Petrological constraints of the 'Channel Flow' model in eastern Nepal

The metamorphic architecture of eastern Nepalese Himalaya is characterized by a welldocumented inverted metamorphic field gradient, with metamorphic grade increasing northward from lower (LHS) to higher (HHC) structural levels across the north-dipping Main Central Thrust Zone (MCTZ). Peak metamorphic conditions experienced by units at different structural levels have been investigated extensively, but their P-T-(t) evolution could be constrained better. A synthesis of our recent petrological studies in eastern Nepal is based on selected geotraverses across the Dudh-Kosi, Arun, and Tamur tectonic windows, where the LHS is exposed beneath MCTZ and HHC. To define the entire P-T evolution experienced by lithotectonic units, detailed petrological investigations were focused on metapelites. P-T trajectories were constrained combining microstructural observations and isochemical phase diagrams modelling. The uniformity of the approach applied is a robust method to quantitatively compare the resulting P-T paths. These P-T paths are compared with the petrological constraints inferred from the 'Channel Flow' model, one of the most popular paradigms to explain the tectonometamorphic evolution and the first-order geological features of the Himalaya. The overall geometries of our P-T paths match the results of the numerical model, suggesting that 'Channel Flow' is compatible, from a petrological viewpoint, as the main process operating during the exhumation of eastern Himalaya.