摘要
东升庙岩体位于华北板块北缘西段,岩性主要为白云母二长花岗岩。采用LA-ICPMS锆石U-Pb微区定年和锆石微量元素及Hf同位素分析方法,对该岩体进行了系统的研究。花岗岩中几乎所有的锆石都显示典型的韵律振荡环带,Th/U比值较高(均大于0.1),锆石稀土元素球粒陨石标准化配分曲线呈左倾型,并显示明显的正Ce异常和负Eu异常,表明这些锆石为岩浆成因。测年结果显示,东升庙岩体形成年龄为(259.4±3.3)Ma,代表成岩年龄,属海西晚期侵入岩;部分核部继承锆石年龄加权平均值为(2 367±63)Ma,提供了该区古元古代结晶基底的年龄信息。锆石具有较均一的Hf初始比值,176 Hf/177 Hf介于0.282 125~0.282 362之间,εHf(259Ma)值为较低的负值(-17.3^-9.0),两阶段Hf模式年龄tDM2为1.91~2.11Ga,指示东升庙岩体起源于古元古代古老地壳部分熔融。对该岩体的综合研究有助于进一步认识和研究华北板块北缘的构造演化过程。
Dongshengmiao intrusion of Inner Mongolia is located on the west segment of the northern mar- gin of the North China Plate, mainly consists of muscovite monzonitic granite. This paper systematically investigates the intrusion by applying the new methods of LA-ICPMS U-Pb zircon dating, REE and LA- MC-ICPMS zircon Hf isotopic analyzing. The results show oscillatory zoning, high Th/U ratios （〉0.1）. The zircons show left-oriented REE pattern with positive Ce anomaly, and negative Eu anomaly. This re- sults indicate that the intrusion is magmatic origin. A weighted average U-Pb age of 259.4± 3.3 Ma of Dongshengmiao representative samples implies that it was emplaced during the late Hercynian Period. The age of weighted average U-Pb of inheritance zircons in the core suggests that the age of basement is 2 367 ± 63 Ma. Zircon Hf isotope analyses show the relatively homogeneous initial Hf isotopic compositions, which is between 0. 282 125 and 0. 282 362, the value of e（Hf） （259 Ma） ranges from -17.3 to -9.0, and the two-stage mode ages（tDM2） ranges from 1. 91 to 2. 11 Ga. Those indicate that the Dongshengmiao intrusion was formed mainly by partial melting of the old Paleoproterozoic continental crust.
出处
《地质科技情报》
CAS
CSCD
北大核心
2013年第6期22-30,共9页
Geological Science and Technology Information
基金
国家自然科学基金重点项目(41030425)
