HR: 17:10h
AN: T34C-06    [Abstracts]
TI: U(-Th)-Pb age Constraints on the Timing and Duration of Channel Flow in the Mt. Everest Region, Eastern Himalaya
AU: * Cottle, J M
EM: John.Cottle@earth.ox.ac.uk
AF: Dept. of Earth Sciences,University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Searle, M P
EM: mikes@earth.ox.ac.uk
AF: Dept. of Earth Sciences,University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Horstwood, M S
EM: msah@bgs.ac.uk
AF: NERC National Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom
AU: Waters, D J
EM: davew@earth.ox.ac.uk
AF: Dept. of Earth Sciences,University of Oxford, Parks Road, Oxford, OX1 3PR, United Kingdom
AU: Noble, S R
EM: srn@nigl.nerc.ac.uk
AF: NERC National Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom
AU: Parrish, R R
EM: rrp@nigl.nerc.ac.uk
AF: NERC National Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, United Kingdom
AB: U(-Th)-Pb dating of accessory phases from metamorphic and igneous rocks at two outcrops along a north-south transect in the Mt. Everest region of southern Tibet provides new constraints on the timing and duration of thermal events associated with ductile extrusion of the Greater Himalayan Series (GHS). At the southern-most outcrop in the Kangshung valley, Th-Pb ages from monazite indicate that prograde metamorphism associated with crustal thickening following the India - Asia collision, peaked at least as early as ~39 Ma, ~7 Ma earlier than previously recognized in the GHS of southern Tibet. A subsequent sillimanite grade metamorphic event at ~28 Ma was followed by two phases of leucogranite emplacement at ~21 Ma and ~17 Ma. At Thongmön, 40 km in the down-tectonic transport direction relative to Kangshung valley, prograde metamorphism was occurring at ~25 Ma and lasted until ~16 Ma, reaching ~740°C and 5 kbar at ~22 Ma. Immediately following metamorphism, two phases of leucogranite were emplaced at ~15 Ma and ~12 Ma, with an intervening phase of ductile deformation. These two outcrops record a northward propagation of metamorphic, magmatic and structural events that are ~5-7 Ma younger in the down-tectonic transport direction. This diachroneity in thermal history provides quantitative geological support for previously proposed models of south-directed mid-crustal channel flow, but suggests that the time-scales over which this process operated require significant revision.
DE: 1115 Radioisotope geochronology
DE: 3652 Pressure-temperature-time paths
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: 2007 Fall Meeting