Geological and geophysical methods relevant to decipher the structure and emplacement of granites: Insights from the Calmayo pluton (Eastern Sierras Pampeanas, Argentina)

Abstract

In this paper, the evolution of the fabric and 3D geometry of the Calmayo trondhjemitic pluton (512.1 ± 3.4 Ma; Sierra Chica, Córdoba, Argentina) is analyzed using Anisotropy of Magnetic Susceptibility (AMS) measurements combined with structural and microstructural data. Gravity data reveal that the pluton is a funnel-shaped body resting on one main root zone detected below the central portion of the pluton. The microstructural observations in the trondhjemite rocks show a progressive textural overprint from magmatic, through high-T to low-T solid-state deformation textures. This overprint is interpreted to be a consequence of the dynamic emplacement and local deformation, particularly close to the adjacent Soconcho shear zone. Late oxidation of the magnetic mineral assemblage (martitization of magnetite) is more intense in the central and southern sectors close to the root zone, explaining the flat magnetic response of this area, and contrasting with a noisy domain to the northeast where magnetite is preserved. We propose that the Calmayo pluton was constructed by several pulses that ascended through a root zone or main conduit. This root zone represents feeder dykes that exploited tension fractures linked to the Soconcho shear zone. Fluids responsible for the late oxidation would have followed similar paths through this protracted shear zone.