How deformation shapes the Salar de Antofalla, southern Puna: Insights from a 4D kinematic-dynamic model

Abstract

The southern Puna, characterized by salt flats, known as salars, offers key insights into how deformation during changing tectonic stress regimes influences sedimentation and basin floor subsidence in subduction-related orogens. This study focuses on the Salar de Antofalla, one of the most elongated salt flat basins in the Puna. Through structural mapping and paleostress reconstruction, we investigate the regional stress field evolution during orogeny and salar basin formation, and propose a 4D kinematic-dynamic model for the formation of the Salar de Antofalla and Salar del Fraile. Results reveal that between ∼20 and ∼ 14 Ma, the region was under a reverse faulting stress regime, followed by a transition to a strike-slip/reverse faulting regime, and eventually to a pure strike-slip faulting regime after 9 Ma. The transition from 14 to 9 Ma was marked by the activation of dextral NW-striking fault systems like the Archibarca fault, which exhibited high dilation and were linked to contemporaneous volcanic activity. From 9 to 4 Ma, the pure strike-slip faulting stress regime, characterized by E-W σ₁ and N-S σ₃, promoted the development of NE-striking dextral faults and the reactivation of sinistral NW-striking faults. This led to the formation of small salt flat basins, such as Salar del Fraile and Lower Juncalito, up to 4 Ma. After 4 Ma, a shift in σ₁ orientation toward SW-NE facilitated the formation of the NNE-striking Salar de Antofalla fault system. The connection of dextral faults of this system played a key role in the salar's formation, with dextral movement and local transtension driving subsidence. This study suggests that the Salar de Antofalla's formation resulted from dextral fault interactions and transtensional activity rather than solely compressional or extensional forces.