On Some Geometric Prism Asymmetries BT - Thrust Belts and Foreland Basins

Abstract

The asymmetry between orogens or accretionary wedges related to geographically opposed subduction zones is marked by volumes of the orogens above sea-level that are about 6–8 times smaller for those belts associated to W-directed subduction zones with respect to the orogens related to E- or NE-directed slabs. The mean slope of wedge topographic surfaces is about 1.9° for W-directed subduction and 4.8° for E-NE-directed subduction respectively. The regional foreland monocline may be >5° along W-directed subduction zones where the fast subsiding and deepest trenches and foredeeps form. Opposingly, along E-NE-directed subduction zones the regional foreland monocline is on average <3°, foredeeps and foreland basins are shallower and slower subsiding. This generates the paradox that smaller accretionary prisms may rather be associated to very deep trenches, and highly elevated orogens may have small foredeep/foreland basins.