赣江流域(南昌段)水系沉积物物源示踪研究：来自锆石U-Pb同位素证据的约束
Tracing the Stream Sediment of the Ganjiang River(Nanchang Section)：Constraint from the Detrital Zircon U-Pb Isotope Evidence

摘要： 赣江为长江八大支流之一，是江西省第一大河流，为研究赣江水系沉积物的物质来源，利用LA-ICP-MS分析技术，对赣江河流(南昌段)沉积物碎屑锆石进行了U-Pb年龄研究。对3个河砂样品中的140颗碎屑锆石进行了测试，获得有效测试点123个。测试结果表明：锆石UPb年龄主要有7个年龄段，分别是134~197 Ma、221~290 Ma、386~484 Ma、520~625 Ma、727~895 Ma、980~1 110 Ma、2 502~2 861 Ma。所表现出来的主要年龄区间分别与已知的构造-岩浆热事件时间相对应(燕山运动、印支－海西运动、加里东运动、晋宁运动、吕梁运动)。大多数锆石颗粒具有明显的岩浆结晶环带且Th/U>0.4，表明这些锆石多为岩浆成因。通过对赣江流域及周边各个地区的年代学对比研究揭示：年龄段为134~197 Ma的锆石大部分来自赣中南—闽西—粤北地区；221~290 Ma的印支期锆石主要来自赣南地区，而海西期的锆石来自赣中、九岭地区；386~484 Ma的锆石主要来自赣中南地区，少量来自赣西北；520~625 Ma的锆石可初步判断来自赣南地区；727~895 Ma的锆石主要来自赣北江南造山带附近的九岭地区；980~1 110 Ma和2 502~2 861 Ma的锆石主要来自华夏地块腹地的赣南—粤北地区。因此，赣江水系沉积物碎屑锆石U-Pb年龄可以有效地限定赣江流域的主要物质来源。
Abstract: The Ganjiang River is the biggest river in Jiangxi Province, which is also one of eight major tributaries of the Yangtze River. In order to investigate the material source of stream sediment in the Ganjiang River, the U-Pb age of detrital zircons from the Ganjiang River (Nanchang Section) were carried out by the LA-ICP-MS analysis technique. One hundred and twenty three spots are effective among the 140 analytical spots. The data suggest that zircons are mainly composed of 7 age stages, including 134-197 Ma, 221-290 Ma, 386-484 Ma, 520-625 Ma, 727-895 Ma, 980-1,110 Ma and 2,502-2,861 Ma, respectively, corresponding to the known tectonic-magmatic thermal events, i.e., Yanshanian Movement, Indosinian-Hercynian Movement, Caledonian Movement, Jinning Movement, Lüliang Movement. The Th/U ratios of most zircons with distinct magmatic zoning are more than 0.4, indicating that they are of magmatic origin. The result reveals that the zircons of 134-197 Ma mainly come from Southern and Central Jiangxi, Western Fujian and Northern Guangdong area. The Indosinian zircons of 221-290 Ma mainly stem from Southern Jiangxi and Hercynian zircons from Central Jiangxi and Jiuling area. The zircons of 386-484 Ma mainly come from Southern and Central Jiangxi and some are from Northwestern Jiangxi Province. The zircons of 520-625 Ma could be judged that they come from Southern Jiangxi. The zircons of 727-895 Ma are mainly from Jiuling area. The zircons of 980-1,100 Ma and 2,502-2,861 Ma mainly come from Southern Jiangxi and Northern Guangdong in Cathaysia Block. Therefore, the main material resource of the Ganjiang River could be effectively constrained by the U-Pb age of the detrital zircon from stream sediment