The Early Cretaceous was the initial period of prolonged Cretaceous-Tertiary magmatic episode in the Korean Peninsula, during which a tectonic transition from compression to extension occurred. The Early Cretaceous Eopyeong granitoids in the Taebaeksan Basin consist of two distinct series of magmas: shoshonitic and high-K calc-alkaline series. We investigated the petrology, whole-rock major and trace element geochemistry, and Sr-Nd-Pb isotope compositions of the Eopyeong granitoids to understand their magma evolution processes and source characteristics. Sensitive high-resolution ion microprobe zircon U-Pb analysis was performed on the Eopyeong granitoids to constrain their intrusion ages. Zircon U-Pb ages of the shoshonitic and high-K calc-alkaline series are 110.63 ± 0.52 and 110.65 ± 0.66 Ma, respectively, indicating that the two series formed during the same magmatic event. The mafic mineral assemblages of the shoshonitic series change from two-pyroxene+biotite to clinopyroxene+amphibole+biotite through magma evolution, whereas those of the high-K calc-alkaline series consist of more hydrous assemblages of amphibole+biotite. The shoshonitic series is also distinguished from the high-K calc-alkaline series by its higher La/Yb ratio and negative anomalies of Rb, Ba, and Eu. Mineral geothermobarometry and hygrometry data and geochemical mass balance modeling results show that the two series evolved mainly by fractional crystallization from two distinct parental magmas containing different water contents. Primitive rocks from each series have high compatible element contents such as MgO, Cr, and Ni with high Mg# compared to crustal melts in a similar range of SiO₂, suggesting their mantle origin. They also have abundant incompatible elements and ‘crust-like’ isotopic compositions [(⁸⁷Sr/⁸⁶Sr)_i = 0.7093–0.7098; εNd(t) = −7.1 to −8.8; (²⁰⁶Pb/²⁰⁴Pb)_i = 18.133–18.327; (²⁰⁷Pb/²⁰⁴Pb)_i = 15.621–15.665; (²⁰⁸Pb/²⁰⁴Pb)_i = 38.691–38.862] with negative Nb-Ta anomalies in the primitive mantle-normalized patterns. The enrichment in both compatible and incompatible elements can be best explained by partial melting of phlogopite-bearing lithospheric mantle metasomatized by isotopically enriched upper crustal sediment-derived melt or fluid. The two magma series may have been generated by different degrees of partial melting of the mantle sources with varying water contents. Changes in subduction angle and direction of the paleo-Pacific plate during the Early Cretaceous may have led to lithospheric thinning and upwelling of asthenospheric mantle, which triggered the partial melting of fusible domains of metasomatized lithospheric mantle. The small igneous bodies of the Early Cretaceous shoshonitic to alkaline mafic rocks occur sporadically throughout the southern part of the Korean Peninsula in close spatial association with the Cretaceous basins. They also show crust-like geochemistry and isotopic compositions, similar to the Eopyeong granitoids, implying that the lithospheric thinning-related melting of the metasomatized lithospheric mantle may have been widespread in the southern part of the Korean Peninsula.

白垩纪早期是朝鲜半岛白垩纪-第三纪岩浆事件延长的初期，在此期间发生了从压缩到伸展的构造过渡。太白山盆地的白垩纪早期的欧平花岗岩体由两个不同的岩浆系列组成：斜生岩浆岩和高K钙碱性岩浆。我们研究了欧平花岗岩类的岩石学，全岩主元素和微量元素地球化学以及Sr-Nd-Pb同位素组成，以了解其岩浆演化过程和物源特征。对欧平花岗岩进行了高分辨率的高分辨率离子微探针锆石U-Pb分析，以限制其侵入年龄。肖氏铁酸钾和高K钙碱性碱系列的锆石U-Pb年龄分别为110.63±0.52和110.65±0.66 Ma，表示这两个系列是在同一岩浆事件中形成的。岩浆岩系列的镁铁质矿物组合通过岩浆演化从二-辉石+黑云母变为斜辉石+闪石+黑云母，而高钾钙碱性系列的镁铁矿矿物组合则由更多的角闪石+黑云母的含水组合组成。肖氏热系列还具有较高的La / Yb比和Rb，Ba和Eu的负异常，从而与高K钙碱性系列区分开。矿物地热和湿度数据以及地球化学质量平衡模型化结果表明，这两个系列主要是通过分馏结晶从两个含水量不同的两个母体岩浆中演化而来的。每个系列的原始岩石都具有较高的相容元素含量，例如MgO，Cr，₂，暗示其地幔起源。它们还具有丰富的不相容元素和“壳状”同位素组成[（⁸⁷ Sr / ⁸⁶ Sr）_i = 0.7093-0.7098; εNd（t）= -7.1至-8.8; （²⁰⁶ Pb / ²⁰⁴ Pb）_i = 18.133–18.327；（²⁰⁷ Pb / ²⁰⁴ Pb）_i = 15.621–15.665; （²⁰⁸ Pb / ²⁰⁴ Pb）_i= 38.691–38.862]，而在原始地幔归一化模式中Nb-Ta异常为负。相容元素和不相容元素的富集可以通过同位素富集的，由同位素富集的上地壳沉积物衍生的熔体或流体交代的含金云母岩石圈地幔来最好地解释。这两个岩浆系列可能是由于含水量变化的地幔源部分融化程度不同而产生的。白垩纪早期古太平洋板块俯冲角和方向的变化可能导致岩石圈地幔变薄和软流圈地幔上升，从而引起交代岩石圈地幔的可熔区部分融化。白垩纪至碱性镁铁质岩石的小火成体散布在整个朝鲜半岛南部，与白垩纪盆地在空间上密切相关。它们还表现出类似于欧平花岗岩的类似地壳的地球化学和同位素组成，这意味着与交代岩石圈地幔的岩石圈变薄有关的融化可能已经在朝鲜半岛南部广泛分布。