Abstract
The Vieirópolis pegmatite field is characterized by amazonite pegmatites inserted in the Borborema Province. The Serra Branca pegmatite is hosted by the Serra Branca granites, which intruded partially the Serra Negra granites, and stands out by its amazonite mineralization. To comprehend the crystallization conditions and the source of this pegmatite and associated Serra Branca and Serra Negra granites, petrographic, mineral chemistry, geochronological and whole-rock geochemical data were used. The Serra Branca pegmatite is Cs-, Rb-, Pb-, Nb-, and Ta-rich. The Serra Branca granites (563 ± 2 Ma) are metaluminous to weakly peraluminous, crystallized under high fO2 conditions, pressure of 2.68-2.80 kbar and temperatures ranging from 667-670°C, with many zircon grains showing inherited cores of Paleoproterozoic ages. The Serra Negra granites (594 ± 4 Ma) comprises metaluminous granites crystallized under high fO2 conditions, temperatures within 711-751°C, pressure varying from 4.72 to 5.42 kbar. Both granites resulted from distinct partial melting degrees of a source similar to the Caicó Complex orthogneisses. The Serra Branca pegmatite geochemical data suggests that it was originated by extreme fractionation of the Serra Branca granites magma. The Serra Branca amazonite pegmatite is the first pegmatite mineralogically and geochemically characterized as Nb-Y-F (NYF)-type from the gadolinite subtype in the Borborema Province.
Highlights
The Borborema Province (BP) in Northeastern Brazil hosts one of the largest, in global scale, pegmatite Province — the Seridó Pegmatite Province (SPP; Santos et al 2014), located in the Rio Grande do Norte domain of the Northern sub-province
This paper focuses on the study of two plutons (Serra Branca and Serra Negra) and the Serra Branca amazonite pegmatite of the Vieirópolis field
This leucogranite facies is characterized by higher Cs, Rb, Pb, Nb, Ta, and lower Ba, K, Sr, P and light rare earth elements (LREE), being similar in shape to those recorded in the Serra Branca amazonite pegmatite (Fig. 15B)
Summary
The Borborema Province (BP) in Northeastern Brazil hosts one of the largest, in global scale, pegmatite Province — the Seridó Pegmatite Province (SPP; Santos et al 2014), located in the Rio Grande do Norte domain of the Northern sub-province. The crystallization age defined to the Serra Negra granitoids is similar to those described in some high-K granitoids from the Transversal sub-province (Guimarães et al 2004, Archanjo & Fetter 2004, Archanjo et al 2008, among others) This sample comprises a biotite amphibole monzogranite collected far away from the pegmatite (6°32’21.4”S, 38°16’45”W). The spidergram from the medium to fine grained leucogranite facies of the Serra Branca pluton is distinct from others Serra Branca and Serra Negra granitoids This leucogranite facies is characterized by higher Cs, Rb, Pb, Nb, Ta, and lower Ba, K, Sr, P and LREE, being similar in shape to those recorded in the Serra Branca amazonite pegmatite (Fig. 15B). Discriminant diagrams reflect the source composition and the processes involved during the magma evolution, rather than the setting in which the melt was generated and crystallized
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