The kinematic and geodynamic significance of the Atacama fault zone, northern Chile

Abstract

The Atacama fault zone (AFZ) is the dominant feature in the structure of the North Chilean Coastal Cordillera. Left lateral displacement took place along its system of longitudinal faults during the Jurassic and early Cretaceous. This development was contemporaneous with arc magmatism and was later reactivated, resulting in a steep normal fault. Strike-slip movements along the AFZ consist of two sets of ductile shear zones of different ages: one Jurassic, formed under amphibolite-facies conditions; the other early Cretaceous, with greenschist-facies mylonites. Structural asymmetries point to a sinistral sense of shear in both sets. The AFZ can be interpreted as a magmatic arc structure which accommodated the oblique subduction of an oceanic plate (trench-linked strike-slip fault). The sinistral sense of shear is consistent with reconstructions of late Jurassic to early Cretaceous plate configurations in the SE Pacific.