Geometric relationships of the Abanico Basin first-order faults: an integration of balanced structural cross sections of the Chilean Principal Cordillera between 32°-36 ° S

RODRIGO QUIROGA; SEBASTIAN HERRERA; VERÓNICA MARDONES; IVAN GOMEZ

Concepción

Congreso; XV Congreso Geológico Chileno; 2018

Universidad de Concepción

Tectonostratigraphic, structural, and geochemical approaches suggest that tectonic inversion of the Abanico basin and subsequent east-vergent propagation of deformation in Principal Cordillera (PC), is the prime mechanism for Andean mountain building. This mechanism deforms late Eocene-late Oligocene Abanico Formation sequences and during compressive phase, the Miocene Farellones Formation, when major inherited extensional fault systems are reactivated. East of this late Cenozoic swath, Mesozoic rocks of the northernmost Neuquén basin, are exposed conforming the Aconcagua and Malargüe fold-and-thrust belts.Several studies focused on the structural characterization and cinematic modeling of deformation, at different latitudes, have helped to understand the possible in-depth geometry of the structures that controlled deformation during Andean orogeny. However, the geometric relationship and time-space evolution between the different structures is not fully understood, and lithostratigraphic-tectonic relationship between the Abanico Formation and Late Cretaceous rocks in the Andes of central Chile is still a matter of discussion.In this contribution, we integrate several structural cross sections of the western slope of the Southern Central Andes (32°-36°S), towards a more comprehensive understanding of the western Andean architecture. This review is intended to shed light on the structural mechanisms responsible for initial extension, subsequent inversion of the Abanico Basin and posterior eastward propagation of deformation in form of fold-and-thrust belts. The cross-sections we integrated along the PC show differences between the 32°-36°S segment, principally in-depth structure interpretation and style of surface deformation. Western segment south to 33°S, present high-angle west-vergent reverse faults that are responsible for folding with Fold wave-lenght that varies from c. 5 to c. 10 km, and are interpreted as fault-propagation and fault-bend folds associated with listric fault geometries. The eastern segment usually shows folds with vergence to the east. However, the faults that would have absorbed deformation are rooted at a detachment shallower than the ones at the western deformation front, suggesting a west-ward tilting of the main detachment. Tectonic shortening across strike varies 15% to 30%, and similar values have been estimated for the eastern and western PC. The general structural configuration that we observe for the PC is coherent with a crustal scale models including initial basin inversion, and eastward migration of deformation.