摘要
本文对昌图地区下二台群盘岭组变质火山岩进行了年代学和地球化学分析。盘岭组角闪变粒岩中锆石阴极发光图像显示,锆石呈半自形晶-自形晶,发育晶棱和清晰的岩浆振荡环带,且具有较高的Th/U比值（0.31-2.5）,表明其为岩浆成因。LA-ICP-MS U-Pb定年结果显示,27个测点的206 Pb/238 U加权平均年龄348±4.4 Ma,代表了角闪变粒岩原岩的形成时代。角闪变粒岩SiO2含量为54.01%,全铁（TFe2O3）含量为15.04%,Mg#值为33.29,属于亚碱性拉斑玄武岩系列。岩石地球化学分析表明,角闪变粒岩相对富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,具有活动大陆边缘火山岩的特征。通过Hf/3-Th-Nb/16、Hf/3-Th-Ta等图解投点分析,结合区域构造演化历史,认为角闪变粒岩原岩形成于活动大陆边缘。因此,推断华北板块北缘东段早石炭世为活动大陆边缘,并受到古亚洲洋板块的俯冲作用。
This paper analyzed the geochronology and geochemistry features of metavolcanic rocks from Panling formation of Xiaertai Group in Changtu area.The CL images of zircons from the Amphibolite leptite of Panling formation show that the zircons are magmatic zircons with euhedral-subhedral crystals,typical magma concussion growth zoning and crystal prism,and a high Th/U（0.31-2.5）.LA-ICPMS U-Pb dating results indicate that the weighted average age of 27 measuring points of 206Pb/238 U is 348±4.4 Ma,which represents the forming age of the volcanic rocks.With 54.01% SiO_2,15.04% TFe_2O_3 and 33.29 Mg#,the amphibolite leptite belongs to Sub-alkali tholeiitic series.The lithogeochemical analysis shows that this sample has relatively enriched LILEs and LREEs and depleted HREEs and HSFEs,displaying characteristics of volcanic rocks of active continental margin.The figures of Hf/3-Th-Nb/16,Hf/3-Th-Ta,together with the history of regional tectonic evolution,shows that the formation environment of the amphibolite leptite should be active continental margin.It is concluded that the eastern section of the northern margin of the North China Plate was active continental margin in Early Carboniferous epoch and was subducted by the Paleo-Asian ocean plate.
出处
《山东科技大学学报（自然科学版）》
CAS
2016年第5期1-8,共8页
Journal of Shandong University of Science and Technology(Natural Science)
基金
国家自然科学基金项目(41372108)
高等学校博士学科点专项科研基金项目(20133718130001)
关键词
盘岭组
角闪变粒岩
U-Pb锆石定年
活动大陆边缘
古亚洲洋
Panling formation
amphibolite leptite
U-Pb zircon dating
active continental margin
the Paleo-Asian ocean
