Crustal dense blocks in the fore-arc and arc region of Chilean ranges and their role in the magma ascent and composition: Breaking paradigms in the Andean metallogeny

Abstract

We use Intermediate-to-short wavelength (20–150 km) gravity anomalies to investigate the role played by crustal scale dense blocks in the genesis of Cu ore depositsalong the Andes. These dense blocks are widespread along the margin and located at the fore-arc, arc, and back-arc domains, including depths in the range of12–18 km, and thickness of 5–8 km. The interplay of these dense blocks with long-lived Trans-Lithospheric-Faults (TLF) controls the emplacement, and most likely,provides the required fertile fluids for the Cu ore genesis. Dense blocks represent impervious crustal domains, surrounded by damage zones at the intersection withTLF systems. Concentration of seismicity, large Vp/Vs ratios, low gravity domains, active volcanism, and structural fabric, demonstrate that these damage zones arein fact the most likely places for magma as well as mineralized flow ascent and emplacement. Basic flow models in porous media show a flow path that migrateshorizontally at the base of dense/impervious blocks until the high permeability edge flanks, where pressure gradients provide the ideal conditions for the upward andfocusing hydrothermal fluid ascent. Although not fully addressed in this paper, evidence suggests that the interaction of subducting-related fluids and the mafic-denseblock might produce a fertile fluid with a concentration of Cu.In contrast with the long-standing view of metallogenic belts of the same age and parallel to the trench axis, we propose a multi-age metallogenic cluster, along theperiphery of dense blocks, and organized oblique to the margin, following the trend of a given TLF.