Hypothesis
In the Palaeogene, the palaeo-Tsangpo drained Tibet into a precursor of Myanmar's Irrawaddy River, so central Myanmar's Eocene sediments should carry a Tibetan source signature.
What failed
Provenance analysis of the Late Middle Eocene–Early Oligocene Pondaung and Yaw Formations (bulk-rock isotopes, petrography, palaeoflow) found no evidence for a palaeo Tsangpo–Irrawaddy River, at least in the Late Eocene.
Broken assumption
The Tsangpo already drained into a proto-Irrawaddy in the Late Eocene.
Why
Low-grade metamorphic fragments, heterogeneous Sr–Nd values and westward palaeoflow point to a proximal source on the eastern Asian margin — an Andean-type cordillera along the Burmese margin — rather than Tibet, although the paper notes Burmese and Tibetan sources share lithological features.
From the published paper: Licht et al. Journal of the Geological Society, 2013. ↗CC BY