The Lusinde late-post-tectonic Variscan granite (Central Iberian Zone): pluton emplacement at the termination of the Juzbado-Penalva shear zone

Abstract

The Lusinde biotite granite constitutes a small late-post-tectonic Variscan massif, emplaced along the western termination of the Juzbado-Penalva Shear Zone (JPCSZ). The main objective of this work is to constrain the time of crystallisation of the Lusinde massif and to apply the technique of anisotropy of magnetic susceptibility to better understand pluton emplacement and internal structure. New LA–ICP–MS U–Pb zircon geochronological data for this intrusion yielded an emplacement age of 295 ± 1 Ma. The Lusinde granite shows relatively low values of magnetic susceptibility (Km = 152 × 10-6 to 271 × 10-6 SI), typical of granites of the ilmenite series in which biotite is the main carrier of magnetic signal. A pyroxene- and amphibole-bearing mafic microgranular enclave exhibits higher Km magnitudes (536 × 10-6 SI). Magnetic foliations are steeply plunging and strike subparallel to the pluton irregular margins. Magnetic lineations show rather variable directions and steep plunges, suggesting that the whole massif may correspond to a feeder zone. The studied pluton seems to belong to an E-W band of steep lineations traced along the northern border of the main mass of the Cota-Viseu late-post-tectonic granite and associated mafic and intermediate rocks, which has been interpreted as an alignment of feeder zones related to the extensional termination of the Juzbado-Penalva Shear Zone (JPCSZ). As a result, it is concluded that the emplacement of the Lusinde granite was tectonically controlled by the JPCSZ.