The Pb isotope ratios of olivine- and nepheline-normative rocks from the Ponte Nova mafic-ultramafic alkaline massif (SE Brazil) corroborate evidence that the assimilation of crustal components played an important role in this small magma chamber. New whole-rock ²⁰⁶Pb/²⁰⁴Pb_i (17.655–18.362) and ²⁰⁸Pb/²⁰⁴Pb_i (38.029–38.591) ratios correlate negatively with ¹⁴³Nd/¹⁴⁴Nd_i (0.512216–0.512555) and positively with ⁸⁷Sr/⁸⁸Sr_i (0.70432–0.70641). The whole-rock ratios of ²⁰⁷Pb/²⁰⁴Pb_i (15.494–15.556) are not clearly correlated with other isotopic pairs. Most of Ponte Nova samples straddle the curve for μ = ∼8.7, but the majority plot to the right of the geochron, indicating U enrichment. The least contaminated samples plot within the Tristan-type isotopic composition and close to the Trindade isotopic field and might have formed through mixing between OIB and EM-I components. Mixing model isotope curves correlating Sr–Nd–Pb isotope ratios, considering the most pristine compositions (central plug) and the main host rocks of this area, indicate low crustal contributions for some intrusions and high contributions for others. More pronounced contributions from local metagranitic host rocks are associated with intrusions showing high amounts of crustal components. The wide interval of calculated Nd depleted-mantle model ages (T_DM: 703–1217 Ma) for Ponte Nova rocks indicates that crustal contamination and clinopyroxene accumulation can strongly modify these values versus those from liquid compositions (nearby alkaline dikes). Therefore, rocks affected by crustal contamination and clinopyroxene accumulation should not be considered for periods of enrichment/metasomatism of the mantle source.

来自蓬特诺瓦（Ponte Nova Nova）镁铁-超氟酸碱性地块（巴西东南部）的橄榄石-和霞石-规范岩石的铅同位素比证实了地壳成分的同化作用在这个小型岩浆室内起着重要作用。新的整岩²⁰⁶ Pb / ²⁰⁴ Pb _i（17.655-18.362）和²⁰⁸ Pb / ²⁰⁴ Pb _i（38.029-38.591）的比率与¹⁴³ Nd / ¹⁴⁴ Nd _i（0.512216-0.512555）负相关，与⁸⁷ Sr / ⁸⁸ Sr正相关_我（0.70432-0.70641）。全岩比²⁰⁷ Pb /²⁰⁴铅_我（15.494–15.556）与其他同位素对没有明确关联。Ponte Nova的大部分样本横跨曲线，μ=约8.7，但大多数标绘在年代钟的右侧，表明U富集。污染最小的样品位于Tristan型同位素组成内且靠近Trindade同位素场，并且可能是通过OIB和EM-1组分之间的混合形成的。考虑到最原始的成分（中心塞）和该地区主要的主岩，混合模型的同位素曲线将Sr–Nd–Pb同位素比值关联起来，表明某些侵入体的地壳贡献较低，而另一些侵入体的贡献较高。局部后生代宿主岩的显着贡献与显示大量地壳成分的侵入有关。计算得出的Nd耗尽幔模型年龄的宽间隔（T_DM：Ponte Nova岩石的703–1217 Ma）表明，与液体成分（附近的碱性堤防）相比，地壳污染和斜辉石的积聚可以极大地改变这些值。因此，在地幔源的富集/成岩作用时期，不应考虑受地壳污染和斜向辉石堆积影响的岩石。