Structural, geochronological and geochemical evidence for two distinct thrust sheets in the ‘Main Central thrust zone’, the Main Central thrust and Ramgarh–Munsiari thrust: implications for upper crustal shortening in central Nepal
Published:January 01, 2015
S. Khanal, D. M. Robinson, S. Mandal, P. Simkhada, 2015. "Structural, geochronological and geochemical evidence for two distinct thrust sheets in the ‘Main Central thrust zone’, the Main Central thrust and Ramgarh–Munsiari thrust: implications for upper crustal shortening in central Nepal", Tectonics of the Himalaya, S. Mukherjee, R. Carosi, P. A. van der Beek, B. K. Mukherjee, D. M. Robinson
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Two orogen-scale thrusts structurally underneath Greater Himalayan (GH) rocks characterize the structural architecture of Himalaya in central Nepal. The Main Central thrust (MCT) is at the base of the GH with the Lesser Himalayan (LH) Robang Formation in the footwall, which is the hanging wall of the Ramgarh–Munsiari thrust (RMT). At Kodari-Tatopani and Malekhu, U–Pb detrital zircon age populations from the RMT sheet yield a maximum depositional age of c. 1838 and c. 1871 Ma. U–Pb analyses of igneous zircons from the RMT sheet yield a crystallization age of c. 1750 Ma at both Galchhi and Kodari-Tatopani. The ɛNd(0) values of pelitic rocks from the RMT sheet at Kodari-Tatopani range from c. −23 to −25; whereas, GH rocks have values from c. −12 to −18. These data indicate that the RMT sheet carries the Palaeoproterozoic LH rock and the MCT carries the GH rock. At Kodari-Tatopani, the thrust previously mapped as the MCT is interpreted to be the RMT. Positively identifying the RMT sheet in all three locations yields a more accurate kinematic evolution and confirms its orogenic-scale presence in central Nepal.
U–Pb geochronological analyses are available at http://www.geolsoc.org.uk/SUP18775
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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.