Thorium distribution on the lunar surface observed by Chang'E 2 gamma ray spectrometer
The thorium distribution on the lunar surface is critical for understanding the lunar evolution. This work reports a global map of the thorium distribution on the lunar surface observed by Chang'E 2 gamma ray spectrometer (GRS) Our work exhibits an interesting symmetrical structure of thorium distribution along the two sides of the belt of Th hot spots. Some potential positions of KREEP volcanism are suggested, which are the Fra Mauro region, Montes Carpatus, Aristarchus Plateau and the adjacent regions of Copernicus Crater. Based on the lunar map of thorium distribution, we draw some conclusions on two critical links of lunar evolution: (1) the thorium abundance within the lunar crust and mantle, in the last stage of Lunar Magma Ocean (LMO) crystallization, may have a positive correlation with the depth in the crust, reaches a peak when coming through the transitional zone between the crust and mantle, and decreases sharply toward the inside of the mantle; thus, the Th enhanced materials originated from the lower crust and the layer between the crust and mantle, (2) in PKT, KREEP volcanism might be the primary mechanism of Th elevated components to the lunar surface, whereas the Imbrium impact acted as a relatively minor role.