This paper has reported the petrography, geochemistry and geochronology of Jianshanzi, Baoxing and Shudetun plutons in the Kaiyuan area of the eastern section of the northern margin of North China, and discussed their formation age, rock genesis and tectonic environment. Zircon U-Pb dating results show that Jianshanzi pluton was formed in Early Triassic (251 +/- 1. 3 Ma), Baoxing pluton was formed in Middle Triassic (235 +/- 1. 3Ma) and Shudetun pluton was formed in Late Triassic (224 +/- 1. 9Ma). The Jianshanzi pluton is dominated by adamellite, with high Si and low Mg content, and belonged to calc-alkaline series. This unit is enriched in the light ion lithophile elements (e. g., Rb, K, Ba and Th) but is relatively depleted in the high field strength elements (e. g., Ta, Nb, Hf and Zr). They have (Eu values of 0. 55-1. 87 and high (La/Yb) N values of 6. 23-47. 9. These characteristics indicate that the Jianshanzi adamellites have fractionated REE compositions that are enriched in the light REE (LREE) and depleted in the heavy REE (HREE). The Baoxing pluton is dominated by granodiorite. This granodiorite is calc-alkaline, with Si02 concentrations of 52. 36% 74. 06%, Al2O3 of 14. 5% - 17. 34% and MgO of 0. 61% - 3. 66%. In addition, this unit is enriched in the light ion lithophile elements (e. g., Rb, K, Ba and Th) and is relatively depleted in the high field strength elements (e. g., Ta, Nb, P and Ti). Furthermore, these samples have negligible Eu anomalies and (La/Yb) N values of 6. 81 +/- 25. 6. These characteristics indicate that the Baoxing granodiorites have fractionated REE compositions that are enriched in the LREE and depleted in the HREE. The Shedetun pluton is dominated by diorite, with low Si and high Mg content. This diorite is enriched in K and depleted in Na, with K2O/Na-2 ratios of 0. 33 similar to 0. 76, and belonged calc-alkaline series. In addition, the Baoxing pluton is enriched in the light ion lithophile elements (e. g., Rb, K, Ba and Th) and is relatively depleted in the high field strength elements (e. g., Ta, Nb, P, Ti, Hf and Zr). The Shudetun pluton has negligible Eu anomalies and (La/Yb), values of 3. 87 similar to 10. 2, with no obvious fractionation of LREE and HREE. According to the above research, the original magma of the Jianshanzi and Baoxing pluton are originated from partial melting of the lower crust basic rocks, but the Shudetun pluton are originated form depleted mantle wedge. The Triassic magmatites of study area are formed in compressional environment of orogenic stage. Meanwhile, extrusion and collision of the eastern section of the northern margin of North China was lasted to Late Triassic (224Ma). The tectonic transformation of orogenic stage and post orogenic stage (extrusion crustal thickening transition to extensional collapse environment) occurred between Late Triassic and Early Jurassic (224 similar to 180Ma), and also means that lithospheric thinning or destruction might begin in Late Triassic to Early Jurassic (224 similar to 180Ma).
