Tectonics, magmatism and paleo-fluid distribution in a strike-slip setting: Insights from the northern termination of the Liquiñe-Ofqui fault System, Chile

- We mapped and logged the architecture and paleo-fluid distribution in faults exposed at the Southern Andes Volcanic Zone.
- The orientation of principal strain and stress axes were calculated at regional and local scales.
- Stress and strain axes rotation was recorded at local scale in specific structural sites.
- Stress field orientation and strain partitioning control fluid-magma pathways at specific fault orientations.

This study addresses the interplay between strain/stress fields and paleo-fluid migration in the Southern Andean Volcanic Zone (SVZ). The SVZ coexists with the margin-parallel Liquiñe-Ofqui Fault System (LOFS) and with NW-striking Andean Transverse Faults (ATF). To tackle the role of different fault-fracture systems on deformation distribution and magma/fluid transport, we map the nature, geometry and kinematics of faults, veins and dikes at various scales.Fault-slip data analysis yields stress and strain fields from the full study area data base (regional scale) and fault zones representative of each fault system (local scale). Regional scale strain analysis shows kinematically heterogeneous faulting. Local strain analyses indicate homogeneous deformation with NE-trending shortening and NW-trending extension at NNE-striking Liquiñe-Ofqui master fault zones. Strain axes are clockwise rotated at second order fault zones, with ENE-trending shortening and NNW-trending stretching. The ATF record polyphasic deformation. Conversely, stress field analysis at regional scale indicates a strike-slip dominated transpressional regime with N64°E-trending σ1 and N30°W-trending σ3. Deformation is further partitioned within the arc through NNE-striking dextral-reverse faults, NE-striking dextral-normal faults and NW-striking sinistral-reverse faults with normal slip activation. The regional tectonic regime controls the geometry of NE-striking dikes and volcanic centers. NE-striking faults record local stress axes that are clockwise rotated with respect to the regional stress field. NNE- and NE-striking faults are favorably oriented for reactivation under the regional stress field and show poorly-developed damage zones. Conversely, NW-striking fault systems, misoriented under the regional stress field, show multiple fault cores, wider damage zones and dense vein networks.Deformation driven by oblique subduction is partially partitioned into strike-slip and shortening components. The trench-parallel component is mostly accommodated by NS-striking right-lateral faults of the LOFS. Trench-perpendicular shortening is accommodated by sinistral-reverse ATF and dextral-reverse NNE-striking faults. We conclude that the SVZ records a deformation history coeval with magma/fluid migration.