Helium isotope geochemistry of oceanic volcanic rocks : implications for mantle heterogeneity and degassing

Kurz, Mark D.

doi:10.1575/1912/2211

Cited by 25 publications

(24 citation statements)

References 187 publications

(377 reference statements)

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“…by Kurz (1982), no size effect is detectable in the much smaller sample range now used (generally less than a few times 10-8 ccSTP; figure 2.4).…”

mentioning

confidence: 75%

“…This means that the relatively narrow range of He/ He ratios of mid-ocean-ridge basalts (e.g. Kurz, 1982;Mamyrin and Tolstikhin, 1984) is related to mantle mixing processes, rather than properties of helium transport. In addition, different regions of the mantle can build up varying helium contents and isotopic compositions by radioactive decay, depending on their uranium and thorium contents.…”

Section: Discussionmentioning

confidence: 99%

“…A faraday cup is used to 4 measure He with a resolution of 1:230 and a electron-multiplier (JLI model MM-2) operated in analog mode with its entrance slit set to a resolution of 625 to separate 3He from the much larger HD-H 3 peak. The instrument has been described before (Kurz, 1982; and is of the general design outlined by Jenkins (1974) and Clarke et al (1976). It was constructed in the Woods Hole laboratory.…”

Section: Mass Spectrometrymentioning

confidence: 99%

“…Because the storage method relies on analysing different splits for the initial and final concentrations of the powders it is subject to uncertainties related to natural variability in glass concentrations, which often vary between subsamples by 10 to 20% or more (table 2.3 and e.g. Graham et al, , 1988.Kurz, 1982). In summary, the storage experiments suggest that the helium diffusivity indicated by Jambon, Weber, and Begemann (1985) was overestimated, but the method is imprecise, and isotopic fractionation associated with diffusion could not be quantified.…”

Section: Gra Tn Radtus (Urm)mentioning

confidence: 99%

“…In order to understand this difference, their data (published in Kurz, 1982) was reexamined. Evidence for prior loss was found in two of their 90 and 160um powder experiments which exhibited increasing apparent D values at constant temperature at low F. In addition, these workers combined D values from several experiments with different grain sizes to obtain an activation energy, a procedure which (as already discussed) introduces grain size measurement errors into the Ea determination.…”

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confidence: 99%

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Diffusion of helium isotopes in silicate glasses and minerals : implications for petrogenesis and geochronology

Trull¹

1989

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Helium mobility in geologic materials is a fundamental constraint on the petrogenetic origins of helium isotopic variability and on the application of radiogenic and cosmogenic helium geochronology. 3 He and 4He volume diffusivities determined at 25-600*C in basaltic glasses by incremental-heating and powder storage experiments (using a diffusion model incorporating grain size and shape information to obtain high precision) are three to four orders of magnitude greater than for common cations. Diffusion in tholeiitic glass can be described by an Arrhenius relation with activation energy -16.85+.13 Kcal/mole and log D 0 = -2.37+.06, although low temperature data are better described by a distribution of activation energies model. The best estimate for D at 0 0 C in tholeiitic glass is 5+2 x 10^16 cm 2 /s, an order of magnitude higher than the results of Kurz and Jenkins (1981) but lower than suggested by Jambon, Weber and Begemann (1985). Measurements in an alkali basalt show that helium diffusion is composition dependent (E -14.4+.5 Kcal/mole; log D 0 = -3.24±.2), and roughly five times faster than in tholeiites at seafloor temperatures. The corresponding timescales for 50% helium loss or exchange with seawater (1 cm spheres) are about one million years for mid-oceanridge-basalts, and about 100,000 years in seamount alkali basalts. Radiogenic 4 He diffusion has a higher activation energy (27±2 Kcal/mole; log D -+2.4+1.0) than inherited (magmatic) helium, suggesting very low mobility ?D -3x10 1 9 cm 2 /s at 0*C; factor of 5 uncertainty) and that U+Th/ 4 He geochronology of fresh seafloor basalt glasses is unlikely to be hampered by helium loss. Measured isotopic diffusivity ratios, D3 He/D 4 He, are not composition dependent, average 1.08+.02, and vary slightly with temperature, consistent with an activation energy difference of 60+20 cal/mole. This result differs from the inverse-square-root of mass prediction of 1.15, and may be explained by quantization of helium vibrational energies. These results suggest preferential loss of 3 He will be minimal at low temperature (D 3 He/D 4 He -1.02+.03 at 0*C). Therefore, alteration of magmatic 3 He/ 4 He ratios in basaltic glasses on the seafloor will occur only by helium exchange with seawater, and be important only for samples with low helium contents (<10 8 ccSTP/g), such as those found in island arc environments. Extrapolating the glass results to magmatic temperatures yields diffusivities similar to melt values, and suggests D 3 He/D 4 He approaches 1.15 at these and higher temperatures.Helium diffusivities in olivine and pyroxene at magmatic and mantle temperatures (900-1400*C) are higher than for cations, (E -100+5 Kcal/ mole, log D -+5.1+ .7; and 70+10 Kcal/mole, log D -+2.T+1.2, respectively), but are still too low to transport or homogenize helium in the mantle or even in magma chambers. However, diffusion equilibrates melts and mantle minerals within decades, and interaction with wall-rocks may be enhanced for helium in comparison to other isotopic tra...

