The juxtaposition of thick-skinned structures and their role on the present-day configuration of the Frontal Cordillera of northern Chile

Abstract

The Frontal Cordillera of northern Chile is a natural laboratory for studying thick-skinned tectonics related to Andean orogenesis. This region preserves a series of structural and stratigraphic elements associated with Triassic and Jurassic rifting and extension, which preceded Andean mountain building, as well as various structural styles associated with tectonic inversion and reverse faulting. In this contribution, we analyzed the Tatul and La Totora basins to reveal the juxtaposition of different thick-skinned structures exposed in the region and thus understand their impact on the configuration of the Frontal Cordillera, a significant thick-skinned fold-and-thrust belt established on the western slope of the Central Andes. This study was supported on multiscale field data, geological maps, and structural cross-sections. We documented three structural styles: (a) inherited and non-inverted Triassic to Jurassic normal faults, (b) partially inverted Triassic to Jurassic normal faults, and (c) large thick-skinned reverse faults. The presence of inversion structures supports the idea that Mesozoic extensional structural and stratigraphic frameworks played a critical role during Andean contraction. Many of these structures accommodated crustal shortening, enabling the upward expulsion of Triassic and Jurassic syn-rift strata from depocenters. The presence of normal and inversion structures in the hanging walls of large reverse faults is key to interpreting the complex 3D structure of the Frontal Cordillera, where structures with varying geometries and kinematics are juxtaposed. This configuration suggests that reverse faults cut through and passively translated the pre-existing normal and inverted faults, creating a complex structural setting. This interpretation challenges the previous paradigm that thick-skinned reverse faults cut through undeformed crust, highlighting the importance of understanding structural inheritance from pre-Andean tectonic extension.