Surface-derived fluid percolation along detachment systems enhanced by syn-kinematic granites: uranium mineralization as an application

Abstract

Detachment zones are privileged areas for the interaction between surface-derived fluids and rocks, potentially leading to ore deposition. However, the hydrodynamics of detachments and specifically the way by which surface-derived fluids reach crustal depths, remain enigmatic. This question is even more puzzling when the heating caused by the emplacement of a syn-kinematic granite increases the buoyancy of fluids, thus impeding their descent. Here, 2D hydrothermal numerical models are performed. The geometry comprises a detachment and secondary normal faults in the hanging wall. Sensitivity tests were carried out to assess the impact of topographic gradients, syn-tectonic magmatic activity and the depth-dependent permeability contrast between the detachment and the crust. Several flow indicators, integrated over time and combined with particle tracking, enable us to highlight the main controls of fluid circulations. Our study reveals that the infiltration of surface-derived fluids into detachment zones is enhanced by the presence of a heat source at depth, such as a syn-kinematic pluton. Secondary faults are the main percolation path for surface-derived fluids infiltrating the detachment. Plume-like thermal anomalies have been spotted between these faults. The dynamic permeabilities of magmatic intrusions, which depend on sub-solidus temperatures, spatially and temporally reproduce the conceptual model of uranium mineralization in the South Armorican Variscan Domain, which is used as an example.

Keywords

• crustal detachments
• meteoric fluids
• syn-kinematic granites
• depth-dependent and dynamic permeabilities
• numerical hydro-thermal coupling
• uranium mobility