Contemporary stress orientations from borehole breakout analysis in the southernmost flat-slab boundary Andean retroarc

摘要

Horizontal stress directions have been determined in the southernmost flat-slab boundary Andean retroarc between 32°44' and 33°40'S within Cuyo Basin, Argentina. These directions were obtained from the borehole breakout analysis of 42 wells using four-arm caliper data. The mean maximum horizontal stress (SHmax) direction for the whole region is 104.1° with a 95% confidence interval of 8.1°. The present-day stress field has an approximately preferred E-W trend maximum horizontal stress direction, consistent with the plate boundary forces (80°) and the topographic forces (near E-W). The calculated SHmax directions are near the expected values, but some local deviations were observed. The SHmax rotates from an E-W orientation in the south to a NW-SE orientation to the north of this sector of the Andean retroarc. A regional variation in the stress field can be observed when these results for the Cuyo Basin are analyzed together with those presented in a previous study in the Neuquen Basin to the south The maximum horizontal stress varies from ~NW-NE along this combined section of the Andean retroarc, with the ~E-W SHmax directions in the northern Neuquen Basin consistent with those observed in the southern sector of Cuyo Basin. These variations in the stress field orientation appear related with the topography geometry. From the analysis between the mean SHmax obtained and the acting forces, it can be concluded that the topographic control on the horizontal stress field seems to be dominant in the Cuyo Basin and in the north of Neuquen Basin. To the south of Neuquen Basin the horizontal stress field should be mainly controlled by the plate boundary forces.