Abstract Numerous studies suggest that various secular geologic and geochemical transitions occurred between ~3.2 Ga and 2.5 Ga. During this age-window, the ~2.70 Ga tectono-thermal event of the Neoarchean is by far the most influential, and is unusual in terms of coeval mafic-felsic magmatic rocks which were interpreted to reflect widespread crustal accretion. Here we report the early Neoarchean TTG and potassic granite association preserved in the Yunmengshan area, Taihang Mountain, North China Craton (NCC). TTG and potassic granites emplaced at 2712 ± 65 to 2644 ± 25 Ma, followed by ~2.57 to 2.50 Ga metamorphism and partial anatexis. TTG has geochemical features corresponding to high-Al medium-pressure (MP) TTG. Their high CaO, low to moderate Al2O3/(FeOT + MgO), and positive eHf (t) values (+3.8 to +7.2) with TDM2 of 2.96 to 2.75 Ga, indicate that they formed by partial melting of juvenile low-K mafic rocks, representative of crustal accretion. Besides, TTG can be subdivided into two groups based on Eu anomalies. Those with Eu/Eu* 300 ppm plus elevated Sr/Y > 40, (La/Yb)N > 12 and Eu/Eu* >1.0). The high Eu/Eu*, Sr/Y and low Yb probably represent the contribution of amphibole fractionation and plagioclase accumulation during the magma evolution. The evidence favors an arc-related setting for the TTG. The early Neoarchean potassic granites are monzogranite to syenogranite, and formed shortly after TTG. They belong to high-K calc-alkaline to shoshonitic I-type granite, and display depleted and concave-upward REE patterns between middle and heavy REEs and higher Zr/Sm ratios (69.6 on average) than TTG (45.4). The calculated eHf (t) values are mainly positive (+1.4 to +7.0) with TDM2 from 3.03 Ga to 2.72 Ga, together with low Al2O3/(FeOT + MgO), low to moderate CaO and high K2O/Na2O ratios, indicating a high-K mafic crustal source with metapelite involvement. Meanwhile, we reviewed geochemical data of the early Neoarchean TTGs published in the NCC and other cratons abroad. The results show that samples from Trans-North China Orogen in NCC have lower Y contents, higher Sr/Y and (La/Yb)N ratios, and more depleted HREE than those from Eastern Block, which could be interpreted to reflect an increase in the depth of melting. Alternatively, according to previous studies and comparison globally, elevated Sr/Y values could also reflect increased consumption of plagioclase in melting reactions due to higher temperatures, or magma fractionation. Therefore, it mostly lacks a clear distinction between the “arc” and “non-arc” settings based on geochemistry. However, many researchers put forward evidence that subduction was well attested in the late Archean (3.0 to 2.5 Ga), but it might be unstable.

中文翻译：

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华北克拉通太行山东南基新太古代早期(2.75～2.70 Ga)地壳生长及改造过程的划分

摘要 大量研究表明~3.2 Ga 和2.5 Ga 之间发生了各种长期地质和地球化学转变。在这个年龄窗口中，新太古代的~2.70 Ga 构造热事件是迄今为止影响最大的，在同期的镁铁质-长英质岩浆岩被解释为反映了广泛的地壳增生。在这里，我们报告了在华北克拉通 (NCC) 太行山云梦山地区保存的早期新太古代 TTG 和钾质花岗岩组合。TTG 和钾质花岗岩在 2712 ± 65 至 2644 ± 25 Ma 发生，随后是~2.57 至 2.50 Ga 变质作用和部分退烧。TTG具有与高铝中压（MP）TTG相对应的地球化学特征。它们的高 CaO、低到中等的 Al2O3/(FeOT + MgO) 和正 eHf (t) 值（+3.8 到 +7.2），TDM2 为 2.96 到 2.75 Ga，表明它们是由年轻的低 K 基性岩的部分熔融形成的，代表地壳增生。此外，TTG 可以根据 Eu 异常分为两组。Eu/Eu* 300 ppm 加上升高的 Sr/Y > 40、(La/Yb)N > 12 和 Eu/Eu* > 1.0）。高 Eu/Eu*、Sr/Y 和低 Yb 可能代表了岩浆演化过程中角闪石分馏和斜长石积累的贡献。证据支持 TTG 的弧相关设置。新太古代早期钾质花岗岩为二长花岗岩至正长花岗岩，形成于TTG后不久。它们属于高钾钙碱性至钾长石 I 型花岗岩，在中重稀土之间显示出贫化和上凹的 REE 模式，Zr/Sm 比（平均 69.6）高于 TTG（45.4）。计算出的 eHf (t) 值主要为正值（+1.4 至 +7。0) 与 TDM2 从 3.03 Ga 到 2.72 Ga，以及低 Al2O3/(FeOT + MgO)、低至中等 CaO 和高 K2O/Na2O 比率，表明高钾基性地壳源与变泥岩参与。同时，我们回顾了NCC和国外其他克拉通发表的新太古代早期TTG的地球化学数据。结果表明，与东部地块相比，华北横贯造山带样品的 Y 含量较低，Sr/Y 和 (La/Yb)N 比值较高，HREE 贫化程度更高，可以解释为熔化的深度。或者，根据先前的研究和全球比较，升高的 Sr/Y 值也可能反映了由于较高的温度或岩浆分馏导致的熔融反应中斜长石消耗量的增加。所以，它主要缺乏基于地球化学的“弧”和“非弧”设置之间的明确区分。然而，许多研究人员提出证据表明，在太古代晚期（3.0 至 2.5 Ga），俯冲作用得到了很好的证明，但它可能不稳定。