Deformation partitioning and insights on crustal fluid migration from models of fault intersections in the compressional margin of the Southern Volcanic Zone, Chile

Fault zones exert first-order control on crustal fluid migration, and fault intersections further enhance permeability both "structurally," via damage, and "geometrically," by partitioning crustal deformation. This study examines how fault intersections affect strain localization and stress regimes during far-field tectonic transpression through two case studies in the Southern Volcanic Zone, Chile (SVZ). Three-dimensional, temperature-dependent, visco-elasto-plastic models simulate the mechanical response of an upper crust segment containing intersecting, pre-existing, weak fault zones set immediatetly above hot, reactive and partially molten domains.

Geometry Type I consists of a margin-parallel vertical fault intersected by a high-angle transverse fault (ATF), while Type II includes two orthogonal, margin-oblique vertical faults; these are inspired by the Puyehue-Cordón Caulle and Nevados de Chillán volcanic complexes (33°S–46°S), respectively. Model results reveal deformation partitioning: NW-striking faults preferentially localize shear strain, whereas NE-trending faults concentrate volumetric strain. In both geometries, fault intersections display local transitions from compressional to strike-slip or transtensional stress regimes within a roughly 2 km radius and down to depths of approximately 2 km. Type I intersections produce nearly twice the dilation of Type II, emphasizing how intersection orientations influence long-term rock damage.

These modeled stress and strain patterns offer a mechanical framework for understanding the spatial distribution of volcanic and hydrothermal features, including the location of the Puyehue stratovolcano and the contrasting alignments of dikes and monogenetic cones at Nevados de Chillán. Further tests incorporating (i) plastic dilatancy and (ii) poro-elasticity illustrate their importance in controlling fluid flow toward the surface. These results provide foundation for future, more evolved self-consistent and coupled fluid-solid rheologies to help understand: (i) why upward magmatic and geothermal fluid migration in the upper crust may not be vertical under transpressional conditions, particularly near fault intersections, and (ii) the link between deformation and geoflluids flow over timescales intermediate between volcanic and geological scales.