论文部分内容阅读
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。
In this paper, the chronological and geochemical analyzes of the Paleingn group Permian metamorphic volcanic rocks in the Changtu area were conducted. The zircon cathodoluminescence images of the hornblende in the Panling Formation show that the zircon is semicircle-shaped, self-shaped, developed with sharp edges and clear magma oscillations, and has a high Th / U ratio (0.31 ~ 2.5), indicating that it is a magmatic origin. LA-ICP-MS U-Pb dating results show that 206 Pb / 238 U weighted average ages of 348 and 4.4 Ma at 27 sites represent the age of formation of hornblende rock. The content of SiO2 is 54.01%, the content of TFe2O3 is 15.04% and the value of Mg # is 33.29, belonging to the series of subbase pullout basalt. Geochemical analysis of rocks shows that hornblende rocks are relatively enriched in LREE and LILE, depleted in heavy rare earth elements and high field strength elements, and are characterized by active continental margin volcanic rocks. Based on the graphical analysis of Hf / 3-Th-Nb / 16, Hf / 3-Th-Ta, and combining with the history of regional tectonic evolution, it is considered that the hornblende rock protolith was formed on the active continental margin. Therefore, it is inferred that the Early Carboniferous in the eastern margin of the North margin of the North China Plate is active continental margin and is subducted by the Paleo-Asian Ocean plate.