Terrestrial-like zircon in a clast from an Apollo 14 breccia
Introduction
No bedrock has been sampled from the Moon and any felsic magmatic rocks from the Moon currently available for study occur as small (millimetre to centimetre) clasts in lunar breccias and soils. As a result, most of the petrological context relevant to their origin and evolution is lost. Thus, all attempts to define the history of felsic magmatism on the Moon must rely on the investigations of the chemical and isotopic characteristics of these clasts and their constituents. However, chemical and isotopic information obtained from the analysis of different rock-forming and accessory minerals within single clasts, as well as bulk clast analyses, can result in conflicting evidence that is difficult to resolve within a single, coherent interpretation accurately describing the genesis and evolution of these felsic clasts.
The aim of this manuscript is to illustrate and attempt to reconcile some of these difficulties using the example of a felsite clast found in the Apollo 14 breccia sample 14321. The presence of zircon (ZrSiO4) and quartz in this clast are particularly valuable for a comparative study between the different chemical and isotopic indicators of petrogenesis. Zircon is considered to be one of the most robust tools for absolute age determination, hosting U and Th, which decay into different Pb isotopes, potentially enabling the use of three independent long-lived chronometers. Additionally, numerous studies of terrestrial and lunar zircon demonstrate that Hf and O isotope data, along with the concentration of trace elements, provide an opportunity to study the source characteristics of zircon host rocks and the conditions of zircon crystallization (e.g., Amelin et al., 1999, Crow et al., 2017, Ferry and Watson, 2007, Taylor et al., 2009, Trail et al., 2012, Valley, 2003, Valley et al., 2014). Specifically, Ti concentrations in zircon can be used to estimate the temperature of zircon crystallization (Ferry and Watson, 2007), whereas rare earth element (REE) concentrations reflect the composition of the parent magma. In particular, the Ce concentration relative to the adjacent light-REE can be used as a proxy of oxygen fugacity (fO2) in the magma because Ce can exist as Ce4+ and Ce3+, in contrast to the solely trivalent state of the other LREE. Since Ce4+ is more compatible within the zircon lattice, it will enter zircon preferentially compared to Ce3+ and the other LREE, forming a positive Ce anomaly in chondrite-normalized diagrams (quantified as Ce/Ce⁎ = [Ce]n/([La]n*[Pr]n)0.5). The size of this anomaly is related to the Ce4+ /LREE3+ of the melt from which the zircon crystallized and, therefore, is an indication of the redox conditions that existed in the melt during zircon crystallization (Burnham and Berry, 2012, Burnham and Berry, 2014; Trail et al., 2012).
This manuscript combines previously obtained U–Pb zircon data, new zircon trace element analyses, and Ti-in-quartz measurements to constrain several important parameters characterizing the felsite melt during zircon crystallization. While these characteristics are supported by other, likely genetically related, accessory minerals present in the clast, they sharply contradict the chemical and isotope data obtained from some rock-forming minerals in the clast and whole-clast geochemistry. Similarly, results from the zircon analyses here are inconsistent with the conditions inferred the host breccia formation determined by modelling of Imbrium impact ejecta, which is believed to be responsible for the delivery of the sample 14321 to the Apollo 14 landing site. These contradictions result in conflicting interpretations of the origin of the felsite clast that are explored in detail below.
Section snippets
Felsite from breccia 14321
Saw cut residue containing two zircon grains was collected during the extraction of a felsite clast from lunar breccia sample 14321 (Section 14321, 1613). Meyer et al. (1996) obtained SHRIMP U–Pb data for these two zircon grains and pointed out that the grains reside in “granitic glass” that also contains grains of quartz showing the same texture as that in the fused portions of the clast, leaving little doubt that these two zircon grains originated from the partially melted “granite” clast in
Analytical methods
All imaging presented in this paper was performed using a FEI Quanta FEG 650 scanning electron microscope at Stockholm University, Sweden or the JEOL JXA-8530F electron microprobe at the Johnson Space Center. Chemical measurements were made using techniques described in the next three sub-sections.
Zircon chemistry and age
The REE analyses of two zircon grains in the thin section 14321,1613 confirm the previous observation of pronounced positive Ce/Ce⁎ anomalies of and (2σ), as calculated with the equation stated in the introduction (Fig. 5A, Table 1) (Hinton and Meyer, 1991; Nemchin et al., 2010). In addition, the crystallization temperatures (T), based on Ti concentrations determined in the two grains range from to °C (2σ) (after Ferry and Watson, 2007) assuming α-TiO2 > 0.8 and α
Excavation of the felsite clast and its delivery to the Apollo 14 landing site
If the felsite clast did originate as Imbrium ejecta, the simple model presented here indicates that the streamtubes responsible for delivering the ejecta to the Apollo 14 landing site cut across the shock pressure contours illustrated by solid black lines in Fig. 8 and radial position(s) within the Imbrium basin. This is supported by the lithological complexity of the breccia 14321, which contains a range of variably modified lithic and mineral clasts surrounded by some crystalline matrix and
Conclusions
Geochemical data from a felsite clast in lunar breccia 14321, interpreted to be Imbrium ejecta, are internally inconsistent and estimates of its crystallization depth obtained from mineral compositions are in disagreement with constraints provided by impact modelling. Disparate oxidation states recorded in the clast require a multistage formation process. Similarly, the calculated pressure of crystallization based on quartz and zircon compositions indicates a depth of origin on the Moon of
Acknowledgments
The authors would like to thank the Apollo 14 astronauts for risking their lives to recover the sample studied here. Ryan Zeigler is thanked for lending the original section used in this work. Dr. Justin Simon is thanked for relending think section 14321,933 so quickly. Dr. Jeff Taylor at the University of Hawaii and Dr. Renaud Merle are thanked for thoughtful and helpful discussions. This work benefited from the work of three anonymous reviewers, Dr. Paul Warren, Dr. James Connelly, and the
References (57)
- et al.
