2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 6
Presentation Time: 9:40 AM


HODGES, Kip, RUHL, Katharine and WOBUS, Cameron, Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, kvhodges@mit.edu

Some of the most powerful tools available for establishing erosional histories in active orogenic systems are the 40Ar/39Ar, (U-Th)/He, and fission-track cooling ages that can be obtained for detrital minerals from stream channels and young river terraces. The 40Ar/39Ar method is well-suited to such studies; the micas (particularly muscovite) are relatively resistant to grain-size communition and alteration during erosion and transport, and yield information pertaining to the cooling of source regions through the ~375-325 C temperature range. Modern laser microprobe systems permit the routine determination of sufficiently large numbers of single-grain dates for a statistically significant characterization of the age population in most detrital samples.

Two applications of this technique will be reviewed here. The first is a thought experiment regarding the value of 40Ar/39Ar thermochronometry for rapid reconnaissance characterization of the thermal history of large regions; such studies may prove critical to efforts such as the U.S. National Science Foundation's Earthscope initiative, where the goal is large-scale studies of the lithosphere. The second focus of the presentation will be the results of detrital 40Ar/39Ar thermochronometry of modern sediments from rivers draining the southern flank of the central Nepalese Himalaya. We show how such data have been used both to model catchment-wide erosion rates, and to monitor the kinematics of recent deformation.