Jurassic hydrothermal mineralization and Cretaceous-Tertiary exhumation in the foreland of the southern Patagonian Andes: new constraints from La Paloma area, Deseado Massif, Argentina

MARÍA LIS FERNANDEZ; STEFANO MAZZOLI; MASSIMILIANO ZATTIN; SAVIGNANO, ELISA; MARIE C GENGE; STEFANO TAVANI; ALEJANDRO ALEJANDRO GARRONE; FRANCHINI MARTA

TECTONOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2020 vol. 775 p. 1 - 22

0040-1951

Fluid-rock interaction occurring within high-permeability conduits represented by fault-fracture meshes is well known to control thedevelopment of hydrothermal ore deposits. In this study we document the fundamental role of four sets of precursor joints, reactivated asdilational faults displaying variable normal dip-slip and strike-slip components of motion, in the formation of epithermal Au-Ag deposits ofeconomic interest. Paleostress analysis unravels how all the resulting four sets of hybrid extension-shear fractures are kinematically compatiblewith an extensional stress field characterized by permutations between the σ3 and the σ2 axes. Such permutations are interpreted to be associatedwith dominantly normal fault reactivation of suitably oriented early joint sets as a result of continued regional extension, and by orthogonalstretching produced by differential downthrow of the hanging-wall blocks of laterally-terminating Jurassic normal faults.Later fault reactivation appears to be associated with far field propagation of Andean stresses, marked by superposed strike-slip and reversefault slip components recording roughly E-W horizontal compression. This late fault reactivation could be related with a late Early Cretaceousshortening event known to have affected the studied sector of the Deseado Massif. The subsequent tectonic evolution the study area occurredwithin the general framework of a slow Cretaceous to Tertiary exhumation recorded by apatite fission track cooling ages. Our newthermochronometric results, recording steady-state cooling at a rate of c. 1°C/Ma during the last 90 Ma, shed new light onto the post-Jurassicgeodynamic evolution of the foreland of the southern Patagonian Andes.