Isotopic evidence for a terminal lunar cataclysm

doi:10.1016/0012-821X(74)90059-4

Earth and Planetary Science Letters

Volume 22, Issue 1, April 1974, Pages 1-21

https://doi.org/10.1016/0012-821X(74)90059-4 Get rights and content

Abstract

Most highland total rock samples define a single U single bond Pb isochron which corresponds to a metamorphism age of ∼ 3.9AE. This age is also obtained for internal UPb isochrons for some of these samples. The data on 18 rock samples range from concordant samples with²³⁸U/²⁰⁶Pb∼ 1.2 to discordant ones with²³⁸U/²⁰⁶Pb∼ 0.02. This feature coupled with a correlated pattern of ²³⁸U/²⁰⁴Pb ratios, indicates that Pb was extensively mobilized at ∼ 3.9AE. The observed Pb single bond U fractionation is essentially due to Pb volatilization during the metamorphic events. Volatile Pb transport is not accompanied by similar effects in Rb and must therefore be attributed to a specific process. RbSr internal isochrons for the same rocks determine distinct metamorphic events in the interval 3.85–4.00 AE. We conclude that highland samples from widely separated areas bear the imprint of an event or series of events in a narrow time interval which can be identified with a cataclysmic impacting rate of the moon at ∼ 3.9AE, although differentiation by internal magma generation cannot be excluded. This cataclysm is associated with the Imbrium impact and very possibly the formation of Crisium and Orientale and possibly several other major basins in a narrow time interval (∼2 × 10⁸yr or less). The U single bond Pb data indicate formation of the lunar crust at ∼ 4.4AE, which is distinctly younger than 4.6 AE, the time generally associated with planetary formation. If the lunar crust started being formed at ∼ 4.6AE, then this process must have continued until times significantly younger than 4.4 AE. Rb single bond Sr data also indicate formation of the lunar crust around 4.5 AE with only minor additions of high Rb/Sr materials to the crust at times younger than 4.3 AE. Using the UPb systematics, K/U and the average U concentration of the moon as obtained from heat-flow measurements, we estimate the lunar concentrations: primordial Pb= 35ppb;Rb= 0.5ppm with Rb/Sr= 0.006.

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Isotopic evidence for a terminal lunar cataclysm

Abstract

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Icarus

Earth Planet. Sci. Lett.

Earth and Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Nature

Lunar Science

Earth Planet. Sci. Lett.

Lunar chronology and evolution from RbSr studies of Apollo 11 and 12 samples

Earth Planet. Sci. Lett.

A lunar cataclysm at ∼ 3.95 AE and the structure of lunar crust

Lunar Science

RbSr ages and initial strontium in basalts from Apollo 15

Earth Planet. Sci. Lett.

A programmable magnetic field mass spectrometer with on-line data processing

Rev. Sci. Instr.

U-Th-Pb analyses of soil from the Sea of Fertility

Earth Planet. Sci. Lett.

Metamorphism of Apollo 16 and 17 and Luna 20 metaclastic rocks about 3.95 AE

An argon bouillabaisse including ages from the Luna 20 site

Lunar Science

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Mineralogic and isotopic investigation on lunar rock 12013

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The age and petrography of two Luna 20 fragments and inferences for wide spread lunar metamorphism

Geochim. Cosmochim. Acta

U-Th-Pb Systematics in three Apollo 14 basalts and the problem of initial Pb in lunar rocks

Earth Planet. Sci. Lett.

Precision measurement of half-lives and specific activities of235U and238U

Phys. Rev.

U-Th-Pb systematics of some Apollo 16 samples (abstract)

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Excess lead in “rusty rock” 66095 and implications for an early lunar differentiation

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⁴⁰Ar-³⁹Ar measurements in Apollo 16 and 17 samples and the chronology of metamorphic and volcanic activity in the Taurus-Littrow region

Precision measurement of half-lives and specific activities of²³⁵U and²³⁸U