HR: 17:20h
AN: T34C-07    [Abstracts]
TI: Empirical Constraints on Extrusion Mechanisms Derived From Pressure-Temperature-Time Histories From the Himalayan Metamorphic Core (Sutlej Valley, NW India)
AU: * Chambers, J
EM: j.a.chambers@open.ac.uk
AF: The Open University, Department of Earth Sciences, Milton Keynes, MK7 6AA, United Kingdom
AU: Caddick, M
EM: mark.caddick@erdw.ethz.ch
AF: ETH Zurich, Institute for Mineralogy and Petrography, Zurich, CH-8092, Switzerland
AU: Argles, T
EM: t.w.argles@open.ac.uk
AF: The Open University, Department of Earth Sciences, Milton Keynes, MK7 6AA, United Kingdom
AU: Horstwood, M
EM: msah@bgs.ac.uk
AF: NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom
AU: Harris, N
EM: n.b.w.harris@open.ac.uk
AF: The Open University, Department of Earth Sciences, Milton Keynes, MK7 6AA, United Kingdom
AU: Parrish, R
EM: rrp@nigl.nerc.ac.uk
AF: NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom
AU: Ahmad, T
EM: tahmad001@gmail.com
AF: University of Delhi, Department of Geology, Delhi, 1100, India
AB: The exhumed Himalayan core in the Sutlej Valley comprises the Greater Himalayan Sequence (GHS), bounded by the Main Central Thrust and the South Tibetan Detachment, and tectonically distinct metamorphosed units above (the Haimanta Group) and below (the Jutogh Group). While pressure-temperature-time (P-T-t) data from the GHS are broadly compatible with predictions of the channel flow model presented by Jamieson et al. (2004), corresponding data for the units bounding the putative channel are not: The underlying Jutogh Group experienced a tightly closed P-T path featuring upper-amphibolite prograde metamorphism at c. 11 Ma, followed by rapid cooling and exhumation. These data are consistent with a) prograde metamorphism during overthrusting (along the Main Central Thrust) and b) subsequent exhumation via accretion to the extruding GHS channel above. However, muscovite cooling ages from the GHS pre-date those from the Jutogh Group by at least 10 Ma, clearly indicating decoupled exhumation of the two crystalline units. Alongside evidence that motion on the Main Central Thrust had ceased by c. 16 Ma, concomitant extrusion of the Jutogh Group as part of a single widening GHS `channel' seems impossible. The Haimanta Group, considered uppermost in the GHS sequence and/or basal to the Tethyan Sedimentary Sequence, also reached upper-amphibolite grade during the Himalayan orogeny. As for the Jutogh Group, exhumation and cooling rapidly followed peak metamorphism. Coupled U-Pb monazite data and detailed textural and pseudosection analyses constrain prograde metamorphism at c. 35 to 30 Ma, the timing of which is compatible with channel flow model predictions. Importantly, however, P-T paths do not match numerical simulations, which imply shallower burial, lower peak temperatures and a distinct phase of isobaric heating. We conclude that the Sutlej Valley presents a tectonically complex metamorphic core for which a single, widening channel flow model does not accurately predict the P-T-t conditions observed in units above and below the proposed channel. Modifications to the model (e.g. migrating focused denudation) may provide more realistic predictions. It also seems likely that tectonic evolution of the Himalaya encompassed aspects of models incorporating both foreland thrust propagation and channel flow, at different stages during its history. Jamieson, R. A., Beaumont, C., Medvedev, S. and Nguyen, M. H. 2004. Crustal Channel Flows: 2. Numerical Models with Implications for Metamorphism in the Himalayan-Tibetan Orogen. Journal of Geophysical Research- Solid Earth, 109, art. no.-B06407.
DE: 1115 Radioisotope geochronology
DE: 3652 Pressure-temperature-time paths
DE: 3660 Metamorphic petrology
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting