Micro-structural and compositional variations of hydrothermal epidote-group minerals from a peralkaline granite, Corupá Pluton, Graciosa Province, South Brazil, and their petrological implications

Anais da Academia Brasileira de Ciências

Silvio R.f. Vlach¹ 

[1] ,Universidade de São Paulo Instituto de Geociências Departamento de Mineralogia e GeotectônicaSão Paulo SP ,Brasil

关键词: allanite;    epidote;    hydrothermal;    compositional variations;    peralkaline granite;    Corupá Pluton;    Graciosa Province;    allanita;    epidoto;    hidrotermal;    variações composicionais;    granito peralcalino;    Pluton Corupá;    Província Graciosa;   

DOI  :  10.1590/S0001-37652012005000024

来源: SciELO

【 摘 要 】

Epidote-group minerals, together with albite, quartz, fluorite, Al-poor and Fe-rich phyllosilicates, zircon, and minor oxides and sulphides, are typical hydrothermal phases in peralkaline alkali-feldspar granites from the Corupá Pluton, Graciosa Province, South Brazil. The epidote-group minerals occur as single crystals and as aggregates filling in rock interstices and miarolitic cavities. They display complex recurrent zoning patterns with an internal zone of ferriallanite-(Ce), followed by allanite-(Ce), then epidote-ferriepidote, and an external zone with allanite-(Ce), with sharp limits, as shown in BSE and X-ray images. REE patterns show decreasing fractionation degrees of LREE over HREE from ferriallanite to epidote. The most external allanite is enriched in MREE. LA-ICP-MS data indicate that ferriallanite is enriched (>10-fold) in Ti, Sr and Ga, and depleted in Mg, Rb, Th and Zr relative to the host granite. Allanite has lower Ga and Mn and higher Zr, Nb and U contents as compared to ferriallanite, while epidote is enriched in Sr, U and depleted in Pb, Zr, Hf, Ti and Ga. The formation of these minerals is related to the variable concentrations of HFSE, Ca, Al, Fe and F in fluids remaining from magmatic crystallization, in an oxidizing environment, close to the HM buffer. L-MREE were in part released by the alteration of chevkinite, their main primary repository in the host rocks.

【 授权许可】

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