New structural, U–Th/Pb and Ar/Ar data along the Nyalam section constrain the
timing of partial melting, crystallization and deformation in the Greater Himalayan Sequence. Prograde
metamorphism was followed by the onset of partial melting at c. 30 Ma. In the central
Greater Himalayan Sequence, in situ melts crystallized between 24 and 18 Ma. Subsequent
cooling was very fast (c. 200 8CMa21) and coeval with the emplacement of undeformed dykes
that lasted until c. 15 Ma. In the upper Greater Himalayan Sequence, fast cooling continued
until c. 13 Ma. Combined with published P–T and thermochronological data from the Langtang
and Dudh Kosi valleys, these data imply that: (a) the partial melt zone thinned over time; (b)
the end of melting preceded the end of motion on the Main Central Thrust and the South
Tibetan Detachment by 6 and 2 Ma, respectively; (c) the South Tibetan Detachment possibly
initiated at c. 25 Ma, probably reactivating a pre-existing thrust; and (d) the present-day topography
has been established for ,6 Ma and focused erosion on the present-day southern slopes of the
Himalaya was not active at the time of the exhumation of the Greater Himalayan Sequence. These
observations suggest that the Main Central Thrust/South Tibetan Detachment systems are not
passive structures induced by focused erosion, as has been suggested previously by some lower
crustal channel flow models.
Mukherjee, S., Carosi, R., van der Beek, P. A., Mukherjee, B. K.&Robinson, D. M. (eds) Tectonics of the
Himalaya. Geological Society, London, Special Publications, 412, http://doi.org/10.1144/SP412.11