Moser D.E., Davis W.J., Reddy S.M., Flemming R.L., Hart R.J.
Department of Earth Sciences, University of Western Ontario, London, Ont. N6A 5B7, Canada; Geological Survey of Canada, 601 Booth St, Ottawa, K1A 0E8, Canada; Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia; iThemba labs, P. Bag 11, Wits 2050 Johannesburg, South Africa
Moser, D.E., Department of Earth Sciences, University of Western Ontario, London, Ont. N6A 5B7, Canada; Davis, W.J., Geological Survey of Canada, 601 Booth St, Ottawa, K1A 0E8, Canada; Reddy, S.M., Department of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia; Flemming, R.L., Department of Earth Sciences, University of Western Ontario, London, Ont. N6A 5B7, Canada; Hart, R.J., iThemba labs, P. Bag 11, Wits 2050 Johannesburg, South Africa
Large (> 100 km) meteorite impact cratering events play important roles in surface and biosphere evolution, however, their potential for widespread ductile modification of the lithosphere has been difficult to assess, due partly to our inability to isotopically age-correlate deep mineral fabrics with surface records. We have integrated benchmark U-Pb zircon dating methods (ID-TIMS, SHRIMP) with new microstructural techniques (EBSD, μXRD) to demonstrate that crystal-plastic deformation can cause rapid out-diffusion of radiogenic Pb and accompanying trace element alteration in crystalline zircon. We have used this phenomenon to directly date fabric in Archean zircons and xenoliths of the lower crust of South Africa at 2023 ± 15 million years, coeval with the 2020 ± 3 million year old Vredefort cratering event at surface, with extent ≥ 20,000 km 2. Our findings indicate that regional exogenic fabrics, similar to high-temperature tectonic fabrics, exist in ancient crust. Moreover, our results establish that crystal-plastic deformation in the lithosphere can now be directly dated and linked to planetary evolution by zircon U-Pb strain chronometry. © 2008 Elsevier B.V. All rights reserved.
Archean; Deep impacts; EBSD; High temperatures; impact; Lower crusts; Meteorite impacts; Microstructural; Mineral fabrics; planetary; Planetary evolutions; South Africa; Tectonic fabrics; U-Pb dating; Zircon dating; Chemical elements; Deformation; Electron diffraction; Fabrics; Geomorphology; Lead; Lead alloys; Meteor impacts; Minerals; Plastic deformation; Silica; Silicate minerals; Tectonics; Trace elements; Zircon; Geochronology; crater; deformation; geochronology; high temperature; planetary evolution; SHRIMP dating; tectonics; trigger mechanism; uranium-lead dating; zircon