Early Moon formation inferred from hafnium–tungsten systematics

Thiemens, M. M.; Sprung, P.; Fonseca, Raúl O. C.; Leitzke, Felipe Padilha; Münker, Carsten

doi:10.1038/s41561-019-0398-3

Cited by 87 publications

(68 citation statements)

References 65 publications

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“…Notably, the processes that affect δ 49 Ti in lunar mantle cumulates and corresponding melts also fractionate high field strength element ratios (HFSE; Münker, 2010). High precision HFSE, W, U, and Th data, obtained for the same samples (Thiemens et al, 2019), can help to constrain δ 49 Ti urKREEP, δ 49 Ti IBC and to identify the processes leading to δ 49 Ti variations in lunar samples.…”

Section: Introductionmentioning

confidence: 99%

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Horan¹,

Hilton

McCoy-West

et al. 2020

Geochem. Persp. Let.

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Formation and crystallisation of the Lunar Magma Ocean (LMO) was one of the most incisive events during the early evolution of the Moon. Lunar Magma Ocean solidification concluded with the coeval formation of K-, REE-and P-rich components (KREEP) and an ilmenite-bearing cumulate (IBC) layer. Gravitational overturn of the lunar mantle generated eruptions of basaltic rocks with variable Ti contents, of which their δ 49 Ti variations may now reflect variable mixtures of ambient lunar mantle and the IBC. To better understand the processes generating the spectrum of lunar low-Ti and high-Ti basalts and the role of Ti-rich phases such as ilmenite, we determined the mass dependent Ti isotope composition of four KREEP-rich samples, 12 low-Ti, and eight high-Ti mare basalts by using a 47 Ti-49 Ti double spike. Our data reveal significant variations in δ 49 Ti for KREEPrich samples (+0.117 to +0.296 ‰) and intra-group variations in the mare basalts (-0.030 to +0.055 ‰ for low-Ti and +0.009 to +0.115 ‰ for high-Ti basalts). We modelled the δ 49 Ti of KREEP using previously published HFSE data as well as the δ 49 Ti evolution during fractional crystallisation of the LMO. Both approaches yield δ 49 Ti KREEP similar to measured values and are in excellent agreement with previous studies. The involvement of ilmenite in the petrogenesis of the lunar mare basalts is further evaluated by combining our results with element ratios of HFSE, U and Th, revealing that partial melting in an overturned lunar mantle and fractional crystallisation of ilmenite must be the main processes accounting for mass dependent Ti isotope variations in lunar basalts. Based on our results we can also exclude formation of high-Ti basalts by simple assimilation of ilmenite by ascending melts from the depleted lunar mantle. Rather, our data are in accord with melting of these basalts from a hybrid mantle source formed in the aftermath of gravitational lunar mantle overturn, which is in good agreement with previous Fe isotope data.

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Section: Introductionmentioning

confidence: 99%

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Horan¹,

Hilton

McCoy-West

et al. 2020

Geochem. Persp. Let.

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“…Given this unique relationship between the Earth and the Moon, the timing of this event represents not just a fundamental starting point for lunar evolution, but a key stage in the early evolution of the Earth. Since the return of the first Apollo samples, there have been numerous efforts to determine the age of the Moon (e.g., Tatsumoto 1970;Tilton and Chen 1979;Carlson and Lugmair 1988), and significant differences exist among recently published age estimates (e.g., Borg et al 2011;McLeod et al 2014;Avice and Marty 2014;Connelly and Bizzarro 2016;Barboni et al 2017;Kruijer and Kleine 2017;Thiemens et al 2019). These age estimates will often be divided into those proposing either an "old Moon" forming at around 4.5 Ga or earlier, and those advocating a "young Moon" age of <4.5 Ga.…”

Section: Overviewmentioning

confidence: 99%

“…9 Ma) and the fact that Hf (lithophile) and W (siderophile) are fractioned during planetary core formation. Therefore, if the formation of a planet's core has occurred during the lifetime of 182 Hf, the remaining silicate fraction of the planet will develop an excess of 182 W. Analyses of lunar samples have identified a relative excess of 182 W (Touboul et al 2015;Kruijer et al 2015) and higher Hf/W ratios (Thiemens et al 2019) compared to terrestrial values. These observations can be explained by radiogenic ingrowth of 182 W in the bulk silicate Moon (BSM), provided lunar differentiation occurred no later than ∼4.51 Ga (Lee et al 1997;Halliday and Lee 1999;Righter and Shearer 2003;Kleine et al 2005;Thiemens et al 2019).…”

