The middle segment of northern margin of the North China Plate was influenced by intense tectonic and magmatic activity during the Permian. Dozens of intrusions formed an E-W trending magmatic belt that extended from the Dongshenmiao to Xianghuang Qi, Inner Mongolia, with a length of 400 km and width of 30 km. As a representative, Bayinzhurihe Pluton consists of quartz diorite and hornblende gabbro, which belong to high-potassium calc-alkaline series. They are characterized by low SiO2 (49.72%~59.34%) and high Al2O3 (15.79%~19.50%) contents, with Mg#=38~44, enrichment in large ion lithophile elements (LILE, e.g., Ba=829×10-6~1104×10-6, Sr=502×10-6~726×10-6), relative depletion in high field strength elements (HFSE, e.g., Nb, Ta) in primitive mantle-normalized spidergrams, and right-inclined rare earth element patterns, mostly with slightly negative Eu anomalies (δEu=0.63~1.09). Their low Sr/Nd ratios (12~24) and La/Nb ratios (1.33~2.39) may reflect intraplate magmatism involved. Hornblende gabbro shows non-arc-like (Nb/Th =9.6-18.4) basalt affinity compositions. LA-ICP-MS U-Pb zircon dating of the Pluton yielded an intrusive age of 265±2Ma. Its zircons haveεHf(t)=-13.0~-17.2 and t DMC=2.12~2.38 Ga, mainly show the characteristics of lower continental crust. These features lead us to conclude that Bayinzhurihe Pluton was generated by mixing of lower crustal-derived mafic melt and minor enriched mantle-derived mafic magma, followed by fractional crystallization, due to crustal extension in post-collisional setting.% 白云鄂博巴音珠日和岩体位于华北板块北缘中段的东升庙—太仆寺旗岩浆岩带上.该岩体由角闪辉长岩和石英闪长岩组成,其地球化学性质显示：低硅高铝,SiO2=49.72%~59.34%,Al2O3=15.79%~19.50%,Mg#=38~44；大离子亲石元素(LILE)富集(如Ba=829×10-6~1104×10-6,Sr=502×10-6~726×10-6)、高场强元素(HFSE,Nb,Ta等)亏损、轻稀土(LREE)富集(La/Yb)N=5.0~11.4,多数样品为弱负铕异常(δEu=0.63~1.09)；低Sr/Nd(12~24)和La/Nb(1.33~2.39)比值显示了板内岩浆作用特征.两个角闪辉长岩的高Nb/Th (9.6~18.4)比值显示了非弧玄武质岩浆特征.岩体的锆石LA-ICP-MS U-Pb年龄为(265±2) Ma,代表岩体侵位年龄.锆石εHf(t)=-13.0~-17.2、t DMC=2.12~2.38 Ga,显示了较明显的下地壳基底组分的加入.巴音珠日和岩体可能为后碰撞背景下,地壳的伸展减薄造成基性下地壳的部分熔融,熔体与来自富集地幔的玄武质岩浆发生部分混合,随后经进一步分异结晶作用形成.
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