Abstract The assembly and long-term evolution of the Eastern Block of the North China Craton are poorly constrained. Here we use bulk rock geochronological and geochemical data from mafic meta-igneous rocks (hornblendites, amphibolites and a metagabbro) of the Liaohe Group to reconstruct the Neoarchean to Paleoproterozoic history of the Jiao-Liao-Ji Belt, located between the Longgang and Nangrim blocks that together form the Eastern Block of the North China Craton. The mafic/ultramafic meta-igneous rocks have intrusive or tectonic contacts with the Liaoji granitic rocks (~2.2–2.0 Ga), which form the basement of the Jiao-Liao-Ji Belt. The major and trace element data indicate that the protoliths had calc-alkaline composition and formed along an active continental margin subduction zone. The mafic rocks form a whole-rock 176Lu/177Hf isochron with an age of 2.25 ± 0.31 Ga, overlapping with U Pb zircon ages for mafic and granitic rocks from the Jiao-Liao-Ji Belt and consistent with being the emplacement age of the mafic protoliths along the active continental margin. In contrast, the whole-rock 147Sm/144Nd isochron age of 2.83 ± 0.18 Ga is likely to reflect the average age of the lithospheric mantle source from which the mafic/ultramafic protoliths were extracted. Together with geological evidence, we propose that the southwestern portion of the Longgang Block was an active continental margin since at least the early Paleoproteorozic. Literature age data from metamorphic zircons show that peak granulite metamorphism took place at ~1.96–1.88 Ga, resulting from the collisional event that fused the Longgang and Nangrim blocks into the Eastern Block of the North China Craton. Our bulk-rock 207Pb/206Pb age of 1824 ± 19 Ma and our 87Rb/86Sr age of 1671 ± 58 Ma reflect retrograde (cooling) stages during the exhumation of the Jiao-Liao-Ji Belt after the orogenesis.

中文翻译：

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从基性辽河变火成岩年代学和地球化学看华北克拉通胶辽冀带2.8～1.7 Ga历史

摘要 华北克拉通东部地块的组装和长期演化约束条件较差。在这里，我们利用辽河群镁铁质变火成岩（角闪石、角闪岩和变辉长岩）的大块岩石年代学和地球化学数据重建位于龙岗和南格里姆地块之间的胶辽冀带的新太古代到古元古代历史。共同构成了华北克拉通东部地块。基性/超基性变火成岩与辽冀花岗岩（~2.2-2.0 Ga）侵入或构造接触，形成胶辽冀带的基底。主量和微量元素数据表明，原岩具有钙碱性成分，沿活动大陆边缘俯冲带形成。基性岩形成全岩176Lu/177Hf等时线，年龄为2.25±0.31 Ga，与胶辽冀带基性岩和花岗岩的U Pb锆石年龄重叠，与基性岩的侵位年龄一致沿活动大陆边缘的原岩。相比之下，2.83 ± 0.18 Ga 的全岩 147Sm/144Nd 等时线年龄可能反映了从中提取基性/超基性原岩的岩石圈地幔源的平均年龄。结合地质证据，我们认为龙岗地块的西南部分至少从古元古代开始就为活动大陆边缘。来自变质锆石的文献时代数据表明，峰值麻粒岩变质作用发生在~1.96-1.88 Ga，由龙岗和南格里姆地块融合成华北克拉通东部地块的碰撞事件产生。我们的大块岩石 207Pb/206Pb 年龄为 1824±19 Ma，我们的 87Rb/86Sr 年龄为 1671±58 Ma，反映了胶辽冀带在造山作用后折返过程中的逆行（冷却）阶段。