Local Stress fields and paleo-fluid distribution within a transtensional duplex: An example from the northern termination of the Liquiñe-Ofqui Fault System.

Abstract:

The northern termination of Liquiñe-Ofqui Fault System (LOFS) is characterized by major NNE-striking dextral strike-slip faults and several second and third-order NE-to-ENE-striking oblique-slip faults. This geometry forms a transtensional duplex structure. The LOFS has a complex crosscutting relationship with inherited NW-striking structures of the Arc-oblique long-lived Fault System (ALFS). We conducted a structural mapping of fault and vein populations at key structural sites representative of each regional structural system. Field observations were combined with different methods of inversion of fault-slip heterogeneous data and with the use of different open-source computer programs that calculate resolved stress tensors and P-T axes for each structural site in order to unravel the significance of this complex architecture. The results of the inversion of fault-slip analysis show that a transtensional strike-slip regime, with NE-SW-trending subhorizontal σ₁, predominate in the first and second order faults in the northern termination of the duplex. A more local tensional regime was calculated for the same area. The inversion solutions are compatible with NE-trending subvertical veins system and dilational jogs and breccia. In contrast, within the central area of the duplex fault slip inversion of fault populations shows both transpressional and compressional regimes. The first tectonic regime is compatible with ENE-striking veins and dikes. In the southern part of the duplex, fault populations are compatible with either a local transtensional stress field with an ESE-trending subhorizontal σ₁ or with a tensional regime with a SW-trending, steeply plunging σ₁. Our results show the complexity in the nature and spatial distribution of stress fields within strike-slip duplexes and its role in the geometrical distribution of paleo-fluid flow, part of which may account for the reactivation of inherited faults or strain incompatibilities at fault intersections.