HR: 16:00h
AN: V34C-01    [Abstracts]
TI: Ductile Zircon Dating of Lithosphere Flow
AU: * Moser, D
EM: desmond.moser@uwo.ca
AF: University of Western Ontario, Dept. of Earth Sciences 1151 Richmond St., London, ON N6A 5B7, Canada
AU: Davis, B
EM: bidavis@nrcan.gc.ca
AF: Geological Survey of Canada, Natural Resources Canada 601 Booth St., Ottawa, K1A 0E8, Canada
AU: Reddy, S
EM: S.Reddy@curtin.edu.au
AF: Curtin University of Technology, Dept. of Applied Geology, Perth, WA 6845,
AU: Flemming, R
EM: rflemmin@uwo.ca
AF: University of Western Ontario, Dept. of Earth Sciences 1151 Richmond St., London, ON N6A 5B7, Canada
AU: Hart, R
EM: hart@tlabs.ac.za
AF: iTHEMBA Labs, Empire Road, Braamfontein, Johanessburg, 7129, South Africa
AB: Ductile flow fabrics in the deep crust are an ubiquitous and valuable record of strain that has often been difficult to correlate with surface structures and other geodynamic records due to an inability to directly measure fabric age. We have combined in situ and single-zircon U-Pb isotope, micro-XRD, EBSD and colour SEM-CL analyses to directly date a crystal-plastic deformation fabric in Archean xenolith samples of the African Moho at 2023+/-15 million years, indicating deep level flow coeval with rebound of the 2020+/-3 Ma giant Vredefort impact crater. The deformed zircons are comparable to those in tectonic settings and are restricted to the main mylonitic fabric whereas undeformed zircons in the same sample occur in the cores of garnet porphyroclasts. LREE enrichment of the deformed and isotopically disturbed ductile zircon zones suggests participation of fluid in the up to 100 percent evacuation of radiogenic Pb from the zircon lattice. Our study demonstrates a new method for strain chronometry of planetary materials while offering a first view into post-impact processes at the unexposed crust- mantle transition of continental lithosphere.
DE: 1115 Radioisotope geochronology
DE: 8012 High strain deformation zones
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting