Boundary Effects of Orogenic Plateaus in the Evolution of the Stress Field: The Southern Puna Study Case (26°30′–27°30′S)

Abstract

We present a study in the southern Puna (26°30′–27°30′S), aiming to explore the late Cenozoic evolution of the deformation and the stress field during its uplift. Through U-Pb geochronology, structural observations, paleostress analysis, and balanced cross-sections, we propose an structural evolutionary model over the past 24 million years, separated in four stages: Stage 1, in the late Oligocene to middle Miocene, the region experienced E-W compression. Stage 2, from middle to late Miocene, a transition from predominant compression to an incipient strike-slip regime is observed. Stage 3, from late Miocene to early Pliocene, showed a further shift in the stress field, resulting in a combination of a predominant strike-slip regime, and less predominant compressional regime. Finally, Stage 4, from late Pliocene to Quaternary, featured a dominance of strike-slip regimes. Our results show that the stress field in each stage is associated with the orogen's internal architecture and its evolution. Vertical stress variations are linked to plateau uplift, creating topographic gradients across the orogen. Horizontal rotations of the principal stress axes are caused mainly by an edge effect resulting from the growth of the plateau while it reaches a critical crustal thickness and elevation. This leads to a transfer of compression from high-lying areas to lower regions. The southernmost Puna region shows no significant evidence of normal faulting, suggesting it is not undergoing orogenic collapse associated with a regional tensional stress regime.