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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%).

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Latitudinal variations in the amount of tectonic shortening and deformation style may have been controlled by regional heterogeneities in the upper continental crust and subducted slab (Jordan et al., 1983;Mpodozis & Ramos, 1989). Among these, the Pampean flat-slab subduction zone (27°S-33°S) is one of the most remarkable features in this orogen (Cahill & Isacks, 1992;Gutscher et al., 2000). It is characterized by a series of tectonic domains, with an accretionary wedge in the Coastal Cordillera, Quaternary deposits in the Central Valley, a hybrid thrust belt in the Principal Cordillera, a rigid block uplift in the Frontal Cordillera, basement uplift in the Precordillera and the Sierras Pampeanas, and a series of Neogene-Quaternary broken foreland basins (

An essential part of the world's remaining mineral resources is expected to reside deep in the crust or under post-mineralization cover. For porphyry copper deposits, the world’s primary source of Cu, Mo, and Re, identifying the dynamic processes that control their emplacement in the upper crust can guide future exploration. Seismic tomography can constrain these processes through imaging deep-seated structures at the regional scale. Here we construct a three-dimensional model of the Vp/Vs ratio, based on arrival times of P and S seismic waves, beneath the Cerro Colorado porphyry Cu–(Mo) deposit in northern Chile. Our images show that low Vp/Vs (~ 1.55–1.65) anomalies, extending to ~ 5–15 km depth, coincide with the surface expression of known porphyry copper deposits and prospects, as well as delimit structures that host orebodies and related hydrothermal alteration zones. Medium Vp/Vs (~ 1.68–1.74) and high Vp/Vs (Vp/Vs ~ 1.85) bodies correspond to intermediate-felsic plutonic precursors for porphyry intrusions and mafic magma reservoirs that underlie shallower orebodies, respectively. Imaging these precursor and parental plutons is crucial to the identification of orebodies as they act as the source of fluids for porphyry copper generation. This study demonstrates the potential of local earthquake tomography as a tool to identify future deep mineral resources with minimal environmental impact.

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