and (U + Th)/3He-enrichment in the underlying Proterozoic lithospheric mantle. This relationship further suggests that the Proterozoic lithosphere mantle in the southwestern US is probably not a highly degassed reservoir which is contaminated by He derived from the underlying asthenosphere. Instead, 3He/4He ratios of 5.7 ± 0.3 RA in the most enriched source regions suggest that their (U + Th)/3He is only slightly elevated compared to the depleted upper mantle, and that processes which enrich the lithospheric mantle in large-ion lithophile elements also enrich it in He.

Original languageEnglish (US)
Pages (from-to)213-222
Number of pages10
JournalEarth and Planetary Science Letters
Volume144
Issue number1-2
StatePublished - Oct 1996
Externally publishedYes

Fingerprint

helium isotope
Helium
helium isotopes
Isotopes
basalt
Earth mantle
mantle
Heavy ions
Rare earths
Proterozoic
asthenosphere
isotope ratios
upper mantle
lithosphere
olivine
affinity
isotope
rare earth elements
derivation
isotopes

Keywords

  • Basalts
  • Geochemistry
  • He-4/He-3
  • Lithosphere

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Resolving lithospheric and sub-lithospheric contributions to helium isotope variations in basalts from the southwestern US. / Reid, Mary; Graham, David W.

In: Earth and Planetary Science Letters, Vol. 144, No. 1-2, 10.1996, p. 213-222.

Research output: Contribution to journalArticle

@article{7b2cb099c5784fcfbe40151d76b41d25,
title = "Resolving lithospheric and sub-lithospheric contributions to helium isotope variations in basalts from the southwestern US",
abstract = "The 3He/4He ratios of continental basalts and their peridotitic xenoliths delimit the (U + Th)/3He evolution of continental lithospheric mantle, but their interpretation is complicated by the potential for differential mobility of He with respect to lithophile elements. In this study we report 3He/4He ratios of 5.5-7.7 RA for olivines separated from young basalts in the southwestern US. Helium isotope ratios are lowest in samples that exhibit Th and Pb isotope evidence for derivation from an enriched source in the lithospheric mantle that has remained unmodified since ∼ 1.7 Ga. There is a strong, positive correlation between 3He/4He and ∈Nd in southwestern US lavas, suggesting a time-integrated affinity between light rare earth- and (U + Th)/3He-enrichment in the underlying Proterozoic lithospheric mantle. This relationship further suggests that the Proterozoic lithosphere mantle in the southwestern US is probably not a highly degassed reservoir which is contaminated by He derived from the underlying asthenosphere. Instead, 3He/4He ratios of 5.7 ± 0.3 RA in the most enriched source regions suggest that their (U + Th)/3He is only slightly elevated compared to the depleted upper mantle, and that processes which enrich the lithospheric mantle in large-ion lithophile elements also enrich it in He.",
keywords = "Basalts, Geochemistry, He-4/He-3, Lithosphere",
author = "Mary Reid and Graham, {David W.}",
year = "1996",
month = "10",
language = "English (US)",
volume = "144",
pages = "213--222",
journal = "Earth and Planetary Sciences Letters",
issn = "0012-821X",
publisher = "Elsevier",
number = "1-2",

}

TY - JOUR

T1 - Resolving lithospheric and sub-lithospheric contributions to helium isotope variations in basalts from the southwestern US

AU - Reid, Mary

AU - Graham, David W.

PY - 1996/10

Y1 - 1996/10

N2 - The 3He/4He ratios of continental basalts and their peridotitic xenoliths delimit the (U + Th)/3He evolution of continental lithospheric mantle, but their interpretation is complicated by the potential for differential mobility of He with respect to lithophile elements. In this study we report 3He/4He ratios of 5.5-7.7 RA for olivines separated from young basalts in the southwestern US. Helium isotope ratios are lowest in samples that exhibit Th and Pb isotope evidence for derivation from an enriched source in the lithospheric mantle that has remained unmodified since ∼ 1.7 Ga. There is a strong, positive correlation between 3He/4He and ∈Nd in southwestern US lavas, suggesting a time-integrated affinity between light rare earth- and (U + Th)/3He-enrichment in the underlying Proterozoic lithospheric mantle. This relationship further suggests that the Proterozoic lithosphere mantle in the southwestern US is probably not a highly degassed reservoir which is contaminated by He derived from the underlying asthenosphere. Instead, 3He/4He ratios of 5.7 ± 0.3 RA in the most enriched source regions suggest that their (U + Th)/3He is only slightly elevated compared to the depleted upper mantle, and that processes which enrich the lithospheric mantle in large-ion lithophile elements also enrich it in He.

AB - The 3He/4He ratios of continental basalts and their peridotitic xenoliths delimit the (U + Th)/3He evolution of continental lithospheric mantle, but their interpretation is complicated by the potential for differential mobility of He with respect to lithophile elements. In this study we report 3He/4He ratios of 5.5-7.7 RA for olivines separated from young basalts in the southwestern US. Helium isotope ratios are lowest in samples that exhibit Th and Pb isotope evidence for derivation from an enriched source in the lithospheric mantle that has remained unmodified since ∼ 1.7 Ga. There is a strong, positive correlation between 3He/4He and ∈Nd in southwestern US lavas, suggesting a time-integrated affinity between light rare earth- and (U + Th)/3He-enrichment in the underlying Proterozoic lithospheric mantle. This relationship further suggests that the Proterozoic lithosphere mantle in the southwestern US is probably not a highly degassed reservoir which is contaminated by He derived from the underlying asthenosphere. Instead, 3He/4He ratios of 5.7 ± 0.3 RA in the most enriched source regions suggest that their (U + Th)/3He is only slightly elevated compared to the depleted upper mantle, and that processes which enrich the lithospheric mantle in large-ion lithophile elements also enrich it in He.

KW - Basalts

KW - Geochemistry

KW - He-4/He-3

KW - Lithosphere

UR - http://www.scopus.com/inward/record.url?scp=0030425461&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0030425461&partnerID=8YFLogxK

M3 - Article

VL - 144

SP - 213

EP - 222

JO - Earth and Planetary Sciences Letters

JF - Earth and Planetary Sciences Letters

SN - 0012-821X

IS - 1-2

ER -