Abstract We report U–Pb/Hf/O isotopic measurements of zircon extracted from meta-igneous rocks exposed in the Assean Lake crustal complex, northwestern Superior craton (Canada). With crystallization ages of ca. 3.22 Ga, zircon from the Assean Lake crustal complex are among the oldest reported in the Superior craton. The Hf and O isotope compositions of zircon indicate that these meta-igneous rocks derive from a mantle component with a relatively primitive Hf isotope composition, similar to chondrites, that was uncontaminated by elevated δ18O material (eHf,initial ~ 0 and δ18OVSMOW ~ 5.5‰). These features are shared by the large majority of the zircon extracted from the oldest (meta)-igneous rocks exposed in Archean terranes. Positive eHf deviations in Archean zircons are typically observed in magmas that post-date the oldest magmatic activity in a given terrain. This temporal variability in magma source regions may reflect a sequence of events comprising: (i) felsic magmatism derived from undepleted mantle components followed by, (ii) re-melting of the same mantle component producing the depleted Hf signatures in zircon and then, (iii) accretion of the proto-craton and reworking of the whole-system enabling stabilization.

中文翻译：

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上克拉通早期地壳演化——Assean 湖复合体锆石的 AU-PB、HF 和 O 同位素研究以及与其他克拉通早期地壳的比较

摘要 我们报告了从出露于苏必利尔克拉通（加拿大）西北部 Assean Lake 地壳复合体中的变质火成岩中提取的锆石的 U-Pb/Hf/O 同位素测量值。随着结晶年龄约。3.22 Ga，来自 Assean Lake 地壳复合体的锆石是苏必利尔克拉通中报道的最古老的锆石。锆石的 Hf 和 O 同位素组成表明，这些变质火成岩来自具有相对原始 Hf 同位素组成的地幔组分，类似于球粒陨石，未受到升高的 δ18O 物质（eHf，初始 ~ 0 和 δ18OVSMOW ~ 5.5‰）的污染）。从太古代地体中暴露的最古老（变质）火成岩中提取的大部分锆石都具有这些特征。太古宙锆石的正 eHf 偏差通常在给定地形中最古老的岩浆活动之后的岩浆中观察到。岩浆源区的这种时间变化可能反映了一系列事件，包括：(i) 来自未耗尽地幔成分的长英质岩浆作用，然后是，(ii) 相同地幔成分的重新熔化，在锆石中产生耗尽的 Hf 特征，然后，( iii) 原始克拉通的增生和整个系统的改造以实现稳定。