The zircon record of complex high-grade gneiss terrains is key to interpreting their tectonothermal evolution. Typically, such studies focus on zircon-rich, felsic rocks, which commonly have a complicated (partial melting, inheritance, partial dissolution, and reprecipitation) zircon record. Here we show that metamorphosed mafic rocks and their retained partial melts (i.e. in situ leucosomes) provide a record of the evolution of crustal blocks that is simpler and easier to interpret. We apply our method to the Archaean high-grade gneisses of the iconic Lewisian complex of NW Scotland and use it to test the proposed terrane model that is based largely on zircon geochronology. Our work focusses on the mafic migmatites of the central region, where we identified the long-established metamorphic age clusters of ca. 2.75 Ga and 2.5 Ga, as well as ca. 2.85 Ga protolith ages. A key finding is that these ages are recognised across both putative terrane blocks of the central region previously proposed to record different tectonothermal histories. Our oldest (inherited) ages are similar to those within other blocks outside the central region. Thus, all these blocks likely share a common pre-metamorphic history, questioning the validity of the terrane model for the Lewisian complex. We demonstrate that mafic lithologies provide a powerful tool for identifying key stages in the polyphase evolution of metamorphic complexes that typify Earth’s earliest rock records and offer additional context for assessing Earth’s geodynamic evolution.

复杂的高级片麻岩地形的锆石记录是解释其构造热演化的关键。通常，此类研究集中在富含锆石的长英质岩石上，这些岩石通常具有复杂的（部分熔融，继承，部分溶解和再沉淀）锆石记录。在这里，我们显示了变质的铁镁质岩及其保留的部分熔体（即原位leucosomes）提供了一个更容易解释的地壳块演化的记录。我们将方法应用于苏格兰西北部标志性刘易斯综合体的古生高级片麻岩，并用它来测试所提出的地层模型，该模型主要基于锆石年代学。我们的工作集中在中部地区的铁镁铁矿化岩上，在那里我们确定了长期存在的大约ca的变质年龄簇。2.75 Ga和2.5 Ga，以及大约 2.85 Ga原生质年龄。一个关键的发现是，这些年龄在先前提议记录不同构造热历史的中部地区的两个假定的地块中都得到了认可。我们最古老的（继承的）年龄与中部地区以外其他街区的年龄相似。因此，所有这些区块都可能具有共同的变质前历史，质疑地形模型对刘易斯群的有效性。我们证明，镁铁质岩性提供了一个强大的工具，可用于识别代表地球最早的岩石记录的变质复合体的多相演化中的关键阶段，并为评估地球的地球动力学演化提供了其他背景。