Abstract The Lower Cretaceous Jacupiranga complex, in the central-southeastern portion of the South American Platform, includes carbonatites in close association with silicate rocks (i.e. strongly and mildly silica-undersaturated series). Here we document the first hafnium isotope data on the Jacupiranga complex, together with new trace element and Pb isotope compositions. Even though liquid immiscibility from a carbonated silicate melt has been proposed for the genesis of several Brazilian carbonatites, isotopic and geochemical (e.g., Ba/La ratios, lack of pronounced Zr-Hf and Nb-Ta decoupling) information argues against a petrogenetic relationship between Jacupiranga carbonatites and their associated silicate rocks. Thus, an origin by direct partial melting of the mantle is considered. The isotopic compositions of the investigated silicate samples are coherent with a heterogeneously enriched subcontinental lithospheric mantle (SCLM) source of rather complex evolution. At least two metasomatic processes are constrained: (1) a first enrichment event, presumably derived from slab-related fluids introduced into the SCLM during Neoproterozoic times, as indicated by consistently old TDM ages and lamprophyre trace signatures, and (2) a Mesozoic carbonatite metasomatism episode of sub-lithospheric origin, as suggested by eNd-eHf values inside the width of the terrestrial array. The Jacupiranga parental magmas might thus derive by partial melting of distinct generations of metasomatic vein assemblages that were hybridized with garnet peridotite wall-rocks.

中文翻译：

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Hf-Pb 同位素和微量元素对 Jacupiranga 杂岩（巴西）起源的限制：对碳酸岩成因和岩石圈地幔多阶段交代作用的洞察

摘要 位于南美地台中东南部的下白垩统 Jacupiranga 杂岩包括与硅酸盐岩（即强和中度二氧化硅不饱和系列）密切相关的碳酸盐岩。在这里，我们记录了 Jacupiranga 复合体的第一个铪同位素数据，以及新的微量元素和 Pb 同位素组成。尽管已提出碳酸盐硅酸盐熔体的液体不混溶性是几种巴西碳酸岩的成因，但同位素和地球化学（例如，Ba/La 比率、缺乏明显的 Zr-Hf 和 Nb-Ta 解耦）信息反对Jacupiranga 碳酸岩及其伴生的硅酸盐岩。因此，考虑了地幔直接部分熔化的起源。所研究的硅酸盐样品的同位素组成与相当复杂演化的非均质富集的次大陆岩石圈地幔 (SCLM) 来源一致。至少有两个交代过程受到限制：（1）第一次富集事件，可能来自于新元古代时期引入 SCLM 的板块相关流体，如始终古老的 TDM 年龄和斑岩痕迹特征所示，以及（2）中生代碳酸岩如地球阵列宽度内的 eNd-eHf 值所表明的那样，次岩石圈起源的交代作用事件。因此，Jacubiranga 母岩浆可能是由与石榴石橄榄岩围岩杂交的不同代交代脉组合的部分熔融产生的。