| 吉林临江八道沟二长花岗岩地球化学、Hf同位素特征及其成因 |
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| 引用本文： | 田力丹,孙丰月,王力,刘金龙,吴琼.吉林临江八道沟二长花岗岩地球化学、Hf同位素特征及其成因[J].地球科学,2018,43(2):436-448. |
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| 作者姓名： | 田力丹 孙丰月 王力 刘金龙 吴琼 |
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| 作者单位： | 1.吉林大学地球科学学院, 吉林长春 130061 |
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| 基金项目： | 吉林省地质勘查基金项目22201300111 |
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| 摘 要： | 八道沟具有复杂的构造环境，且侏罗纪花岗岩在该地区分布较为有限，因此十分缺乏对区域构造演化环境判断的证据.对八道沟二长花岗岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究，结果显示:岩石样品中的锆石主要为长柱状，自形程度较好，发育较清晰的韵律生长环带结构，具岩浆锆石特征，该岩石形成于早侏罗世（176±1 Ma）；岩石SiO2含量为68.93%~70.02%，贫MgO（1.27%~1.45%）、CaO（1.80%~2.78%），A/CNK值为0.92~1.02，轻稀土元素明显富集，铕异常不明显（0.96~1.03），属于准铝质高钾钙碱性系列，显示为I型花岗岩特征；岩石εHf（t）值为-20.21~-24.08，二阶段模式年龄tDM2（Hf）为2 498~2 740 Ma，且富集大离子亲石元素，亏损高场强元素Nb、Ta、P、Ti，Mg#值介于45~47，由此推断岩石源于新太古代下地壳熔融.结合区域同时代岩浆岩展布，认为八道沟地区二长花岗岩的形成与古太平洋板块向欧亚大陆俯冲有关.
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| 关 键 词： | 二长花岗岩 锆石U-Pb定年 Hf同位素 早侏罗世 八道沟 地球化学 地质年代学 |
| 收稿时间： | 2017-09-22 |
Geochemistry,Hf Isotopes and Petrogenesis of Badaogou Monzonotic Granites from Linjiang,Jilin Province |
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| Abstract: | The tectonic setting is complex while Jurassic granite is relatively limited in the Badaogou area, which results in a lack of theoretical basis for its regional tectonic evolution studies. This paper presents a synthesis of geochemical and zircon U-Pb chronological and Hf isotopic study on the Badaogou monzonitic granites. The zircons of rock samples which have distinct rhythmic growth zoning are long cylindrical and euhedral well-formed, implying the features of magmatic origin. Dating results indicate that the rocks were formed in the Early Jurassic (176±1 Ma). The rocks which obviously are rich in LREE and have unconspicuous europium anomalies (0.96-1.03) with regard to high SiO2 (68.93%-70.02%), low MgO (1.27%-1.45%), CaO (1.80%-2.78%) as well as A/CNK (0.92-1.02) belong to sub-aluminous and high-K calc-alkaline granites, being of the characteristics of Ⅰ-type granites. The εHf(t) values vary from -20.21 to -24.08, and the two-stage model age (tDM2) ranges from 2 498 to 2 740 Ma. These samples are enriched in LILE and depleted in HFSE (such as Nb, Ta, P, Ti), with Mg# values of 45-47. Analyses show that the rocks came from the melting of neo-Archean lower crust. Combining with the background of regional contemporary magmatic distribution, it is concluded that the formation of monzonotic granites from Badaogou could be related to the subduction of the Paleo-Pacific plate under the Eurasian continent. |
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