Active deformation in the northern Sierra de Valle Fértil, Sierras Pampeanas, Argentina

Abstract

The Western Sierras Pampeanas region in the San Juan Province is characterized by thickskinned deformation with approximately N-S trending ranges of average heights of m and a high frequency occurrence of seismic activity. Its location to the east of the mainly thinskinned tectonics of the Argentine Precordillera fold-and-thrust belt suggests that at 30°S, deformation is concentrated in a narrow zone involving these two morphostructural units. In this paper, we present new apatite (U-Th)/He results (AHe) across the northern part of the Sierra de Valle Fértil (around 30ºS) and analyze them in a framework of thermochronologic available datasets. We found Pliocene AHe results for Carboniferous and Triassic strata in the northern Sierra de Valle Fértil consistent with the hypothesis of recent cooling and inferred erosional denudation concentrated along the northern end of this mountain range. Our analysis shows that this northern region may have evolved under different conditions than the central part of the Sierra de Valle Fértil. Previous studies have observed AHe ages consistent with Permian through Cretaceous cooling, indicating the middle part of the Sierra de Valle Fértil remained near surface before the Pampean slab subduction flattening process. Those studies also obtained ~ 5 My cooling ages in the southern part of the Sierra de Valle Fértil, which are similar to our results in the northern end of the range. Taken together, these results suggest a pattern of young deformation in the northern and southern low elevation ends of the Sierra de Valle Fértil consistent with regions of high seismic activity, and Quaternary active faulting along the western-bounding thrust fault of the Sierra de Valle Fértil.

Latitudinal and Longitudinal Patterns of Exhumation in the Andes of North‐Central Chile

“…The geology of the Main Cordillera presents a marked change around~31.5°S. North of 31.5°S it is composed of a core of Paleozoic intrusive (mainly Carboniferous to Permian and minor Permo-Triassic) and minor metamorphic units (Ordovician) flanked to the west by a folded stratified succession of Mesozoic (Triassic to Upper Cretaceous) volcano-sedimentary rocks intruded by a Mesozoic (Upper Cretaceous to Paleocene) belt of plutonic units (Figure 2; Mpodozis & Cornejo, 1988;Nasi et al, 1990;Pineda & Calderón, 2008;Bissig et al, 2011;Martínez et al, 2012Martínez et al, , 2016. In this area the eastern border of the Main Cordillera is marked by the eastvergent La Plata reverse fault (Moscoso & Mpodozis, 1988;Mpodozis & Cornejo, 1988;Nasi et al, 1990).…”

“…North of 31.5°S it is composed of a core of Paleozoic intrusive (mainly Carboniferous to Permian and minor Permo-Triassic) and minor metamorphic units (Ordovician) flanked to the west by a folded stratified succession of Mesozoic (Triassic to Upper Cretaceous) volcano-sedimentary rocks intruded by a Mesozoic (Upper Cretaceous to Paleocene) belt of plutonic units (Figure 2; Mpodozis & Cornejo, 1988;Nasi et al, 1990;Pineda & Calderón, 2008;Bissig et al, 2011;Martínez et al, 2012Martínez et al, , 2016. In this area the eastern border of the Main Cordillera is marked by the eastvergent La Plata reverse fault (Moscoso & Mpodozis, 1988;Mpodozis & Cornejo, 1988;Nasi et al, 1990). Conversely, south of 31.5°S the core of the Main Cordillera consists of Cenozoic (upper Oligocene and Miocene) volcano-sedimentary rocks (Jara & Charrier, 2014;Mpodozis et al, 2009) In Chile and Argentina the Frontal Cordillera consists of uplifted blocks of mostly Paleozoic to Mesozoic (Permo-Triassic) volcanic and intrusive rocks.…”

“…The plateau is bounded by topographic fronts to the east and west that separate the highest Andes from the adjacent lower elevated areas (Figures a and b). The eastern topographic front systematically coincides along strike with east vergent active thrust systems that cause intense crustal seismicity along the foreland, (Figure a; Alvarado et al, ; Alvarado & Ramos, ; Costa et al, ; Lamb, ; Ortiz et al, ). In contrast, evidence of active deformation along the western topographic front is scarce and has been recognized only in northern Chile (Figure a; west vergent thrust system; Farías et al, ; Garcia & Herail, ; Hall et al, ; Jordan et al, ; Muñoz & Charrier, ; Pinto et al, ; Victor et al, ) and in central Chile (Figure a; San Ramón Fault; Armijo et al, ; Charrier et al, ; Pérez et al, ; Rauld, ; Vargas et al, ).…”

Modelo petrofísico del borde oriental de las sierras de Valle Fértil- La Huerta, Argentina a partir de datos sísmicos y petrológicos

“…Como resultado de los esfuerzos tectónicos pasados y actuales, las SVF-LH constituyen un bloque cristalino de aproximadamente 140 km de largo por 30 km de ancho que está siendo elevado diferencialmente por la tectónica andina (González Bonorino, 1950;Jordan y Allmendinger, 1986;Ortiz et al, 2014Ortiz et al, , 2015. La falla principal que eleva el bloque serrano coincide, a escala regional, con la megafractura de Valle Fértil (Baldis et al, 1990), la cual se extiende a lo largo del borde occidental de las sierras (Snyder et al, 1990;Zapata y Allmendinger, 1996;Zapata, 1998;Ortiz et al, 2015).…”

“…La falla principal que eleva el bloque serrano coincide, a escala regional, con la megafractura de Valle Fértil (Baldis et al, 1990), la cual se extiende a lo largo del borde occidental de las sierras (Snyder et al, 1990;Zapata y Allmendinger, 1996;Zapata, 1998;Ortiz et al, 2015). Datos de gravimetría indican la existencia de una discontinuidad en la cuenca del río Bermejo que flanquea las sierras por el oeste (Giménez et al, 2000;Lince et al, 2008), la cual correspondería con la megafractura de Valle Fértil sugerida como el límite entre el terreno aloctóno derivado de Laurentia y el margen autóctono de Gondwana (Thomas y Astini, 1996;Ramos et al, 1996).…”