Rummaging through Earth's Attic for remains of ancient life
Icarus
(2002) - et al.
Post-Hadean transitions in Jack Hills zircon provenance: a signal of the Late Heavy Bombardment?
Earth Planet. Sci. Lett.
(2013) - et al.
An experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity
Geochim. Cosmochim. Acta
(2012) - et al.
The effect of oxygen fugacity, melt composition, temperature and pressure on the oxidation state of cerium in silicate melts
Chem. Geol.
(2014) - et al.
Iceland is not a magmatic analog for the Hadean: evidence from the zircon record
Earth Planet. Sci. Lett.
(2014) - et al.
Rare-earth diffusion in zircon
Chem. Geol.
(1997) - et al.
Pb diffusion in zircon
Chem. Geol.
(2001) - et al.
Ti diffusion in zircon
Chem. Geol.
(2007) - et al.
Ti diffusion in quartz
Chem. Geol.
(2007) - et al.
Coordinated U–Pb geochronology, trace element, Ti-in-zircon thermometry and microstructural analysis of Apollo zircons
Geochim. Cosmochim. Acta
(2017)
The redox geodynamics linking basalts and their mantle sources through space and time
Chem. Geol.
Interpreting U–Pb data from primary and secondary features in lunar zircon
Geochim. Cosmochim. Acta
Ejecta from impact craters
Icarus
The composition of the Earth
Chem. Geol.
Pb–Pb ages of feldspathic clasts in two Apollo 14 breccia samples
Geochim. Cosmochim. Acta
A re-evaluation of impact melt production
Icarus
Trace element partitioning between apatite and silicate melts
Geochim. Cosmochim. Acta
Some recent advances in the scaling of impact and explosion cratering
Int. J. Impact Eng.
Chronology and petrogenesis of a 1.8 g lunar granitic clast: 14321, 1062
Geochim. Cosmochim. Acta
Lu–Hf zircon evidence for rapid lunar differentiation
Earth Planet. Sci. Lett.
Ce and Eu anomalies in zircon as proxies for the oxidation state of magmas
Geochim. Cosmochim. Acta
Petrology and chemistry of two “large” granite clasts from the Moon
Earth Planet. Sci. Lett.
Lunar multiring basins and the cratering process
Icarus
Nature of the Earth's earliest crust from hafnium isotopes in single detrital zircons
Nature
Modeling prograde TiO2 activity and its significance for Ti-in-quartz thermobarometry of politic metamorphic rocks
Contrib. Mineral. Petrol.
Redox evolution of a degassing magma rising to the surface
Nature
Initial Pb isotopic compositions of lunar granites as determined by ion microprobe
On the survivability and detectability of terrestrial meteorites on the Moon
Astrobiology
Cited by (32)
Deciphering the origin(s) of H and Cl in Apollo 15 quartz monzodiorites: Evidence for multiple processes and reservoirs
2023, Geochimica et Cosmochimica ActaJet onset time and velocity for various natural hypervelocity impacts
2022, International Journal of Impact EngineeringEarly steps toward the lunar base deployment: Some prospects
2021, Acta AstronauticaAssessing the survivability of biomarkers within terrestrial material impacting the lunar surface
2021, IcarusCitation Excerpt :Even higher rates of delivery of terrestrial material to the Moon would be expected before 3.9 Ga owing to the higher rate of basin-forming impacts on the Earth. The recent discovery of a possible terrestrial clast in Apollo sample 14,321 by Bellucci et al. (2019) may provide physical evidence for terrestrial material surviving impact with the lunar surface, although this interpretation has now been questioned (Warren and Rubin, 2020). The mass of solid terrestrial material that experiences low shock pressures yet is ejected at greater than Earth's escape velocity is a matter of debate.
Composition of planetary crusts and planetary differentiation
2021, Planetary Volcanism across the Solar SystemEvidence for diverse lunar melt compositions and mixing of the pre-3.9 Ga crust from zircon chemistry
2020, Geochimica et Cosmochimica ActaCitation Excerpt :The preferred interpretation of Bellucci et al. (2019) is that the zircons from 14321 were derived from a terrestrial meteorite, based on analysis of Ti-in-quartz, Ti-in-zircon, Ce anomalies in zircon, and application of experimental calibrations (Ferry and Watson, 2007; Thomas et al., 2010; Trail et al., 2011b). If Bellucci et al. (2019) are correct, it is reasonable to suspect these other zircons are of terrestrial origin, which would mean that terrestrial fragments on the Moon would now be documented in two breccia samples (14311, 14321) and a soil sample (14259). On the other hand, however, if these samples are endogenous to the Moon, it implies the existence of moderately volatile igneous conditions at least sporadically over a long time frame (4.3, 4.22, and 4 Ga).