Using low-temperature thermochronometers to determine the long-term erosion rate pattern in the Olympic Mountains of Washington State
Abstract
Models of convergent mountain building can be tested with low-temperature thermochronometers and similar data sets provided that mass and heat transport are reasonably well-understood in the setting of interest. Here, we consider the topographically-highest and most deeply-exhumed portion of the Cascadia accretionary wedge, the Olympic Mountains of Washington State, where previous work suggests the long-term steadiness of the pattern of surface erosion and, hence, the mean topography and the temperature and rock velocity fields since soon after the onset of exhumation around 15-18 Ma. We test the hypothesis of a steady erosion rate pattern in the Olympic Mountains by using a thermo- mechanical model of a steady-state accretionary wedge and multiple low-temperature thermochronometers to solve for the patterns of mass influx (accretion) and mass outflux (surface erosion) through the Cascadia margin. Inversions of synthetic data indicate that the methodology is capable of accurately resolving the pattern of surface erosion. Inversions of real data appear to constrain both the duration and pattern of steady surface erosion. Vitrinite reflectance (VR) data, which record maximum temperatures, suggest that exhumation began ~15 Ma, matching previous estimates. Estimates of the erosion rate pattern from inversions of reset apatite fission track (AFT) and apatite (U-Th)/He (AHe) ages are in rough agreement with each other and with fluvial incision rates near the western coast of the Olympic Peninsula, suggesting a steady erosion rate pattern over many millions of years. Inversions of reset zircon fission track (ZFT) ages suggest higher erosion rates in the core of the range than indicated by either the AFT or AHe data. Because the youngest reset ZFT age in the range is 9 Ma, we infer that the erosion rate pattern has remained relatively steady since 8 Ma. Finally, the erosion rate pattern determined from a simultaneous inversion of the AFT and AHe ages does not agree with the predicted pattern from a recently-proposed tectonic-erosional model.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.T12B..07S
- Keywords:
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- 1140 Thermochronology;
- 8140 Ophiolites (3042);
- 8170 Subduction zone processes (1031;
- 3060;
- 3613;
- 8413);
- 8175 Tectonics and landscape evolution