The Chongba leucogranites, located in the east part of the Greater Himalayan leucogranite belt, are exposed along the South Tibet detachment system (STDS). Their emplacement and cooling ages are significant for evaluating the time span of the magmatism in Himalayan orogeny, constraining the timing of the STDS and revealing the history of the uplift-exhumation-cooling. In this paper, the authors collected leucogranite samples from Chongba area and carried out systematic LA-ICP-MS zircon U-Pb and muscovite ⁴⁰Ar-³⁹Ar dating. The results of zircon U-Pb dating show that the Chongba leucogranites were emplaced at 12.4±0.4 Ma. This age lies on the border between Neo-Himalaya and Post-Himalaya subdivision based on previously published data. However, taking into account the characteristics of the distribution along the STDS,the authors classify it as Neo-Himalaya. The Chongba leucogranites were generated through decompression-dehydration melting of the metapelite in Greater Himalayan Crystalline complex (GHC) triggered by the STDS activity. Thus, the emplacement age of 12.4±0.4 Ma represents the activating timing of the STDS and apparently postdates the timing in the middle and west part of the Himalayan orogeny, which shows a regularity of getting later from west to east. Muscovite ⁴⁰Ar-³⁹Ar cooling ages of the Chongba leucogranites are 9.11±0.25 Ma and 9.62±0.10 Ma, respectively. Combined with the ages and the close temperatures of zircon and muscovite, the authors hold that the rapid cooling exhumation might have occurred between 12.4 Ma to 9.11 Ma, whose cooling rate was up to 137℃/Ma to 162℃/Ma. These calculated results are in accord with previous conclusion obtained by metamorphic P-T-t of the granulite from GHC in Chongba area. It is considered that the rapid cooling event during 12.4~9.11 Ma was probably associated with the structural exhumation caused by the extension and detachment of the STDS in the study area.