Records of Earth's primitive crust are scarce. Eoarchean (older than 3.6 Ga) banded mafic to felsic gneisses have been discovered in the São Francisco Craton, Brazil, pushing back by over 100 million years the oldest gneisses known to date in South America (3.5 Ga). Zircon U‐Pb data yield rock ages from 3,598 to 3,642 Ma with a few ca. 3.65–3.69 Ga grains suggesting even older rocks in the area. Zircon grains show significantly negative to nearly chondritic initial εHf values and two‐stage model ages from 3.82 to 4.33 Ga, which may indicate the existence of a recycled Hadean to early Eoarchean crust in the region. The felsic gneisses are chemically similar to the low‐pressure Tonalite‐Trondhjemite‐Granodiorite association whereas the mafic gneisses have geochemical signatures that resemble within‐plate basaltic andesite to andesite of Iceland (icelandites). The results are relevant to constrain the composition of Earth's first continental crust.

中文翻译：

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巴西圣弗朗西斯科·克雷顿的出生地：从3.60到3.64的Mairi片麻岩复合体的Ga片麻岩的证据

缺乏关于地球原始地壳的记录。在巴西圣弗朗西斯科·克拉顿发现了Eoarchean（年龄大于3.6 Ga）带镁铁质至长英质的片麻岩，将迄今已知的南美最古老的片麻岩（3.5 Ga）推回了超过一亿年。Zircon U-Pb数据产生的岩石年龄为3,598至3,642 Ma，大约有3。3.65–3.69的Ga晶粒暗示该地区的岩石更老。锆石晶粒显示出明显的负碎屑至初始软骨碎屑的初始εHf值，且两阶段模型年龄为3.82至4.33 Ga，这可能表明该地区存在着从哈德族到早期欧陶纪地壳的再生哈德族。长笛质片麻岩在化学上类似于低压Tonalite-Trondhjemite-Granodiorite组合，而镁铁质片麻岩的地球化学特征类似于板内玄武质安山岩到冰岛安山岩（冰岛）。这些结果与限制地球上第一个大陆壳的组成有关。