Dating of gabbro in the Shemalagou ophiolite in the western segment of the Bangong Co-Nujiang ophiolite belt, Tibet—with a discussion of the age of the Bangong Co-Nujiang ophiolite belt

Abstract: Sm-Nd and K-Ar dating of layered gabbro in the Shemalagou ophiolite in the western segment of the Bangong Co-Nujiang ophiolite belt indicates a combined internal and whole-rock Sm-Nd isochron age of 191±22 Ma and K-Ar ages of 140±4.07 Ma and 152.30±3.60 Ma. According to the dating results, combined with geological data, it is suggested that the Sm-Nd age represents the age of ocean basin opening, i.e. Early Jurassic, while the latter is the time of alteration influenced by the subduction of oceanic crust. Based on the available data in the central and eastern segments of the Bangong Co-Nujiang ophiolite belt, the ages of opening, subduction and closing of the ocean basin are discussed. The authors think that the Bangong Co-Nujiang ocean basin probably opened from east to west simultaneously in the Early Jurassic, began to be subducted southward in the Middle Jurassic and finally closed at the end of the Early Cretaceous.