We report the oldest I-type granites in the Lengshui Complex of the Yangtze Craton, providing new insights for its tectonic evolution during the Neoarchean. An approach-combined study of zircon U-Pb dating and Lu-Hf isotopes, as well as whole-rock element geochemistry and Nd isotopes, were employed. LA-ICP-MS zircon U-Pb dating for the monzogranite sample LSG03 and LSG16 yielded ages of 2732 ± 13 Ma and 2738 ± 25 Ma, respectively. The more precise age of 2732 ± 13 Ma for the sample LSG03 was taken as the crystallization age of the monzogranite. These rocks have high SiO₂ (73.11–74.01 wt%), K₂O (3.93–5.48 wt%), Na₂O (3.93–4.86 wt%) and low CaO (0.30–0.69 wt%), MgO (0.17–0.30 wt%), TiO₂ (0.14–0.17 wt%), P₂O₅ (0.01–0.06 wt%), Al₂O₃ (14.11–14.37 wt%) content with weakly peraluminous affinity (A/CNK = 1.04–1.11). Geochemically, they belong to I-type granites, indicating partial melting of a thickened lower crust. Their relatively high Nb/Ta (15.2–34.8) ratios further suggest they formed under eclogite-facies conditions. The consistent whole-rock Nd and zircon Hf isotopic compositions indicate a homogeneous source. According to their ε_Hf(t) values (−2.0 to 0.8), two-stage Hf model ages (3.1 to 3.2 Ga) and positive ε_Nd(t) (1.4 to 2.1), we argue that they were probably generated by partial melting of a juvenile lower crust with little ancient materials. Monzogranites formed in a late-orogenic or collisional compressive tectonic regime, whereas subsequent ca. 2.73 Ga and 2.67–2.62 Ga A-type granites in the Zhongxiang Uplift (including the Lengshui Complex) may represent a prolonged extensional setting. Thus, Archean subduction (probably unlike modern subduction) likely occurred prior to ca. 2.73 Ga. Similar magmatism in the Kongling Complex implies that the Zhongxiang Uplift may have accrete to the Kongling Complex during the early Neoarchean. The transition from I-type to A-type magmatism may have resulted from a change in the geodynamic regime from the late-orogenic or collisional compressive environment to an extensional environment caused by the subsequent lithospheric collapse and mantle upwelling, suggesting an early Neoarchean orogenic event in the eastern Yangtze Craton.

我们报道了长江克拉通的冷水综合体中最古老的I型花岗岩，为新构造时代的构造演化提供了新的见识。进行了锆石U-Pb测年和Lu-Hf同位素以及全岩元素地球化学和Nd同位素的方法组合研究。LA-ICP-MS锆石U-Pb年代为辉长花岗岩样品LSG03和LSG16的年龄分别为2732±13 Ma和2738±25 Ma。样品LSG03的更精确的年龄2732±13 Ma被认为是辉长花岗岩的结晶年龄。这些岩石具有较高的SiO ₂（73.11-74.01 wt％），K ₂ O（3.93-5.48 wt％），Na ₂ O（3.93-4.86 wt％）和低的CaO（0.30-0.69 wt％），MgO（0.17- 0.30 wt％），TiO ₂（0.14-0.17 wt％），P ₂ O₅（0.01–0.06 wt％），Al ₂ O ₃（14.11–14.37 wt％）含量，具有弱的过铝亲和力（A / CNK = 1.04–1.11）。从地球化学角度看，它们属于I型花岗岩，表明增厚的下地壳部分熔融。它们相对较高的Nb / Ta（15.2-34.8）比值进一步表明它们是在榴辉岩相条件下形成的。一致的全岩Nd和锆石Hf同位素组成表明其来源均一。根据其_εHf（t）值（-2.0至0.8），两阶段Hf模型年龄（3.1至3.2 Ga）和正_εNd（t）（1.4到2.1），我们认为它们可能是由少量古老材料导致的下部下部地壳部分融化而产生的。辉长花岗岩形成于晚造山带或碰撞压缩构造体系中，而随后大约在２００５年。钟祥隆起（包括冷水群）中的2.73 Ga和2.67–2.62 Ga A型花岗岩可能代表了延长的伸展期。因此，太古代俯冲作用（可能与现代俯冲作用不同）可能发生在约公元前。2.73 Ga。孔岭岩浆中类似的岩浆作用表明，中新世隆起可能在新archarean早期就积累了Kongling岩浆。