Temporal variation of the stress field during the construction of the central Andes: Constrains from the volcanic arc region (22-26°S), Western Cordillera, Chile, during the last 20 Ma

Abstract

In order to understand the response of the stress field state to intrinsic processes during the construction of the Andes, such as thickening of the continental crust, lithospheric delamination, and/or thermal weakening, we investigate the stress field evolution of the arc region since the last 20 Myr, in the central Andes (22–26.5°S). The 43 reduced paleostress tensors derived from inversion of 682 fault slip data reveal a complex pattern of stress states during the last episode of orogenic construction and topographic uplift. We identify two geodynamic stages: the first stage corresponds to the construction of the Altiplano/Puna plateau and the second one to its gravitational collapse. Four stress states that have prevailed in the Altiplano/Puna plateau since middle Miocene times characterize the transition from one stage to the other. Along the study latitudes, a spatiotemporal change in stress state is clearly observed, which led to an understanding that a change in the stress field may be related not only to the boundary conditions but also to intrinsic factors associated with the construction of the Andean orogeny. Our results suggest that approximately at 13–10 Ma and approximately 8–5 Ma, in the southern Altiplano and northern Puna, and in the southern Puna, respectively, regional elevation and crustal thicknesses reached threshold values necessary to generate the orogenic collapse.

Cenozoic Shift From Compression to Strike‐Slip Stress Regime in the High Andes at 30°S, During the Shallowing of the Slab: Implications for the El Indio/Tambo Mineral District

“…The simultaneity between the transitional stress period and the flattening of the subducted plate at these latitudes (14-10 Ma, Yáñez et al, 2001;Kay & Mpodozis, 2002), argues against the first mechanism. The gradual increase in crustal thickness and, as a result, in the relative magnitude of the vertical stress component, predicts a main phase of compression, followed by a strike-slip phase, as has been suggested for the Altiplano/Puna region (Giambiagi et al, 2016). An initial compressional regime prevailed in the whole study area, during the construction of the inner sector of the orogen.…”

“…During the past 30 years, studies carried out in areas located above 4,000 m of the central Andes of Chile and Argentina, between 18° and 28°S latitudes, show Quaternary extensional to strike‐slip stress regimes (Allmendinger et al, ; Giambiagi et al, ; Riller et al, ; Schoenbohm & Strecker, ). South of these latitudes (28°–32°S), where the slab has been subducting subhorizontally (Cahill & Isacks, ) since the middle Miocene (Kay et al, ), the stress regime has been inferred to be dominantly compressional across the Argentine fold‐and‐thrust belts located in the high Andes (Allmendinger et al, ; Cristallini & Ramos, ; Ramos, ; Ramos et al, ) and in the magmatic arc of central Chile (Kurtz et al, ; Yáñez et al, ).…”

Crustal anisotropy and state of stress at Uturuncu Volcano, Bolivia, from shear-wave splitting measurements and magnitude–frequency distributions in seismicity

“…The upper crustal stress state beneath this volcano is expected to reflect an interaction between the arc-scale E-W SHmax controlled by plate convergence, NE-SW anisotropy revealed by previous studies, regional stresses parallel to NW-SE faults in the area, and local perturbations by magmatism associated with the APMB. We note here that sub-parallel NW-striking faults in the Central Andes have been attributed with both left-lateral strike slip and extensional displacement (Riller et al, 2001;Giambiagi et al, 2016)…”

“…Uturuncu and a NE-SW striking fault to the northeast. The near-orthogonal orientations of these faults reflects their formation during different time periods when variations in plate convergence rate, subduction angle and crustal thickness caused permutations in the stress regime of the Central Andes (Giambiagi et al, 2016). Today these faults accommodate both E-W compression associated with plate convergence and N-S extension (SHmin) associated with gravitational spreading of the overthickened plateau, resulting in both extensional and strike-slip displacements (Giambiagi et al, 2016).…”

“…These coincidences suggest that local stresses are in part controlled by a pre-existing fault running through the volcano. This fault may have previously accommodated transtension as left-lateral strike-slip displacement associated with E-W compression and N-S gravitational spreading of the high Andes(Giambiagi et al, 2016), however, moment tensors of earthquakes beneath Uturuncu reveal positively isotropic and tensional crack opening source mechanisms(Alvizuri and Tape, 2016). The agreement of location between these moment tensors and the dominant NW-SE ϕ is interpreted as the result of outward volume expansion along a pre-existing fault caused by pressurization from magmatic inflation above the APMB.…”