The Huarpe hidden aseismic ridge and its exhumation and mineralization effects in the central Andes

The subduction of oceanic plate heterogeneities—drives profound tectonic and metallogenic modification of the overriding upper plates. Along the central Chile-Argentinean subduction margin, the collision of the Juan Fernández and Copiapó aseismic ridges and the adjacent Challenger fracture zone with the trench is the primary control on regional deformation. Through an integrated analysis of gravity fields and Moho depth—aided by upward continuation of spherical harmonics—we identify a previously unmapped aseismic ridge segment between these known features. This structure, here denominated the Huarpe ridge, lacks prominent bathymetry but exhibits a clear geophysical fingerprint: an isostatic anomaly indicating crustal overcompensation and a correlated flexure of the Moho. Our results demonstrate that the simultaneous subduction of these three buoyant ridges, together with the Challenger fracture zone, segments the outer rise of the Nazca plate, narrowing the Andean crustal root, and providing a mechanism for the Neogene to Recent uplift of the Greenvillian basement blocks in the Sierra de Maz, Umango, and Espinal ranges in the Western Sierras Pampeanas, representing an anomaly at the orogenic front area. In addition, we highlight the significant mineralization associated with hydrothermal and magmatic fluids related to the deformation imprinted by this ridge and the associated mantle magmas. In this process, the subducted plate adjacent to the oceanic ridge tears, inducing mantle decompression and partial melting of the oceanic crust, which metasomatizes the overlying mantle wedge and ultimately generates porphyry, gold, and volcanogenic massive sulfide deposits, among others. Notable examples include Pascua Lama (Cordillera Frontal, San Juan), San José (Precordillera, San Juan), Cerro Alumbre (Cordillera Frontal, San Juan), and Sierra de Maz (Western Sierras Pampeanas, San Juan). This study establishes that the Huarpe a-seismic ridge, together with the Challenger fracture zone, are first-order tectonic elements that actively shape the orogenic structure of the Andes and its associated metallogeny.