下车河岩体出露于华北克拉通中部地区，是典型的中生代中酸性侵入岩体。目前华北克拉通中部地区中生代区域构造演化研究程度相对较低，限制了对华北克拉通中生代破坏机制的整体认识，因此有必要对该岩体的岩石成因和构造背景进行深入研究。文章对下车河岩体中较新鲜的花岗斑岩首次开展地球化学、锆石年代学和Hf同位素的研究。结果表明，下车河花岗斑岩形成于早白垩世（135.1±0.8 Ma）；该岩石富硅、富碱，为高钾钙碱性弱过铝质花岗岩；岩石富集轻稀土元素（LREE）和大离子亲石元素（K、Ba、Eu），亏损重稀土元素（HREE）和高场强元素（Nb、Ce、Zr、Ti），具有明显的Eu负异常；Hf同位素显示εHf(t)变化范围为-19.4~-20.7，对应地壳模式年龄介于2417~2501 Ma。研究显示，下车河花岗斑岩显示出I型花岗岩成因，是古老下地壳部分熔融产物，源区有幔源物质输入。下车河花岗斑岩形成于早白垩世古太平洋板块西向俯冲背景下的伸展构造环境，为中生代华北克拉通构造体制转折的产物。

The Xiachehe intrusion is located in the Trans-North China Orogen (TNCO) that is a part of the North China Craton
(NCC). Compared with the Eastern Block (EB) of the NCC, relatively little attention has been paid to the research on Mesozoic regional tectonic evolution of the TNCO , which impedes the overall understanding of Mesozoic lithospheric destruction mechanism of the NCC. In this paper, we report new geochronological, Hf isotopes and geochemical data of the fresh granite porphyry from the Xiachehe intrusion in Shanxi Province to constrain petrogenesis and tectonic setting of the Xiachehe intrusion. The results show the zircon U-Pb ages of 135.1±0.8 Ma for the granite porphyry, indicating formation in the Early Cretaceous. The major elements of granite porphyry are characterized by high Si, Al2O3 and alkali (Na2O+K2O) with low σ values (2.11 and 2,59) and A/CNK ratios (1.07 to 1.15), belonging to the typical high-K calc-alkaline series and weakly peraluminous granite composition. Trace element analysis reveals enrichment in large ion lithophile elements (LILEs) (such as K, Ba and Eu) and light rare earth elements (LREE), depleted in high field strength elements (HFSEs) (such as Nb, Ce, Zr and Ti) and heavy rare-earth elements (HREE), with negative Eu anomalies. The Xiachehe granite porphyry has homogeneous zircon Hf isotopic compositions, their zircons show negative εHf(t) values ranging from -19.4 to -20.7, with two-stage Hf model ages (TMD2) ranging from 2417 Ma to 2501 Ma. The genetic type of granite porphyry is I-type granite. Xiachehe granite porphyry characteristics indicate that the rocks were formed from partial melting of Neoarchean-Paleoproterozoic lower crustal materials with mantle-derived inputs. Therefore, it is suggested that the Xiachehe granite porphyry formed in an extensional setting likely associated with the ancient Pacific Plate subduction beneath the Eurasian continent, and was the production of the transition of Mesozoic tectonic evolution of the NCC.