Abstract The petrological and geochemical compositions of Archean crust hold important information about the interaction between continental crust and lithospheric mantle. Here we apply in-situ microanalysis of Pb isotopes of the feldspars, which were collected from the high-grade terranes of the Taihua Group in Lushan area along the Southern North China Craton (S-NCC), by femtosecond laser ablation (fLA)-MC-ICPMS technique. The results show large variation in Pb isotopic compositions in plagioclase grains in different rock types. The feldspars in the granitoid gneisses show lower and variable radiogenic Pb isotopic ratios (206Pb/204Pb = 13.8–16.8, 207Pb/204Pb = 14.6–15.1 and 208Pb/204Pb = 33.9–36.6) than that in the amphibolites (206Pb/204Pb = 14.1–17.7, 207Pb/204Pb = 14.6–15.6, 208Pb/204Pb = 33.6–38.1) and lenticular garnet granulites (206Pb/204Pb = 14.4–17.7, 207Pb/204Pb = 14.7–15.7, 208Pb/204Pb = 33.7–37.7). Moreover, based on the single-stage Pb evolution model (common Pb in plagioclase), the age of the granitoid gneisses extracted from the mantle was estimated at 2.74 ± 0.33 Ga, corresponding to the age of important period of crustal growth (~2.7 Ga), and suggesting that the low-Pb granitoid gneisses are representative of the direct samples of the Archean crust. In addition, we also newly reported what was the Pb isotope characteristics of garnet granulites and pyroxene granulites in the Lower Taihua Group once located at the lower crustal level. The ubiquitous Pb isotope disequilibrium among different feldspar grains, especially in the overgrowth rims possessing more radiogenic Pb isotopes, suggests input of exotic melt/fluid with high μ (238U/204Pb) during the process of retrograde metamorphism. The large present-day Pb isotopic heterogeneity is probably due to various geological conditions experienced by different rocks.

中文翻译：

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太古宙大陆下地壳中高异质铅同位素组成：来自华北克拉通南部太华群高级变质岩套的洞察

摘要 太古代地壳的岩石和地球化学成分是大陆地壳与岩石圈地幔相互作用的重要信息。在这里，我们应用飞秒激光烧蚀 (fLA) 对从华北克拉通南部芦山地区泰华​​群高品位地体 (S-NCC) 收集的长石 Pb 同位素进行原位微量分析 - MC-ICPMS 技术。结果表明，不同岩石类型的斜长石颗粒中铅同位素组成存在较大差异。花岗岩类片麻岩中的长石显示出较低且可变的放射成因 Pb 同位素比（206Pb/204Pb = 13.8-16.8、207Pb/204Pb = 14.6-15.1 和 208Pb/204Pb = 33.9-36.9Pb = 33.9-36Pb = 36.9-36Pb）106Pb/26Pb –17.7, 207Pb/204Pb = 14.6–15.6, 208Pb/204Pb = 33.6–38。1) 和透镜状石榴石麻粒岩 (206Pb/204Pb = 14.4–17.7, 207Pb/204Pb = 14.7–15.7, 208Pb/204Pb = 33.7–37.7)。此外，基于单阶段铅演化模型（斜长石中常见铅），从地幔中提取的花岗岩类片麻岩的年龄估计为2.74±0.33 Ga，对应地壳生长的重要时期（~2.7 Ga )，并表明低铅花岗岩类片麻岩是太古代地壳直接样本的代表。此外，我们还新报道了曾经位于下地壳水平的下太华群石榴石麻粒岩和辉石麻粒岩的Pb同位素特征。不同长石颗粒之间普遍存在的铅同位素不平衡，特别是在具有更多放射性铅同位素的过度生长边缘，表明在逆行变质过程中输入了具有高 μ (238U/204Pb) 的奇异熔体/流体。当今较大的 Pb 同位素非均质性可能是由于不同岩石经历的各种地质​​条件造成的。