关键词: 花岗斑岩, 早白垩世, 华北克拉通, 构造背景, 下车河

Abstract: 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. 

Key words: granite porphyry, Early Cretaceous, North China Craton, tectonic background, Xiachehe region