Jaillard Etienne. (2025). Did the evolution from oblique to normal convergence contribute to the Andean building ?. Journal of South American Earth Sciences, 152, 105312 [14 p.]. ISSN 0895-9811.
Titre du document
Did the evolution from oblique to normal convergence contribute to the Andean building ?
Journal of South American Earth Sciences, 2025,
152, 105312 [14 p.] ISSN 0895-9811
Although submitted to subduction since at least the Triassic (approximate to 230 Ma), the Andean active margin changed in the Late Cretaceous (approximate to 80 Ma) from a mainly extension-dominated, marine area to a compressively deformed, mainly emergent zone. At the same time and until the Miocene, convergence direction of the Farallon plate evolved step after step from strongly oblique, to almost orthogonal to the Andean margin. I propose that these major changes are related to each other. Change in a subduction system from an oblique to a more normal convergence direction geometrically implies a decrease in the distance necessary to acquire the dip of the subduction zone. This triggers an increase in the deformation rate of the subducting slab, and therefore, an increase of its elastic modulus, i.e. an increase of forces resisting bending. This should trigger, either the more rapid bending of the subducting slab, or the contractional deformation and subduction erosion of the upper plate. Because the oceanic lithosphere is mechanically stronger than the continental lithosphere, the second consequence is more probable, and would cause the flattening of the subduction zone, and therefore, subduction erosion of the upper plate. Subduction erosion would explain the periodic compressional deformation and subsequent subsidence observed in the forearc zones, while flattening of the subducting slab would explain the landward migration and widening of the magmatic arc, observed on the Peruvian-Ecuadorian margin during the Late Cretaceous-Paleogene (approximate to 80, 55-60, approximate to 40 and approximate to 25 Ma). From the Neogene onwards, the direction of ocean-continent convergence did not change significantly, and contractional deformation may be interpreted as almost continuous.
