The discovery of Late Carboniferous-Early Permian oceanic island in the Lungmu Co-Shuanghu-Lancang River suture zone

Located in the middle and western segments of the Lungmu Co-Shuanghu-Lancang River suture zone, Tianquan archipelago is the only set of oceanic islands in this suture zone. Based on field reconnaissance and profile measurement, the authors have reached the conclusion that Tianquan archipelago is composed of nine isolated oceanic islands, whose rocky combinations are different from each other. The rocky combination of Duquangou oceanic island and that of Pingfengling oceanic island of Tianquan archipelago are complete, comprising basalts, limestone, conglomerate and cherts, whereas the rocky combinations of the other oceanic islands are incomplete. Tianquan archipelago is in conformity with the flysch of Zhanjin Formation, indicating that it was formed in Late Carboniferous-Early Permian. The discovery of Tianquan archipelago demonstrates that the Lungmu Co-Shuanghu-Lancang River Ocean had a mature ocean basin in Late Carboniferous-Early Permian. The results achieved by the authors have enriched the study of the evolution of the Lungmu Co-Shuanghu-Lancang River suture zone and provided the basis for reconstructing the regional geological evolution.