Abstract
Petrologic analysis of the lunar surface is critical for determining lunar formation and evolution. Here, we report the first global petrologic map that includes the five most important lunar lithological units: the Ferroan Anorthositic (FAN) Unit, the Magnesian Suite (MS) Unit, the Alkali Suite (AS) Unit, the KREEP Basalt (KB) Unit and the Mare Basalt (MB) Unit. Based on the petrologic map and focusing on four long-debated and important issues related to lunar formation and evolution, we draw the following conclusions from the new insights into the global distribution of the five petrologic units: (1) there may be no petrogenetic relationship between MS rocks and KB; (2) there may be no petrogenetic link between MS and AS rocks; (3) the exposure of the KREEP component on the lunar surface is likely not a result of MB volcanism but is instead mainly associated with the combined action of plutonic intrusion, KREEP volcanism and celestial collision; (4) the impact size of the South Pole-Aitken basin is constrained, i.e., the basin has been excavated through the whole crust to exhume a vast majority of lower-crustal material and a very limited mantle components to the lunar surface.
Highlights
On the lunar surface, there are four primary crustal rock types (FAN suite, magnesian suite (MS), alkali suite (AS) and KREEP Basalt (KB)) and one primary mantle rock type (MBs)[2]
Two data sets are adopted to determine the petrologic distribution on the lunar surface: the lunar rock samples from “New Views of the Moon”[2] and the abundance data of major oxides and elements of the whole lunar surface[4,21], which were extracted from Lunar Prospector (LP) Gamma Ray and Neutron Spectrometer (GRNS) data and released in 2012
In terms of the petrologic map (Fig. 1), we present a discussion and analysis of the following four aspects: (1) the distribution characteristics of three petrologic units, i.e., the Ferroan Anorthositic (FAN) Unit, the Magnesian Suite (MS) Unit and the Alkali Suite (AS) Unit; the petrologic relationship between Mg-rich rocks and KB; and the petrologic connection between Mg-rich rocks and AS; (2) the exposure area of the KB on the lunar surface and the excavation and exposure reason of the KREEP component; (3) the exposed region of Mare Basalt (MB); and (4) the constraints on the rock types and impact size of the South Pole-Aitken (SPA) basin
Summary
There are four primary crustal rock types (FAN suite, magnesian suite (MS), alkali suite (AS) and KBs) and one primary mantle rock type (MBs)[2]. Polymict breccias and lunar soils are mixing materials from fragments of the primary rock types[2,20]. Each locale on the moon is attributed to the corresponding geological unit based on its dominant petrologic feature. This paper makes five major contributions: (1) the first global petrologic map, which includes five geological units and reflects, at the macro level, the distribution of the most important rock types on the moon. (3) By superimposing the petrologic map on LRO LOLA elevation data, the global distribution characteristics of five geological units on the lunar surface are discussed. (5) The petrologic features and impact size of the South Pole-Aitken (SPA) basin, a particular area on the moon, are constrained from the new insights into the distribution of five geological units This paper makes five major contributions: (1) the first global petrologic map, which includes five geological units and reflects, at the macro level, the distribution of the most important rock types on the moon. (2) The abundances of six oxides or elements (TiO2, Al2O3, FeO, MgO, CaO and Th), as the signature of lunar primary rocks, are employed to generate the petrologic map, which makes the map more precise. (3) By superimposing the petrologic map on LRO LOLA elevation data, the global distribution characteristics of five geological units on the lunar surface are discussed. (4) Three long-debated and important issues are analyzed: Is there a petrogenetic link between MS rocks and KB? Is there a petrogenetic relationship between MS and AS rocks? What is the evolutionary process that brought KREEP materials to the lunar surface? (5) The petrologic features and impact size of the South Pole-Aitken (SPA) basin, a particular area on the moon, are constrained from the new insights into the distribution of five geological units
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