Regional exhumation and kinematic history of the central Andes in response to cyclical orogenic processes

Low-temperature thermochronological ages of samples from the central Andes correlate with major tectonic events during Late Cretaceous and Cenozoic times. Apatite fission-track (AFT) ages show prominent clusters during the Early-Late Cretaceous in the Coastal Cordillera and the Cordillera de Domeyko; Paleocene- Oligocene ages in the western Puna Plateau and Cordillera de Domeyko; and latest Eocene- Pliocene ages in the Eastern Cordillera. These ages track the expansion of the Andean orogenic edifice, the eastern front of which migrated rapidly eastward ∼200 km and ∼150 km during late Eocene and Pliocene times, respectively. During the intervening time interval, ca. 35-5 Ma, the orogenic strain front migrated slowly eastward through the Eastern Cordillera. A second cluster of Cretaceous ages in the Eastern Cordillera and Santa Bárbara Ranges documents exhumation related to extension in the Salta rift. The highly unsteady pace of orogenic wedge propagation suggests that kinematics controlled local climate, rather than vice versa. The frequency of AFT ages is anticorrelated with magmatic production in the central Andean arc and the rate of convergence between the Nazca and South American plates. We propose a link between AFT bedrock cooling ages in the central Andes and exhumation related to cyclical processes of shortening, wedge propagation, magmatism, and removal of dense roots from beneath the magmatic arc and thickened hinterland region. In particular, periods of sustained exhumation associated with local crustal shortening alternate with periods of rapid eastward wedge propagation during which exhumation was more spatially diffuse across the high-elevation hinterland. Episodes of spatially confined exhumation are correlated with periods of relatively low magmatic production in the central Andean arc and relatively slow or declining plate convergence rates. We speculate that shortening in the upper crust was contemporaneous with underthrusting of lower crust and mantle lithosphere beneath the magmatic arc. Because of thermal inertia, melting of these underthrusted rocks lagged behind the shortening events themselves, thus producing the observed temporal anticorrelation between rapid shortening-induced exhumation and arc magmatism.