Constraints on evolution of Earth's mantle from rare gas systematics

Allègre, Claude J.; Staudacher, Thomas; Sarda, Philippe; Kurz, Mark D.

doi:10.1038/303762a0

Cited by 424 publications

(140 citation statements)

References 35 publications

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“…To effect the extreme convection required for such efficient outgassing will require a substantial advance in our understanding of the mantle rheology of the early Earth. Until then, we argue that the strongest explanation for the observed mantle 3 He/ 4 He, low [ 3 He] and [UCTh] remains a flux of high 3 He/ 4 He material from a gas-rich reservoir deeper in the mantle system (Kurz et al 1982;Allègre et al 1983;O'Nions & Oxburgh 1983;Kellogg & Wasserburg 1990;Porcelli & Wasserburg 1995).…”

Section: Helium: the Case For An Accretionary Volatile Reservoir In Tmentioning

confidence: 99%

“…This points to a terrestrial mantle reservoir supplying the mid-ocean ridges that is relatively homogeneous with respect to its 3 He/(UCTh) composition and provides a critical insight into the volatile-solid evolution of the mantle system (e.g. Kurz et al 1982;Allègre et al 1983;O'Nions & Oxburgh 1983). Isotopic evidence for the existence of a mantle reservoir separate and distinct from the convecting mantle is provided by high 3 He / 4 He ocean island volcanism (Kurz et al 1982; figure 1).…”

Section: Helium: the Case For An Accretionary Volatile Reservoir In Tmentioning

confidence: 99%

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What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Ballentine

Holland²

2008

Phil. Trans. R. Soc. A.

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Study of commercially produced volcanic CO 2 gas associated with the Colorado Plateau, USA, has revealed substantial new information about the noble gas isotopic composition and elemental abundance pattern of the mantle. Combined with published data from midocean ridge basalts, it is now clear that the convecting mantle has a maximum 20 Ne/ 22 Ne isotopic composition, indistinguishable from that attributed to solar wind-implanted (SWI) neon in meteorites. This is distinct from the higher 20 Ne/ 22 Ne isotopic value expected for solar nebula gases. The non-radiogenic xenon isotopic composition of the well gases shows that 20 per cent of the mantle Xe is 'solar-like' in origin, but cannot resolve the small isotopic difference between the trapped meteorite 'Q'-component and solar Xe. The mantle primordial 20 Ne/ 132 Xe is approximately 1400 and is comparable with the upper end of that observed in meteorites. Previous work using the terrestrial 129 I-129 Xe mass balance demands that almost 99 per cent of the Xe (and therefore other noble gases) has been lost from the accreting solids and that Pu-I closure age models have shown this to have occurred in the first ca 100 Ma of the Earth's history. The highest concentrations of Q-Xe and solar wind-implanted (SWI)-Ne measured in meteorites allow for this loss and these high-abundance samples have a Ne/Xe ratio range compatible with the 'recycled-aircorrected' terrestrial mantle. These observations do not support models in which the terrestrial mantle acquired its volatiles from the primary capture of solar nebula gases and, in turn, strongly suggest that the primary terrestrial atmosphere, before isotopic fractionation, is most probably derived from degassed trapped volatiles in accreting material.By contrast, the non-radiogenic argon, krypton and 80 per cent of the xenon in the convecting mantle have the same isotopic composition and elemental abundance pattern as that found in seawater with a small sedimentary Kr and Xe admix. These mantle heavy noble gases are dominated by recycling of air dissolved in seawater back into the mantle. Numerical simulations suggest that plumes sampling the core-mantle boundary would be enriched in seawater-derived noble gases compared with the convecting mantle, and therefore have substantially lower 40 Ar/ 36 Ar. This is compatible with observation. The subduction process is not a complete barrier to volatile return to the mantle.

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Section: Helium: the Case For An Accretionary Volatile Reservoir In Tmentioning

confidence: 99%

Section: Helium: the Case For An Accretionary Volatile Reservoir In Tmentioning

confidence: 99%

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Ballentine

Holland²

2008

Phil. Trans. R. Soc. A.

