How and to what extent does the emergence of orogens above sea level influence their tectonic development?


Guy D. H. Simpson, Geological Institute, Haldenbachstrasse 44, ETH Zentrum, 8092 Zurich, Switzerland. Tel.: +41 1 632 3648; fax: +41 1 632 1422; e-mail:


Geodynamic modelling indicates that the emergence of initially submarine convergent orogens above sea level can have a significant influence on their subsequent tectonic development. This is because of two effects. First, surface uplift under submarine conditions, and the resulting decrease in gravitational loads, tends to reactivate deformation in the uplifting part of the submerged orogen. Second, an increase in the rate of erosion associated with the emergence of land can cause increased exhumation rates, reduced thrust-front advance rates, narrowing of the orogen width, and a shift from slow deposition in piggyback basins to rapid deposition in the foredeep. These effects result from the ability of erosion to perturb mass balance at the orogen-scale. Based on these results, I hypothesize that the emergence of initially submerged orogens such as the Alps and Taiwan played a direct role in explaining major changes in orogen dynamics and basin evolution that are known to occur in these examples.