Post-tectonic uplift of the Cordillera Darwin orogenic core complex: evidence from fission track geochronology and closing temperature–time relationships

The Cordillera Darwin orogenic core complex is a structural and topographic culmination in the southern Andes, which underwent mid-Cretaceous penetrative deformation and metamorphism associated with the deformation and incipient obduction of a partly ophiolitic back-are basin (Rocas Verdes) block along its southern boundary. Whereas structural evidence suggests uplift of the Rocas Verdes terrane relative to the Cordillera Darwin during this event, metamorphic assemblages reflect a greater net uplift of the opposite sense. New fission track ages together with existing K-Ar and Rb-Sr ages were used to estimate cooling and uplift histories and their relationships to foreland sedimentation and present-day topographic relief. The results suggest that, whereas initiation of uplift in the Cordillera Darwin and Rocas Verdes blocks may have accompanied mid-Cretaceous deformation, the major, rapid uplift (around 0.5–1.5 mm/y) occurred after the deformation. Also, uplift occurred earlier in the Rocas Verdes block than in the Cordillera Darwin block, the latter having experienced a greater net uplift since the mid-Cretaceous. The major, post-tectonic uplift of the Cordillera Darwin occurred at a slower rate (0.05–0.20 mm/y) and coincides with the deposition of thick flysch and conglomerates in the foreland basin