Abstract The Aracuai orogen of SE Brazil exposes numerous amounts of magnesian, metaluminous, calc-alkaline, and medium- to high-K granitoid batholiths that were emplaced during early convergence between the Sao Francisco and Congo cratons during West Gondwana assembly in the late Neoproterozoic. Previously proposed sources for these pre-collisional granitoids include the Paleoproterozoic basement and mantle-derived magma based on isotopic signatures, abundant microgranular enclaves and contemporaneous mafic intrusions. Zircons from migmatitic basement gneiss, a noritic intrusion and five granitoid intrusions were analysed for U–Pb–Hf isotopes to evaluate their magma source. Paleoproterozoic migmatites represent addition of juvenile crust in an accretionary orogenic setting at ca. 2.2–2.0 Ga evidenced by their positive zircon eHf values. The Hf isotopic composition of zircon from pre-collisional granitoids has a large range of negative eHf values between −28.8 and −1.7 indicating crustal protoliths. This range of unradiogenic Hf isotopic compositions is explained by inefficient mixing of magmas derived from felsic and mafic Paleoproterozoic sources that hybridised during incremental growth of the plutons. Zircon grains of contemporaneous mafic intrusions display slightly higher, yet enriched, Hf isotopic compositions consistent with crustal contamination of mantle magmas. The new Hf isotope data, integrated with other chemical and isotopic evidence, suggest derivation of the pre-collisional granitoids from lower crustal sources of the Paleoproterozoic basement, with only minor contributions from mantle-derived magmas. Thus, magmatism of the Aracuai orogen related to the assembly of West Gondwana was dominantly a crustal-reworking event.

中文翻译：

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来自 Araçuaí 造山带（巴西东南部）的 Cordilleran 型新元古代花岗岩的古元古代来源：Hf 同位素锆石成分的限制

摘要 巴西东南部的 Aracuai 造山带出露了大量的镁质、金属铝质、钙碱性和中高 K 花岗岩基岩，这些基岩是在新元古代晚期西冈瓦纳大陆组装期间，在圣弗朗西斯科克拉通和刚果克拉通之间的早期辐合期间形成的。先前提出的这些碰撞前花岗岩的来源包括古元古代基底和基于同位素特征的地幔衍生岩浆、丰富的微粒飞地和同时期的镁铁质侵入体。分析了混合岩基底片麻岩、一个紫砂岩侵入体和五个花岗岩侵入体中的锆石的 U-Pb-Hf 同位素，以评估它们的岩浆来源。古元古代混合岩代表了在约 100 年的增生造山环境中新生地壳的添加。2.2–2.0 Ga 由它们的正锆石 eHf 值证明。来自碰撞前花岗岩的锆石的 Hf 同位素组成在 -28.8 和 -1.7 之间具有很大范围的负 eHf 值，表明是地壳原岩。这种非放射性 Hf 同位素组成的范围是由源自长英质和镁铁质古元古代源的岩浆的低效混合解释的，这些岩浆在岩体的增量生长过程中杂交。同时代镁铁质侵入体的锆石颗粒显示出略高但富集的 Hf 同位素组成，与地幔岩浆的地壳污染一致。新的 Hf 同位素数据与其他化学和同位素证据相结合，表明碰撞前花岗岩来自古元古代基底的下地壳源，而仅少量来自地幔的岩浆。因此，