Publication Date:
2012-11-06
Description:
Nature Geoscience 5, 775 (2012). doi:10.1038/ngeo1614 Authors: Ryosuke Nakamura, Satoru Yamamoto, Tsuneo Matsunaga, Yoshiaki Ishihara, Tomokatsu Morota, Takahiro Hiroi, Hiroshi Takeda, Yoshiko Ogawa, Yasuhiro Yokota, Naru Hirata, Makiko Ohtake & Kazuto Saiki The asymmetry between the nearside and farside of the Moon is evident in the distribution of mare basalt, crustal thickness and concentrations of radioactive elements, but its origin remains controversial. According to one attractive scenario, a gigantic impact early in the Moon’s history produced the observed dichotomy; the putative 3,000-km-diameter Procellarum basin has been suggested to be a relic of this ancient impact. Low-calcium pyroxene can be formed during an impact by melting a mixture of crust and mantle materials or by excavating differentiated cumulates from the lunar magma ocean. Therefore, the association of low-calcium pyroxene with a lunar basin could indicate an impact origin. Here we use spectral mapping data from KAGUYA/SELENE (ref. ) to show that low-calcium pyroxene is concentrated around two established impact structures, the South Pole–Aitken and Imbrium basins. In addition, we detect a high concentration of low-calcium pyroxene at Procellarum, which supports an impact origin of the ancient basin. We propose that, in forming the largest known basin on the Moon, the impact excavated the nearside’s primary feldspathic crust, which derived from the lunar magma ocean. A secondary feldspathic crust would have later recrystallized from the sea of impact melt, leading to two distinct sides of the Moon.
Print ISSN:
1752-0894
Electronic ISSN:
1752-0908
Topics:
Geosciences
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