Timing, Kinematics, and Displacement of the Taltal Fault System, Northern Chile: Implications for the Cretaceous Tectonic Evolution of the Andean Margin

Abstract

An extensive system of NW striking faults constitutes a major tectonic feature of the Coastal Cordillera in northern Chile, but fundamental questions remain about timing and kinematics of these structures. We present new geologic mapping and geochronology that provide insight into the structural evolution and tectonic significance of the Taltal fault system (TFS). The TFS displaces the Early Cretaceous arc-parallel Atacama fault system (AFS) with~10.6 km cumulative offset across a~15 km wide zone. Brittle fault data demonstrate that the TFS is vertical to steeply NE dipping with an average sinistral slip vector plunging 11°from the NW, compatible with E-W shortening. Two late Early Cretaceous dikes cut the AFS but are cut by TFS faults, and synkinematic calcite on a TFS strand yielded a U-Pb calcite date of 114.1 ± 7.0 Ma. These data demonstrate that the AFS was abandoned and deformation (re) initiated on the TFS between~114-107 Ma, with continued slip after intrusion of the Tropezón (~110 Ma) and Librillo (106-101 Ma) plutonic complexes. Emplacement of a~146 Ma rhyolite dike along the main Taltal fault and 141 ± 11 Ma calcite mineralization in the fault core suggests that a precursor structure influenced magma emplacement and fluid flow in the Late Jurassic/Early Cretaceous, supporting the hypothesis that the TFS reactivated long-lived inherited crustal weaknesses. The Early Cretaceous shift from arc-parallel shear to slip on the TFS and E-W shortening shortly preceded migration of the magmatic arc and records a change in the Chilean margin subduction dynamics.

The Relationship Between Magmatism and Deformation Along the Intra‐arc Strike‐Slip Atacama Fault System, Northern Chile

“…As such, we report the weighted mean average of the youngest three concordant grains: 109.9 ± 4.0 Ma (Figure ). Both the dike and the AFS are cut by NW striking sinistral faults parallel to the younger Taltal fault system (see also Mavor et al, ).…”

“…The dike is sinistrally offset ~148 m by the westernmost strand, suggesting intrusion during the end stages of brittle deformation. The dike and the AFS are cut and displaced sinistrally by a NW‐SE striking fault parallel to the Taltal fault that displaces the AFS further north (see also Mavor et al, ). Location of the zircon U‐Pb sample (161‐43) is shown by the yellow star.…”

“…Published 113‐ to 100‐Ma apatite fission track dates (Gana & Zentilli, ; Maksaev, ) and our ~116‐ to 96‐Ma ZHe dates (Figure ) postdate the crystallization age of the youngest intrusion at all sites and indicate cooling of the arc was coeval with the end of slip along the AFS (e.g., Brown et al, ). In addition, the cessation of slip along the AFS broadly corresponds with a shift to transpressive crustal shortening recorded by a regional unconformity (Scheuber et al, ), the transition to slip along NW striking fault systems such as the Taltal fault (Arabasz, , ; Mavor et al, ), and westward acceleration of the South American plate due to the final breakup of South American and Africa during the opening of the South Atlantic (Granot & Dyment, ; Maloney et al, ; Seton et al, ). Together, this suggests that the end of slip along the AFS may be related to changing plate motion that resulted in a shift from SE directed to NE directed convergence (e.g., Maloney et al, ; Seton et al, ), uplift and erosion of the continental margin, eastern migration of the magmatic arc, and development of both a wide forearc and continental foreland basin (Coira et al, ).…”

“…Motion along the AFS was dominantly sinistral strike slip with variable components of extension or shortening (Grocott & Taylor, ; Ruthven et al, ; Scheuber & Andriessen, ; Veloso et al, ). The NW striking Taltal fault system cuts the AFS (Arabasz, ; Mavor et al, ).…”

Structural Characterization of the Taltal Segment in Northern Chile Between 22°S and 26°S Using Local Earthquake Tomography

“…Several recent investigations have focused on understanding the type and mechanisms of the seismicity in northern Chile. For example, Mavor et al (2020) described the kinematics and tectonic evolution of the Taltal Fault, Sippl et al (2023) used a 15-year seismic catalog to summarize the activity in northern Chile, and González-Vidal et al (2023) deployed a temporary network to explore the relations between heterogeneity in the subducting plate and the degree of interplate locking. In terms of seismic imaging of this zone, Husen et al (2000), together with Haberland and Rietbrock (2001), set foundations for tomographic analysis by deriving seismic velocity and attenuation models, respectively.…”