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Thermochronometric reconstruction of the prethrust paleogeothermal gradient and initial thickness of the Lewis thrust sheet, southeastern Canadian Cordillera foreland belt

By
Shimon Feinstein
Shimon Feinstein
Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer Sheva 84105, Israel
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Barry Kohn
Barry Kohn
School of Earth Sciences, University of Melbourne, Victoria 3010, Australia
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Kirk Osadetz
Kirk Osadetz
Natural Resources Canada, Earth Sciences Sector, Geological Survey of Canada–Calgary, 3303 33rd St. NW, Calgary, Alberta T2L 2A7, Canada
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Raymond A. Price
Raymond A. Price
Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada
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Published:
January 01, 2007

The Lewis thrust, which is >225 km long and has a maximum displacement of >80 km, is a major Foreland belt structural element in the southeastern Canadian Cordillera. We use low-temperature thermochronometry in the preserved Lewis thrust sheet stratigraphic succession to constrain variations in both paleogeothermal gradient and Lewis thrust sheet thickness immediately prior to motion on the Lewis thrust fault. Fission-track and vitrinite reflectance data combined with stratigraphic data suggest that maximum Phanerozoic burial and heating occurred in the Lewis thrust sheet during a short interval (<15 m.y.) in late Campanian time immediately prior to thrusting (ca. 75 Ma). The data suggest that the late predeformational Lewis thrust sheet paleogeothermal gradient was between ∼18 and 22.5 °C/km, which is higher than that inferred for subsequent syn- and postdeformational intervals by other studies. The inferred paleotemperatures and geothermal gradients indicate that the preserved Lewis thrust sheet stratigraphic succession was overlain by ∼4–5.5 km of additional Late Cretaceous strata that were subsequently removed by erosional denudation. We estimate that the Lewis thrust sheet was ∼12–13.5 km thick when thrusting commenced. Deposition of the Late Cretaceous succession was terminated by the onset of displacement on the Lewis thrust (ca. 75 ± 5 Ma) and was followed by intervals of erosional denudation that are constrained stratigraphically by both early Oligocene and current erosion surfaces on the Lewis thrust sheet.

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GSA Special Papers

Whence the Mountains? Inquiries into the Evolution of Orogenic Systems: A Volume in Honor of Raymond A. Price

James W. Sears
James W. Sears
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Tekla A. Harms
Tekla A. Harms
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Carol A. Evenchick
Carol A. Evenchick
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Geological Society of America
Volume
433
ISBN print:
9780813724331
Publication date:
January 01, 2007

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