Deformation and magnetic fabric of the Capinha granite (Fund&#227;o, Central Portugal): ascent and emplacement mechanisms during the late-Variscan crustal thinning
Authors: Gonçalves Ana , Sant'Ovaia Helena , Noronha Fernando 
Published: March 2020

&lt;p&gt;The Capinha area is located in the Central Iberian zone and is characterized by several Variscan granites intruded in the Neoproterozoic&amp;#8211;Cambrian metasedimentary rocks. The main goal of the study is to identify the deformation patterns and provide crucial information to investigate the evolution of the magnetic fabrics in a post-Variscan granite emplaced during the crustal thinning, at the end of the Variscan orogeny. In order to achieve these purposes, fieldwork, petrography, microstructures and anisotropy of magnetic susceptibility (AMS) analysis were undertaken. The AMS was measured in 160 oriented cores, collected from 20 sampling sites homogeneously distributed, allowing the quantification of scalar (magnetic susceptibility, K; paramagnetic anisotropy, P&lt;sub&gt;para&lt;/sub&gt;; magnetic ellipsoid shape, T) and directional data (magnetic lineation, //K&lt;sub&gt;1&lt;/sub&gt;; magnetic foliation, perpendicular to K&lt;sub&gt;3&lt;/sub&gt;). The Capinha granite (CG), exposed over an area of about 7 km&lt;sup&gt;2&lt;/sup&gt;, is a small circular circumscribed outcrop in the NE-SW contact between the regional Belmonte&amp;#8211;Caria granite (301.1&amp;#177;2.2 Ma) and the metasedimentary sequences. The CG is cut by two main fracturing systems: N30&amp;#186;-40&amp;#186;E and N110&amp;#186;-120&amp;#186;E, both subvertical. The contact is sharp, intrusive and discordant with the general trending of the D&lt;sub&gt;1&lt;/sub&gt; and D&lt;sub&gt;3&lt;/sub&gt; Variscan structures registered in the metasedimentary rocks. The CG is homogeneous in the whole area and consists of a fine- to medium-grained, muscovite-biotite leucogranite. The CG exhibit a paramagnetic behaviour with a K mean of 73 &amp;#181;SI, belonging to the ilmenite-type granites. At several scales, the CG does not show any magmatic flow or ductile deformation patterns displaying P&lt;sub&gt;para&lt;/sub&gt; of about 1.6%, which corresponds to dominant magmatic to submagmatic microstructures. The P&lt;sub&gt;para&lt;/sub&gt; highest values are concentrated in the NE border associated to prolate ellipsoids (linear fabric). Based on the interpretation of the magnetic fabric, is possible to observe that the orientation of the magnetic foliation is variable ranging from NNW-SSE to NNE-SSW. Generally, the magnetic foliations are sub-horizontal, being the vertical dips observed in the NE border, near the intersection of the N100&amp;#186;-120&amp;#186;E and the N30&amp;#186;-40&amp;#186;E fractures. The arrangement of the magnetic foliations follow concentric trajectories, with the symmetry axe parallel to the major axis of the outcrop (roughly NNE-SSW). The magnetic lineations are mainly sub-horizontal NNE-SSW parallel to the granite major axis; although, in the SW border the lineations tend to be parallelized to the contact. The magnetic lineation arrangement develops linear trajectories converging to the NE zone, where the dip is strong. The common gently magnetic fabric suggests the roof of the CG intrusion. During the late stages of the Variscan orogeny (D&lt;sub&gt;3&lt;/sub&gt;, 321-300 Ma), ductile extensional detachments promoted the thinning of a previously thickened crust, providing the opening of pre-existing structures and the production of new ones. These structures act as conduits for a passive magma ascending and emplacement at shallow levels. Therefore, it is suggested that the CG magma ascent and emplaced in the intersection of pre-existing fractures, located in the NE zone, and flowed to the SW, developing a small asymmetric laccolith, poorly eroded, with a tongue-shaped body.&lt;/p&gt;