Multiple Shallow Crustal Origins for Spinel‐Bearing Lithologies on the Moon: A Perspective From the Luna 20 Mission

Simon, S. B.; Shearer, C. K.; Haggerty, Stephen E.; Moriarty, D. P.; Petro, N. E.; Papike, J. J.; Vaci, Z.

doi:10.1029/2022je007249

Cited by 10 publications

(42 citation statements)

References 71 publications

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“…The crystallization textures, mineral compositions, and inferred crystallization sequences indicate crystallization at low pressures, consistent with formation in the shallow crust at depths less than a few km. As noted above, these spinels exhibit a broad range in composition, including those associated with plagioclase-rich impact melts (Simon et al, 2022). This is consistent with the geologic associations observed in M 3 data, where spinel is observed to be a minor but widely distributed component of the well-developed soils across the Hilly and Furrowed Terrain.…”

Section: Insight From Luna 20 Samplessupporting

confidence: 85%

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Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples

et al. 2023

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Spinels represent a small fraction of lunar surface materials but provide important insights into the petrological evolution of the lunar crust and mantle. Previous remote sensing analyses of highlands spinel‐bearing lithologies have focused on pure Mg‐Al spinels, which are rare in the lunar sample collection. Using Moon Mineralogy Mapper data, we develop and test an approach for detecting spectral signatures of spinel across a wider range of Mg, Al, Fe, Cr, Ti‐bearing compositions than have been addressed in previous studies, including within mafic‐bearing assemblages. This approach is validated through integration with laboratory‐measured spinel spectra and petrographic observations of samples returned by the Luna 20 mission from the Hilly and Furrowed Terrain surrounding the Crisium Basin. Applying this approach to data from the Crisium region, small abundances of spinel (<∼5 vol%) with a range of Mg, Al, Fe, Cr, and Ti content and petrologic origin (inferred from Luna 20 samples) were found to be widespread within highlands soils across the Crisium region. This result diverges from previous remote sensing analyses, which only reported small, isolated exposures of pure Mg‐Al spinel (as well as a possible detection of Fe, Cr‐bearing spinels localized within pyroclastic materials at Sinus Aestuum). Geologic associations of candidate spinel detections across this region are consistent with a shallow crustal origin rather than excavation from depth during the Crisium‐forming impact. These spinels are detectible in near‐infrared spectroscopic data, particularly in areas of low optical maturity and may influence the spectral continuum of highlands soils.

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Section: Insight From Luna 20 Samplessupporting

confidence: 85%

“…Simon et al. (2022) report that spinel‐bearing lithic fragments in Luna 20 samples are typically dominated by plagioclase with smaller amounts of olivine, spinel, and pyroxene. This too is consistent with the spectral properties and geologic associations observed in M 3 data.…”

Section: Discussion: Interpretation and Implicationsmentioning

confidence: 99%

Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples

et al. 2023

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“…Luna 20 soil was collected from the South rim of the Crisium Basin. Meanwhile, the spinel-bearing lithologies have been detected near Crisium Basin (Moriarty et al, 2022;Simon et al, 2022). The comparative study between the spinel-bearing clasts in NWA 13191 and spinel-bearing Luna 20 lithics will be published in the future paper.…”

Section: Discussionmentioning

confidence: 95%

A possible origin of the lunar spinel-bearing lithologies as told by the meteorite NWA 13191

