Abstract A decimetre-thick, deeply weathered sill intrusive in the Itabira iron formation and exposed at the historical Veloso underground mine in Ouro Preto, Minas Gerais, contains three populations of magmatic zircon grains: (i) xenocrysts with Archaean Pb–Pb and Hf model ages; (ii) xenocrysts of Palaeoproterozoic crystallisation ages of ca. 2200 Ma, with superchondritic eHf2.2 Ga values between 1.5 and 11.6; (iii) autocrysts and overgrowths formed at ca. 620 Ma, with eHf0.62 Ga values between −17.6 and 11.5 (mean = 1.5 ± 6.9, n = 15). Furthermore, there is evidence for zircon age reset at ca. 565 Ma. The three magmatic zircon populations indicate that the sill emplaced during the Neoproterozoic and probed different magmatic sources at depth, comprising anatectically reworked Palaeoproterozoic and Archaean felsic rocks. Variable Hf-isotope compositions of zircon rims and whole-rock geochemical data additionally suggest a hybrid origin for the sill magma. Our results provide the first evidence that the southern edge of the Quadrilatero Ferrifero is underlain not only by Archaean, but also by juvenile Palaeoproterozoic rocks, similar to those exposed in the adjacent Mineiro belt, and that the latter became accreted to the Sao Francisco craton prior to lower crustal anatexis during an early extension at ca. 620 Ma.

中文翻译：

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巴西米纳斯吉拉斯州 Quadrilátero Ferrífero 中新元古代岩浆活动的第一个证据，以及大地构造意义

摘要 在 Itabira 铁地层侵入并暴露在位于米纳斯吉拉斯州 Ouro Preto 历史悠久的 Veloso 地下矿中的一个分米厚、深度风化的基石包含三个岩浆锆石颗粒群：(i) 具有太古代 Pb-Pb 和 Hf 模型的异种晶体年龄；(ii) 古元古代结晶年龄的异种晶体。2200 Ma，超球粒陨石 eHf2.2 Ga 值在 1.5 和 11.6 之间；（iii）自晶和过度生长形成于约。620 Ma，eHf0.62 Ga 值介于 -17.6 和 11.5 之间（平均值 = 1.5 ± 6.9，n = 15）。此外，有证据表明锆石年龄在大约 10 小时重置。565 马。三个岩浆锆石群表明该基石在新元古代期间就位，并在深处探测了不同的岩浆源，包括深熔改造的古元古代和太古代长英质岩石。锆石边缘的可变 Hf 同位素组成和全岩地球化学数据另外表明基石岩浆的混合来源。我们的研究结果提供了第一个证据，即 Quadrilatero Ferrifero 的南边缘不仅有太古宙，而且还有幼年的古元古代岩石，类似于邻近的 Mineiro 带中暴露的岩石，并且后者在之前已被吸积到圣弗朗西斯科克拉通在约 . 620 毫安。并且后者在下地壳深熔之前在大约 10 的早期延伸过程中被吸积到了圣弗朗西斯科克拉通。620 毫安。并且后者在下地壳深熔之前在大约 10 的早期延伸过程中被吸积到了圣弗朗西斯科克拉通。620 毫安。