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

Abstract

The Triassic and Jurassic tectonic history of northern Chile has been dominated by extension, althoughclear evidence about the nature and geometry of the extensional basins and subsequent inversion structures has beenadequately illustrated in only a few cases. In this contribution we present a structural study of the Lautaro Basin locatedat the western edge of the Frontal Cordillera in the Atacama region of northern Chile. The Lautaro Basin is a Jurassichalf-graben, filled by at least 2,600 m of marine deposits of the Lautaro Formation and developed on top of, at least 2,000m of Triassic volcanic successions of the La Ternera Formation, also accumulated during an earlier period of extensionaldeformation. Detailed field mapping and construction of a regional balanced cross-section, supported by good exposuresalong the Copiapó River valley, allow reconstruction of the structural style of both the Jurassic and Triassic extensionaldepocenters. New structural data have shown that the Lautaro Basin has a complex structural framework reflected intwo 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 offootwall 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%).