HR: 1340h
AN: T23C-1537 [WITHDRAWN]    [Abstracts]
TI: Detrital-zircon fission-track geochronology of the Lower Cenozoic sediments, NW Himalayan foreland basin: Clues for exhumation and denudation of the Himalaya during the India-Asia collision
AU: * Jain, A
EM: himalfes@iitr.ernet.in
AF: Department of Earth Sciences, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India, Roorkee, UA 247667, India
AU: Lal, N
EM: lalkuk@gmail.com
AF: Department of Geophysics, Department of Geophysics, Kurukshetra University, Kurukshetra 136 119, India, Kurukshetra, Har 136119, India
AU: Suelmani, B
EM: himalfes@iitr.ernet.in
AF: Department of Earth Sciences, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India, Roorkee, UA 247667, India
AU: Awasthi, A K
EM: prachfes@iitr.ernet.in
AF: Department of Earth Sciences, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India, Roorkee, UA 247667, India
AU: Singh, S
AF: Department of Earth Sciences, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India, Roorkee, UA 247667, India
AU: Kumar, R
EM: rajkrdes@iitr.ernet.in
AF: Department of Earth Sciences, Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee 247 667, India, Roorkee, UA 247667, India
AB: Detrital-zircon fission-track geochronology of the synorogenically-deposited Subathu–Dagshai–Kasauli–Lower Siwalik Formations of the Sub-Himalayan Lower Cenozoic foreland basin reflects progressive effects of the Himalayan tectonometamorphic events on the Proterozoic–Paleozoic source rock as a consequence of the India–Asia collision. The oldest transgressive marine Subathu Formation (57.0–41.5 Ma) contains a very dominant 302.4 ± 21.9 Ma old detrital zircon FT suite with a few determinable 520.0 Ma grains. This old suite was derived by mild erosion of the Zircon Partially Annealed Zone (ZPAZ) of 240–180 oC, which affected the Himalayan Proterozoic basement and its Tethyan sedimentary cover as a consequence of first imprint of the collision. In addition, 50.0 Ma old detrital zircons in this formation were derived possibly from the Indus Tsangpo Suture Zone and the Trans-Himalayan Ladakh Batholith. Sudden source rock changes and unroofing are manifested in the overlying fluvial Dagshai (~30–20 Ma) and Kasauli (20–13 Ma) molassic sediments, which are characterised by dominant 30.0 and 25.0 Ma old youngest zircon FT peaks, respectively. A distinct unconformity spanning for about 10 Myr gets established between the Subathu–Dagshai formations on the basis of detrital- zircon FT ages. Molassic sedimentation since ~30 Ma coincides with the depletion of detritus from the suture zone, and the bulk derivation from the main Higher Himalayan source rock, which has undergone sequentially the UHP–HP–amphibolite facies metamorphism (53–40 Ma) in the extreme north and widespread Eo– and Neo–Himalayan tectonothermal events in the middle. Strength of the Pre–Himalayan Peaks (PHP) >50 Ma in these younger sediments gradually decreases with the intensification of the Himalayan thermal events till the end of the Kasauli sedimentation. Widespread Eo– and Neo–Himalayan metamorphic events (40.0–30.0 and 25.0–15.0 Ma) have almost remobilised the provenance and obliterated most of the evidences of the Pre–Himalayan Peaks in zircon FT ages and appear to be responsible for incoming of the Himalayan (HP) ~30.0 Ma and Young Himalayan Peaks (YHP) of ~15.0 Ma, respectively; the latter appears only between 13.0 and 11.0 Ma sedimentation of the Lower Siwalik Formation. Three distinct metamorphic events get recognised in source area of the Himalayan Metamorphic Belt. Though the Dagshai-Kasauli-Lower Siwalik sequence records uninterrupted fluvial sedimentation since 30 Ma, distinct breaks in zircon FT ages ~5.0-7.0 Myr at the beginning of each formation records pulsative exhumation of the source area in response to the collision between India and Asia.
DE: 8169 Sedimentary basin processes
DE: 8175 Tectonics and landscape evolution
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: 2007 Fall Meeting