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Timing, Kinematics, and Displacement of the Taltal Fault System, Northern

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Timing, Kinematics, and Displacement of the Taltal Fault System, Northern RESEARCH ARTICLE Timing, Kinematics, and Displacement of the Taltal Fault 10.1029/2019TC005832 System, Northern Chile: Implications for the Cretaceous Key Points: • The Taltal fault system became Tectonic Evolution of the Andean Margin active between 114 and 107 Ma, S. P. Mavor1 , J. S. Singleton1, R. Gomila2 , G. Heuser2, N. M. Seymour1 , S. A. Williams1, shortly after the end of brittle 2 3 4 5 deformation on the Atacama fault G. Arancibia , S. M. Johnston , A. R. C. Kylander‐Clark , and D. F. Stockli system 1 2 • Older dates of structurally controlled Department of Geosciences, Colorado State University, Fort Collins, CO, USA, Departamento de Ingeniería Estructural intrusions and veining suggest that y Geotécnica, Pontificia Universidad Católica de Chile, Santiago, Chile, 3Physics Department, California Polytechnic State the Taltal fault system reactivated University, San Luis Obispo, CA, USA, 4Department of Earth Science, University of California, Santa Barbara, CA, USA, precursor structures 5Department of Geological Sciences, The University of Texas at Austin, Austin, TX, USA • The Taltal fault system records a shift from arc‐parallel shear to E‐W shortening and likely a change in early‐Andean subduction dynamics 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 Supporting Information: structures. We present new geologic mapping and geochronology that provide insight into the structural • Supporting Information S1 evolution and tectonic significance of the Taltal fault system (TFS). The TFS displaces the Early Cretaceous • Table S1 • Table S2 arc‐parallel Atacama fault system (AFS) with ~10.6 km cumulative offset across a ~15 km wide zone. • Table S3 Brittle fault data demonstrate that the TFS is vertical to steeply NE dipping with an average sinistral slip • Table S4 vector plunging 11° from the NW, compatible with E‐W shortening. Two late Early Cretaceous dikes cut • Figure S1 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 Correspondence to: the TFS between ~114–107 Ma, with continued slip after intrusion of the Tropezón (~110 Ma) and Librillo S. P. Mavor, (106–101 Ma) plutonic complexes. Emplacement of a ~146 Ma rhyolite dike along the main Taltal fault [email protected] 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 Citation: the TFS reactivated long‐lived inherited crustal weaknesses. The Early Cretaceous shift from arc‐parallel Mavor, S. P., Singleton, J. S., Gomila, R., shear to slip on the TFS and E‐W shortening shortly preceded migration of the magmatic arc and records a Heuser, G., Seymour, N. M., Williams, S. A., et al. (2020). Timing, kinematics, change in the Chilean margin subduction dynamics. and displacement of the Taltal fault system, northern Chile: Implications for the Cretaceous tectonic evolution of the Andean margin. Tectonics, 39, 1. Introduction e2019TC005832. https://doi.org/ 10.1029/2019TC005832 Tectonic activity in northern Chile has been dominated by subduction and arc magmatism since at least the Early Jurassic (e.g., Coira et al., 1982; Parada et al., 2007). In the Coastal Cordillera, plutons and volcanic Received 20 AUG 2019 deposits of the Jurassic to Early Cretaceous arc are dissected by an extensive system of NW striking sinistral Accepted 19 JAN 2020 faults from 25.4° to 27.2°S (Figure 1). Timing constraints suggest that some of these faults were active only in Accepted article online 30 JAN 2020 the Jurassic (Bonson, 1998; Contreras et al., 2013), whereas others clearly displace Early Cretaceous units. The largest magnitude sinistral displacement on an individual NW striking fault (7.5 km) occurs at the Taltal fault (Figures 1 and 2). The Taltal fault and nearby parallel faults (herein referred to as the Taltal fault system, TFS) displace the Atacama fault system (AFS), a major tectonic feature that traces more than 1,000 km north‐south in the Coastal Cordillera and accommodated brittle‐ductile sinistral shear in response to oblique convergence in the Early Cretaceous (Scheuber & Andriessen, 1990). The shift from slip on the AFS to TFS marks a notable change in deformation geometry and style near the active margin. While AFS deformation timing is well documented, the timing of slip on the TFS is largely unconstrained beyond its relative timing with the AFS. Evidence that AFS brittle deformation continued as late as ~110 Ma (Seymour et al., 2020) suggests that the most recently published 125–110 Ma age estimates for the younger