HR: 0800h
AN: T21C-0513    [Abstracts]
TI: Testing exhumation models using PTt paths: an Alpine perspective based on deformation ages
AU: * Reddy, S
EM: s.reddy@curtin.edu.au
AF: Curtin University of Technology, Tectonics Special Research Centre, Perth, WA 6845 Australia
AU: Butler, R
EM: butler@earth.leeds.ac.uk
AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AU: Wheeler, J
EM: johnwh@liv.ac.uk
AF: University of Liverpool, Department of Earth Sciences, Liverpool, L69 3BX United Kingdom
AU: Cliff, B
T21C-0513 AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AU: Freeman, S
T21C-0513 AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AU: Biggs, A
T21C-0513 AF: University of Leeds, School of Earth and Environment, Leeds, LS2 9JT United Kingdom
AB: Geochronological data are now commonly used to establish the timing and rates of exhumation of high pressure metamorphic rocks, critical for testing geodynamic models of orogenic belts. Such approaches must be used with care. Ages of peak pressure metamorphic assemblages allied to younger cooling ages give a general insight into the rates of exhumation when tied to PT paths. However, the results of this workflow are difficult to relate to the kinematic history and therefore maybe of limited use in the critical testing of exhumation models. An alternative strategy is to date directly synkinematic mineral phases in characterised deformation zones. Examples are drawn from the deformed and variably subducted "European" continental crust now exposed in the Western Alps to illustrate this, chiefly using Rb-Sr mica dating, applied to greenschist facies shear zones. Some structures are synchronously active for c. 100km along strike (e.g. the regional "retrocharriage" shear system of the Eastern Brianconnais: 34 Ma). However, UHP terrains of the basement massifs attained peak pressures and were exhumed diachronously (38 Ma - 32 Ma). These results indicate that tectono-metamorphic histories based on single orogenic transects may give misleading pictures of geodynamic evolution. In an Alpine context it appears that exhumation of UHP and shallower parts of the evolving continental subduction channel occurred as variably detached flakes rather than relate to the dynamics of larger scale plate processes.
DE: 1115 Radioisotope geochronology
DE: 3654 Ultra-high pressure metamorphism
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 9335 Europe
SC: Tectonophysics [T]
MN: Fall Meeting 2005