白云鄂博中二叠世巴音珠日和岩体地球化学特征及构造意义

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。

Geochemical Characteristics of Bayinzhurihe Pluton and Its Tectonic Significance,Bayan Obo,Inner Mongolia

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 have εHf(t )= -13.0~-17.2 and t DM
C=2.12~2.38 Ga, mainly show the characteristics of lower continental crust. These features lead us to conclude that Bayinzhurihe Pluton was generated bymixing 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.