Master thesis presented by Anabela Carreira Mendes, 1994, 157p.

Abstract
Situated in the Northeastern limit of the Minho province, the Peneda - Gerês massif is, in the context of the Iberian hercynian granitoids, a good example of a post-F3 composite and zoned batholith. It is a discordant massif, dominantly surrounded by syn- and late-hercynian granites while Silurian metasedimentary rocks bound the Western and Southeatern margins.

This massif is spatially associated with the NNE faults of Gerês - Lovios and Tibo - Gavião (Serra da Peneda). It is composed of three roughly concentric granitic facies (the Gerês, Paufito and Illa granites) and a fourth facies (the Carris granite) that crops out as various irregular masses in the two outermost granites.
The most extensive and external facies, the Gerês granite, is a porphyritic coarse-grained biotite granite, frequently rose-coloured. It contacts gradationally with the Paufito granite, a porphyritic medium-grained biotite granite that crops out in the Serra da Peneda and especially in Spain. This facies becomes uneven-grained towards the massif's interior. With the gradual decrease in grain-size and increase of muscovite, a two-mica medium- to fine-grained facies appears, the Illa granite. Masses of fine-grained biotite granite (Carris granite) occur especially in the Gerês granite with sharp but lobated contacts. The field relations suggest a synchronous emplacement of these granites.

These granites are essentially peraluminous and the parameter Al-(K+Na+2Ca) varies between -4 and 40. The Illa granite shows the highest peraluminous character in opposition to the Gerês granite whose values are the lowest The Paufito granite occupies an intermediate position. They present characteristics of very differentiated I-type granites and all except the Carris granite belong to the ilmenite series.

The geochemical data from whole rock and mineral phases reveal the compositional individuality of the Gerês granite and a compositional and evolutionary continuity between the Paufito and Illa granites. Some of the samples of Carris granite have a chemical composition identical to the Paufito granite, while samples from other granitic masses show a compositional identity with the Gerês granite. This geochemical variability is in accordance with the petrographical variability observed in the various masses.

The Gerês and Paufito - Illa granites present internal chemical-mineralogical evolutions which may be interpreted as primary trends controlled by fractional crystallization. The results obtained with the modelization of this process permit to consider this hypothesis valid.

The Gerês granite's chemical-mineralogical characteristics, zircon typology and biotite chemical composition indicate a subalkaline (ferropotassic) magmatic affinity. For the Paufito and Illa granites, indications from the zircon typology and the X vs. Or*-MM* chemical-mineralogical diagram are that these granites are also subalkaline although the biotite compositions are typical of aluminopotassic granitoids.

The low 87Sr/86Sr isotopic initial ratios referred in the literature for the Gerês and Carris granites suggest that they resulted from mantle-derived and/or infracrust-derived magmas. In fact, they are generated during a period of intense relaxation of the regional strain. This favours the ocurrence of crustal injection of basic magmas derived from the upper mantle and causing crustal anatexis.

Considering all available data, the following genetic hypothesis are put forward:
The Peneda - Gerês massif is the result of subcontemporaneous ascent and emplacement of two distinct and immiscible granitic magmas of subalkaline affinity.
The Gerês granite constitutes the outermost facies of the massif and evolved through in situ fractional crystallization. The more evolved granitic term would be represented by the fine-grained leucogranitic bodies that occur included in the Gerês granite, in the Serra da Peneda region.
During it's ascent the Gerês magma would have surrounded and transported small masses of Paufito magma (local phenomena of magmatic interaction would have taken place), represented by some of the fine-grained granitic masses associated with the Gerês granite (region of Borrageiro - Carris - Las Sombras).
The Paufito magma evolved by in situ centripetal fractional crystallization. The less evolved granitic term is represented by the Paufito granite, situated between the other two concentric facies. The Illa granite, which occurs in the massif's nucleus, represents the most evolved compositional term.