Insights into the felsic vein magmatism in northern Portugal (central iberian zone): An integrated geochemical and petrophysical study

• Type: Article in International Conference Proceedings Book
• Date: 2020

Authors

Oliveira, A (Author) Other; H. C. B. Martins (Author) FCUP; Sant'Ovaia, H (Author) FCUP

Conference proceedings International

Title: International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM

Pages: 139-146

20th International Multidisciplinary Scientific Geoconference: Science and Technologies in Geology, Exploration and Mining, SGEM 2020

18 August 2020 through 24 August 2020

Indexing

Scopus - 2 Citations

Other information

Authenticus ID: P-00T-CYZ

DOI: 10.5593/sgem2020/1.1/s01.018

Abstract (EN): 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 Póvoa de Agrações (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 Póvoa de Agrações 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.

Language: English

Type (Professor's evaluation): Scientific