HR: 11:05h
AN: T52A-04    [Abstracts]
TI: Rapid Exhumation of the Greater Himalaya Persisted Until 10 Ma: New Evidence Concerning Himalayan Evolution During the Neogene From a Detrital Investigation of the Siwalik Group in SW Nepal
AU: * Szulc, A G
EM: s0129966@sms.ed.ac.uk
AF: Department of Geoscience, University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh, EH9 3JW
AU: Najman, Y
AF: Department of Environmental Science, University of Lancaster, IENS, Lancaster, LA1 4YQ
AU: Sinclair, H
AF: Department of Geoscience, University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh, EH9 3JW
AU: Pringle, M
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, MA 02139
AU: Bickle, M
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ
AU: Chapman, H
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ
AU: Garzanti, E
AF: Dipartimento di Scienze, Geologiche e Geotecnologie, University of Milan, Piazza Della Scienza, Milan, 20126
AU: Ando, S
AF: Dipartimento di Scienze, Geologiche e Geotecnologie, University of Milan, Piazza Della Scienza, Milan, 20126
AU: Carter, A
AF: Thermochronological Research Group, University College London, Gower Street, London, WC1E 6BT
AU: Ojha, T
AF: Himalayan Experience, Mhepi, Kathmandu, 659-1
AU: DeCelles, P
AF: Department of Geosciences, University of Arizona, University of Arizona, Tucson, AZ 85721
AB: We have applied 40Ar-39Ar dating of detrital white micas, petrography, and whole-rock Sr and Nd geochemistry to three contemporaneous sedimentary sections (Tinau Khola, 12-6.3 Ma; Surai Khola, 12-1 Ma; Karnali, 16-5 Ma) through the Siwalik molasse of SW Nepal. Mica ages suggest rapid exhumation of the Greater Himalaya persisted until 10 Ma. Subsequent exhumation was slower or had ceased with no evidence for late-stage reactivation of the Main Central Thrust. Rapid uplift of the Greater Himalaya between 12-10 Ma may be responsible for the well documented increase in sediment flux to the foreland between 11-9 Ma as opposed to initiation of the Main Boundary Thrust. We also conducted apatite and zircon fission-track dating on samples from the immediate hanging wall of the Main Boundary Thrust in central Nepal. Surprisingly old zircon ages could reflect rapid cooling along the structure as early as 20 Ma. An abundance of carbonate, sedimentary, and low-grade metasedimentary material testifies to the exposure of the Lesser Himalaya by at least 16 Ma. There is no evidence for perturbations in the detrital signals or sedimentology during the last 10 Ma despite the dramatic climate change indicated by various studies. Our findings are consistent for all three Siwalik sections, indicating the reliability of the data and rendering any potential detrital `hazards' such as sediment ponding unlikely. This work has major implications for the timing and duration of regional Himalayan structures and their relationship to the erosional history of the orogen and also for the patterns of hinterland reorganisation throughout the Neogene.
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting