Deformation of Isochrones and Implications for Detrital Thermochronology
Abstract
We demonstrate the remedy for a key assumption in the use of detrital thermochronology to trace sediment bedrock sources by correcting bedrock cooling age distributions to account for deformation. In the south-central European Alps, the western Sierra Nevada, and Icicle Creek, Washington State, isochrones, or planes of equal cooling age, are ubiquitously sheared away from horizontal by as much as sixty degrees between origin at the closure isotherm and surface exposure. Established techniques based on probability-density functions (PDFs) fail in these localities because shearing compromises age-elevation relationships, thereby precluding the accurate prediction of age PDFs. This pitfall is evidently common to the flanks of orogens, especially those with wedge-type geometries. However, modeling of the deformed isochrones allows the production of just such predicted distributions. In this study, the modeled, best-fit isochrones account for both tilting and the possibility of a change in exhumation rate. Comparison of predicted with observed PDFs provides an estimate of which areas of the basin contribute sediment--effectively the relative erosion rates throughout the basin. Absolute erosion rates depend on the transport time through the basin's hillslopes and streams. In the Alps, we show agreement among this new detrital measure of erosion rates and other geologically short-term measures, including cosmogenic dates and leveling data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.T21E..08M
- Keywords:
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- 8108 Continental tectonics: compressional;
- 8169 Sedimentary basin processes;
- 8175 Tectonics and landscape evolution