【摘要】 内蒙古白云鄂博北部巴特敖包、查干呼绍一带分布着一系列岛弧型侵入岩,其岩石地球化学特征与典型的埃达克岩(adakite)一致:SiO2 多≥56 %,Al2O3 >15 %,MgO<3 %(很少大于 6 %),Yb(0.726 ~ 2.789)×10-6,La/Yb>10 ~ 20,Y(6.842 ~ 28.734)×10-6,Sr>400×10-6,Sr/Y≥20 ~ 40;Mg#值在0.51 ~ 0.58之间,多大于0.40;稀土元素分析,显示为轻稀土富集、重稀土亏损型,具正铕异常或微弱负铕异常;微量元素蛛网图中具明显的Sr峰和Nb、Ti低谷。9组锆石 U Pb同位素年龄值(206 Pb/238 U)范围在 345.06 ~ 552.671 Ma间,反映了本区大洋板块消减事件的年龄。构造环境判别证明它们是在岛弧环境下形成,为早古生代期间南蒙古洋板块向宝音图微陆块发生强烈斜向俯冲(oblique subduction),古洋壳板块发生部分熔融、消减而形成的产物。更多还原

【Abstract】 In the Xing’an-Mongolia fold belt in the north of Bayan Obo, there is a sequence of arc-type intrusion rocks distributing in Bart-Obo and Chagenhosao, Inner Mongolia, which have an identical chemical composition with a typical adakite: SiO2≥56 %,Al2O3>15 %,MgO<3 %（Less>6 %）,Yb（0.726 ～ 2.789）×10^-6,La/Yb>10 ～ 20,Y（6.842 ～ 28.734）×10^-6,Sr>400×10^-6,Sr/Y≥20 ～ 40, Mg^#=0.51 ～ 0.58（most > 0.40）, rich LREE and depleted HREE, positive or little negative Eu-anomaly, and obvious Sr apex and Nd vale and Ti vale. Nine isotopic ages of U - Pb (²⁰⁶Pb - ²³⁸U) arrange between 345.06 ～ 552.671 Ma, indicating the subduction time of the subducted ocean crust. A series of diagrams for tectonic setting suggest that these intrusion rocks formed in an island arc environment, representing the subductive and partial-melting production of the ancient ocean crust under oblique subduction of the southern Mongolia oceanic plate towards the Buyant micro-block during the early Paleozoic.更多还原