Core growth and siderophile element depletion of the mantle during homogeneous Earth accretion

Azbel, I. Ya.; Tolstikhin, Igor; Kramers, D.; Pechernikova, V.; Vityazev, A. V.

doi:10.1016/0016-7037(93)90396-e

Cited by 31 publications

(10 citation statements)

References 25 publications

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“…Repeated processing of metal through the mantle, as a result of growth by giant impacts and the resulting multiple stages of magma ocean formation and evolution, would lead to a biasing of the MSE present in the mantle today towards the mass added by the later major stages of accretion (Azbel et al, 1993;Kramers, 1998;Rubie et al, 2011Rubie et al, , 2015b. For example, calculations using the progressive growth model of Kramers (1998) suggest that ≥80% of the W present in the mantle today was added by accretion of the final 10-20 wt.% of the Earth.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

In search of late-stage planetary building blocks

et al. 2015

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Section: Accepted Manuscriptmentioning

confidence: 99%

In search of late-stage planetary building blocks

et al. 2015

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“…Their parameters for the degassed mantle are: the mean time of Xe degassing 20 Ma; for simplicity, we will also consider the degassed mantle as closed system since 4.5 Ga ago, the degree of degassing =0.0005, mass =200 x 10 25 g, initial and modem ratios of 129Xe/1JOxe = 6.34 age of diamonds, in accordance with the Xe(Pu) hypothesis. The different contributions of the radiogenic components in CO2 and atmospheric Xe might suggest (i) heterogeneous Earth accretion Marty, 1989), in a contradiction with the basic assumption of other models that mixing was a principal process during accretion of planetesimals (Vityazev et al, 1990;Azbel et al, 1993), or (ii) different closure ages of terrestrial reservoirs (Ozima et al, 1985).…”

Section: Xenon(l) In the Upper Mantlementioning

confidence: 95%

“…For all Versionsof the model, this coefficientis rather small «0.05): according to this result, the impact degassing was a principal process during accretion. The recycling coefficient is Q; Q = 1 corresponds to the addition of [130Xel = 2.4-10-12 cc STP/g from the atmosphere into a developed segment of the present-day oceanic crust (Azbel and Tolstikhin, 1993). Z&Z and A&A show present-day mantle endmembers by Zhang and Zindler (1989) and Allegre et al (1986/87).…”

Section: Xenon(l) In the Upper Mantlementioning

confidence: 99%

Accretion and early degassing of the Earth: Constraints from Pu‐U‐I‐Xe Isotopic systematics

Azbel

Tolstikhin

1993

Meteoritics

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Abstrad-A reviewof problems related to Xe isotopicabundancesin meteorites and terrestrial materials leads to four postulates whichshould be taken into account to build a model of the Earth's accretionand early evolution. 1. The pre-planetary accretion time scale was shorter than the 129{ half-life, 17 Ma, so the initial ratio of 129y 1271 bad not been decreased considerably when planetary accretion started; therefore, this must alsobe the case for the 244Pu abundance. 2. The initial relative abundance of involatilerefractory 244Pu in fIoto-planetary materials should be the same as in chondrites, that is, 244pu,t238U = 0.0068; this value corresponds to initial 2 Pu a 0.30 ppb in the bulk silicate earth. In contrast, I is a highly volatile element; its initial abundance, accretion history and even the present-daymean concentrationsin principalterrestrial reservoirs are~rly known. 3. There is much less fissionXe in the upper mantle,crust,and atmosphere tban is predictablefrom the fission of 2 Pu (Xe(Pu» based on the above argument. Therefore, Xe(Pu) has been mainlyreleased from these reservoirs. 4. A mechanism for Xe(Pu) escape from the complementary upper mantle-crust-atmosphere reservoirs, for example, atmospheric escape via collisionsof a growingEarth with large embryosand/or hydrodynamic hydrogenflux, etc., operated duringthe Earth's accretion.These postulates have been used as a background for a balance model of homogeneous Earth accretion which envisages: growth of the Earth due to accumulation of planetesimals; fractionation inside the Earth and segregation of the core; degassing via collision and fractionation; and escape of volatilesfrom the atmosphere. During the post-accretion terrestrial history, the processesdescribed by the model are continuousfractionation, degassingandrecycling of the upper mantle and crust. The lower mantle is considered as an isolated reservoir.Depending on the scenario invoked, the accretion time scale varies within the limits of 50-200 Ma. In the light of recent experimentaldata, the latter value is inferred to the most realisticversionwhich explains a high Xe(U)/Xe(Pu) ratio in the upper mantle. Contrary to previoussuggestions, the 1291_129Xe subsystem is consideredto be meaningless with regard to the terrestrial accretion time scale. The terrestrial inventoryof 129xe(l) is controlled by the initialabundanceof volatile elements (includingI and Xe) in proto-terrestrial materials and the subsequentdegassinghistoryof the Earth.The residence time of a volatile element (e.g., Xe) in the bulk mantle (bm) duringaccretion, , is approximated by the ratio of "" IIlbm(t)/tPbm,mf S 10 Ma, where IIlbm(t) is the mantle mass, and tPbm,mf is the rate of metal/silicate fractionation, whichprovided segregation of the core; tPbm,mfis determined by involatile siderophile element abundances in the upper mantle. This relationship implies a link between the abundance of involatile siderofhile and volatile incompatible elements. A short reflects a highdegassing rate due to...

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“…Subsequent experimental studies, focused on MSE, have confirmed that the abundances of most MSE can be accounted for by metal-silicate partitioning at pressures of 40-60 GPa [27][28][29]. Although a number of issues remain, such as the mechanisms of metal-silicate equilibration [30], and the effects of multiple generations of magma oceans or seas where this took place [31,32], much of the geochemical community currently appears to accept the general outline of this hypothesis.…”

Section: The Origin Of Siderophile Elements In the Terrestrial Mantlementioning

confidence: 99%

Siderophile element constraints on the origin of the Moon

Walker

2014

Phil. Trans. R. Soc. A.

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Discovery of small enrichments in 182 W/ 184 W in some Archaean rocks, relative to modern mantle, suggests both exogeneous and endogenous modifications to highly siderophile element (HSE) and moderately siderophile element abundances in the terrestrial mantle. Collectively, these isotopic enrichments suggest the formation of chemically fractionated reservoirs in the terrestrial mantle that survived the putative Moon-forming giant impact, and also provide support for the late accretion hypothesis. The lunar mantle sources of volcanic glasses and basalts were depleted in HSEs relative to the terrestrial mantle by at least a factor of 20. The most likely explanations for the disparity between the Earth and Moon are either that the Moon received a disproportionately lower share of late accreted materials than the Earth, such as may have resulted from stochastic late accretion, or the major phase of late accretion occurred prior to the Moon-forming event, and the putative giant impact led to little drawdown of HSEs to the Earth's core. High precision determination of the 182 W isotopic composition of the Moon can help to resolve this issue.

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Core growth and siderophile element depletion of the mantle during homogeneous Earth accretion

Cited by 31 publications

References 25 publications

In search of late-stage planetary building blocks

In search of late-stage planetary building blocks

Accretion and early degassing of the Earth: Constraints from Pu‐U‐I‐Xe Isotopic systematics

Siderophile element constraints on the origin of the Moon

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