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The genesis of I- and S-type granitoid rocks of the Early Ordovician Oledo pluton, Central Iberian Zone (central Portugal)
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Orientador(es)
Resumo(s)
The Early Ordovician Oledo pluton consists of four distinct granodioritic to granitic phase (G1–G4), which
intruded a Cambrian schist-metagraywacke complex, but were themselves intruded by a Late Carboniferous
pluton. ID-TIMS U–Pb ages for zircon and monazite from these granitic rocks indicate emplacements within
a short period of time at 479–480 Ma. Granodiorite G1 is the most deformed rock with shear zones and
deformation at the border. G1 and G3 contain fine-grained biotite tonalite and biotite granodiorite
microgranular enclaves, which are darker and richer in mafic minerals than the host granodiorites. The
geological, mineralogical, geochemical and Sr, Nd and O isotopic data show that tonalitic and granodioritic
enclaves and host G1 are of I-type and were related predominantly by a fractional crystallization process.
Least-square analysis of major elements and modelling of trace elements indicate that granodioritic enclaves
and host G1 could be derived from the tonalitic enclave magma by fractional crystallization of plagioclase,
grunerite, biotite and ilmenite. Granodiorite G2 is of hybrid origin. Most variation diagrams for granodioritic
enclaves and host G3 granodiorite and their biotites show linear trends. Modelling of major and trace
elements of granodioritic enclaves indicate that they result from mixing of relatively primitive granodiorite
magma with magma derived from crustal melting. Tonalitic enclaves correspond to globules of a more mafic
relatively primitive magma. Granite G4 has the most pronounced crustal signature and is of S-type.
Descrição
Palavras-chave
ID-TIMS U–Pb ages Fractional crystallization I- Microgranular enclaves Magma mixing Ordovician S-type rocks
Contexto Educativo
Citação
ANTUNES, I.M.H.R. [et al.] (2009) - The genesis of I- and S-type granitoid rocks of the Early Ordovician Oledo pluton, Central Iberian Zone (central Portugal). Lithos. 111. P. 168-185.