Connection between deep and shallow deformation during the upper Cenozoic tectonic evolution of the Southern Central Andes: insights from kinematic models with thermomechanical constraints.

GIAMBIAGI, L. B.; MESCUA, J. F.; TASSARA, A.

Denver

Congreso; Geological Society of America 125th Anniversary Annual Meeting and Exposition; 2013

Geological Society of America

We propose a kinematic model with thermomechanical constraints for the Miocene to Present evolution of the Southern Central Andes, at the latitude of the city of Santiago. Our model assumes a main décollement located at the base of the upper crust (15-12 km in depth) which produces the underthrusting of the South American craton beneath the Andean strip. During the 18-5 Ma period, the main phase of deformation is located in the Aconcagua FTB. As the crust thickens from 40 to 50 km and the upper crust shortens 52 km, the thrust front migrates from the Principal Cordillera to the Frontal Cordillera, with a peak of deformation at ca. 12-10 Ma. After the Andean crust achieves its present thickness of 50 km beneath the western Principal Cordillera, gravitational stresses drive the lateral expansion of the crustal root westward and eastward, driving surface uplift of the Central Depression and both slopes of the Principal Cordillera by isostatic response. Afterwards, during the Pliocene, from 5 to 2.5 Ma, there was a lull in deformation both in the eastern and western slope of the Andes with a deactivation of the master décollement. Uplift at this time is concentrated in the easternmost sector of the Frontal Cordillera and the Cacheuta basin. During the Quaternary, there is a reactivation of contractional deformation in the actual thrust front and in the Frontal range close to the city of Santiago, as evidenced by seismological studies, suggesting the reactivation of the western sector of the main décollement.