The Lautaro Basin: A record of inversion tectonics in northern Chile

Abstract

ABsTrACT. The Triassic and Jurassic tectonic history of northern Chile has been dominated by extension, although clear evidence about the nature and geometry of the extensional basins and subsequent inversion structures has been adequately illustrated in only a few cases. In this contribution we present a structural study of the Lautaro Basin located at the western edge of the Frontal Cordillera in the Atacama region of northern Chile. The Lautaro Basin is a Jurassic half-graben, filled by at least 2,600 m of marine deposits of the Lautaro Formation and developed on top of, at least 2,000 m of Triassic volcanic successions of the La Ternera Formation, also accumulated during an earlier period of extensional deformation. Detailed field mapping and construction of a regional balanced cross-section, supported by good exposures along the Copiapó River valley, allow reconstruction of the structural style of both the Jurassic and Triassic extensional depocenters. New structural data have shown that the Lautaro Basin has a complex structural framework reflected in two major Mesozoic extensional periods, overprinted by Cenozoic inversion involving thin-and thick-skinned tectonics. Shortening was accommodated by a combination of inversion of pre-existing normal faults, buttresses, development of footwall short-cuts, and both thin and thick-skinned thrusting. New estimates of shortening are up to 13.1 km (30%), while Mesozoic extension is estimated to be 3 km (7%). resuMen. La Cuenca Lautaro: un registro de inversión tectónica en el norte de Chile. Durante el Triásico y Jurá-sico la evolución tectónica del norte de Chile fue dominada por extensión cortical. No obstante, evidencias claras acerca del estilo estructural y subsecuente inversión de las cuencas asociadas con el evento extensional, han sido ilustradas en pocos casos. En este trabajo, se presenta un estudio estructural de la Cuenca Lautaro, localizada en el borde occidental de la Cordillera Frontal, en la región de Atacama del norte de Chile. La Cuenca Lautaro, es un hemigraben que aloja al menos 2.600 m de depósitos marinos de la Formación Lautaro, acumulados sobre al menos 2.000 m de sucesiones volcánicas triásicas de la Formación La Ternera. Los excelentes afloramientos de la región permitieron construir una sección balanceada y restaurar el estilo estructural de los depocentros extensionales triásicos y jurásicos. Los resultados obtenidos muestran que la Cuenca Lautaro tiene una arquitectura estructural compleja, reflejada en dos episodios extensionales mayores. Posteriormente, se sobreimpone al menos un evento de inversión tectónica que desarrolla una tectónica mixta de piel fina y piel gruesa. El acortamiento se acomoda por una combinación de inversión de fallas preexistentes, desarrollo de fallas de atajo y corrimientos de piel fina y piel gruesa, que involucran bloques rígidos o 'buttresses'. Las estimaciones de acortamiento son de 13,1 km (30%), mientras que la extensión mesozoica es de 3 km (7%).

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

“…90–55 Ma) recognized for sample LE04 (Figures a and a) cannot be related to magmatic effects as intrusive rocks of such age crop out farther west, at the border between the Coastal and Main Cordilleras (Figures , and a). Accelerated cooling during the Late Cretaceous or early Paleocene is interpreted as rather reflecting exhumation of rocks related to partial tectonic inversion of early Mesozoic extensional basins during the Peruvian (late Early to early Late Cretaceous) or K‐T (Cretaceous‐Paleogene boundary) orogenic phases as it has been shown to have occurred along the border between the Main and Frontal Cordilleras in the Copiapó River area approximately 50 km north of the studied region (Martínez et al, ). The following period of cooling observed in this sample that started at some point during the Eocene or early Oligocene (approximately 40–30 Ma) is not easily explicable (Figures a and a).…”

“…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).…”

Basin evolution of Upper Cretaceous–Lower Cenozoic strata in the Malargüe fold‐and‐thrust belt: northern Neuquén Basin, Argentina

“…In the same area, inversion structures documented by Martínez et al . (, ) also record shortening near the Cretaceous–Palaeocene boundary. In the southern Patagonian Andes, Fildani et al .…”

Basin inversion and structural architecture as constraints on fluid flow and Pb-Zn mineralisation in the Paleo-Mesoproterozoic sedimentary sequences of northern Australia

“…Further enhancements of the basic inverted structure may occur where the normal fault locks up early and strain is transferred to a footwall shortcut thrust or taken up by some other structure such as a strike-slip fault (Dooley and McClay, 1997;McClay, 1995;McClay et al, 2002). These and other variations on structural architecture developed during basin inversion (Martínez et al, 2012) are illustrated in Figure 10.…”