Abstract Early and Late Cretaceous alkaline and alkaline–carbonatitic complexes from southern Brazil are located along the main tectonic lineaments of the South America Platform. Calcium-, magnesium-, and ferrocarbonatites are well represented and frequently associated even in the same complex. Primary carbonates present significant variations in C–O isotopic compositions, which are mainly due to isotope exchange with H2O–CO2-rich hydrothermal fluids, whereas fractional crystallization or liquid immiscibility probably affects the δ18O and δ13C values by no more than 2δ‰. Our isotope exchange model implies that the most significant isotopic variations took place in a hydrothermal environment, e.g., in the range 400–80°C, involving fluids with the CO2/H2O ratio ranging from 0.8 to 1. Sr–Nd–Pb isotope systematics highlight heterogeneous mixtures between HIMU and EMI mantle components, similar to the associated alkaline rocks and the flood tholeiites from southern Brazil. In spite of the strong variation shown by C–O isotopes, Sr–Nd–Pb–Os isotopic systematics could be related to an isotopically enriched source where the chemical heterogeneities reflect a depleted mantle “metasomatized” by small-volume melts and fluids rich in incompatible elements. These fluids are expected to have promoted crystallization of K-rich phases in the mantle, which produced a veined network variously enriched in LILE and LREE. The newly formed veins (enriched component) and peridotite matrix (depleted component) underwent a different isotopic evolution with time as reflected by the carbonatites. These conclusions may be extended to the whole Paraná–Etendeka system, where isotopically distinct parent magmas were generated following two main enrichment events of the subcontinental lithospheric mantle at 2.0–1.4 and 1.0–0.5 Ga, respectively, as also supported by Re–Os systematics. The mantle sources preserved the isotopic heterogeneities over a long time, suggesting a nonconvective lithospheric mantle beneath different cratons or intercratonic regions. Overall, the data indicate that the alkaline–carbonatitic magmatism originated from a locally heterogeneous subcontinental mantle.

中文翻译：

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来自巴西南部地台的碳酸岩：综述。二：同位素证据

摘要 巴西南部早、晚白垩世碱性和碱性-碳酸盐岩杂岩位于南美洲地台主要构造线沿线。钙-、镁-和碳酸亚铁具有很好的代表性，甚至在同一个复合物中也经常伴生。原生碳酸盐的 C-O 同位素组成存在显着变化，这主要是由于与富含 H2O-CO2 的热液流体的同位素交换，而分步结晶或液体不混溶可能影响 δ18O 和 δ13C 值不超过 2δ‰。我们的同位素交换模型表明，最显着的同位素变化发生在热液环境中，例如，在 400-80°C 的范围内，涉及 CO2/H2O 比率范围为 0.8 到 1 的流体。Sr-Nd-Pb 同位素系统学突出了 HIMU 和 EMI 地幔组分之间的异质混合物，类似于巴西南部相关的碱性岩石和泛滥拉斑岩。尽管 C-O 同位素显示出强烈的变化，但 Sr-Nd-Pb-Os 同位素系统学可能与同位素富集源有关，其中化学异质性反映了被小体积熔体和富含不相容的元素。预计这些流体会促进地幔中富钾相的结晶，从而产生富含 LILE 和 LREE 的脉络网络。正如碳酸岩所反映的那样，新形成的脉（富集组分）和橄榄岩基质（贫化组分）随着时间经历了不同的同位素演化。这些结论可以扩展到整个巴拉那-埃滕德卡系统，其中同位素不同的母岩浆是在次大陆岩石圈地幔分别在 2.0-1.4 和 1.0-0.5 Ga 的两次主要富集事件之后产生的，这也得到 Re-Os 系统学的支持. 地幔源长期保留了同位素异质性，表明不同克拉通或克拉通间区域下方存在非对流岩石圈地幔。总体而言，数据表明碱性-碳酸岩岩浆作用起源于局部异质次大陆地幔。地幔源长期保留了同位素异质性，表明不同克拉通或克拉通间区域下方存在非对流岩石圈地幔。总体而言，数据表明碱性-碳酸岩岩浆作用起源于局部异质次大陆地幔。地幔源长期保留了同位素异质性，表明不同克拉通或克拉通间区域下方存在非对流岩石圈地幔。总体而言，数据表明碱性-碳酸岩岩浆作用起源于局部异质次大陆地幔。