Geochemistry and evolution of Jales granitic system, northern Portugal

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Authors:Neiva, A. M. R.
Author Affiliations:Primary:
Univ. Coimbra, Dep. Mineral. Geol., Coimbra, Portugal
Volume Title:Chemie der Erde
Source:Chemie der Erde, 52(3), p.225-241. Publisher: Gustav Fischer Verlag, Jena, Federal Republic of Germany. ISSN: 0009-2819
Publication Date:1992
Note:In English with German summary. 14 refs.; illus. incl. 29 anals., 3 tables, geol. sketch map
Summary:Most of the Jales granitic system consists of peraluminous medium- to coarse-grained porphyritic seriate two-mica granite (309 +- 3 m.y.), coarse-grained slightly porphyritic muscovite-biotite granite, fine-grained muscovite granite with tourmaline and aplite- pegmatite; aplite and pegmatite veins cut the two-mica granite. The author presents diagrams of major and trace elements of rocks and some trace elements of muscovites and major elements of tourmalines showing fractionation trends. Least-squares analysis of major elements and modelling of trace elements indicate that these granitic rocks were probably derived from the porphyritic two-mica granite magma by fractional crystallization of plagioclase, biotite and quartz, but also of K-feldspar and muscovite in the case of the last differentiates. However, it was impossible to test fractional crystallization for some of the granitic rocks because they show metasomatic effects. Diffusive differentiation was probably responsible for depletion of aplite- pegmatite, aplite and pegmatite veins in F, Li, Th and REE. The porphyritic two-mica granite magma was generated at 3.5-3 kbar and 690 degrees C. The granitic rocks were completely crystallized at approx 600-440 degrees C (granites) and 430-350 degrees C (aplite- pegmatite, aplite and pegmatite veins). The aplite-pegmatite- aplite and pegmatite veins and Jales gold quartz veins cut the porphyritic two-mica granite and mica schists. The gold quartz veins contain albite, microcline and white micas of similar or more evolved compositions and sulphides of similar compositions to those of former veins. The gold quartz veins and the later barren quartz veins probably result from hydrothermal fluids of late stages of fractional crystallization of the porphyritic two-mica granite magma. [J.M.H.]
Subjects:Aplite; Dikes; Feldspar group; Fractional crystallization; Framework silicates; Genesis; Granites; Graphic methods; Igneous rocks; Intrusions; Magmas; Major elements; Mica group; Muscovite; Muscovite granite; P-T conditions; Pegmatite; Plutonic rocks; Porphyritic texture; Ring silicates; Sheet silicates; Silicates; Textures; Tourmaline group; Trace elements; Two-mica granite; Variations; Whole rock; Europe; Iberian Peninsula; Portugal; Southern Europe
Abstract Numbers:93M/3008
Record ID:1993040426
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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