Contamination in mafic mineral-rich calc-alkaline granites: a geochemical and Sr-Nd isotope study of the Neoproterozoic Piedade Granite, SE Brazil

Anais da Academia Brasileira de Ciências

Renato J. Leite¹  Valdecir A. Janasi¹  Lucelene Martins¹ 

[1],Universidade de São Paulo Instituto de Geociências São Paulo SP ,Brasil

关键词: granite;    calc-alkaline;    peraluminous;    magma contamination;    Sr-Nd isotope geochemistry;    granito;    cálcio-alcalino;    peraluminoso;    contaminação de magmas;    geoquímica isotópica Sr-Nd;   

DOI  :  10.1590/S0001-37652006000200013

来源: SciELO

【 摘 要 】

The Piedade Granite (~600 Ma) was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit) and core (metaluminous titanite-bearing biotite monzogranite BmgT unit) and felsic pink inequigranular granite (Bmg unit) between them. Bmg has high LaN/YbN (up to 100), Th/U (>10) and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (~45), Ba and Sr, fractionated REE patterns (LaN/YbN= 45), 87Sr/86Sr(t)~ 0.710, epsilonNd(t) ~ -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta). The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t) = 0.713-0.714; epsilonNd(t)= -14 to -16), similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

【 授权许可】

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