Section: Estimates For the Time Of Lunar Formationmentioning

confidence: 99%

“…Therefore, if the formation of a planet's core has occurred during the lifetime of 182 Hf, the remaining silicate fraction of the planet will develop an excess of 182 W. Analyses of lunar samples have identified a relative excess of 182 W (Touboul et al 2015;Kruijer et al 2015) and higher Hf/W ratios (Thiemens et al 2019) compared to terrestrial values. These observations can be explained by radiogenic ingrowth of 182 W in the bulk silicate Moon (BSM), provided lunar differentiation occurred no later than ∼4.51 Ga (Lee et al 1997;Halliday and Lee 1999;Righter and Shearer 2003;Kleine et al 2005;Thiemens et al 2019). Conversely, it has also been suggested that the Moon could have formed later than 4.5 Ga, with the 182 W excess in lunar samples being explained via a disproportionate accretion of meteoritic material to the Earth-Moon system during the so-called "late veneer" (Touboul et al 2015;Kruijer et al 2015;Kruijer and Kleine 2017).…”

Section: Estimates For the Time Of Lunar Formationmentioning

confidence: 99%

“…In case of the Sm-Nd and Lu-Hf model ages described above, an important constraint is whether or not the mantle sources of the Apollo samples evolved from a BSM with a chondritic composition. The 182 Hf-182 W studies used to constrain the Moon's age rely on estimates for the ratio of Hf/W in the early BSM (Kruijer and Kleine 2017;Thiemens et al 2019). Similarly, although recent studies of lunar basalts have made it possible to construct a multistage model of Pb isotopic evolution in the Moon (Snape et al 2016a), using this model to determine the age of the Moon would require a better understanding of the BSM 238 U/ 204 Pb ratio (known as the μ-value) during the Moon's early differentiation.…”

Section: How Can New Lunar Samples Help Address This Issue?mentioning

confidence: 99%

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Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

et al. 2019

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The Moon is the only planetary body other than the Earth for which samples have been collected in situ by humans and robotic missions and returned to Earth. Scientific investigations of the first lunar samples returned by the Apollo 11 astronauts 50 years ago transformed the way we think most planetary bodies form and evolve. Identification of anorthositic clasts in Apollo 11 samples led to the formulation of the magma ocean concept, and by extension the idea that the Moon experienced large-scale melting and differentiation. This concept of magma oceans would soon be applied to other terrestrial planets and large asteroidal bodies. Dating of basaltic fragments returned from the Moon also showed that a relatively small planetary body could sustain volcanic activity for more than a billion years after its formation. Finally, studies of the lunar regolith showed that in addition to containing a treasure trove of the Moon's history, it also provided us with a rich archive of the past 4.5 billion years of evolution of the inner Solar System. Further investigations of samples returned from the Moon over the past five decades led to many additional discoveries, but also raised new and fundamental questions that are difficult to address with currently available samples, such as those related to the age of the Moon, duration of lunar volcanism, the

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The redox dependence of titanium isotope fractionation in synthetic Ti-rich lunar melts

Rzehak

Kommescher

Kurzweil

et al. 2021

Contrib Mineral Petrol

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Equilibria between Ti oxides and silicate melt lead to Ti isotope fractionation in terrestrial samples, with isotopically light Ti oxides and isotopically heavy coexisting melt. However, while Ti is mostly tetravalent in terrestrial samples, around 10% of the overall Ti is trivalent at fO2 relevant to lunar magmatism (~ IW-1). The different valences of Ti in lunar samples, could additionally influence Ti stable isotope fractionation during petrogenesis of lunar basalts to an unknown extent. We performed an experimental approach using gas mixing furnaces to investigate the effect of Ti oxide formation at different fO2 on Ti stable isotope fractionation during mare basalt petrogenesis. Two identical bulk compositions were equilibrated simultaneously during each experiment to guarantee comparability. One experiment was investigated with the EPMA to characterize the petrology of experimental run products, whereas the second experiment was crushed, and fabricated phases (i.e., oxides, silicates and glass) were handpicked, separated and digested. An aliquot of each sample was mixed with a Ti double-spike, before Ti was separated from matrix and interfering elements using a modified HFSE chemistry. Our study shows fO2-dependent fractionation within seven samples from air to IW-1, especially ∆49Tiarmalcolite-melt and ∆49Tiarmalcolite-orthopyroxene become more fractionated from oxidized to reduced conditions (− 0.092 ± 0.028- − 0.200 ± 0.033 ‰ and − 0.089 ± 0.027- − 0.250 ± 0.049 ‰, respectively), whereas ∆49Tiorthopyroxene-melt shows only a minor fractionation (− 0.002 ± 0.017-0.050 ± 0.025 ‰). The results of this study show that Ti isotope fractionation during mare basalt petrogenesis is expected to be redox dependent and mineral-melt fractionation as commonly determined for terrestrial fO2 may not be directly applied to a lunar setting. This is important for the evaluation of Ti isotope fractionation resulting from lunar magmatism, which takes place under more reducing conditions compared to the more oxidized terrestrial magmatism.

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Early Moon formation inferred from hafnium–tungsten systematics

Cited by 87 publications

References 65 publications

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Unravelling lunar mantle source processes via the Ti isotope composition of lunar basalts

Constraining the Evolutionary History of the Moon and the Inner Solar System: A Case for New Returned Lunar Samples

The redox dependence of titanium isotope fractionation in synthetic Ti-rich lunar melts

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