DERAILING A CORDILLERAN SYSTEM IN THE SOUTHERN PERUVIAN ANDES

The archetypal Cordilleran system makes specific predictions about the linkages between plate margin dynamics, upper plate deformation, and foreland basin development. The central Andes are the classic modern analog of a Cordilleran system, but key aspects of the timing, controls, and style of paired deformation and deposition remain unclear. This work presents a synthesis of existing and new results constraining sediment dispersal patterns and the timing and position of deformation spanning development of the Andes in southern Peru. Results show that Cordilleran sediment routing patterns initiated in the late Cretaceous, but the location of early deformation was atypical for Cordilleran fold-thrust belts and likely reactivated an inboard inherited rift basin. As orogenesis progressed, an Eocene to Oligocene phase of shallow slab subduction further shifted this segment of the margin away from classic Cordilleran arrangement. The emerging pattern of deformation shows protracted dispersed deformation, rather than dominantly in-sequence fold-thrust belt advance. This deformation style likely contributed to the apparently partitioned and spatially heterogeneous basin evolution that resulted in multiple stratigraphic sections that lack some of the hallmarks of foreland basin systems. Early in the history of this portion of the Andean margin, the combined influence of the inherited crustal architecture and changes to the subduction zone geometry derailed the development of the classic Cordilleran system.