Sequential melting and fractional crystallization: Granites from Guarda-Sabugal area, central Portugal |
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| Authors: | Ana Margarida Ribeiro Neiva Paulo Bravo Silva Fernando Corfu João Manuel Farinha Ramos |
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| Institution: | aDepartment of Earth Sciences and Geosciences Centre, University of Coimbra, 3000-272 Coimbra, Portugal;bLNEG National Laboratory of Energy and Geology, Apartado 1089, 4466-956 S. Mamede de Infesta, Portugal;cDepartment of Geosciences, University of Oslo, PB1047 Blindern, N-0316, Norway |
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| Abstract: | Seven distinct phases of Variscan two-mica granite are recognized in the Guarda-Sabugal area. They intruded the Cambrian schist-metagraywacke complex, crystallized in the middle crust, and are syn- to late-D3 (309.2 ± 1.8 Ma), late-D3 (304–300 Ma) and late- to post-D3 (299 ± 3 Ma; ID-TIMS ages on zircon and monazite). Two of the granites, G2 and G5, are close in age and have similar Sr, Nd and O isotope characteristics but contrasting whole rock and mineral features and formed by sequential increasing degree of partial melting of a common metasedimentary protolith. During sequential melting Ti, total Fe, Mg, Ca, Zr, Zn, Sr, Ba and REE contents and (La/Yb)N increase and Si and Rb contents decrease, plagioclase becomes richer in anorthite and biotite and muscovite richer in Ti and Mg. Each of these granites evolved subsequently by fractional crystallization of quartz, K-feldspar, plagioclase, biotite and ilmenite, defining separate series G2–G3–G7 and G5–G6 containing late Sn-bearing differentiates. Two other granites G1 and G4 represent distinct pulses of magma with individual fractionation trends for major and trace elements and distinct (87Sr/86Sr)300, ?Nd300 and δ18O values. |
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| Keywords: | Granite Geochronology Geochemistry Sequential melting Fractional crystallization |
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