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“…by Kurz (1982), no size effect is detectable in the much smaller sample range now used (generally less than a few times 10-8 ccSTP; figure 2.4).…”

mentioning

confidence: 75%

Section: Discussionmentioning

confidence: 99%

Section: Mass Spectrometrymentioning

confidence: 99%

Section: Gra Tn Radtus (Urm)mentioning

confidence: 99%

mentioning

confidence: 99%

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Diffusion of helium isotopes in silicate glasses and minerals : implications for petrogenesis and geochronology

Trull¹

1989

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Composition of plume‐influenced mid‐ocean ridge lavas and glasses from the Mid‐Atlantic Ridge, East Pacific Rise, Galápagos Spreading Center, and Gulf of Aden

Kelley

Kingsley

Schilling

2013

Geochem Geophys Geosyst

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The global mid‐ocean ridge system is peppered with localities where mantle plumes impinge on oceanic spreading centers. Here, we present new, high resolution and high precision data for 40 trace elements in 573 samples of variably plume‐influenced mid‐ocean ridge basalts from the Mid‐Atlantic ridge, the Easter Microplate and Salas y Gomez seamounts, the Galápagos spreading center, and the Gulf of Aden, in addition to previously unpublished major element and isotopic data for these regions. Included in the data set are the unconventional trace elements Mo, Cd, Sn, Sb, W, and Tl, which are not commonly reported by most geochemical studies. We show variations in the ratios Mo/Ce, Cd/Dy, Sn/Sm, Sb/Ce, W/U, and Rb/Tl, which are expected not to fractionate significantly during melting or crystallization, as a function of proximity to plume‐related features on these ridges. The Cd/Dy and Sn/Sm ratios show little variation with plume proximity, although higher Cd/Dy may signal increases in the role of garnet in the mantle source beneath some plumes. Globally, the Rb/Tl ratio closely approximates the La/SmN ratio, and thus provides a sensitive tracer of enriched mantle domains. The W/U ratio is not elevated at plume centers, but we find significant enrichments in W/U, and to a lesser extent the Mo/Ce and Sb/Ce ratios, at mid‐ocean ridges proximal to plumes. Such enrichments may provide evidence of far‐field entrainment of lower mantle material that has interacted with the core by deeply‐rooted, upwelling mantle plumes.

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He, Pb, Sr and Nd isotope constraints on magma genesis and mantle heterogeneity beneath young Pacific seamounts

Graham

Zindler

Kurz

et al. 1988

Contr. Mineral. and Petrol.

134

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Helium isotope geochemistry of oceanic volcanic rocks : implications for mantle heterogeneity and degassing

Cited by 25 publications

References 187 publications

Diffusion of helium isotopes in silicate glasses and minerals : implications for petrogenesis and geochronology

Diffusion of helium isotopes in silicate glasses and minerals : implications for petrogenesis and geochronology

Composition of plume‐influenced mid‐ocean ridge lavas and glasses from the Mid‐Atlantic Ridge, East Pacific Rise, Galápagos Spreading Center, and Gulf of Aden

He, Pb, Sr and Nd isotope constraints on magma genesis and mantle heterogeneity beneath young Pacific seamounts

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