HR: 0830h
AN: H51D-1091    [PDF]
TI: Constraining the Erosion History of Ancient Mountain Belts by Thermochronology: the Effect of Flexural Isostasy
AU: Robert, X
EM: xrobert@ens-lyon.fr
AF: Ecole Normale Superieure de Lyon, Laboratoire de Sciences de la Terre, 46 Allee d'Italie, Lyon, 69364 France
AU: * Braun, J
EM: Jean.Braun@anu.edu.au
AF: Australian National University, Research School of Earth Sciences, Canberra, ACT 0200 Australia
AB: Much work has recently been done to understand the coupling between tectonic and erosion. Regions characterized by a finite amplitude relief are subject to erosion, leading to rock exhumation and cooling. We can therefore obtain information about rock exhumation and the evolution of the relief from thermochronological data, especially when considering the relationship between age and elevation at a range of lengthscales. In post-orogenic settings, exhumation is driven by the isostatic response to erosion. Using a coupled thermo-isostatic model, we demonstrate that the distribution of cooling ages at the surface of an ancient mountain belt is not only determined by the rate at which the ancient topography has evolved through time but also by the nature of the isostatic rebound which is, in turn, controlled by the flexural strength of the underlying lithosphere. Using published low-temperature thermochronological data from the Dabie Shan in eastern China, we demonstrate that a careful quantitative analysis of the age distribution and its relationship to present-day surface topography provide information on the rate at which the surface topography of the mountain belt has evolved through time to reach its present-day morphology but also on the elastic thickness of the underlying lithosphere. The data suggest that, over the last 60 to 70 Myr, relief has decreased almost linearly by a factor of 4 to 5 and that the lithosphere is characterized by an effective elastic thickness of 20 km. The data also provide constraints on the thermal structure of the crust beneath the Dabie Shan.
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting