Detrital Zircon Dating, Deformation Stages, and Tectonics of the Pane Chaung Formation and Surrounding Units in the Western Indo-Burma Range, Southeast Asia

The Indo-Burma Range (IBR), as one of the youngest accreted units in the Eastern Neotethys, plays a crucial role in understanding the interactive relationships between the Gondwana supercontinent and its rifted microcontinents in SE Asia. However, its basement nature and tectonic evolution remain debated. Here, we conducted a comprehensive structural analysis across six sections within the IBR and correlated Late Triassic flysch units between the Western IBR (Pane Chaung Formation) and the Tethyan Himalaya. Within the Mindat section, the eastern segment of the Pane Chaung Formation unit displays top-to-east vergent overturned folds, indicating eastward backthrusting, in contrast to the prevailing top-to-west vergence structures in Kalemyo, Natchaung, Magwe and the western segment of the Mindat flysch unit. By reconstruction of this backthrust sheet, a megathrust separates the Pane Chaung Formation unit in the footwall to the west from schist units in the hanging wall to the east. The Pane Chaung Formation unit in the Western IBR and its counterparts in the Tethyan Himalaya share common characteristics, including herringbone cross-beddings, Carnian–Norian Halobia fossils, and dominant detrital zircons of 220–280, 500–620, 900–1000, and 1100–1140 Ma. Alongside the Paleozoic strata and Precambrian one-stage model ages of Mesozoic dikes, as evidenced by ɛNd (t) (−13.4 to −0.1) and ɛHf (t) (−24.2 to −0.1) in the Tethyan Himalaya, these facts suggest that the major tectonic units of the Western IBR–Tethyan Himalaya are the result of the amalgamation of a microcontinent with the West Burma Block. The transition from OIB to E-MORB and N-MORB, the rapid deepening of sedimentary waters, and the presence of the 155–152 Ma Indian ocean crust collectively indicate that the microcontinent rifted from the host East Gondwana as a fragment of the Argoland archipelago in the Late Jurassic. This identification sheds light on the orogenic processes of the doublet subduction zones in the Indo-Myanmar orogenic belt.