Ultramafic impact melt sheet beneath the South Pole–Aitken basin on the Moon

Nakamura, Ryosuke; Matsunaga, Tsuneo; Ogawa, Y.; Yamamoto, Sakae; Hiroi, T.; Saiki, Kazuto; Hirata, Naru; Arai, Tomoko; Kitazato, K.; Takeda, Hiroshi; Sugihara, Takamitsu; Kodama, Shinsuke; Ohtake, M.; Haruyama, Junichi; Yokota, Yasuhiro

doi:10.1029/2009gl040765

Cited by 63 publications

(69 citation statements)

References 34 publications

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“…Although the basin contains several mare basalt emplacements, the dominant mafic signature is nonmare and is dominated by low-Ca pyroxene (LCP) [Pieters et al, 1997]. As noted above, many central peaks within SPA exhibit a limited compositional range, suggesting the presence of a thick, homogeneous, LCP-rich layer in the SPA subsurface [Tompkins and Pieters, 1999;Nakamura et al, 2009]. Additionally, small exposures of olivine, pure plagioclase, spinel, and nonmare high-Ca pyroxene in SPA have been observed using Clementine, Kaguya Spectral Profiler, and the Moon Mineralogy Mapper data Ohtake et al, 2009;Kramer et al, 2013;Yamamoto et al, 2012;Moriarty et al, 2013].…”

Section: The South Pole-aitken Basinmentioning

confidence: 99%

“…Since the depth of melting is thought to exceed the depth of excavation for basin-scale impacts [e.g., Cintala and Grieve, 1998], significant volumes of mantle could have melted during SPA formation. Although some of this melt may have been ejected from the basin, large volumes are probably retained in a region corresponding to the transient cavity, forming a central melt sheet [Morrison, 1998;Potter et al, 2012;Vaughan and Head, 2013]. Since SPA melt and ejecta are derived from great depths, characterization of these materials, if they can be identified, would constrain the composition (and thus evolution) of the lower crust and upper mantle.…”

Section: The South Pole-aitken Basinmentioning

confidence: 99%

“…In this scenario, a thick layer of impact melt (~45 km) is predicted to line the inner portion of the basin [Morrison, 1998;Vaughan and Head, 2013]. If the melt volume is thick, has low viscosity, convects, and cools slowly, then melt differentiation is possible [Warren, 1993].…”

Section: Compositional Differences Among Spa Mafic Peaksmentioning

confidence: 99%

“…[46] Impact crater scaling laws predict that the SPA impact excavated through the crust and melted a potentially large volume of mantle material [Melosh, 1989;Pierazzo et al, 1997;Morrison, 1998;Potter et al, 2012;Vaughan and Head, 2013]. In this scenario, a thick layer of impact melt (~45 km) is predicted to line the inner portion of the basin [Morrison, 1998;Vaughan and Head, 2013].…”

Section: Compositional Differences Among Spa Mafic Peaksmentioning

confidence: 99%

“…Central peak craters are especially useful, as they uplift material from beneath the excavation cavity, often from depths of~10 km or greater (depending on crater diameter) [e.g., Melosh, 1989;Cintala and Grieve, 1998]. A number of studies have been performed using central peak craters to evaluate the stratigraphy of the lunar subsurface [e.g., Tompkins and Pieters, 1999;Wieczorek and Zuber, 2001;Cahill et al, 2009;Nakamura et al, 2009;Song et al, 2013]. The primary objective of these papers has been to discern global and regional stratigraphic trends through the compositional assessment of multiple central peaks.…”

Section: Introductionmentioning

confidence: 99%

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Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

