The Indo-Myanmar Ranges (IMR) are an enigmatic mountain belt that occupy a complex tectonic zone in western Myanmar extending from the northern continuation of the active Sunda-Andaman arc into the eastern Himalayan syntaxis. The IMR are part of an accretionary fore-arc basin-arc complex that includes the Central Myanmar Basin and the Wuntho-Popa Arc to the east. New biostratigraphic, petrologic, and detrital zircon U-Pb age data are presented that are used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest: 1) that 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) that the Upper Cretaceous – Paleogene rocks of the IBR 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 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 Neo-Tethyan ocean floor.

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