We report textural and compositional data for the titanosilicate narsarsukite [Na2(Ti,Fe3+)Si4(O,F)11] in peralkaline granites from the Papanduva Pluton in Graciosa Province, south-southeastern Brazil. Two distinct narsarsukite generations, one late magmatic and the other post-magmatic, were identified on the basis of textural and compositional features. The magmatic generation consists of larger, euhedral to subhedral variably zoned crystals and late poikilitic intergrowths between narsarsukite and albite laths, representing the crystallisation of the latest melt pockets. The post-magmatic generation forms smaller, typically fibrous crystals and irregular aggregates that occur interstitially or replace the primary mafic minerals, particularly arfvedsonite. Compositions of narsarsukite from the Papanduva Pluton cover most of the compositional range described in known occurrences. The magmatic generation is enriched in Zr and depleted in Al. The Fe3+ and Al contents show a positive correlation for the magmatic crystals, but a negative correlation for the post-magmatic narsarsukite. The Al/Fe3+ ratios are higher in the post-magmatic crystals and can be used to discriminate between the two generations. The compositional variations are controlled mainly by the heterovalent substitution (Ti, Zr)4+ + O2– = (Al, Fe)3+ + F1–, and are compatible with (OH)1– ions in the O site. Narsarsukite has significantly higher concentrations of mid REE+Y and HFSE and very low to absent contents of LREE and LILE relative to the host-rocks. The average REE pattern of the magmatic crystals is highly fractionated, consistent with the expected strong preference for the smaller HREE. The post-magmatic crystals that replace arfvedsonite have flatter patterns, with higher concentrations of LREE and MREE. Their compositions suggest a fluid phase relatively rich in HFSE, REE, Y, Pb, Th and U. Narsarsukite is a common phase in strongly peralkaline granites such as the Papanduva Pluton and the well-known Strange Lake Complex, and should be considered a diagnostic mineral of highly peralkaline SiO2-oversaturated rocks containing rare Ti and Zr mineral assemblages.

我们报告了巴西东南部格拉西奥萨省帕潘杜瓦岩体的过碱性花岗岩中钛硅酸盐纳沙苏铁矿 [Na 2 (Ti,Fe 3+ )Si 4 (O,F) 11 ] 的结构和成分数据。根据结构和成分特征，确定了两个不同的纳沙苏克岩代，一个是晚期岩浆期，另一个是后岩浆期。岩浆生成由较大的自形到亚面体可变分区晶体和纳沙苏铁矿和钠长石板条之间的晚期异晶质共生体组成，代表了最新熔池的结晶。岩浆后生成物形成较小的、通常为纤维状的晶体和不规则的聚集体，它们出现在间隙中或取代原生镁铁质矿物，特别是铝镁铁矿。帕潘杜瓦岩体中的纳沙苏铁矿的成分涵盖了已知矿点中描述的大部分成分范围。岩浆生成富锆、贫铝。 Fe 3+和Al 含量对于岩浆晶体呈正相关，而对于岩浆后纳沙苏铁矿则呈负相关。岩浆后晶体中的Al/Fe 3+比率较高，可用于区分两代。组成变化主要由异价取代(Ti, Zr) 4+ + O 2– = (Al, Fe) 3+ + F 1–控制，并且与O 位中的(OH) 1–离子相容。相对于主岩，纳沙苏特矿的中 REE+Y 和 HFSE 浓度显着较高，而轻稀土元素 (LREE) 和 LILE 含量极低甚至不存在。岩浆晶体的平均稀土元素模式高度分异，与预期的对较小重稀土元素的强烈偏好一致。取代 arfvedsonite 的岩浆后晶体具有更平坦的图案，含有更高浓度的轻稀土和重稀土。它们的成分表明流体相相对富含 HFSE、REE、Y、Pb、Th 和 U。Narsarsukite 是强过碱性花岗岩（例如 Papanduva 岩体和著名的 Strange Lake Complex）中的常见相，应被视为诊断性相高过碱性SiO 2矿物——含有稀有Ti 和Zr 矿物组合的过饱和岩石。