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Geology; September 2006; v. 34; no. 9; p. 765-768; DOI: 10.1130/G22507.1
© 2006 Geological Society of America
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Apatite (U-Th)/He signal of large-magnitude accelerated glacial erosion, southwest British Columbia

Todd A. Ehlers*,1, Kenneth A. Farley2, Margaret E. Rusmore3 and Glenn J. Woodsworth4

1 Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
2 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
3 Department of Geology, Occidental College, Los Angeles, California 90041, USA
4 Geological Survey of Canada, 101-605 Robson St., Vancouver, British Columbia V6B 5J3, Canada

Alpine glaciers are efficient agents of erosion and capable of significantly modifying topography. Despite recent advances in theoretical and field studies that quantify glacial erosion processes, few studies have documented glacial erosion rates over long (>106 yr) or large (more than tens of kilometers) scales. We use apatite (U-Th)/He (AHe) and apatite fission track (AFT) cooling ages to address the late Miocene to Holocene erosion history across two 60-km-long transects of the heavily glaciated southern Coast Mountains, British Columbia. Observed AHe cooling ages from equal elevation samples range between 1.5 and 8 Ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1.5–4.0 m.y. We evaluated temporal and spatial variations in erosion rates using a three-dimensional thermal-kinematic model that predicted AHe and AFT ages at the surface for different erosion histories. Comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300% over the past 1.5–7 m.y., coincident with the onset of glaciation of this range.

Key Words: glacial erosion • apatite (U-Th)/He • numerical modeling • Coast Mountains • paleotopography




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