The Boundary Between Gondwana and Pacifica and the Suturing Ages of Their Allied Terranes in Southwestern China1

Abstract

Abstract Two terranes formed since the Late Palaeozoic can be distinguished in southwestern China. One is characterized by the Permo‐Carboniferous ice‐rafted marine gravel‐bearing clastic formation and the cold‐water fauna of the Gondwana facies, including the Gangmar Co, Lhasa, Sa ' gya, Tengchong and Baoshan terranes and the other is marked by the Upper Palaeozoic of the Yangtze type with the Cathaysian flora and the Pacific‐type fusulinids, comprising the Changning‐Menglian, Shuangjiang‐Lancang, Qamdo and Bayan Har terranes. The Longmu Co‐Shuanghu‐Dêngqên‐North Lancang River‐Kejie‐Mengding suture zone between the two groups of terranes is the boundary between Gondwana and Pacifica in southwestern China. On the grounds of the sedimentary formation and successive southwestward migration of the Asian nonmarine Jurassic‐Cretaceous endemic bivalves, the ages of the suture and some terranes to the southwest of the suture zone are discussed. The Baoshan terrane and the Nyainrong‐Sog terrane in the Lhasa composite terrane were firstly pieced together with the Asian continent in the early Early Jurassic. The northern Tibet‐western Yunnan microplate, including the Gangmar Co, Lhasa and Tengchong terranes, collided with the Asian continent at the end of the Early Cretaceous Neocomian.