Petrological constraints of the ‘Channel Flow’ model in eastern Nepal
Published:January 01, 2015
F. Rolfo, C. Groppo, P. Mosca, 2015. "Petrological constraints of the ‘Channel Flow’ model in eastern Nepal", Tectonics of the Himalaya, S. Mukherjee, R. Carosi, P. A. van der Beek, B. K. Mukherjee, D. M. Robinson
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The metamorphic architecture of eastern Nepalese Himalaya is characterized by a well-documented 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.
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Tectonics of the Himalaya
The Himalayan mountain belt, which developed during the India–Asia collision starting about 55 Ma ago, is a dramatically active orogen and it is regarded as the classic collisional orogen. It is characterized by an impressively continuous 2500 km of tectonic units, thrusts and normal faults, as well as large volumes of high-grade metamorphic rocks and granites exposed at the surface. This constitutes an invaluable field laboratory, where amazing crustal sections can be observed directly in very deep gorges. It is possible to unravel the tectonic and metamorphic evolution of litho-units, to observe the mechanisms of exhumation of deep-seated rocks and the propagation of the deformation. Himalayan tectonics has been the target of many studies from numerous international researchers over the years. In the last 15 years there has been an explosion of data and theories from both geological and geophysical perspectives.
This book presents the results of integrated multidisciplinary studies, including geology, petrology, magmatism, geochemistry, geochronology and geophysics, of the structures and processes affecting the continental lithosphere. These processes and their spatial and temporal evolution have major consequences on the geometry and kinematics of the India–Eurasia collision zone.