Restoring a syntectonic transtensional pluton by integrating structural geology, anisotropy of magnetic susceptibility, and gravimetric modelling

Abstract

The kinematic analysis of magmatic structures is key evidence for the tectonic settings and deformation mechanisms related to the emplacement of intrusive bodies. The Dom Feliciano Belt (DFB), southernmost Brazil, registers voluminous post-collisional magmatism during the Neoproterozoic and the Arroio do Silva Pluton (ASP) is a diorite-monzonite-syenite body emplaced in this tectonic setting. The ASP structural investigation and magnetic fabric analysis showed the coexistence of flat-lying and steeply-dipping planar structures in most rock types. Heterogeneous shearing along the steeply-dipping planes led to heterogeneities in the fabric, providing individual analyses of zones affected and unaffected by shearing. The magnetic fabric analysis corroborated the interpretation of dextral kinematics based on field structural data. Complementary gravimetric modelling of the ASP demonstrates its continuity in the subsurface along an NNE-SSW axis. The integration of structural and magnetic fabric analyses combined with gravimetric modelling indicates that the older ASP rock types register a syntectonic emplacement within a transtensional setting, whereas younger magmatic activity in the pluton occurred under extensional conditions. The integrative approach allowed a comprehensive characterisation of the magmatic structures developed under different tectonic stresses and their association with emplacement conditions for the pluton.