Age, depositional history and tectonics of the Indo-Myanmar Ranges, Myanmar

The Indo-Myanmar Ranges make up an enigmatic mountain belt occupying a complex tectonic zone in western Myanmar, extending from the northern continuation of the active Sunda-Andaman arc into the eastern Himalayan Syntaxis. The Indo-Myanmar Ranges are part of an accretionary forearc basin-arc complex that includes the Central Myanmar Basin and the Wuntho-Popa Arc to the east. New biostratigraphic, petrological and detrital zircon U-Pb age data are presented and used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest that: (1) the Upper Triassic Pane Chaung Formation was originally deposited adjacent to the NE Indian continental margin within northern Gondwana during the Late Triassic; and (2) the Upper Cretaceous-Paleogene rocks of the Indo-Myanmar Ranges were mainly derived from the Wuntho-Popa Arc and Inner Belt, with a subordinate input from a crustal source, potentially from the Naga metamorphic-type Paleozoic basement. The Kalemyo Ophiolite has an Early Cretaceous age similar to the ages of ophiolites in the Indus-Yarlung Tsangpo Suture Zone, south Tibet and Nagaland, reinforcing the hypothesis that they were once part of the same Neotethyan ocean floor.