From orthogonal shortening to transpression: The >20 Myr polyphase structural and thermal evolution of the Carboneras fault in the Betics, SE Spain

The architecture of mature faults commonly reflects long-lasting, cumulative tectonic histories marked by multiple episodes of deformation localization, fluid inflow, and variable slip behaviors. Hence, reconstructing fault tectonic histories and associated seismotectonic patterns requires the integration of (micro)structural, geochemical, thermal, petrophysical, and mechanical data throughout the fault’s lifespan. Using a multitechnique approach, we investigate the Carboneras fault (CF), a NE-SW–striking, ~140-km-long active strike-slip fault in the Betics of SE Spain that has accommodated up to ~40 km of displacement since the Miocene. To unravel the spatio-temporal-thermal evolution of the CF, we combine multiscale structural analysis, X-ray diffraction, and illite K-Ar geochronology of six fault gouge samples with previously published data. Our results reveal a >20 Myr-long polyphase thermotectonic evolution including (1) late Oligocene N-S orthogonal shortening leading to nappe stacking and E-W fabrics, (2) Middle–Late Miocene sinistral transpression along a NE-SW shear corridor with selective reactivation of earlier E-W fabrics, and (3) Early Pliocene–Middle Pleistocene reactivation of the inherited fabrics. Faulting occurred under progressively cooler conditions (from >275 °C to ~70 °C) and at progressively shallower structural levels during the evolution of the eastern Betic orogen of SE Spain. Although the CF is widely regarded as an archetypal strike-slip fault, our results reveal a significantly more complex structural evolution, resulting in the superposition of multiple deformation phases with distinct kinematics and deformation styles. These findings provide valuable insights into the growth and exhumation of crustal-scale faults recording complex thermotectonic histories and contribute to a better understanding of their seismotectonic behavior.