Dating of two metamorphic events on the basalt granulite from the Nabang area on the border of China and Burma.

The Nabang metamorphic basalt, discovered on the border of China and Burma recently, experienced two metamorphic events. The early metamorphism is gra nulite-facies and the later one is amphibolite-facies. Ar-40/Ar-39 isochron age on a laser microscope scale of the early mineral assemblage including garnet and clinopyroxene is 74. 44+/-1. 5Ma. Ar-40/ Ar-39 plateau and isoch ron age of garnet and cliopyroxene, is about 74 similar to 76Ma correspondi ng to the age of the early metamorpnism and 23 similar to 24Ma to the later one. As the age of the later metamorphism, Ar-40/Ar-39 plateauand isochron age of hornblende and plagooclase is between 23 and 24Ma, the same as the K-Ar apparent age of hornblende. Consequently, it is concluded that the ear ly metamorphic age of the Nabang metamorphic basalt is about 74 similar to 77Ma which is consistent with the Mytikyina oceanic crustal subduction age and the later is about 23 similar to 24Ma relating to the dextral strike-sl ip deformation. It is concluded that the Nabang metamorphic basalt is one o f the youngest granulite discovered all over the world. The ages of two met amorphic events can be used to study the geological process developping in the western edge of the Tengchong block.