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INSIGHTS INTO THE FELSIC VEIN MAGMATISM IN NORTHERN PORTUGAL (CENTRAL IBERIAN ZONE): AN INTEGRATED GEOCHEMICAL AND PETROPHYSICAL STUDY

António Oliveira, Helena Brites, Helena Sant ́Ovaia

First published: 2020-09-20https://doi.org/10.5593/sgem2020/1.1/s01.018View metrics

Abstract

Multiple veins of subvolcanic lithologies, including porphyries, lamprophyres and dolerites, outcrop in northern Portugal intruding both the pre-variscan metasedimentary basement (known as the Schist-Greywacke Complex) and variscan granites of high compositional variability. The N-S trending, granitic/rhyolitic porphyries of Vila Pouca de Aguiar (VPA) constitute two of the most important examples of these veins. Both porphyries intrude the main facies of the regional pluton (the VPA granite). The present study constitutes a multidisciplinary approach, involving whole-rock geochemistry, SEM-EDS and anisotropy of magnetic susceptibility, whose goal is to better understand the subvolcanic geology of northern Portugal. The VPA porphyries are individually referred to as Loivos (at west) and Povoa de Agracoes (at east). Both exhibit a characteristically porphyritic texture, microcrystalline groundmass, and a mineral assemblage of quartz + potassium feldspar + plagioclase + muscovite ± biotite ± cordierite ± apatite ± chlorite ± zircon ± monazite ± allanite ± ilmenite. Rare Fe-Mn-Al/Na phosphates (childrenite, scorzalite (?) and gayite (?)), which only occur in the Povoa de Agracoes vein, were identified using SEM-EDS. Geochemically, the VPA porphyries derived from an extremely evolved magma of highly felsic peraluminous nature and their chemistry is typical of a post-orogenic setting. The veins are also enriched in Li, Be, Rb, Sn, Cs, Nb, Ta and W, when compared to the host pluton. Petrophysical analyses were only performed on the Loivos porphyry. This vein has a paramagnetic behaviour, with normal type magnetic fabric. Magnetic foliations and lineations suggest a deep rooting of the magma that fed the vein, and a subhorizontal magma flow. Geochemical and petrophysical results suggest that the VPA porphyries and the host granite had different sources.

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Title
INSIGHTS INTO THE FELSIC VEIN MAGMATISM IN NORTHERN PORTUGAL (CENTRAL IBERIAN ZONE): AN INTEGRATED GEOCHEMICAL AND PETROPHYSICAL STUDY
Authors
António Oliveira, Helena Brites, Helena Sant ́Ovaia
Proceedings
SGEM International Multidisciplinary Scientific GeoConference EXPO Proceedings; 20th SGEM International Multidisciplinary Scientific GeoConference Proceedings 2020, Science and Technologies in Geology, Exploration And Mining
Publisher
STEF92 Technology
Year
2020
Pages
139-146
SWS Citekey
Oliveira20201139146
ISSN
1314-2704
ISBN
978-619-7603-04-0
Language
en
Publication type
Conference Paper
Keywords
Granitic porphyryVila Pouca de AguiarSEM-EDSGeochemistryAMS
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