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Tectonic evolution of the Himalaya constrained by detrital 40Ar^39Ar, Sm-Nd and petrographic data from the Siwalik foreland basin succession, SW NepalNormal access

Authors: A.G. Szulc, Y. Najman, H.D. Sinclair, M. Pringle, M. Bickle, H. Chapman, E. Garzanti, S. Andò, P. Huyghe, J-L. Mugnier, T. Ojha and P. DeCelles
Journal name: Basin Research
Issue: Vol 18, No 4, December 2006 pp. 375 - 391
DOI: 10.1111/j.1365-2117.2006.00307.x r
Organisations: Wiley
Language: English
Info: Article, PDF ( 633.41Kb )

Summary:
40Ar-39Ar dating of detrital white micas, petrography and heavy mineral analysis and whole-rock geochemistry has been applied to three time- equivalent sections through the Siwalik Group molasse in SW Nepal [Tinau Khola section (12-6Ma), Surai Khola section (12-1Ma) and Karnali section(16-5Ma)]. 40Ar-39Ar ages from 1415 single detrital white micas show a peak of ages between 20 and 15Ma for all the three sections, corresponding to the period of most extensive exhumation of the Greater Himalaya. Lag times of less than 5 Myr persist until 10Ma, indicating Greater Himalayan exhumation rates of up to 2.6mm year-1, using one-dimensional thermal modelling. There are few micas younger than 12Ma, no lag times of less than 6Myr after 10Ma and whole-rock geochemistry and petrography show a significant provenance change at 12Ma indicating erosion from the Lesser Himalaya at this time. These changes suggest a switch in the dynamics of the orogen that took place during the 12-10Ma period whereby most strain began to be accommodated by structures within the Lesser Himalaya as opposed to the Greater Himalaya. Consistent data from all three Siwalik sections suggest a lateral continuity in tectonic evolution for the central Himalayas.

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