The Esmolfe-Matanca granite (Penalva do Castelo, central Portugal): A keystone to understand the ascent and emplacement of magmas under low tectonic stress

摘要

The Esmolfe-Matanca ilmenite-type granite is analyzed using petrography, microstructures, anisotropy of magnetic susceptibility and microfracturing. The granite occurs in two separated bodies outcropping in distinct villages, Esmolfe and Matanca, which are located in the termination of the Juzbado-Penalva do Castelo (JPCSZ) and Durico-Beirao (DBSZ) shear zones. The petrography shows a progressive textural overprint from magmatic, through high-, medium- and low-T solid-state deformation microstructures. The presence of dominantly magmatic microstructures and the absence of deformation patterns at macroscopic scale, may indicate an emplacement under low tectonic stress. The directional magnetic data indicates a magma ascending and emplacement conditioned by the JPCSZ and DBSZ. The magma passive intruded upwards, along the confluence zone between the JPCSZ and DBSZ, and it spread laterally forming an asymmetric laccolithic body. The DBSZ worked as physical barrier in Esmolfe, avoiding the spreading of the magma to the north, leading to the rotation of the magnetic lineations and foliations, drawing onion-type trajectories. In Matanca the magnetic lineations and foliations are dominantly NW-SE oriented in the western side, and ENE-WSW oriented in the eastern side, parallel to the JPCSZ regional trend. The fluid inclusions planes demonstrated three distinct brittle deformational events linked to the rotation of sigma(1).