The effects of positive tectonic inversion structures on the formation of thrust systems on the western Domeyko Cordillera, northern Chile: Implications for the orogenic development of the outer Andean forearc

Abstract

This work aims to propose a novel structural setting for the outer Andean forearc. Specifically, we propose a new deformation mechanism related to thrusting belt systems induced by positive tectonic inversion processes in the western flank of the Domeyko Cordillera in northern Chile. Thrust belt systems have been rarely understood for the outer Andean forearc; in fact, the mention of thrusting is scarce and structural interpretations are restricted only to strike-slip faulting and positive tectonic inversion processes. In this study, we have constructed novel balanced cross-sections from new structural fieldwork and combined them with 2-D reflection seismic line re-interpretations, thus offering new ideas about the evolution and development of the forearc of the Central Andes. Based on this, we propose integrated kinematic models that describe the relationships between inherited extensional structures, positive tectonic inversion structures, and the formation of thrust systems. The proposed balanced cross-sections have been restored to a pre-shortening condition. In this way, two structural styles are proposed for the western flank of the Domeyko Cordillera. The first corresponds to west-directed positive tectonic inversion structures, which expose and extrude the Middle Jurassic syn-rift deposit of the ancient Mesozoic rift basin. The second consists of east-directed thin-skinned thrust systems, mainly affecting the Upper Cretaceous to Eocene volcano-sedimentary synorogenic sequences. The interaction between inversion structures and thrust system structural styles would generate a west-directed intracutaneous wedge. Finally, the minimum shortening obtained from our balanced cross-section restorations is ca. 11% for the Río Loa and the San Salvador Canyons segment and ca. 56% for the Quebrada Mala segment. The formation of thrusting structures is controlled by a major detachment fault activated from a regional-scale angular unconformity, which we have named the Quebrada Mala detachment fault. An important part of the shortening was taken up and accommodated by buttressing structures and their associated intraformational detachment-thrust levels.