DOI: 10.5593/SGEM2015/B11/S1.017


H.Sant Ovaia, A.Dуria, F.Noronha
Tuesday 4 August 2015 by Libadmin2015

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-31-5 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 1, 127-134 pp

The microganite of Argemela (Central Portugal) constitutes a small intrusion consisting of quartz, albite, white mica (partly replaced by lepidolite) and amblygonite. The Argemela intrusion displays mineralogical and chemical features characteristic of a high-fluorine, rare-element magma. This intrusion sharply crosscuts the weakly metamorphosed schist-greywacke complex of the regional Beira series, Upper Cambrian in age. An emplacement model for the microgranite of Argemela is proposed considering the magnetic fabric and fluid inclusion planes studies. Systematically measurement of the anisotropy of magnetic susceptibility (AMS) has been taken on 119 oriented cores (25 mm in diameter and 22 mm in length) of the Argemela microgranite. The magnetic susceptibility values are homogeneous and range between 4 and 10 × 10-6 SI, indicating a paramagnetic behavior, due mainly to the iron contained in the phylossilicate phase. The NE-SW to NNE-SSW subvertical magnetic foliations associated to subvertical magnetic lineations is directly related to the mica fabric. The magnetic fabric points a magma emplacement controlled by NE-SW to NNE-SSW offsets with a vertical injection of the magma and a lateral inflation of the intrusion due to the magma pressure. A similar magnetic fabric was found in the muscovite granite from Serra da Estrela, offering the possibility of a genetic relation. After emplacement, Argemela microgranite recorded increments of the late Variscan stress field documented by NE-SW, E-W and NW-SE fluid inclusion planes in quartz.

Keywords: anisotropy of magnetic susceptibility, emplacement, rare element magma, variscan orogeny.

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