Upper-crustal architecture and transpressional controls in the formation of the El Abra, Radomiro Tomic, and Chuquicamata porphyry copper systems, northern Chile: Insights from local earthquake tomography

Le résumé fourni par la source

• A 3D Vp/Vs model using local earthquake tomography was obtained beneath the El Abra, Radomiro Tomic, and the Chuquicamata deposits. • Low Vp/Vs anomalies spatially coincide with the major mineral deposits in the area. • High Vp/Vs anomalies are aligned with the West Fault System and an intersecting NW–SE trending lineament. • Structural architecture reveals strike-slip and positive tectonic inversion controlling the El Abra–La Fortuna Intrusive Complex. Crustal architecture plays a secondary yet critical role in porphyry copper formation by controlling the transport and focusing of metal-rich hydrothermal fluids. Although upper crustal structures often guide porphyry emplacement, their identification though geological mapping alone remains challenging, necessitating geophysical imaging for robust subsurface characterization. The Late Eocene–Early Oligocene porphyry copper belt of the Chilean Andes hosts one of the world́s largest concentrations of copper mineralization. Within this belt, the El Abra (EA), Radomiro Tomic (RT), and Chuquicamata (CH) deposits (∼22°S)—collectively referred to as the EA–RT–CH cluster—are spatially associated with the N–S strike-slip fault West Fault System (WFS) in the Domeyko Cordillera of northern Chile. We present a 3D subsurface model beneath the EA–RT–CH cluster constructed from local earthquake tomography using seismic velocities (Vp, Vs) and the Vp/Vs ratio, integrated with comprehensive structural interpretation. Low Vp/Vs anomalies (∼1.6–1.7) at depths ≤ 3 km spatially coincide with intrusive complexes hosting porphyry intrusions, interpreted as quartz-rich, mechanically rigid cores. Conversely, high Vp/Vs anomalies (∼1.8–1.9) delineate structural corridors aligned with the WFS and a previously unrecognized NW–SE high-angle lineament that segments the intrusive complexes. This regional-scale NW–SE lineament not only intersects low Vp/Vs anomalies but also the WFS. We attribute Vp/Vs variations primarily to differences in rock composition, fracture density, and fluid presence rather than mechanical rigidity alone. Our results reveal a transpressional subsurface architecture beneath the EA–RT–CH cluster, where structural intersections between the arc-parallel WFS and major concealed, NW-trending lineaments exert control on segmentation, emplacement, and exhumation of porphyry copper clusters in northern Chile. These findings provide new structural and geophysical constraints for one of the world́s most economically significant porphyry copper districts.

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