Paper No. 5
Presentation Time: 2:40 PM
LOW TEMPERATURE THERMOCHRONOLOGY USING OSL: APPROACH AND PRELIMINARY ASSESSMENT
RHODES, Edward J., Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Los Angeles, CA 90095, HERMAN, Frédéric, ETH, Geologisches Institut HAD G 4, Haldenbachstr. 44, Zurich, 8092, Switzerland, JAISWAL, Manoj, Department of Earth Sciences, Indian Institute of Science Education and Research (IISER)-Kolkata, BCKV main office, Mohanpur, West Bengal, Mohanpur, distt: Nadia, 741252, India and SCHWENNINGER, Jean-Luc, Research Laboratory for Archaeology and the History of Art, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford, OX1 3QY, United Kingdom, erhodes@ess.ucla.edu
Thermal detrapping of electrons from OSL (Optically Stimulated Luminescence) traps when mineral grains are held at raised temperatures provides the mechanism for OSL thermochronology. Calculations based on published trapping parameters (E and s) for the fast component of the quartz OSL signal implies a closure temperature in the range 30 - 35°C at a cooling rate of 10°C/Myr. Empirical OSL thermochronology measurements based on 13 quartz samples from the Whataroa catchment, New Zealand incorporating published trapping parameters, provide a mean exhumation rate consistent with longer term thermochronometers (apatite fission track, (U-Th)/He), and a pattern of cooling consistent with steady state erosion throughout the last glacial cycle (Herman et al., 2010).
We assess a significant body of new luminescence measurements made on samples from the Himalaya, Swiss Alps, and the Southern Alps of New Zealand. We explore the origins of the signals measured, and discuss the potential for wider application of OSL thermochronology, including current limitations and possible improvements. OSL signals in samples from Zermatt, Switzerland, tentatively attributed to feldspar based on thermal quenching characteristics, show an elevation-age relationship which suggests a strong thermochronological control; for IRSL the relationship is less convincing. The utility of signals observed in this manner is not as clear-cut as for the quartz fast component. Simple numerical simulations are used to illustrate the potential of this approach, and indicate the range of geologic problems which may be addressed.
Reference cited: Herman, F., Rhodes, E.J., Braun, J., Heiniger, L., (2010) Uniform erosion rates and relief amplitude during glacial cycles in the Southern Alps of New Zealand, as revealed from OSL-thermochronology. Earth Planet. Sci. Lett. doi:10.1016/j.epsl.2010.06.019