Taltal fault (Espinoza et al., 2014) require revision. The paleomagnetic studies suggest that NW striking faults in the Coastal Cordillera accommodated vertical‐ axis clockwise block rotation that cannot be fully explained by the development of the Bolivian orocline (Randall et al., 1996) and reveal that the Taltal fault is an important structural boundary that separates ©2020. American Geophysical Union. domains with a marked difference in tectonic rotations (Contreras, 2018). One kinematic model for clock- All Rights Reserved. wise rotation links NW striking faults to the transpressional Chivato fault system to form a crustal MAVOR ET AL. 1of24 Tectonics 10.1029/2019TC005832 sinistral strike‐slip duplex in the Late Cretaceous after AFS abandonment (e.g., Grocott & Taylor, 2002; Randall et al., 1996; Taylor et al., 1998). According to this model, oblique convergence was largely partitioned between margin‐parallel sinistral shear east of the AFS and margin‐ orthogonal shortening along NW striking faults in the Coastal Cordillera. Another tectonic model relies on kilometer‐scale displacement of the Taltal fault during dextral transpression and rotation of large‐scale domino blocks in the middle‐late Eocene (Abels & Bischoff, 1999), yet it is unclear if the fault was active at that time. Regionally, some NW striking faults are interpreted that wholly predate the AFS, whereas others postdate or evolved contemporaneously with the AFS (Bonson, 1998). Mapped relationships in the Jurassic La Negra Formation suggest that slip on NW striking sinistral faults near Cifuncho ceased in the Late Jurassic (Contreras et al., 2013). NW striking faults near Antofagasta are well documented as secondary faults that splay from and developed contemporaneously with AFS fault strands in a transtensional duplex arrangement (Cembrano et al., 2005; Jensen et al., 2011; Veloso et al., 2015). Northwest striking faults in the Precordillera have well‐documented sinistral offset in the Eocene; how- ever, an along‐strike connection of these faults to the Taltal fault has been hypothesized but not demonstrated (Abels & Bischoff, 1999). While some TFS slip clearly postdates the AFS, the origin of the TFS and genetic rela- tionship to parallel Jurassic faults are unclear. In addition, detailed kine- matic data from the TFS and related NW striking faults in the Coastal Cordillera have not been published, so it is unclear to what extent this fault system records transpression or transtension. Here we present new geologic mapping and geochronology of units with prekinematic and syn- kinematic relationships to the TFS that constrain the slip history of the fault system, and we present brittle fault data that record the changing kinematic regime of the Cretaceous Chilean Coastal Cordillera. 2. Geologic Setting The oldest rocks exposed in the Coastal Cordillera of northern Chile are late Paleozoic metasedimentary rocks of the Chañaral epimetamorphic complex. These rocks recorded multiple episodes of deformation during late Paleozoic subduction and terrane accretion (Bell, 1982; Fuentes et al., 2016). Triassic clastic strata overlying the Chañaral epimetamorphic complex record syndepositional extension and sedimentation patterns that suggest structural control by NW striking half‐graben basins in north- ern Chile (Suarez & Bell, 1992; Tankard et al., 1995). Additional structu- rally controlled Triassic depocenters are widespread across central Chile Figure 1. Digital elevation map of the Coastal Cordillera between 23° and and eastern Argentina (Charrier et al., 2007). The Andean orogenic cycle 27°S, showing major regional faults (black). Structures not pertaining to began by the Early Jurassic and in the early stages was characterized by the AFS or system of NW striking faults are omitted for clarity. Locations of arc‐normal extension recorded by dikes and back‐arc basin sedimentation faults are simplified from Álvarez et al. (2016), Cembrano et al. (2005), (Charrier et al., 2007; Scheuber, 1994; Scheuber & Gonzalez, 1999). Escribano et al. (2013), and Grocott and Taylor (2002). The long‐lived crustal ‐ weaknesses hypothesized by Abels and Bischoff (1999) are shown as dashed Southeast directed subduction oblique to the N S trench imparted a sinis- white lines. The modern Nazca‐South America convergence direction is tral margin‐parallel shear component with some deformation recorded in from Angermann et al. (1999), and an approximate Phoenix‐South America the Early‐Middle Jurassic and clearly recorded by the trench‐linked AFS oblique convergence direction is after Scheuber and Andriessen (1990). in the Early Cretaceous (Scheuber &
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