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“…The rare gases also show that some islands may be more primitive [Kurz et al, 1983;Allegre et al, 1983], but this interpretation has been claimed to be model dependent [Fisher, 1985].…”

Section: Large-scale Recyclingmentioning

confidence: 99%

Mixing in numerical models of mantle convection incorporating plate kinematics

Gurnis¹,

Davies²

1986

J. Geophys. Res.

128

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Abstract.The process by which subducted lithosphere is mixed by mantle convection is investigated in numerical calculations.The results show that the observed isotopic heterogeneity of mantle sources and their ancient (1-2 b.y.) apparent ages are consistent with convective mixing.Passive tracers, which are introduced below "trenches," are efficiently dispersed, but nonetheless, heterogeneities in tracer density with a large range of length scales are observed to persist for 40 or more transit times (one transit time is the time to travel the fluid depth with the boundary velocity). In particular, there is a strong tendency to form high-density folds of the tracer strings, which persist much longer than simple shearing indicates. The folds persist because there is a strong tendency for material that enters the flow at the margins of cells to be transferred to adjacent cells, where it is "unmixed."When the simulations are scaled to the whole mantle, the tight clumps (folds) of tracers are shown to persist for up to 1-2 b .y. There is also a tendency for large-scale convection cells to remain isolated from recycled material for 1-2 b.y. These results are consistent with the significant chemical heterogeneity of the mantle as revealed by isotopic studies of oceanic basalts. Despite the spatial heterogeneity in tracer density, the average time tracers remain in the box from subduction at trenches to sampling at ridges (i.e., the residence time) is well constrained and within 20% of the mean residence time expected from an analytic model in which tracers are assumed to be sampled randomly. Model ages of the mantle that explicitly incorporate increased convection rates in the past and assume random sampling of heterogeneities bracket the -2 b.y. apparent Pb-Pb and Rb-Sr isochrons of midocean ridge basalts and oceanic island basalts. The conclusion of persistent spatial heterogeneity is different from the conclusions drawn from other studies. The different conclusions result, primarily, from our emphasis on the details of spatial variations as opposed to some average of the mixing, from a difference in flow unsteadiness, and from the different ways tracers have been introduced into the flow.

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“…Over the last 30 years, the prevailing view among geochemists has been that the high 3 He/ 4 He values are associated with deep-rooted plumes originating from a primordial 3 Herich reservoir isolated from the well-mixed upper mantle (Allègre et al, 1983). This "standard" model has come under increasing scrutiny since tomographic seismic images have shown that subducted slabs are capable of sinking through the 660 km-discontinuity deep into the lower mantle ( Van der Hilst et al, 1997).…”

Section: Thementioning

confidence: 99%

Helium isotopic composition of hydrothermal fluids from the Manus back-arc Basin, Papua New Guinea

et al. 2006

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We present isotopic analysis of helium in hydrothermal fluids from the Manus back-arc basin, collected during the French-Japanese Manusflux and Manaute cruises in 1995 and 2000, respectively. The helium isotope composition of the fluids is comparable to that measured elsewhere in similar subduction environments, with 3 He/ 4 He values (7.4 to 7.9 R a ) slightly lower than typical MORB values, except on the Manus Spreading Center (MSC) where higher values (12 ± 0.1 R a ) are observed. The causal link between the narrow spatial extent of the 3 He/ 4 He anomaly at the MSC and a 3 He-rich deep mantle component remains elusive, based on available geophysical data. Thus, the Manus Spreading Center results may be an interesting example of small scale upper-mantle heterogeneity.

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Constraints on evolution of Earth's mantle from rare gas systematics

Cited by 424 publications

References 35 publications

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Mixing in numerical models of mantle convection incorporating plate kinematics

Helium isotopic composition of hydrothermal fluids from the Manus back-arc Basin, Papua New Guinea

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Constraints on evolution of Earth's mantle from rare gas systematics

Cited by 424 publications

References 35 publications

What CO 2 well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

What CO 2 well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Mixing in numerical models of mantle convection incorporating plate kinematics

Helium isotopic composition of hydrothermal fluids from the Manus back-arc Basin, Papua New Guinea

Contact Info

Product

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What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere