Troctolite 76535: A sample of the Moon's South Pole-Aitken basin?

Garrick‐Bethell, I.; Miljković, K.; Hiesinger, H.; Bogert, C. H. van der; Laneuville, M.; Shuster, David L.; Korycansky, D. G.

doi:10.1016/j.icarus.2019.113430

Cited by 28 publications

(16 citation statements)

References 86 publications

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“…The oldest sample purported to record a lunar dynamo, the 4.2-Ga-old coarse-grained troctolite 76535 ( 93 ), has a history inherently related to one or more impacts because these are needed to bring the sample to the surface from a great depth ( 94 ). The magnetism of this sample was first studied in ( 9 ), and it was noted that the removal of almost 80% of the signal occurred by 540°C, with a unidirectional signal.…”

Section: Methodsmentioning

confidence: 99%

Absence of a long-lived lunar paleomagnetosphere

et al. 2021

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Determining the presence or absence of a past long-lived lunar magnetic field is crucial for understanding how the Moon’s interior and surface evolved. Here, we show that Apollo impact glass associated with a young 2 million–year–old crater records a strong Earth-like magnetization, providing evidence that impacts can impart intense signals to samples recovered from the Moon and other planetary bodies. Moreover, we show that silicate crystals bearing magnetic inclusions from Apollo samples formed at ∼3.9, 3.6, 3.3, and 3.2 billion years ago are capable of recording strong core dynamo–like fields but do not. Together, these data indicate that the Moon did not have a long-lived core dynamo. As a result, the Moon was not sheltered by a sustained paleomagnetosphere, and the lunar regolith should hold buried 3He, water, and other volatile resources acquired from solar winds and Earth’s magnetosphere over some 4 billion years.

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Section: Methodsmentioning

confidence: 99%

Absence of a long-lived lunar paleomagnetosphere

et al. 2021

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“…Lunar troctolite 76535, sampled by the Apollo 17 mission, is one of the most intensively studied samples from the Moon [5][6][7] . An unshocked, coarse-grained example of the Mg-suite, petrological observations suggest 76535 likely crystallized at a depth of 10 to 30 km within the lunar crust 8 before ejection and transportation to the Apollo sampling sites, potentially from as far afield as the South Pole Aitken basin 9 . This low-shock state is common among samples collected by the Apollo astronauts, with only ~1% of materials containing maskelynite, a diaplectic glass of feldspar composition only formed at high pressure (> 28 GPa) 10 .…”

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confidence: 99%

“…Generated baddeleyite ages fall within previously defined age estimates for both the FAN and Mg suites of lunar rocks. For reference, ages of the oldest measured lunar zircon 30 and the estimated age of the South Pole Aitken basin 40,41 , which has been modelled to be a potential source terrane 9 , are also presented.…”

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confidence: 99%

Evidence of extensive lunar crust formation in impact melt sheets 4,330 Myr ago

et al. 2020

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Accurately constraining the formation and evolution of the lunar magnesian (Mg) suite is key to understanding the earliest periods of magmatic crustal building that followed accretion and primordial differentiation of the Moon. However, the origin and evolution of these unique rocks is highly debated. Here, we report on the microstructural characterisation of a large (~250 µm) baddeleyite (monoclinic-ZrO2) grain in Apollo troctolite 76535 that preserves quantifiable crystallographic relationships indicative of reversion from a precursor cubic-ZrO2 phase. This observation places important constraints on the formation temperature of the grain (> 2300 °C) which endogenic processes alone fail to reconcile. We conclude that the troctolite crystallized directly from a large, differentiated impact melt sheet 4326 ± 14 million years (Myr) ago. These results suggest that impact bombardment would have played a critical role in the evolution of the earliest planetary crusts. Insights into the formation, differentiation and impact bombardment of planetary bodies have been derived through geodynamic modelling, remote sensing observations, and isotopic analysis of planetary meteorites and returned samples. The resulting models are hindered by the paucity of mineralogical evidence that can place direct constraints on these very high temperature and pressure processes. Although many mineral thermobarometers can record geological temperatures ranging up to a maximum of ~1500 °C, empirical mineralogical and geochemical evidence of higher temperatures is often lost due to extensive

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“…Here we consider the pre‐Nectarian period to be from the formation of SPA to 3.9 Ga. While isotopic dating and crater counting put the age of SPA at 4.25–4.3 Ga (Garrick‐Bethell et al., 2020; Orgel et al., 2018), debates regarding the source of the dated samples and uncertainty in the early cratering chronology cast doubt on this age. To be conservative, herein we test a range of 4.1–4.45 Ga for the SPA formation.…”

Section: Resultsmentioning

confidence: 99%

Investigating the Influences of Crustal Thickness and Temperature on the Uplift of Mantle Materials Beneath Large Impact Craters on the Moon

et al. 2021

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It has long been recognized that impact basins are associated with notable uplift of mantle materials (e.g., Cintala & Grieve, 1998; Pilkington & Grieve, 1992). The impact-induced mantle uplift has been investigated by both laboratory (e.g., Schmidt & Housen, 1987) and numerical experiments (e.g., Milbury et al., 2015; Potter et al., 2013). On the Moon, the onset of mantle (or more precisely the crust-mantle boundary, Moho) uplift coincides with the morphologic transition from complex craters to peak-ring basins. This coincidence has strong implications for the formation mechanism of the peak ring. Dynamic collapse models (Baker et al., 2016; Collins et al., 2002; Morgan et al., 2016) show that the peak ring is formed by convergence of the outward collapse of initially uplifted deep crustal rocks and the inward collapsing rim materials of the transient cavity.

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Troctolite 76535: A sample of the Moon's South Pole-Aitken basin?

Cited by 28 publications

References 86 publications

Absence of a long-lived lunar paleomagnetosphere

Absence of a long-lived lunar paleomagnetosphere

Evidence of extensive lunar crust formation in impact melt sheets 4,330 Myr ago

Investigating the Influences of Crustal Thickness and Temperature on the Uplift of Mantle Materials Beneath Large Impact Craters on the Moon

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