Magnitude, timing, and rate of slip along the Atacama fault system, northern Chile: implications for Early Cretaceous slip partitioning and plate convergence

Abstract

Displacement estimates along the Atacama fault system (AFS), a crustal-scale sinistral structure that accommodated oblique convergence in the Mesozoic Coastal Cordillera arc, vary widely due to a lack of piercing points. We mapped the distribution of plutons and mylonitic deformation along the northern ∼70 km of the El Salado segment and use U-Pb geochronology to establish the slip history of the AFS. Along the eastern branch, mylonitic fabrics associated with the synkinematic ∼134–132 Ma Cerro del Pingo Complex are separated by 34–38 km, and mylonites associated with a synkinematic ∼120–119 Ma tonalite are separated by 20.5–25 km. We interpret leucocratic intrusions to be separated across the western branch by ∼16–20 km, giving a total slip magnitude of ∼54 ± 6 km across the El Salado segment. Kinematic indicators consistently record sinistral shear and zircon (U-Th)/He data suggest dip-slip motion was insignificant. Displacement occurred between ∼133–110 Ma at a slip rate of ∼2.1–2.6 km/Myr. This slip rate is low compared to modern intra-arc strike-slip faults, suggesting (1) the majority of lateral slip was accommodated along the slab interface or distributed through the forearc or (2) plate convergence rates/obliquity were significantly lower than previously modeled.Supplementary material including full U-Pb, (U-Th)/He, petrographic, and structural data with locations is available at https://doi.org/10.6084/m9.figshare.c.5262177.

Fault‐Driven Differential Exhumation in a Transpressional Tectonic Setting: A Combined Microstructural and Thermochronologic Approach From the Liquiñe‐Ofqui Fault System, Southern Andes (39°S)

“…Sinistral shear was attributed to an early deformation stage pre-dating the mid-Cretaceous based on a 100 ± 2 Ma amphibole Ar/Ar step-heating age obtained from an undeformed dacitic dike cutting the mylonites (Cembrano et al, 2000). Given that crustal depths of 7-12 km correspond to temperatures of 140°C-240°C for a geothermal gradient of 20°C/km and 245°C-420°C for a geothermal gradient of 35°C/km, this period of sinistral mylonitization could have been related to additional heat brought in by the Cretaceous (∼116-104 Ma) pulse of magmatism in the study area (similar to depths along the Atacama Fault System, see Seymour et al, 2020Seymour et al, , 2021.…”

Geological and hypogene mineralization characteristics of the hematite‐rich Pelusa IOCG prospect, Antofagasta Region, Northern Chile

“…Several IOCG (Casualidad, Barreal Seco) and Manto‐type (Franke‐San Guillermo) deposits occur in the district (Figure 2). The Altamira district is mainly composed of various volcano‐sedimentary sequences of Jurassic to Lower Tertiary ages and Lower Cretaceous dioritic to monzonitic intrusions (Correa, 2000; García, 1967; Marinovic et al, 1992; Matthews et al, 2010; Naranjo & Puig, 1984; Seymour et al, 2021; Suares et al, 1985; Ulriksen, 1979). The former is basically comprised of lavas, breccias and ignimbrites of basaltic to dacitic compositions and minor amounts of sandstone and limestone.…”

“…The NW‐NNW fault system characteristically occurs in the Altamira district including the Taltal to Barreal Seco sectors. This system is regarded as a segment of the transtensional Atacama fault extending in 20° to 32°S regions at Early Cretaceous ages (Brown et al, 1993; Charrier et al, 2007; Dallmeyer et al, 1996; Grocott & Taylor, 2002; Kojima, 2019; Scheuber & González, 1999; Seymour et al, 2021).…”

Structural Evolution of a Crustal‐Scale Seismogenic Fault in a Magmatic Arc: The Bolfin Fault Zone (Atacama Fault System)

“…10.1029/2021TC006818 4 of 29 The AFS developed in the Early Cretaceous accommodating intra-arc sinistral and sinistral transtensional deformation, once the axis of arc magmatism migrated eastwards (Scheuber & González, 1999;Scheuber et al, 1995). Brittle faults overprinted mylonites of similar kinematics and the age of ductile and brittle deformation varies along strike (Brown et al, 1993;Scheuber & González, 1999;Scheuber et al, 1995;Seymour et al, 2020Seymour et al, , 2021. Along the Paposo segment, in the outer shell of the Cerro Paranal Pluton, syn-mylonitic hornblende and biotite yield 40 Ar/ 39 Ar and Rb-Sr ages in the range between 138 and 125 Ma (Scheuber et al, 1995).…”

“…The AFS developed in the Early Cretaceous accommodating intra-arc sinistral and sinistral transtensional deformation, once the axis of arc magmatism migrated eastwards (Scheuber & González, 1999;Scheuber et al, 1995). Brittle faults overprinted mylonites of similar kinematics and the age of ductile and brittle deformation varies along strike (Brown et al, 1993;Scheuber & González, 1999;Scheuber et al, 1995;Seymour et al, 2020Seymour et al, , 2021.…”