Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases

By J. Tucker, S. Mukhopadhyay. 2013

146 citations recorded by the source corpus.

Abstract The energy associated with giant impacts is large enough to generate global magma oceans during Earth's accretion. However, geochemical evidence requiring a terrestrial magma ocean is scarce. Here we present evidence for at least two separate magma ocean outgassing episodes on Earth based on the ratio of primordial 3 He to 22 Ne in the present-day mantle. We demonstrate that the depleted mantle 3 He/ 22 Ne ratio is at least 10 while a more primitive mantle reservoir has a 3 He/ 22 Ne ratio of 2.3 to 3. The 3 He/ 22 Ne ratios of the mantle reservoirs are higher than possible sources of terrestrial volatiles, including the solar nebula ratio of 1.5. Therefore, a planetary process must have raised the mantle's 3 He/ 22 Ne ratio. We show that long-term plate tectonic cycling is incapable of raising the mantle 3 He/ 22 Ne ratio and may even lower it. However, ingassing of a gravitationally accreted nebular atmosphere into a magma ocean on the proto-Earth explains the 3 He/ 22 Ne and 20 Ne/ 22 Ne ratios of the primitive mantle reservoir. Increasing the mantle 3 He/ 22 Ne ratio to a value of 10 in the depleted mantle requires at least two episodes of atmospheric blow-off and magma ocean outgassing associated with giant impacts during subsequent terrestrial accretion. The preservation of a low 3 He/ 22 Ne ratio in a primitive reservoir sampled by plumes suggests that the later giant impacts, including the Moon-forming giant impact, did not generate a whole mantle magma ocean. Atmospheric loss episodes associated with giant impacts provide an explanation for Earth's subchondritic C/H, N/H, and Cl/F elemental ratios while preserving chondritic isotopic ratios. If so, a significant proportion of terrestrial water and potentially other major volatiles were accreted prior to the last giant impact, otherwise the fractionated elemental ratios would have been overprinted by the late veneer.

Subfields: Astronomy and Astrophysics, Geophysics

View Paper: https://www.semanticscholar.org/paper/d37fcf432ebab694057d4d861a65eab00c9b060a

How researchers see this paper

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In Astronomy and Astrophysics

1. Z. Leinhardt
2. S. Stewart
3. M. Gudel
4. H. Lammer
5. M. Mace
6. L. Noack
7. M. Godolt
8. E. Pilat-Lohinger

In Geophysics

1. Z. Leinhardt
2. S. Stewart
3. M. Mace
4. L. Noack
5. M. Godolt
6. E. Pilat-Lohinger
7. Simon J. Lock
8. M. Petaev

Citations in the corpus

• The Origin of the Moon Within a Terrestrial Synestia (2018, background): “…deep terrestrial mantle sample a reservoir that is isotopically distinct from the upper mantle (Holland & Ballentine, 2006; Mukhopadhyay, 2012; Mundl et al., 2017; Parai et al., 2012; Pető et al., 2013; Rizo et al., 2016; Tucker & Mukhopadhyay, 2014; Tucker et al., 2012; Yokochi & Marty, 2004).”
• Origin and evolution of the atmospheres of early Venus, Earth and Mars (2018, background): “This is also consistent with He/Ne isotopic data, suggesting that the bulk amount of Earth’s volatiles was delivered to Earth before the Moon-forming impact (Tucker and Mukhopadhyay 2014).”
• Atmospheric mass loss during planet formation: The importance of planetesimal impacts (2014, unknown): “Furthermore, atmospheric mass loss due to small impactors will proceed without generating a global magma ocean, which is supported by recent interpretations of low (3)He/(22)Ne ratios in a primitive reservoir sampled by plumes (Tucker and Mukhopadhyay, 2014).”