Abstract Melanges are a chaotic mixture of different rock assemblages that can be associated with orogenic belts and suture zones. The Brasilia Belt is a Neoproterozoic orogenic belt in central Brazil, which contains a poorly understood ophiolitic melange. In order to better understand the sedimentation that was associated with this melange, isotopic U–Pb and Lu–Hf analyses on single zircon grains, and Sm–Nd on whole rock samples was conducted on melange metasedimentary rock (garnet-mica-quartz schists and quartzites) and basement (mylonitic granites) assemblages. The quartzite samples have a maximum age of deposition of about 930 Ma, while their negative ƐNd (T) values and TDM, −7.78 to −11.57 and 1.70 to 2.07 Ga, respectively, are similar to other metasedimentary rock units interpreted to have formed in a passive margin environment. ƐHf and Hf TDM model values from the quartzite samples range from −12.72 to 8.99 and 2.56 to 1.36 Ga, respectively. The mylonitic granite has an age of ∼2.1 Ga, ƐHf values ranging from −0.97 to 2.18, and TDM model values ranging from 2.38 to 2.53 Ga, indicating that it was derived from juvenile Paleoproterozoic basement. Results of the garnet-mica schists reveal that they represent two different rock units, defined by two different periods of sedimentation. The first group of garnet-mica schist has a maximum age of deposition of 672 Ma and ƐNd (T) values and TDM -7.90 to −7.62 and 1.82 to 1.88 Ga, respectively. ƐHf and TDM model values range from −23.50 to 11.69 and 3.23 to 1.45 Ga, respectively, and indicate the presence of similar zircon populations as the passive margin sequence and basement zircon population; there is also a contribution of a younger zircon population derived from older reworked crustal material. The second group of garnet-mica schists is marked by a maximum age of deposition of 616 Ma and ƐNd (T) values and TDM ranging from 0.61 to 0.22 and 1.16 to 1.25 Ga, respectively. ƐHf and TDM model values range from −8.24 to 16.04 and 2.97 to 0.79 Ga, respectively. These results also indicate the presence of passive margin and basement zircon populations, but the younger zircon populations are derived from juvenile sources. The depositional periods of the garnet-mica schists occurred between roughly 800 to 650 Ma and 650 to 600 Ma, and indicate that the rocks from the Brasilia Belt register the presence of different depositional environments and basins, which opened, closed and were later dismembered. The quartzites, mylonitic granites and ophiolites most likely represent blocks that were introduced into the melange by sedimentation or tectonic processes.

中文翻译：

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巴西中部巴西利亚带新元古代蛇绿混杂沉积物的来源

摘要 混杂岩是不同岩石组合的混沌混合物，可能与造山带和缝合带有关。巴西利亚带是巴西中部的一个新元古代造山带，其中包含知之甚少的蛇绿混杂岩。为了更好地了解与这种混杂岩有关的沉积作用，对单个锆石颗粒进行同位素 U-Pb 和 Lu-Hf 分析，并对混杂变质沉积岩（石榴石-云母-石英片岩和石英岩）和基底（糜棱花岗岩）组合。石英岩样品的最大沉积年龄约为 930 Ma，而它们的负 ƐNd (T) 值和 TDM，分别为 -7.78 至 -11.57 和 1.70 至 2.07 Ga，与解释为形成于被动保证金环境。来自石英岩样品的 ƐHf 和 Hf TDM 模型值分别介于 -12.72 至 8.99 和 2.56 至 1.36 Ga。糜棱花岗岩的年龄为~2.1 Ga，ƐHf 值范围为-0.97 至2.18，TDM 模型值范围为2.38 至2.53 Ga，表明它来自于幼年古元古代基底。石榴石-云母片岩的结果表明，它们代表了两个不同的岩石单元，由两个不同的沉积时期定义。第一组石榴石-云母片岩的最大沉积年龄分别为 672 Ma 和 ƐNd (T) 值，TDM 分别为 -7.90 至 -7.62 和 1.82 至 1.88 Ga。ƐHf 和 TDM 模型值的范围分别为 -23.50 至 11.69 和 3.23 至 1.45 Ga，表明存在与被动边缘序列和基底锆石群相似的锆石群；更年轻的锆石种群也有贡献，这些锆石来自较旧的重新加工的地壳材料。第二组石榴石-云母片岩的最大沉积年龄为 616 Ma 和 ƐNd (T) 值，TDM 分别为 0.61 至 0.22 和 1.16 至 1.25 Ga。ƐHf 和 TDM 模型值的范围分别为 -8.24 至 16.04 和 2.97 至 0.79 Ga。这些结果还表明存在被动边缘和基底锆石种群，但较年轻的锆石种群来自幼年锆石种群。石榴石-云母片岩的沉积时期大约发生在 800 至 650 Ma 和 650 至 600 Ma 之间，表明巴西利亚带的岩石记录了不同沉积环境和盆地的存在，这些环境和盆地打开、关闭并随后被肢解。石英岩，