Long-term landscape evolution and denudation rates in shield and platform areas: a morphostratigraphic approach
Résumé
In shield and platform areas, various methods are expected to give indications on surface ages, e.g. dating of weathering mantles or reconstruction of the thermal history of upper crust rocks which presently crop out. Radiochronometry and thermochronology were widely used in the last decades to give estimated denudation depths and rates in active orogens as well as in shield and platform areas. Although usefully integrated in the modern geomorphology, these methods sometimes reveal discrepancies with the results of field-based geomorphology. The principles of morphostratigraphy are first presented, and then the paper presents a review of some French researches, which were recently carried out in Québec, north-eastern Brazil and southern Africa. We explain why possible discrepancies occur between the results of physical analyses and morphostratigraphic methods. Finally the paper highlights how significant is to relate the thermal history of each sample to the local geological and geomorphic history.