Stratigraphic record of dynamic topography in the Andean foreland basin, South America

Abstract

<p>Variations in subduction configuration and mantle dynamics can be detected in retroarc foreland basins.  Modern and ancient examples from western South America show how discrete geodynamic mechanisms drive regional unconformity development in the Andean foreland basin.  Positive dynamic topography in the basin, fold-thrust belt, and broader convergent plate margin can be generated by (1) flat slab subduction, (2) slab window formation, (3) slab breakoff, (4) elevated intraplate (in-plane) stress, or (5) mantle flow variations.  A survey of long duration (>1–20 Myr) unconformities considers these and alternative mechanisms, including (6) local shortening-induced uplift in the frontal thrust belt and proximal foreland, (7) growth and advance of a broad flexural forebulge in the distal foreland, (8) uplift of intraforeland basement blocks along crustal-scale reverse faults, (9) tectonic quiescence with regional isostatic rebound, and (10) diminished accommodation or sediment supply due to changes in sea level, climate, erosion, or sediment transport.  These contrasting mechanisms can be readily observed in the modern foreland, particularly in the case of increased interplate coupling during active flat slab subduction and slab window generation associated with subduction of an active oceanic spreading ridge.  In the ancient record, the operative geodynamic mechanisms can be distinguished on the basis of the spatial distribution, stratigraphic position, paleoenvironmental context, and duration of foreland unconformities within the Cretaceous to Quaternary geodynamic framework of the Andean orogenic system.</p>