On the composition of the lunar interior

Abstract

There is now abundant geophysical and geochemical evidence suggesting that the moon has a thick plagioclase rich outer shell. This is most easily explained by early and extensive melting of a CaO and Al,0 8 rich moon followed by fractional crystallization involving p1agioclase notation. Melilite is probably an important constituent of the interior. This model explains the seismic velocities, the mean density, and the moment of inertia of the moon. The moon is 73-88% high-temperature condensa~e.In a previous paper [Anderson, I 913b] I concluded that the gross physical properties of the moon such as its mass and moment of inertia did not place significant constraints on the major element abundances of the deep lunar interior except that the moon was clearly deficient in iron in relation to cosmic, chondritic, or terrestrial abundances. In particular, this kind of data cannot be used to place upper bounds on the CaO and Al 2 0 3 content. However, the surface evidence suggests that the moon is also deficient in elements and compounds more volatile than iron. This led to the suggestion [Anderson, 1972[Anderson, , 1973a that the interior of the moon was enriched in CaO and Al 2 0 3 • This is in direct conflict with the conclusion of (1970) andRingwood [1970). In the model of Anderson [1972, 1973a] the moon is refractory rich and is composed predominantly of material less volatile than iron. Such a moon would be enriched in the refractory trace elements by about a factor of 16 relative to chondritic abundances and upon melting or fractional crystallization would yield a plagioclase-pyroxene outer shell of the order of 250-km thickness. A mixture of about 14% basalt and 86% anorthosite satisfies the bulk chemistry of this layer and eliminates the Eu 1 anomaly. Melilite, an important component of the interior in this model, can also retain Eu relative to the other REE (rare earth elements). This would reduce the required thickness of a plagioclase rich outer shell. However, these proportions are broadly consistent with the areal extent of the maria and the volumetric relationships implied by elevation differences, offset of center of mass, and the moments of inertia [Wood et al., 1970;Wood, 1973). The Allende inclusions have many of the properties inferred for the moon, such as depletion of volatiles and appropriate levels of the incompatible trace elements, The inclusions show that compounds in the nebula can be separated on the basis of their volatility. Ringwood and EsseneIn most discussions of the composition of the deep lunar interior the assumption is made that the lqnar mantle is predominantly olivine and pyroxene. There is a strong terrestrial and meteoritic bias behind these assumptions. The fact that the moon is clearly depleted in iron compared with the terrestrial planets and cosmic abundances suggests that the moon may be unique in other respects. Trace element studies support this suggestion and imply that the source region of lunar igneous rocks is enriched in refractories. Ringwood [1970, p. 6467) sugg...

The Constitution and Structure of the Lunar Interior

“…The geochemical evidence for garnet in the lunar mantle is consistent with both the predicted range of thermodynamically stable phase assemblages with depth and the lunar seismic data (e.g., Anderson 1975;Hood 1986;Hood and Jones 1987;Mueller et al 1988 Only one datum is available for the volcanic glasses (Shearer et al 1990). Low-Ti basalts cluster around the chondritic ratio for Nb/Ta, whereas the high-Ti basalts have Ta/Nb ratios generally less than chondritic.…”

Solar Eclipses and the Surface Properties of Water

“…Such scattering has been demonstrated, which has included showing the scattering of the solar neutrino flux by a sapphire crystal (Nicolescu 2013;Weber 1988). Seismology data suggests the presence of a layer 65 km below the lunar surface that contains material such as the corundum (Anderson 1975). Such material would have exactly the characteristics required to diffract neutrinos such that the Moon would act as a neutrino diffuser, deflecting solar neutrinos from their original trajectory as they passed through the Moon.…”

The Lunar Geophysical Network Landing Sites Science Rationale

“…However, it is now evident that, due in part to the relatively narrow geographical extent of the Apollo passive seismic network, our understanding of the lunar interior, and especially the deep interior and core, remains incomplete (Figure 1). For example, garnet has been hypothesized to exist below ∼500 km within the Moon (e.g., Anderson 1975;Hood 1986;Hood & Jones 1987;Neal 2001). However, interpretations based on the limited seismic data are ambiguous.…”

“…Regolith formation and overturn are dependent on crater flux, the influence of secondary impacts, and the size of the impact (Costello et al 2018). Various authors estimated regolith formation on the order of ∼3-5 mm of new regolith per million years at ∼3.8 Ga and about 1 mm Myr −1 from ∼3.5 Ga to the present day , 1975Hörz et al 1991;Fa et al 2014;Costello et al 2018Costello et al , 2020Hirabayashi et al 2018;Yue et al 2019). This equates to 1 m of regolith formation per billion years.…”