Xie,

Chen,

Miao

et al. 2024

American Mineralogist

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Pink spinel anorthosite (PSA) and pink spinel troctolite (PST) are two lunar lithologies known to contain Mgrich spinel. PSA rich in spinel and lacking mafic minerals, was detected by the visible and near-infrared reflectance spectroscopy. PST clasts were found in returned lunar samples and meteorites. NWA 13191 is a recently approved lunar meteorite that contains a large amount of spinel-bearing clasts and provides an opportunity to discuss its origin. In this paper, 64 spinel-bearing clasts are studied. These clasts are dominated by anorthitic feldspars (20.8 -80.9 vol.%, An90.9-96.8), mafic-rich and aluminum-rich melt (14.7 -72.1 vol.%) and spinels (0.19 -5.18 vol.%). 49 of these clasts appears to have an unusually low modal abundance of mafic silicates (avg. olivine ± pyroxene, 1.87 vol.%), which distinguishes it from known spinel-bearing lunar samples (e.g., PST). The spinel composition (avg. Mg # = 90.6, Al # = 97.4) and mafic minerals content are basically consistent with those of PSA. The absorption characteristics of the melt in the reflection spectrum are not obvious, so it is not clear if the PSA contains melt. The simulated crystallization experiment clearly shows that it contains a large amount of melt at the spinel crystallization stage. These phenomena provide experimental and sample evidences for the existence of melt in the lunar spinel-bearing lithologies. NWA 13191 records the highest known bulk Mg # (avg. 89.8) and the spinel records the highest Al # (98.8) and Mg # (93.1) of lunar samples to date. The chemical properties of spinel-bearing clasts in NWA 13191 are consistent with the slightly REE-enriched and alkali-poor Mg-suite rocks, such as PST, magnesian anorthosites (MANs), and olivine-enriched Mg-suite rocks. These phenomena and previous simulated crystallization experiments indicate that the Mg-Al-rich melt may be produced by impact melting of Mg-rich anorthosite precursors. The spinel is a metastable crystallization product along with plagioclase and vitric melt near the Moon's surface. This realization provides sample observational evidence for previous simulated crystallization experiments and theoretical speculations.

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“…Although unrelated to the Mg‐suite rocks at the Luna 20 site, Simon et al. (2021, 2022) illustrated that the crystallization of Mg‐Al spinel occurs at lower pressures in fairly rapidly cooled impact‐produced melt breccia. In Luna 20 sample 22003, 6 (fragment 3), subhedral Cr‐Fe spinel is enclosed in subhedral Mg‐Al spinel, and relatively Fe‐rich olivine is enclosed in more forsteritic olivine.…”

Section: Discussionmentioning

confidence: 99%

“…The composition fields for FANs, Mg-suite, and Alkali-suite are modified fromWarren (1993),Norman et al, 1995, Shervais andMcGee (1999), andShearer et al (2015). Data from this study (see Figure3), companion paper bySimon et al (2022), unpublished analyses ofConrad et al (1973), and published analyses in special issue of Geochimica et Cosmochimica Acta 37(1973). Data points do not include lithic fragments that are unambiguously impact melts such as shown in Figure3hor lithologies that exhibit substantial mineral composition heterogeneity.…”

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confidence: 93%

Where Is the Lunar Mantle and Deep Crust at Crisium? A Perspective From the Luna 20 Samples

et al. 2023

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Remote sensing observations have been interpreted to indicate that the Crisium basin‐forming event excavated deep crust and upper mantle. Samples from the highlands adjacent to the Crisium basin returned by Luna 20 (L‐20) bring a unique perspective for evaluating this concept. The magmatic lithologies returned from the noritic Hilly and Furrowed Terrain (nHFT) by L‐20 are coarse‐grained feldspar (>300 μm) with inclusions of pyroxene, and finer‐grained norites, troctolites, spinel troctolites, and gabbros (<100 μm). These two suites represent ferroan anorthosites (FANs) and the Mg‐suite, respectively. There is limited evidence for mantle or deep crustal material within the nHFT samples. Ultramafic rocks such as dunites and orthopyroxenites are absent, and Mg‐rich olivine‐ and orthopyroxene‐bearing‐assemblages are derived from magmatic rocks emplaced in the shallow crust. These lithic fragments represent pre‐Crisium episodes of magmatism (Mg‐suite) and lunar magma ocean products (FANs). The lack of deep lithologies at the L‐20 site seems contradictory to excavation models for Crisium. Mineralogical‐chemical differences suggest a higher FAN component in the rim and that this represents FANs excavated from the deep lunar crust. If it exists, the Mg‐rich olivine previously identified within the Crisium rim is most likely related to deep, complementary versions of the Mg‐suite rocks from L‐20. The material associated with the Crisium basin is not derived from the lunar mantle but represents crustal lithologies from the shallow to deep crust, a substantial mantle component may have been incorporated into the Crisium basin impact melt sheet, or that our “Earth‐analog” for the lunar upper mantle is incorrect.

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Multiple Shallow Crustal Origins for Spinel‐Bearing Lithologies on the Moon: A Perspective From the Luna 20 Mission

Cited by 10 publications

References 71 publications

Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples

Orbital Characterization of the Composition and Distribution of Spinels Across the Crisium Region: Insight From Luna 20 Samples

A possible origin of the lunar spinel-bearing lithologies as told by the meteorite NWA 13191

Where Is the Lunar Mantle and Deep Crust at Crisium? A Perspective From the Luna 20 Samples

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