Other
Scientific paper
Mar 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51..439n&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 3, pp.439-454
Other
6
Scientific paper
Several types of Hercynian peraluminous granitic rocks ranging from biotite-muscovite granodiorite to muscovite granite occur in the horst of Serra da Estrela. Variation diagrams of most major and trace elements of the rocks and biotites and Cr and V of muscovites show fractionation trends. However, Nb, Li, Rb, K / Rb , Li / Mg variation diagrams of the rocks and muscovites and also of Sn, Cs, Cs / K of the muscovites indicate that the muscovite granite probably originated by another mechanism. Least squares analysis of major elements and modelling of trace elements indicate that the coarse grained porphyritic biotite-muscovite granite, granite porphyry and fine to medium grained muscovite-biotite granite were derived from the granodiorite magma by fractional crystallization of plagioclase, quartz and biotite. Emplacement of granodiorite magma took place at 3.5-3 Kb and 720°C: granites and granite porphyry probably originated about 690°C, but were completely crystallized about 520°C. f O2 was about 10 -17 for the granodiorite and <10 -18 for the two mica granites and granite porphyry. Log ( f HCl / f HF ) was higher, whereas log ( f h 2 o / f hcl ) was lower in the granodiorite than in the other granitic rocks of the fractionated series. The coarse-grained porphyritic biotite-muscovite granite was hydrothermally altered between 400-350°C and 260-230°C at about 1.5-1 Kb. The hydrothermal fluids were probably mainly meteoric in origin, but some fluids released during the late stage of granite solidification might also have been involved.
Neiva Ana Margarida Ribeiro
Neiva João M. C.
Parry Susan J.
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