2.Distributionofdeformation-ExtraMaterials-Springer.docVIP

Deformation of the Central Andean upper plate system – facts, fiction, and constraints for plateau models Onno Oncken1, David Hindle2, Jonas Kley3, Kirsten Elger1, Pia Victor1, Kerstin Schemmann1 1 GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam 2 Ifm-GEOMAR, Wischhofstr. 1-3, 24148 Kiel 3 Friedrich-Schiller-Universit?t Jena, Institut für Geowissenschaften, Burgweg 11, 07749 Jena Abstract We quantitatively analyse the spatial pattern of deformation partitioning and of temporal accumulation of deformation in the Central Andes (15-26°S) with the aim of identifying those mechanisms responsible for initiating and controlling Cenozoic plateau evolution in this region. Our results show that the differential velocity between upper plate velocity and oceanic plate slab rollback velocity is crucial for determining the amount and rate of shortening, as well as their lateral variability at the leading edge of the upper plate. This primary control is modulated by factors affecting the strength balance between the upper plate lithosphere and the Nazca/South American plate interface. These factors particularly include a stage of reduced slab dip (33 to 20?Ma) that accelerated shortening and an earlier phase (45 to 33?Ma) of higher trenchward sediment flux that reduced coupling at the plate interface, resulting in slowed shortening and enhanced slab rollback. Because high sediment flux and transfer of convergence into upper plate shortening constitute a negative feedback, we suggest that interruption of this feedback is critical for sustaining high shortening transfer, as observed for the Andes. Although we show that climate trends have no influence on the evolution of the Central Andes, the position of this region in the global arid belt in a low erosion regime is the key that provides this interruption; it inhibits high sediment flux into the trench despite the formation of relief from ongoing shortening. Along-strike variations in Andean shortening are clearly rela