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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。
The Dongshengmiao granite is located in the western segment of the northern margin of the North China Plate, and is mainly composed of muscovite monzogranite. The LA-ICPMS zircon U-Pb zircon dating and zircon trace elements and Hf isotope analysis methods were used to systematically study the rock mass. Almost all zircons in granite show typical rhythmic oscillating zoning with high Th / U ratio (all greater than 0.1). The normalized distribution pattern of zircon REE chondrite is left-leaning and shows obvious positive Ce anomaly and The negative Eu anomalies indicate that these zircons are of magmatic origin. The dating results show that the age of formation of Dongsimiao Mudstone is (259.4 ± 3.3) Ma, which represents diagenetic age and belongs to the late Hercynian intrusive rocks. The weighted mean zircon ages of some cores are (2 367 ± 63) Ma, The age of the ancient palaeo-crystalline basement in the area. The zircons have a relatively uniform initial Hf ratio, 176 Hf / 177 Hf between 0.282 125 and 0.282 362, and εHf (259Ma) lower negative values (-17.3 to -9.0). The two-stage Hf model age tDM2 1.91 ~ 2.11Ga, indicating that the Dongshengmiao granite originated from the partial melting of the ancient crust in the Paleoproterozoic. The comprehensive study of the rock mass is helpful to further understand and study the tectonic evolution of the northern margin of the North China Plate.