Nujiang Canyon ophiolites(eastern Tibetan Plateau): Records of early Jurassic subduction initiation at passive continental margin of the Lhasa block?

The formation ages and genesis of the Nujiang Canyon ophiolites in the eastern Tibetan Plateau are still unclear, and it has been debated whether they belong to the Neo-Tethyan or Paleo-Tethyan suture zones. This study exhibits that the Diba and Youba ophiolites in Zogang formed at 190–185 Ma and are of supra-subduction zone(SSZ) type, and belong to the Neo-Tethyan Bangong-Nujiang suture zone. The parental magmas of cumulates in the ophiolites were likely boninitic, and the mantle sources had been metasomatized by subduction fluids and melts derived from subducted sediments with components of ancient continental crust. It is further proposed that subduction initiation in the Bangong-Nujiang oceanic basin developed during the early Jurassic(195–184 Ma) at the northern passive continental margin of the Lhasa block. The inception of subduction beneath the Lhasa block occurred simultaneously along >2000 km length, resulting in synchronous arc granitoids on its northern margin. The early Jurassic ophiolites in the Bangong-Nujiang suture zone represent the fragments of forearc oceanic lithosphere during subduction initiation, which was probably induced by abrupt global plate reorganization during the Pangea breakup.