2013

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[1] Using high-spectral and -spatial resolution Moon Mineralogy Mapper data, we investigate compositional variations across the central peak structures of four impact craters within the South Pole-Aitken Basin (SPA). Two distinct causes of spectral diversity are observed. Spectral variations across the central peaks of Bhabha, Finsen, and Lyman are dominated by soil development, including the effects of space weathering and mixing with local materials. For these craters, the central peak structure is homogeneous in composition, although small compositional differences between the craters are observed. This group of craters is located within the estimated transient cavity of SPA, and their central uplifts exhibit similar mafic abundances. Therefore, it is plausible that they have all uplifted material associated with melts of the lower crust or upper mantle produced during the SPA impact. Compositional differences observed between the peaks of these craters reflect heterogeneities in the SPA subsurface, although the origin of this heterogeneity is uncertain. In contrast to these craters, Leeuwenhoek exhibits compositional heterogeneity across its central peak structure. The peak is areally dominated by feldspathic materials, interspersed with several smaller exposures exhibiting a mafic spectral signature. Leeuwenhoek is the largest crater included in the study and is located in a region of complex stratigraphy involving both crustal (feldspathic) and SPA (mafic melt and ejecta) materials. The compositional diversity observed in Leeuwenhoek's central peak indicates that kilometer-scale heterogeneities persist to depths of more than 10 km in this region.

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Section: The South Pole-aitken Basinmentioning

confidence: 99%

Section: The South Pole-aitken Basinmentioning

confidence: 99%

Section: Compositional Differences Among Spa Mafic Peaksmentioning

confidence: 99%

Section: Compositional Differences Among Spa Mafic Peaksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

2013

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Geology and composition of the Orientale Basin impact melt sheet

2014

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[1] The Orientale Basin is one of the largest (930 km diameter) and youngest (~3.8 Ga) impact craters on the Moon. As the basin is only partly flooded by mare lava, its floor materials expose a major portion of the basin impact melt sheet, which some previous work has suggested might have undergone igneous differentiation. To test this idea, we remapped the geology of the Orientale Basin using images and topography from the Lunar Reconnaissance Orbiter, mineralogical information from the Chandrayaan-1 Moon Mineralogy Mapper, and elemental concentration maps from Clementine multispectral imaging and Lunar Prospector gamma ray data. The Maunder Formation (impact melt sheet of the basin) is uniform in chemical composition (equivalent to "anorthositic norite") in at least the upper 2 km of the deposit. The deepest sampling of the basin melt sheet (maximum depths of~3-5 km by the crater Maunder, 55 km in diameter) shows a variety of lithologies, but these rock types (anorthosite, anorthositic norite melt rocks, mare basalt, and gabbro) are not those predicted by the differentiation model. We conclude that no differentiation of the Orientale Basin melt sheet has occurred and that such a process is not evident from new remote sensing data for the Moon or in the Apollo lunar samples.

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Differentiation of the South Pole–Aitken basin impact melt sheet: Implications for lunar exploration

2014

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We modeled the differentiation of the South Pole-Aitken (SPA) impact melt sheet to determine whether noritic lithologies observed within SPA formed as a result of the impact. Results indicate differentiation of SPA impact melt can produce noritic layers that may accommodate observed surface compositions but only in specific scenarios. One of nine modeled impact melt compositions yielded layers of noritic materials that account for observations of noritic lithologies at depths of~6 km. In this scenario, impact occurred before a hypothesized lunar magma ocean cumulate overturn. The 50 km deep melt sheet would have formed an insulating quenched layer at the surface before differentiating. The uppermost differentiated layers in this scenario have FeO and TiO 2 contents consistent with orbital observations if they were subsequently mixed with the uppermost quenched melt layer and with less FeO-and TiO 2 -enriched materials such as ejecta emplaced during younger impacts. These results verify that noritic lithologies observed within SPA could have formed as a direct result of the impact. Therefore, locations within SPA that contain noritic materials represent potential destinations for collecting samples that can be analyzed to determine the age of the SPA impact. Potential destinations include central peaks of Bhabha, Bose, Finsen, and Antoniadi craters, as well as walls of Leibnitz and Schrödinger basins. Additionally, potential remnants of the uppermost quenched melt may be preserved in gabbroic material exposed in "Mafic Mound." Exploring and sampling these locations can constrain the absolute age of SPA, a task that ranks among the highest priorities in lunar science.

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Ultramafic impact melt sheet beneath the South Pole–Aitken basin on the Moon

Cited by 63 publications

References 34 publications

Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

Compositional heterogeneity of central peaks within the South Pole‐Aitken Basin

Geology and composition of the Orientale Basin impact melt sheet

Differentiation of the South Pole–Aitken basin impact melt sheet: Implications for lunar exploration

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