Glaciers and rivers control the shape of the high relief topography of
mountain ranges. However, their relative contribution in response to
climatic oscillations and tectonic forcing and whether landscapes can
reach equilibrium conditions during the Quaternary are still unclear.
Here we introduce a new thermochronometer of exceptionally low closure
temperature (ca. 30-35 degrees C) based on Optically Stimulated
Luminescence (OSL) dating and illustrate how it may be used to measure
relief evolution and exhumation rates within the last glacial cycle in
the Southern Alps of New Zealand, one of the most tectonically active
orogens and an area that has experienced rapid, high magnitude climate
changes. We find that exhumation rates have remained steady over the
last glacial cycle and match rates observed at a million year timescale.
This suggests that, despite an extreme exhumation rate of the order of
800 m in 100 ka, and the fact that in the last ca. 11-18 ka most
hillslope sides have changed from U to V-shape valleys and have been
dissected by debris-flows, landslides and rock avalanches, the mean
exhumation rates have remained nearly constant. This may imply that
tectonics, not climate, has a primary control on the rates of exhumation
in tectonically active and wet mountain belts. On the contrary,
tectonically active mountain ranges might not attain equilibrium on
similar timescales in weathering and/or transport limited landscapes as,
for example, in arid regions. (C) 2010 Elsevier B.V. All rights
reserved.