Recognition of tectonic switching is of great significance for understanding the formation and evolution of ancient accretionary orogens. In this study, whole‐rock geochemical and Sm‐Nd isotopic and zircon U‐Pb, Lu‐Hf isotopic, and trace element data are reported for two generations of metamorphosed mafic rocks from the Lüliang Complex, middle Trans‐North China Orogen. Although both episodes of mafic magmatism were derived from variable degrees of interaction between a subcontinental lithospheric mantle and slab‐derived hydrous fluids and melts, the younger ones (2.09–2.06 Ga) had higher whole‐rock ε_Nd(t) and zircon ε_Hf(t) values, higher (Ta/La)_N ratios, and weaker Nb, Ta, and Ti anomalies in the primitive mantle‐normalized trace element diagram compared with the older ones (2.18–2.15 Ga), implying a less‐enriched mantle source and subdued subduction features. More importantly, a decrease of U/Yb and Ce/Ce* ratios of magmatic zircons and whole‐rocks V/Ti ratios from the older to younger ones implied less slab‐derived fluid addition, and a decrease of whole‐rock (Sm/Yb)_N and Hf/Lu ratios suggests decreasing pressure of melt extraction and so lithosphere thickness. In consideration of other tectonothermal activity and paleogeography observed from the middle Trans‐North China Orogen, we propose a tectonic switching model to explain the middle to late Paleoproterozoic tectonic evolution caused by early subduction hinge retreat to later advance and ultimately continental collision.

中文翻译：

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古元古代中跨华北造山带的构造转换：吕梁构造体的镁铁质岩浆作用的见解

认识构造转换对了解古代增生造山带的形成和演化具有重要意义。在这项研究中，报道了华北中部造山带吕梁复杂的两代变质镁铁质岩石的全岩石地球化学和Sm-Nd同位素和锆石U-Pb，Lu-Hf同位素和痕量元素数据。虽然镁铁质岩浆的两个情节被从可变度相互作用的次大陆地幔和板坯衍生含水流体和熔体时，将年轻的（2.09-2.06 Ga）的衍生之间具有较高的全岩ε_钕（t）和锆石ε_铪（t）值，更高（Ta / La）_N原始地幔归一化的痕量元素图中Nb，Ta和Ti的比值较小，并且Nb，Ta和Ti异常较弱（2.18–2.15 Ga），这意味着地幔源的富集程度较低，俯冲特征减弱。更重要的是，岩浆锆石的U / Yb和Ce / Ce *比值降低，而全岩石的V / Ti比值从老到小降低，这意味着板状衍生流体的添加量减少，而全岩石（Sm / Yb）_NHf / Lu比表明熔体抽出压力降低，岩石圈厚度减小。考虑到从华北中部造山带中部观察到的其他构造热活动和古地理，我们提出了一种构造转换模型来解释由早期俯冲铰链撤退到后来推进并最终与大陆碰撞的中元古代元古代构造演化。